I Acc-19^ THE FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA MINISTRY OF WATER RESOURCES Arjo-Dedessa Irrigation Project Feasibility Study Report VOLUME - III Water Resources VOLUME - III (a) Annexure - 7 Meteorological And Hydrological Studies Annexure - 8 Hydrogeological Studies May. 2007 Addis Ababa <£E WATER WORKS DESIGN & SUPERVISION ENTERPRISE IM ASSOCIATION WITH INTERCOimMENYJU COMSOITMITS MO HCHWCMTS !N0W PYT LTD P.O Box 2561 Addis Ababa Ethiopia Tcl:(251 >1 614501/631X90 Fax.(1251)1 6l5371E-inail. w w d s c tHclecoin.net.clARJO-DEDESSA IRRIGATION PROJECT FEASIBILITY STUDY REPORT CONTENTS OF THE REPORT SERIAL NO. 1 2 3 VOLUME NO. PARTICULARS EXECUTIVE SUMMARY MAIN REPORT Part I - Report Part II - Maps & Drawings ANNEXURES VOLUME -1 SURVEY AND INVETIGATION (ANNEXURES - 1 to 3) 4 5 6 Volume -1 (a) Volume -1 (b) VOLUME -II Topographic Survey, Geomorphological Studies & Geological & Geotechnical Investigation Part I - Report Part II - Appendices NATURAL RESOURCES (ANNEXURES - 4 to 6) Forestry, Energy & Catchment Development Plan VOLUME - III WATER RESOURCES (ANNEXURES - 7 to 11) 7 Volume - III (a) Meteorological & Hydrological & Hydrogeological Studies Dam & Appurtenant Works Part I - Report 8 9 10 11 12 13 14 15 16 Volume - III (b) Part II - Drawings Irrigation & Drainage Volume-III (c) Part I - Report Part II - Drawings Hydraulic Structures Volume - III (d) Part I - Report Part II - Drawings VOLUME IV AGRICUTLRUE (ANNEXURES - 12 to 18) Volume - IV (a) Soil Survey & Land Evaluation Volume - IV (b) Agricultural Planning Volume - IV (c) Livestock, Fisheries, Agricultural Mechanization & Agricultural Marketing VOLUME-V ENVIRONMENTAL AND SOCIO - ECONOMIC ASPECTS (ANNEXURES-19 to 25) 17 Volume - v (a) Environment, Health & Socio-economic Aspects 18 Volume - v (b) Organization & Management, Physical Infrastructure Resettlement, Financial & Economic AnalysisAnnexure - 7 METEOROLOGICAL AND HYDROLOGICAL STUDIESArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Table of Contents TABLE OF CONTENTS LISTOFTABLES-HI LIST OF ANNEXUREIV LIST OF FIGURESV 1. INTRODUCTION..1 II The Nile Basinl 1.2 abbay Basin 1 1.3 The Dedessa Catchments3 2. REVIEW OF PREVIOUS STUDIES! 2.1 Lahmayer 1962 Study 2.2 Land and Water Resources of the Blue Nile Basin Ethiopia 2.3 Country wide Master Plan studies - EVDSA/WAPCOS (1988-90) 8 2.4 Study by BCEOM - in association with ISL and BRG 1999 .................................................................... 9 3. 2.5 Study by Ministry of Water resources for Lower Dedessa (2001)15 2 6 Utility of Earlier Studies DATA BASE 3.1 Climatological Data 16 17 3.2. 3.3. 3.4 4. 4.1 4.2 Rain fall River Discharge Sedment Data ESTIMATION OF REFERENCE EVAPOTRANSPIRATION Introduction......................................................................... Meteorological Data 19 19 20 4.2.! 4.2.2 Meteorological Observation Stations................... ... Air temperature...................................................................... 4 2.3 4.2.4 4.2.5 4.3 Air humidity. 20 21 22 23 23 5. Arjo Didesa Project Area RAINFALL ANALYSIS INTRODUCTION Wind speed Solar radiation......................................................................... Penman-Monteith Equation Arjo Dedessa Project Area 32 Rainfall Internal and External Consistency Estimation of Rainfall Reliability Level Estimation of Maximum Rainfall Frequencies 6. MONTHLY STREAMFLOW ANALYSIS 6.1 6.2 6.3 Hydrological Observation Stations EXTENSION OF RECORDS Synthetic flows...................................... 7 ESTIMATION OF FLOODS FOR UNGAUGED CATCHMENTS Rational Method SCS Method.................................................................................. Transferring Gauged Data Estimation of weighted Average ..... Synder Method of Constructing Synthetic Hydrograph. 8 FLOOD FREQUENCY ANALYSIS 24 30 32 32 33 34 46 46 46 47 51 .51 .53 .54 .54 55 59 __________________________________________________________________________ I Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects 8 1 Introduction59 May 2007 8.2 Estimation of Probability Weighted Moments60 8.3 Generalized Extreme Value Distribution61 8.4 Log-Logistic Distribution61 8.5 Regionally averaged quantiles62 8.6 Choice of Distribution63 9. PROBABLE MAXIMUM FLOOD-...........................................................................................................................65 10 SEDIMENT ANALYSIS69 10. l Estimation of Sediment yield69 10.2 Distribution of sediment in the reservoir70 11. WATER QUALITY73 12. DESIGN FLOOD75 12.1 Synthetic Hydrograph75 12.2 Flood Routing Through the Reservoir75 12.3 Routed Design Flood at the Coffer Dam78 13. RESERVOIR SIMULATION87 14. DEDESSA SUB-BASIN MODELING91 14.1. Modeling for arjo Dedessa dam for irrigation 91 14 2 THE SUB BASIN MODELING 92 14.2.1 Power Generation in Dedessa Dani93 14.2.2 Optimal Power Generation 94 14.2.3 Reduction In flows al Dedessa Sub-basin 96 14.2.4 Conclusi ons96 15. RECOMMENDATIONS ON TRAINING NEEDS...101 REFERENCES _____________________________________ __________ ____________ II Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 LIST OF TABLES Table 1.1: Break up of Abbay Basin Area4 Table 4.1: Table Details of Meteorological Observation Stations located in and around the PROJECT AREA26 Table 4.2: Types of Climatic Data available at the various Meteorological Observation Stations26 Table 4.3: Summary of Meteorological Characteristics at Project Area Table 4.4: Summary of Estimated Mean ETo of Arjo Dedessa Project Area 28 Table 4.5: Magnitude of ETo at given non-exeedance probability level 29 Table 5.1: Cross Correlation Matrix of Annual Rainfall........................................................................ 36 Table 5.2: Mean Monthly Rainfall36 Table 5.3: Parameter Estimates of Weibull Distribution..........................................................................36 Table 5.4: Monthly Rainfalls Corresponding to Different Reliability Levels 37 Table 5.5: Parameter Estimates of Half-Monthly Rainfall 37 Table 5.6: Half-Monthly Rainfall Magnitudes at Different Reliability Levels . 38 Table 5.7: Half-Monthly Rainfall Magnitudes in Percent of the Mean Corresponding to Different Reliability Levels39 Table 5.8: Maximum Annual 24-hr Rainfall40 Table 5.9: Maximum Rainfall Magnitudes and Frequencies40 Table 5.10: Maximum Rainfall Magnitudes for Higher Durations4i Table 6.1: Availability of Streamflow Data in the Region Table 6.2: Mean Monthly Flow (in Mm3/sec) Table 6.3: Coefficient of Variation of Monthly Discharges48 Table 6.4: Summary of Regional monthly flow characteristics 49 Table 6.5: Table Statistics of monthly flows at Arjo Dedessa dam site. Table 6.6: Reliability Level Vs Monthly Streamflows at Dam Site49 Table 6.7: Characteristics of Random Numbers Used for Flow Generation Table 8.1: Estimated Flood Quantiles Based on GEV Distribution Table 8.2: Estimated Flood Quantiles Based on LLG Distribution Table 9.1: Table Cumulative Volume of Probable Maximum Flood67 Table 9.2: Design Flood Hydrograph Derived from Estimated PMF 68 Table 10.1: Relationships between water discharge and sediment load 70 Table 10.2: Monthly Total Sediment Load at the Reservoir Site 71 Table 10.3: Accumulated Total Sediment Load at the Reservoir Site 71 Table 10.4: Distribution of Sediment in the Arjo Dedessa Reservoir72 Table 11.1: Water quality results for sites on the Dedessa river 74 Table 12.1: Catchment Characteristics80 Table 12.2: Routed Design Flood at FRL Corresponding to 1352 m Table 12.3: Routed Design Flood at FRL Corresponding to 1555 m 81 Table 12.4: Routed Design Flood at FRL Corresponding to 1356m 82 Table 12.5: Routed Design Flood at Coffer Dam of Arjo Didessa Reservoir 83 Table 13.1: Irrigation Water Requirements for Various Scenarios 88 Table13.2: Reservoir Characteristics at Dead Storage Level Table 13.3: Storage Reservoir Characteristics and Reliability Levels Table 14.1: Total Monthly Release (Irrigation plus Power) options for various FRL values CONSIDERED97 Table 14.2: Annual Energy generations at Dedessa dam for the various options 97 48 .48 49 50 64 .64 so .89 90 ____________________________________ _____________________________________III Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 LIST OF ANNEXURE Annex A: Results obtained from the Meteorological Analysis............................ »................................... 103 A1: estimated Mean Temperature at Arjo Dedessa Project Area (in C)q........................................ 103 A2: Estimated Minimum Temperature at Arjo Dedessa Project Area (in C).................................... 104 A3: Estimated Maximum Temperature at Arjo Dedessa Project Area (in C).................................. 105 A4: Estimated Relative Humidity at Arjo Dedessa Project Area (in percent).............................. 106 A5: Estimated Mean Daily Sunshine Duration at Arjo Dedessa Project Area...............................107 A6: Estimated Mean Daily ETo of Arjo Dedessa Project Area......................................................... 108 A7: Estimated Mean Monthly ETo of Arjo Dedessa Project Area................................................... 109 A8: Estimated Mean Monthly Rainfall at Arjo Dedessa Project Area 110 A9: Estimated Mean Half-Monthly Rainfal at the Project Area (in mm/hr)....................................... ill Annex B: Results obtained from the Hydrological Analysis........................................................................... 113 B1: Estimated Monthly Flows at Arjo Dedessa Dam Site................................................................... 113 B2: Regional monthly coefficient of variations (CV)........................................................................... 114 B3: Regional monthly coefficient of skewness..................................................................................... 114 B4: 16 Regional monthly coefficient of correlations (R)................................................................... 114 B5 Standardized probability weighted moments................................................................................... 115 B6: Mean Monthly Total (Suspended and Bed) Sediment load ......................................................... 116 B7: Eleveation-Area-Capacitv Relationships of Arjo Dedessa Reservoir 117 B8: Sample Simulation Results of Arjo Dedessa Reservoir.............................................................. 118 Annex C: Standards.................................................................................................................................................... 121 C1: Commonly used values of runoff coefficients.............................................................................. 121 C2: Runoff coefficient for pervious surfaces by selected hydrologic soil.................................... 121 C3: SCS Curve Numbers for Various Conditions1................................................................................. 122 C4: Reservoir Flood Standards................................................................................................................... 124 C5: Ratios of the basic dimensionless hydrograph of the SCS.............................................................125 C6: Guidelines for Interpretations of Water Quality for Irrigation................................................. 126 Annex D: Meteorological Data...................................................................................................................................127 D1: Details of Meteorological Observation Stations......................................... 127 D2: Types of Climatic Data available at the various Meteorological...............................................127 D3: Mean Monthly Rainfall at Bedele Station....................................................................................... 128 D4: Mean Monthly Rainfall at Jimma Station.......................................................................................... 129 D5: Mean Monthly Rainfall at Dedessa Station..................................................................................... 131 D6: Mean Temperature at Bedele Station................................................................................................ 132 D7; Relative Humidity at Bedele Station (in%)........................................................................................ 133 D8: Wind Speed at Jimma Station................................................................................................................ 134 D9: Sunshine Duration at Bedele Station..................... 135 Annexe: Hydrological Data.......................................................................................... .................................... )36 E1: List of Selected Hydrological Observation Stations..................................................................... 136 E2: Mean Monthly Streamflow at Dedessan near Arjo Station................................................ 137 E3: Mean Monthly Stream flow at Dedessan near Dembi Station E4: Annual Maximum Floods............................................................................. l40 E5: Measured Sediment Concentration at Gumara Gauging Station............................ , 4i 139 _________________________ _ _________________________________ _ IV Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects LIST OF FIGURES May 2007 Figure 4.1: mean Monthly Temperature at figure 4.2: Mean Monthly Relative Humidity at............. 30 Figure 4.3: Mean Monthly Wind Speed at Figure 4.4: Mean Monthly Sunshine Hours at................ 30 Figure 4.5 Mean Monthly ETo at Arjo Dedessa Project Area............................................................ 31 Figure 5.1 (a): Trend Analysis of Annual Rainfall at Jimma Station 42 Figure 5.1(b): Trend Analysis of Annual Rainfall at Bedelle Station.................................................... 42 Figure 5.1 (c): Trend Analysis of Annual Rainfall at Dedessa Station.................................................... 43 Figure 5.2(a): Single Mass Curve of Jimma Rainfall .................................................................................... 43 Figure 5.2(b): Single Mass Curve of Bedelle Rainfall.................................................................................44 Figure 5.2(c): Single Mass Curve of Dedessa Rainfall................................................................................44 Figure 5.3: Mean Monthly Rainfall at Arjo Dedessa Projetct Area.................................................. 45 Figure 12.1: Elevation-Area-Capacity Curves of Arjo Dedessa Reservoir 84 Figure 12.2: Inflow and Outflow Flood Hydrographs at Arjo Dedessa Reservoir.......................... 84 Figure 12.3: Inflow and Outflow Flood Hydrographs at Arjo Dedessa Reservoir ......................... 85 Figure 12.4: Average Hydrograph of Maximum flows at Arjo Dedessa Dam Site............................... 86 Figure 14 1: Power Duration Curves............................................................................................................. 98 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects 1. INTRODUCTION 1.1 The Nile Basin May 2007 Having a length of 6,825 km., the Nile River takes the rank of number one with respect to length, in the world. It drains a total drainage area of 2.96 M.Km , with its annual total flow 2 of about 84 Bm . As one could appreciate, 3 the discharge per Km2 is small when compared to other large rivers of the world. From the Lake Victoria, to the Mediterranean Sea, the river crosses very many different areas associated with different climate, relief and geology. The main sources of the river are the equatorial lake plateau and the Ethiopian Highlands. The three major tributaries which emanate from the Ethiopian Highlands are, from south to the north, the Baro Akobo, the Blue Nile, familiarly known as Abbay and the Tekeze -Atbara System. 1.2 Abbay Basin The Abbay Basin is one of the most important basims, in Ethiopia. It accounts for about 17.5% of Ethiopian land area, 25% of its population and 50% of its annual average surface water resources. In the Lake Tana, it has the country's largest fresh water lake, covering an extent of 3000 km . The Abbay has an average annual 2 run off of about 50 B m3. The rivers of Abbay contribute on an average, 62% of Nile river flows in Aswan dam. The climate of the Abbay Basin is dominated by two features, namely, it’s near equatorial location and in altitude range between 590 m.amsl to 4000 m. amsl. These influences result in rich variety of local climates, ranging from hot/desert like, along the Sudan border to the temperate type on the high plateau with depiction of cold in the high mountains. The Basin can g enerally be d escribed a s t emperate a t h igher e levation a nd tropical a t lower elevations. However due to the distinctive aspects of the highland climate, it is perhaps better to describe it using the local climatic zones, that have bean established with elevation (and resultant temperature) as controlling factors. The Qolla zone lies below 1800 meters and has annual temperature range from 20°C to 28°C. The Woina Dega zone lies between 1800 meters and 2400 maters and has annual average temperature ranging from 16°C to 20°C. The Dega zone, above 2400 meters has average annual temperature ranging from 10°C to 16°C. The major portion of the population inhabit in the more climatically pleasant and healthier upper two zones, which leaves the lower Qolla zone sparsely populated. Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. IArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 There are mainly 3 rainy seasons. The main one (kiremt) lasts generally from June to September, during which, the south west winds bring rains from the Atlantic Ocean. About 70% to even up to 90% of the rainfall occurs during this season. This season obviously is associated with minimum levels of sunshine, low variations in daily temperature and high relative humidity. A dry season (Bega) lasts from October to January, during which clear skies are associated with maximum sunshine hours, high daily temperature variation and low relative humidity. F inally the m inor rainy season (Belg) lasts from February to May, during which south east winds bring the small rains from the Indian Ocean The temperature range is very high in this season. The precise timing and duration of these seasons vary considerably depending upon location within Abbay Basin, and to some lesser extent, year to year as well. Generally speaking, the low altitude depicts the pattern of 11.5 to even 12.5 hours of sunshine and temperature varying only for a small range from 3°C to 7°C through out the year. The mean annual rainfall over the entire basin could be reckoned at 1400 millimeters; where as the mean evapotranspiration is about 1 300 millimeter. Broadly, based on the rainfall pattern, 4 different areas have been identified by the earlier Master Plan study (Abbay River Basin Integrated Master Plan Project - BCEOM in association with BRGM, ad ISL consulting Engineers - 1998). These are: i) Southern area covering East and West Wellega, Jimma and lllubabor Zones with relatively high rainfall (1400-2200 millimeters) and a long wet season. ii) A central area covering most of Western Gojam and parts of neighboring zones as well, characterized by relatively high rainfall (1400 - 2200 millimeters). But there is a more pronounced seasonal pattern associated with short wet and longer dry seasons. iii) An area covering most of the eastern part of the basin including North and South Wello, Eastern part of East Gojam and South Gondar and much of North and North West Shewa region, excluding small proportion of mountain areas. This area is characterized by relatively low rainfall (less than 1200 millimeter) distributed in both the rainy seasons, depicting bimodality. Water Works Design & Supervision Enterprise 2 In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 iv) The West and North West area covering North Gondar region. The rainfall is about 1200 millimeters, falling predominantly, in the main rainy season associated with high average rates of evapotranspiration. With respect to the hydrographic scenario, the Basin is dominated by Abbay River which rises in the center of the catchment and develops its course in a clock wise spinal. It collects tributaries all along its 992 km. journey up to Sudan border. As said earlier, the Abbay Basin catchment area of 199,812 km2 is encompassing the break up as below: As Gilgel Abbay, the main river flows north from its source near Sekela into the wide and shallow Lake Tana. The lake also receives other tributaries from a catchment of 15,054 km2 including tributaries Megech, Ribb and Gumara. Shortly after leaving the lake, the river reaches the celebrated Tis Abbay falls, thereafter flowing in a deep and rugged gorge on its way to Sudan Border. The break-up of Abay basin catchment area is available in Table 1.1. 1.3 The Dedessa Catchments The Dedessa River is the largest tributary of the Abbay in terms of the volume of water contribution to the total flow of Abbay at the Sudan border. Draining nearly an area of 34,000 square kilo meters, the Dedessa river originates in the Mt.Vennio and Mt.Wache ranges, flowing in an easterly direction for about 75 kilo meters, then turning rather sharply to the north until it reaches the Abbay River. The major tributaries of the Dedessa river are the Wama, entering from the east, the Dabana from the west, and the Angar from the east. Dedessa Catchment is situated in the south-west part of Abbay Basin. The catchment area at a gauging station near Arjo town is 9,981 km . The climate of the Dedessa Catchment results from its location and elevation (1220 to 3012 meters). The catchment is characterized by mountainous, highly rugged and dissected topography with deep slopes. The lowest part of the catchment is characterized by valley floor with flat to gentle slopes. Most of the rainfall in the Dedessa Catchment is concentrated in the June to September period with virtual drought from November through February. Annual totals, average from less than 150 centimeters to more than 200 centimeters. The Dedessa catchment, besides reflecting a marked rainfall increase with higher elevation, also receives heavier annual quantities than most of the catchments in the Abbay basin. Examination of the rainfall records from this area shows that this is due to a longer (May through October) rainy season rather than heavier maximum monthly quantities 2 Water Works Design & Supervision Enterprise 3 In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.ArjoDedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 The mean annual flow of Dedessa river at Arjo station is about 3,800 million m3 having its maximum flow in August and September (52 percent of the annual) and minimum flow in February and March (less than 1.5 percent of the annual). Further vivid description of the climatic factors, rainfall and hydrological parameters are made in the ensuing respective sections of this report. Table 1.1: Break up of Abbay Basin Area System Tributary Joining From Catchment Area (Km ) 2 Lake Tana — 15,054 North Gojam Right side 14,389 Beshilo Left side 13,242 Weleka Jemma South Gojam Right side Muger Guder Fincha Dedessa Angar Wonbera Dabus Beles Left side u it u •4 Right side Left side Right side Dinder — 14,891 Rahad — 8,269 6,415 15,782 16,762 8,188 7,011 4,089 19,630 7,901 12,957 21,032 14,200 Total 199,812 Water Works Design & Supervision Enterprise 4 In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects 2. REVIEW OF PREVIOUS STUDIES May 2007 Because of the importance of the Abbay, very many studies had been carried out in the past, concerning the basin. Though, there was not any specific study for the development of Dedessa sub basin exclusively, all the studies under taken, pertaining to Abbay or the country as a whole, spoke of Dedessa development. Hence, though such a review has to be more exhaustive, it is necessary to undertake such a review, before attempting Dedessa sub basin development especially the aspects connected with hydrology in this sectoral study. Such a review is presented in the following sub paragraphs. 2.1 Lahmayer 1962 Study This was mainly concerned with Gilgel Abbay Scheme. Although, it was not having adequate data base, the study provided interesting information about Gilgel Abbay and its tributaries, which could be considered as a data base for review and up dating in the light of the raw data. 2.2 Land and Water Resources of the Blue Nile Basin Ethiopia The study was under taken by the United States Department of the Interior Bureau of Reclamation during 1958 - 1964. This detailed study on land and water resources development of the Abbay basin is worth mentioning important study. Even at a time, when there was a little or no data, very exhaustive analysis of the available data had been carried out to establish hydrological studies. In fact, the pioneering works undertaken during that time, has made Abbay basin in Ethiopia, to be proud of a possessing a good net work of hydrometric stations for making reliable estimates. The hydrological aspects have been covered in Appendix III of the report. In 4 different sections of this Appendix, the various facets of hydrological analysis have been put forth as below: Section I: A general description on climate, availability of water, sedimentation rates and possible irrigation requirements. Section II: A presentation of the status of historical stream flow and their elaborations. Section III: A presentation on flood flows and the analysis attempted. Section IV: A presentation on water use. s Water Works Design & Supervision Enterprise in Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 In the Section I, on giving an account of the synoptic and climatic situations, the 22 stations with long data have been analyzed for precipitation and temperature. The basin isotherm and precipitation maps have been prepared based on above analysis. The water availability aspects have been also addressed in this Section I. The samples analyzed at 5 stations indicated a Iow sodium hazard; most of them showed Iow to m edium s alinity h azard, some samples contained from none to a maximum of 0.2 ppm of Boron, which was found to be tolerable by most sensitive crops. The samples showing highest salinity were from Mugger and Dinder. With respect to sedimentation, ratings were established at 4 stations and based on extrapolation; the sediment rate was computed at all the identified potential dam sites. The pattern of sediment distribution in reservoirs, expected after 50 years of useful life was adopted uniformly in a water balance type of simulation, for establishing the success of each of the identified projects. In the section, 3 regions have been identified for development with respective crop projections, cropping calendar and crop water requirement. The water requirements varied from 782 millimeters in Gilgel Abbay to 1375 millimeters in Dinder area. The section II has addressed the stream flow development for locations of the identified dam sites by possible best set of analysis available at the time. In the study period 59 gauging stations were established, including 14 stations with automatic stage records. By the various analysis including graphical rainfall runoff correlations, the flow series were built up at all dam locations and at salient locations. The annual mean flows at Sudan border was estimated at 50 Bm3. For the Dedessa at Arjo, the correlated flows were established for 8 years (1911 to 1917 and 1932). The mean annual flow estimate was 4332.82 Mm3 (catchment area 9486 Square kilo meters) For the Dabana at Abasina, the mean annual flow was established at 1757.26 Mm3 (catchment area 3080 Square kilometers) For the Angar near Nekemte, the flow estimate at annual mean level was 2523 33 Mm3 (Catchment area 4350 square kilometers) 6 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 3 For the proposed Dedessa dam, with a catchment area of 3360 square kilo meters, the flow was estimated to be 1533.75 Mm . Similarly, for the dam site at Dabana, with a catchment area of 2654 kilo meters, the annual flow at mean level was estimated at 1515.63 Mm3. For the Angar, 2 dam sites had been identified, one at a location with a catchment area of 1780 square kilo m eters (AG-2 D am) a nd a nother a 11 ocation with a c atchment a rea o f 4 523 s quare k ilo meters (AG-6 Dam). The mean annual flows estimated respectively at these two locations were, 983.125 and 2251.26 Mm3. The section III, addresses the causative factors of floods in Abbay. The design rainfall for the basin was estimated based on 6 representative station's data. These are presented below, which are forming a data base, worth for review and up dating for adoption. 1 day design rainfall = 87 Milli meters 2 day design rainfall = 126 “ 5 day design rainfall = 185 “ 10 day design rainfall = 251 “ 15 day design rainfall = 321 “ 3 3 The design flood was estimated by physical approach using unit hydrograph, storm analysis and design flood hydrograph convolution for 21 dam sites. F or the others, flood frequency analysis based statistical return period floods were estimated. For the Dedessa DD-2 reservoir, the PMF was computed as 5390 m /sec with a base period of 99 hours. For the Dabana storage reservoir, the PMF estimate was at 4860 m /sec with a base period of 91 hours. For the Angar-2 reservoir with a catchment area of 1780 square Kilometers the PMF and the duration of the hydrograph were 3970 m /sec and 80 hours respectively. For the Angar-6 reservoir, the above respective figures were 6180 m /sec and 111 hours. For the Dedessa storage dam, the 5, 10, 25, 50,100, year floods were estimated to be 1700. 1900, 2100, 2300 and 2400 m /sec respectively. These formed a good data base for review in the present study. 3 3 3 7 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 The section IV, as indicated in the beginning deals with the water use studies. The 1960 watt use status was reviewed along with such water uses in villages. Then, the run off estimate have been adopted considering the envisaged irrigation and power developments in respectiv simulation study. Due to Dedessa dam USBR study, estimated a reduction of about 139 M nr in Dedessa flows to the Abbay.. On the whole, this USBR study is a useful one for the basin as a whole, though with paucity c data, because of its systematic treatment of hydrological and simulation aspects. 2.3 Country wide Master Plan studies - EVDSA/WAPCOS (1988-90) These studies were carried out during 1988-90 for country wide water and land resource development, covering all river basins. These were primarily desk studies for identifyin potential irrigation and hydropower sites based on country wide data collection and analyst coupled with detailed map studies. The study was addressing the Abbay basin also, along wit other basins. The USBR studies were reviewed in detail for the Abbay basin, an subsequently this study came out with modifications in the USBR sites in some cases an proposed many other sites as well. Though desk study, the data base available to this stud> on hydrological and hydro meteorological aspects were fairly adequate, because of the earlie pioneering works by USBR in establishing a good net work of such data observation stations. In this study, the rainfall as well as run off data for the vicinity of the identified projects wer collected and analyzed even though elaborate consistency checks were not under taken. Th data gaps filling and extrapolation of data have been done using statistical regression analysis using mostly bi-variate linear as well non linear correlations. In certain major dams, syntheti data generation by single site multi season stochastic models as well has been under taken. With respect to floods, the flood frequency analysis of the annual maximum flood series ha been carried out for the observation stations, in the vicinity of all identified potential dam sites The EV1 distribution with the method of maximum likelihood fitting has been followed in th above flood frequency analysis. On deciding the appropriate design criteria for the inflow design flood for each identified dam site, the flood peaks of the nearest gauging station hav been transferred to the dam site by empirical formula. For deriving the shape of the complet design inflow hydrograph at the dam site, the procedure as indicated below has been followed Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 For the nearest gauging station, the observed maximum flood hydrograph were isolated. For these a relationship between time and Q/QP ratio were established (t against Q/QP) where, t represents time, Q represents the discharge at't’ and QP is the peak discharge. Using this pattern of relationship the dam site hydrograph has been developed using the peak as estimated by flood frequency analysis. Simulation studies have been systematically carried out to judge the success of a scheme at criteria based reliability levels. Climatic data other than rainfall have also been documented, though without detailed processing or elaborations. The sediment rates as quoted by various previous studies of different basins have been adopted and used in simulation studies, considering life expectancy of projects as 50 years. The data base on the geometry of identified studies could be considered to be only approximate, as were based on purely topographic maps. The hydrological and hydro meteorological data were also not put into rigorous analysis, which is called for design of identified projects. However, this study along with USBR study back up gave a very good data base/ inventory of all possible exploitable dam sites in Abbay basin. This EVDSA/WAPCOS study has carried out such exercise in all the other river basins of the country as well. The dams identified in the Dedessa sub basin by this study is the Arjo Dedessa irrigation project. This proposal envisaged a dam, a chute spillway, an irrigation outlet with in take structure and a canal taking off on the right side. The project envisaged irrigation over 139,000 hectares with 160% irrigation intensity. The inflow in a 75% reliable year was estimated to be 776.80 Mm3. The 10,000 year flood with a peak of 890 cubic meters per second was getting moderated to an out flow hydrograph of peak of 642 cubic meters per second. The dead storage was fixed as 93 Mm , on the basis of annual rate of around 1.9 Mm . 2.4 Study by BCEOM - in association with ISL and BRG 1999 The study entitled "Abbay River Basin integrated development Master Plan Project" has been carried out with the following water resources oriented objectives. 3 3 9 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa Irrigation Project Meteorolo gical and Hydrolo gical Aspects May 2007 • Pr eparation of the river basin development m aster plan that will guid e the development of the resources of the basin potentially wit h respect to occurrence, distribution, quality and quantity of water resources for the coming 30 to 50 years. • To prepare water allocation and utilization plans under alternative development scenarios and to generate data, information and knowledge that will contribute to the future water allocation negotiations with downstream countries. The hydrological and hydro meteorological studies are more relevant for review in this section. These aspects have been covered in Section II, volume III of the Master Plan Study report. The basic climatic features and the climatological data of the Abbay river basin are discussed first. The rainfall data procured by the study was for 173 stations; the data length varied from 3 to 40 years, with associated monthly gaps. The data for other climatic factors were available for 108 stations. The field verification of these stations and equipments has also been under taken. The data is said to have been subjected to analysis and some errors connected with observations or processing were identified. The study has perhaps not attempted to improve the quality of such data on the plea that it was outside the consultant's capacity or responsibility. As such, the data base after screening and omitting such erroneous data is stated to be good. With respect to Hydrology in the part 2 of the above volume III, the following aspects have been covered systematically. • Basic Hydrographic Features • The Hydrometric net work • Review of previous studies • Data collection and Analysis • Sectoral methodology In the basic hydrographic aspects, a good work of preparing a map of the basin has been presented dividing the basin in to reasonably homogeneous areas, named Basin Units representing each of the catchment of one tributary or of several minor ones., with similar behaviors. With respect to the hydrometric net work, it has been considered to be adequate as Water Works Design & Supervision Enterprise ~ In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 per WMO norms, taking in to consideration 116 effective stations. The list of station, their locations, and drainage areas controlled have been well documented in Tables, appendices and maps. The master plan has found that the spatial distribution of the stations is not even or equitable. The parts of Beshilo, Weleka and Jemma were not adequately represented. Based on visit to all accessible observation stations, the master plan could identify. • In many cases, those stations which have been abandoned are not worth reconstruction either they had not been installed at optimal locations or the catchment area controlled by them was too small. • The numbers of automatic water level recorders still operational at the study time were low, though most of the stations had been equipped with such recorders at the time of their installations. • In many gauges stations the cables of bank operated cable way were missing. • On the other hand most staff gauges were in good condition and water level data was considered to be quite reasonable. There upon recommendations have been spelt out to be executed as and when budget, equipment and man power are made available. In the first observation, it is felt that what is meant as optimum could have been indicated. As far as hydrological net works are concerned, optimality varies depending upon the purpose of the net work. It could be a general purpose net work or could be a specific purpose net work. It is not clear that what is the master plan ascribed optimality. Further, since because a gauging station controls a small catchment, it seems they have been ignored by the master plan study. Measurement of discharges have a multipurpose oriented utilities like, ascertaining the sensitive or non sensitive areas, flood rate estimation or for a specific purpose including community based water harvesting schemes etc. Hence, the approach of ignoring stations with small catchments does not seem to be based on analysis of vivid concepts. Subsequently, the Master Plan has made a very brief review of hydrological aspects of previous studies. Again it is felt that a Master Plan of the magnitude could have reviewed in a 11 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt LtdArjoDedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 more elaborate manner. The review could have brought out each aspect of hydrological and hydro meteorological and simulation studies attempted by the earlier studies. Only, such detailed review would hare formed the datum to appreciate the further studies taken up by the Master Plan. Next, the data collection and analysis part is discussed in the report. The data sets processed were mean daily levels, discharge measurements and suspended sediment concentration data. With respect to data processing, the major study carried out seems to be review and reestablishing rating curves. The details on very many hydrological analysis, which should have been carried out before final use of he data in basin simulation are not finding a place in the hydrology volume (not explicitly described). With respect to rating curve analysis, detailed exploration of the discharge data of 121 stations, have been made and equation of the form. Q = a (H-H ) o b have been fitted, which is common practice in Hydrology. It is a good thing that Master Plan has used both analytical and graphical methods in parallel in establishing such rating curves. For all the stations analyzed, a total of 253 equations have been arrived with good correlation coefficients of 0.90 and above in 90% of the pairs of data. The discharges have been estimated using these equations. Then Master Plan study states that on checking homogeneity, the monthly values wee extracted. It would have been better to appreciate if the nomenclature of Homogeneity with justifications had been indicated in the report. It is also stated further in the Master Plan that the discharges were compared with earlier studies and the results did not have major variations. Again it is felt that better appreciation could have been made, if the concept of major variation had been spelt out. Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Subsequently, water Balance model of the basin has been formulated taking only representative s tations so a s t o m ake t he m odel comprehensive without o ver loading. T he selection criteria used for identification and inclusion of hydrometric stations in the model seem to be appropriate. The input hydrological discharges were established on daily time resolution level for the period of 33 years (1960-1992). The gap filling techniques seem to have in built subjective inferences. With respect to assessment of water availability, a map has been prepared on a scale of 1:1000, 000 to estimate the global water availability to be applied to all potential water resources development sites in Abbay basin. This map could be of use just for a preliminary estimate of annual flows at pre-feasibility level. The water availability has been further estimated by detailed water balance model. In this, in the first run, the present scenario has been in built and for 18 net work stations, and water availability has been estimated. The salient findings of this run are as below which are in order • The annual average volume flowing across the border from Abbay River is 50.30 Bm . • About 83% of the average annual volume at border is flowing in 4 months (July - 3 October), while the 4 months from February to May ac count for les s than 4 % of the mean annual flow. • The average annua l flow at the out let from T ana repr esent s about 7% of t he above annual flows at borde r. Floods: The highest flood hydrographs recorded at each of the water balance net work stations have been put to analyses to establish the relation between time and Q/Qm ratios. Then flood frequency analysis of the annual maximum discharges has been carried out by Gumbel's EV1 distribution to estimate the return period flood peaks. (It is not clear whether the annual maximum observed peaks were converted in to instantaneous peaks). Further another relationship connecting catchment size to flood peak has been derived for 2 groups of catchment sizes; one for catchment groups having catchment area less than 10,000 km2 and another one for catchment sizes more than 10,000 km2. It has been concluded that the formulae derived so can be used for pre-feasibility level studies only. Master Plan has --------------------------------------------------- ------- ---------------------- ---------------------------- _-----------------------13 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 attempted to link slope of different catchme nts with flood discharge rates, which also did not exhibit any correlation. It has been opined in the Master Plan that rainfall runoff correlations were not applicable. No data or study results on flood side will be of any use to the present project specific study. The flood studies adopted by the Master Plan might be useful for preliminary estimates level only. Sediment transportation: For 96 stations, sediment rating curves have been analyzed with available data, on the basis of following type of relationships. QL = a (H-Ha)b linking water level with flow QS = aQL? linking sediment discharge QS with liquid discharge QL with a and |3 as parameters. The total sedimentation transported is accounted as the sum of suspended sediment load and bed load. For bed load estimation, 3 different options are indicated, with a sort of recommendation on Meyer Peter equation. However, at the end of sediment deliberations, Master Plan study has felt that a global estimate of bed load transport for the whole Abbay basin or for any of the large sub basins has no meaning; Hence the study has further stated that at Master Plan level, considering the amount of bed load transport definitely being small compared to suspended load and considering the size of the Abbay basin, it was not necessary to proceed with data collection for evaluation of bed load estimation. The above statement of Master Plan is not able to be appreciated without elucidation. Subsequently, the Master Plan has prepared maps related to erosion. The other studies connected with water balance and water resources modeling seem to be in order. Software WATBAL has been used in the modeling for various scenarios of development after initial calibration for the present scenario. These have been done for 14 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.ArjoDedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 present situation • Future situation encompassing ■ tai fei fti ■ ■ H M ■ 0 o Scenario N° 1 (identified projects 1) o Scenario N° 2 o Scenario N° 3 o Scenario N° 4 (identified projects 2 including Tana Beles) (identified projects in main stream) (Full development) The results could be utilized for comparing the results of specific sub basin oriented modelinc studies, like the one under taken in the present study. 2.5 Study by Ministry of Water resources for Lower Dedessa (2001) This is a reconnaissance level study for the Lower Dedessa Medium hydro power project. Thu gives a vivid analysis of the data and the Hydrological features of the Dedessa sub basin. The dam site controlling a catchment area of 18,200 square Kilo meters, has the following watei resources potential according to this study. Mean annual flow =7290 Mm3 Annual Flow in 75% exceedance year=6300 Mm3 Annual Flow in 80% exceedance year=6100 Mm3 Annual Flow in 90% exceedance year=5230 Mm3 Annual Flow in 95% exceedance year=4600 Mm3 The following are the frequency floods estimates 10 Year return period flood 20 Year return period flood 100 Year return period flood 1000 Year return period flood 10000 Year return period flood = 1977 cubic meter per second =2210 cubic meter per second =2735 cubic meter per second =3480 cubic meter per second =4224 cubic meter per second A sediment rate of 500tons per square kilo meter per year has been adopted. This give annual sediment load of 9.1 million tons per year. The 50 year sediment volume of 329 Mm had been accounted for reservoir sizing. Water Works Design & Supervision Enterprise 1: In Associate with Intercontinental Consultants and Technocrats Pvt. LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 The study had analyzed the energy generation with a net head of 133 meters and with the assumption of regulation of 70% of the mean annual flow. The energy that could be generated so, was estimated to be 1580 GWh per year, with an installed capacity of 299 MW, on adopting a plant factor of 0.6. This is very relevant to Dedessa sub basin and the present study. The useful data were taken in to account. 2.6 Utility of Earlier Studies All the earlier studies reviewed have some useful data base. All the useful information (data of all the above studies have been reviewed and utilized as per need and appropriateness). However, the present study is specific sub basin (Dedessa) development study, and as such, systematic hydrological and modeling studies are warranted with modern tools of analysis. This sectoral report narrates these specific studies. 16Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects 3. DATA BASE May 2007 For the study towards the development of the Dedessa sub basin, the data on climate, river flows and sedimentation become relevant with respect to Hydrological Modeling and W ater Resources Planning. 3.1 Climatological Data The climatological data like sunshine duration, relative humidity, wind speeds temperature in the resolution levels of monthly means of daily means, monthly mean of daily maximum and monthly mean of daily minimum, become very important parameters with respect to the proposed command area development. These, in association with command area rainfall form the basic inputs for the estimation of the crop water requirement exercise. A vivid analysis follows on these important parameters in the section 4 of this report. 3.2. Rain fall The rainfall requires critical analysis for the dam site and the upstream for appreciating and developing floods; either as a full hydrograph or in the form of flood peak rate, expected at different Exceedance probability levels (return periods). The rainfall data needs to be analyzed in its various forms, like maximum of observed 1 day/2 day or 3 to 15 days values, or as a time series of observed annual maximum 1 day rainfall or as monthly / fortnightly totals as per analysis at different stages. The analysis has to under take the gambit of short duration rainfall intensities as well, in connection with design of drainages, and return period rainfall peaks for the design of flood control works, in the downstream of the dam, in and in the vicinity of the proposed command area. 3.3. River Discharge Likewise, the river flows data time series, preferably on monthly or fortnightly time resolution levels, forms the fore runner for establishing water resources availability, for performing simulation whether as basic historical time series or indirectly through synthetically generated time series (mostly generated by a stochastic generation scheme); where as, the same flow data has to be analyzed in a different form as discharge (flow rates instead of flow volumes) with respect to flood analysis. Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 17ArjoDedessa Irrigation Project Meteorological and Hydrological Aspects 3.4. Sedment Data May 2007 The sediment data is obviously required to plan the size of the storages, for apportioning the active and inactive storage spaces and for determining the revised geometry of the storage after certain design life, (revised elevation - area - capacity relationship); as this revised relation is used in the simulation modeling. The water quality is another aspect, which needs to be addressed in Hydrological study along with low flow analysis for mandatory downstream releases, closely associated with the concerns of environmental and ecological aspects. With such appreciation of the frame work of hydrological studies and modeling, the data base was established, as elaborately discussed in the Interim report. However in the following sections and in the annexure enclosed with this report, the data base on climatology, hydrology including sedimentation, floods are indicated. All the data available in a regional sense, up to date (2004) were brought to analysis desk and appropriately included. Water Works Design & Supervision Enterprise IS In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa Irrigation Project u^nrntogical and Hydrological Aspects- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - «n of reference evapotranspiration May 2007 4. 4.1 Introduction The climate of the Arjo Didessa catchment results from its location and elevation (1300 to 3012 meters). The list of stations for observations of meteorological data along with length of records and availability of data types is given in Table 4.1. All relevant types of data have been recorded at Jimma (located very close to the head of the Didessa catchment) stations since 1953. Rainfall and temperature have been observed at Didessa and Bedele. Rainfall and temperature have been also recorded at Dembi and Agara stations. Climatic data for the project area such as temperature, relative humidity, sunshine hours, wind speed and rainfall have been collected and reviewed. Consistency tests, data rectification and other adjustments have been performed as necessary, data gaps have been filled using interpolation and correlations methods as appropriate. The FAO Penman-Monteith method is maintained as the sole standard method for the computation of crop reference evapotranspiration (ET0) from meteorological data. This section describes how the monthly ET0 is determined from temperature, humidity, wind-speed and sunshine hours data collected at Bahir Dar station. The ET0 calculation has been carried out by means of a computer. The FAO Penman-Monteith equation determines the evapotranspiration from the hypothetical grass reference surface and provides a standard to which evapotranspiration for various crops growing in the Arjo-Dedessa project command area can be related. The methods for calculating evapotranspiration from meteorological data require various climatological and physical parameters. Some of the data are measured directly in Bahir Dar meteorological station. Other parameters are related to commonly measured data and can be derived with the help of a direct or empirical relationship. This section discusses the source and computation of all data required for the calculation of the reference evapotranspiration by means of the FAO Penman-Monteith method. 19 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 The meteorological factors determining evapotranspiration are weather parameters whict provide energy for vaporization and remove water vapour from the evaporating surface. The principal weather parameters to consider are presented below. The data obtained from the Bedele, Dedessa and Jimma stations are assumed directly applicable to the Arjo Dedesss Irrigation Project with application of appropriate information transfer mechanisms. 4.2 Meteorological Data 4.2.1 Meteorological Observation Stations Five meteorological observation stations are located in and around the Arjo-Dedessa Irrigation Project area. These meteorological data are obtained from the National Meteorological Services Agency (NMSA). Out of these Jimma is Class 1 station that include observations of rainfall, temperature, relative humidity, sunshine duration, wind speed, and evaporation. Bedele and Dedessa are also Class 1 stations but do not include sunshine duration. In addition, Agaro and Dembi are Class 3 stations that include observations of rainfall and temperature. The longest record that covers 50 years of meteorological data is available at Jimma station that includes rainfall and temperature data since 1952. Agaro and Dembi stations are located within the cachment area of the proposed dam site Jimma station is located at approximately at 10 km from the divide of Dedessa catchment. Bedelle station is located close to the proposed irrigation command area of the project. Dedessa station is located further downstream of the command area. The details like location altitude, year of establishment along with their class are available in Table 4.1. Meteorological data available at the five observation stations located in and around the project area have been collected. The types of meteorological data available at these stations along with the length of data are given in Table 4.2. Jimma Airport meteorological station is taken to be the most reliable Class I station from which meteorological information relevant to the project area has been derived. The data from Jimma station has been used for both the catchment study and estimation of meteorological variables at the irrigation command area. The necessary adjustment for the differences in elevation has been made in transferring the data. Meteorological information from Agaro and Dembi stations 20 Water Works Design & Supervision Enterprise in Associate with Intercontinental Consultants and Technocrats Pvt LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 which are located within the dam site catchment have been used for catchment study, in addition to Jimma station. Similarly, meteorological data of Bedelle and Dedessa have been used in addition to the data obtained from Jimma station for estimating rainfall and evapotranspiration at the proposed irrigation command. In summary, climatologicall data obtained from Bedele, Dedessa and Jimma stations were found to be the most reliable and relevant for use in the analysis of rainfall for the Arjo Dedessa irrigation project. Bedele is geographically the closest station to the command area Dedessa station and the command area are located at the same elevation (i.e, both 1330 m asl). Jimma station (which is Class I) has the longest record of all the stations within the neighbourhood of the command area so as to be index station in extrapolating and interpolating missing and short term of climatic data relevant to the Arjo Dedessa catchment and command area. 4.2.2 Air temperature In the project farm area, the mean monthly temperature variations throughout the year are minor, being 20.0°C in December to 25.4°C in March. The mean monthly temperatures of the command area is given in Table 4.3 and graphically illustrated by Figure 4.1. Temperature data have been used in estimating evapotranspiration rates from reference crops. Agrometeorology is concerned with the air temperature near the level of the crop canopy. In traditional and modern automatic weather stations the air temperature is measured inside shelters (Stevenson screens or ventilated radiation shields) placed in line with World Meteorological Organization (WMO) standards at 2 m above the ground. Minimum and maximum thermometers record the minimum and maximum air temperature over a 24-hour period. Due to the non-linearity of humidity data required in the FAO Penman-Monteith equation, the vapour pressure for a certain period should be computed as the mean between the vapour pressure at the daily maximum and minimum air temperatures of that period. The daily maximum air temperature (Tmax) and daily minimum air temperature (Tmin) are, respectively, the maximum and minimum air temperature observed during the 24-hour period. The mean daily air temperature (Tmean) is only employed in the FAO Penman-Monteith equation to calculate the 21 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 slope of the saturation vapour pressure curves (A), estimating saturation vapour pressure (e°(T) and oTK4 (Stefan-Boltzmann law). The solar radiation absorbed by the atmosphere and the heat emitted by the earth increase the air temperature. The sensible heat of the surrounding air transfers energy to the crop and exerts as such a controlling influence on the rate of evapotranspiration. In sunny, warm weather the loss of water by evapotranspiration is greater than in cloudy and cool weather. 4.2.3 Air humidity Mean humidity values vary between 56.63 percent in March to 88.63 percent in September. The mean monthly humidity of the command area is given in Table 4.3 and graphically illustrated by Figure 4.2. Data of humidity have been used in estimating evapotranspiration rates from reference crops. The relative humidity (RH) expresses the degree of saturation of the air as a ratio of the actual (e ) to the saturation (e°(T)) vapour pressure at the same temperature (T). Relative humidity is a the ratio between the amount of water the ambient air actually holds and the amount it could hold at the same temperature. It is dimensionless and is commonly given as a percentage. Although the actual vapour pressure might be relatively constant throughout the day, the relative humidity fluctuates between a maximum near sunrise and a minimum around early afternoon. The variation of the relative humidity is the result of the fact that the saturation vapour pressure is determined by the air temperature As the temperature changes during the day, the relative humidity also changes substantially. While the energy supply from the sun and surrounding air is the main driving force for the vaporization of water, the difference between the water vapour pressure at the evapotranspiring surface and the surrounding air is the determining factor for the vapour removal. Well-watered fields in hot dry arid areas consume large amounts of water due to the abundance of energy and the desiccating power of the atmosphere. In humid tropical regions, notwithstanding the high energy input, the high humidity of the air will reduce the evapotranspiration demand. In such an environment, the air is already close to saturation, so that less additional water can be stored and hence the evapotranspiration rate is lower than in arid regions. 22 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects . 4.2.4 Wind speed Mean wind speed values vary between 0.48 meter per second in November to 1.08 meter per second in April. The mean monthly wind speeds of the command area are given in Table 4.3 and graphically illustrated by Figure 4.3. Average wind speed recorded at Jimma station in meters per second (m/s) is taken as wind speed information relevant for the Arjo-Dedessa command area as there is no reliable data at other climatic stations nearby. Time series aspect of the wind data is not considered as it exhibits unacceptable erratic variation within the record period. Using the mean values against the time series data has been tested for Bahir Dar station and resulted in equal result for monthly and annual evapotranspriation estimates. However, the mean wind values produced an estimated coefficient of variation (CV) of 2.2% instead of 2.4% estimated from the time series. Wind is characterized by its direction and velocity. Wind direction refers to the direction from which the wind is blowing. For the computation of evapotranspiration, wind speed is the relevant variable. Wind speed is measured with anemometers. The anemometers commonly used in weather stations are composed of cups or propellers which are turned by the force of the wind. By counting the number of revolutions over a given time period, the average wind speed over the measuring period is computed. The process of vapour removal depends to a large extent on wind and air turbulence which transfers large quantities of air over the evaporating surface. When vaporizing water, the air above the evaporating surface becomes gradually saturated with water vapour If this air is not continuously replaced with drier air, the driving force for water vapour removal and the evapotranspiration rate decreases. 4.2.5 Solar radiation Mean sunshine duration is 8.3 hours in December and is reduced to 3.7 hours during July. The mean monthly sunshine durations of the command area are given in Table 4.3 and graphically illustrated by Figure 4.4. Data of sunshine hours have been used in estimating evapotranspiration rates from reference crops. The relative sunshine duration (n/N) is another ratio that expresses the cloudiness of the atmosphere. It is the ratio of the actual duration of sunshine, n, to the maximum possible 23 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 duration of sunshine or daylight hours N. In the absence of any clouds, the actual duration of sunshine is equal to the daylight hours (n = N) and the ratio is one, while on cloudy days n and consequently the ratio may be zero. In the absence of a direct measurement of R , s the relative sunshine duration, n/N, is often used to derive solar radiation from extraterrestrial radiation. As with extraterrestrial radiation, the day length N depends on the position of the sun and is hence a function of latitude and date. The evapotranspiration process is determined by the amount of energy available to vaporize water. Solar radiation is the largest energy source and is able to change large quantities of liquid water into water vapour. The potential amount of radiation that can reach the evaporating surface is determined by its location and time of the year. Due to differences in the position of the sun, the potential radiation differs at various latitudes and in different seasons. The actual solar radiation reaching the evaporating surface depends on the turbidity of the atmosphere and the presence of clouds which reflect and absorb major parts of the radiation. When assessing the effect of solar radiation on evapotranspiration, one should also bear in mind that not all available energy is used to vaporize water. Part of the solar energy is used to heat up the atmosphere and the soil profile. 4.3 Penman-Monteith Equation From the original Penman-Monteith equation and the equations of the aerodynamic and canopy resistance, the FAO Penman-Monteith equation can be expressed as follows: ETo = Q408AJP.J] T) + y [900/(T + 273)1 uJe, - eJ. A+ y (1+0.34 ET0 = reference evapotranspiration [mm day ], (2.1) where R = net radiation at the crop surface [MJ m' n 1 2 day' ], 1 G = soil heat flux density [MJ m'2 day' ], 1 1 T = air temperature at 2 m height [°C], u 2 = wind speed at 2 m height [m s' ], e = saturation vapour pressure [kPa], e = actual vapour pressure [kPa] = e RH s a s mean, Water Works Design & Supervision Enterprise 24 in Associate with Intercontinental Consultants and Technocrats Pvt. LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects e s - ea = saturation vapour pressure deficit [kPa], A = slope vapour pressure curve [kPa °C'1], Y = psychrometric constant [kPa °C ]. RH = relative humidity divided by 100 Rn = Ros - Rm 1 and R ns = 0.77 Rs Rs = (0.25 + 0.50 n/N) Ra n = ctTk4 (0.34-0.14 ea05) (0.135 Rs/Ro - 0.35) R, R so = [0.75 + 2 (Altitude)/100000] Ra (2-2) (2-3) (2.4) (2.5) (2.6) The calculation procedure consists of the following steps: 1. Derivation of s ome c limatic p arameters from t he d aily m aximum (Tmax) a nd m inimum (Tmin ) air temperature, altitude (z) and mean wind speed (u ). 2 2. Calculation of the vapour pressure deficit (es - e ). The saturation vapour pressure (es) a is derived from Tmax and Tmin, while the actual vapour pressure (e ) can be derived from a the dewpoint temperature (Tdew), from maximum (RHmax) and minimum (RHmin) relative humidity, from the maximum (RHmax), or from mean relative humidity (RHmean). 3. Determination of the net radiation (R„) as the difference between the net shortwave radiation (Rns) and the net longwave radiation (R ,). n In the calculation sheet, the effect of soil heat flux (G) is ignored for daily calculations as the magnitude of the flux in this case is relatively small. The net radiation, expressed in MJ rn2 day'1, is converted to mm/day (equivalent evaporation) in the FAO Penman-Monteith equation by using 0.408 as the conversion factor within the equation. 4. ET0 is obtained by combining the results of the previous steps. The following values were selected from FAO 1998 (Crop Evapotranspiration - Guidelines for computing crop water requirements - FAO Irrigation and drainage paper 56). o Psychometric constant (y) for different altitudes (z), 25 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Mete orological and Hydrological Aspects May 2007 o Slope of vapour pressure curve (A) for different temperatures (T), o Saturation vapour pressure [(e°(T)] for different temperatures (T), o Daily extraterrestrial radiation (R ) for different latitudes, a o Mean maximum possible daylight hours (N) for different latitudes, 4 o oTk (Stefan-Boltzmann law) at different temperatures (T) The estimated mean daily and monthly reference crop evapotranspiration magnitudes (in mm) from 1991 to 2004, based on Penman-Monteith Equation, are presented by Tables 4.3 and 4.4, respectively and graphically illustrated by Figure 4.5 The results of the meteorological analysis including the rainfall are provided in the annexture A. Table 4.1: Table Details of Meteorological Observation Stations located in and around the project area. S.No Station Name Latitude North Longitude East Deg. | Min. Deg. Min. Altitude (m) Period 1 Agaro 2 Bedelle 3 Dedessa 4 Dembi 5 Jimma 07 51 08 27 09 33 08 04 07 40 36 36 36 20 36 06 36 37 36 50 1700 2005 1300 1950 1725 1980-2004 1967-2004 1971-2004 1954-2004 1952-2004 Table 4.2: Types of Climatic Data available at the various Meteorological Observation Stations No I Station name Yrs RF Tm RH WS SD 1 hr 1 day Rday 1 Didessa 2 Bedele 3 Dembi 4 Agaro 5 Jimma 30 28 20 21 50 XXX X XXX X XX XX XXXXXXXX Yrs refer to rainfall series RF monthly rainfall Tm SD sunshine duration average temperature 1 hr RH relative humidity maximum 1-hour rainfall 1 day WS wind speed maximum 1-day rainfall Rday number of rain days 26 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.ArjoDedessa Irrigation Project Meteorologic al and Hydrological Aspects May 2007 Table 4.3: Summary of Meteorological Characteristics at Project Area Jan Feb March April May June July Aug Sept Oct Nov Dec Monthly Mean Temperature in oC Average 21.9 23.15 25.4 25.05 24.03 22.09 21.32 21.19 21.83 22.35 22.144 19.99 CV 0.048 0.044 0.036 0.065 0.071 0.029 0.028 0.031 0.027 0.038 0.0544 0.066 Skew 0.071 -0.58 0.067 -3.628 -3.23 0.117 0.275 0.007 0.93 0.353 -0.118 -0.02 Min 19.5 20.44 23.63 16.26 15.89 20.96 19.99 19.88 21.06 20.19 19.081 16.92 Max 24.6 24.9 27.37 27.72 26.19 23.41 22.72 22.34 23.2 24.25 25.051 22.88 Relative Humidity (%) Average 64.77 58.97 56.63 67.97 75.72 81.07 87.46 88.52 88.63 84.55 79.366 72.44 CV 0.099 0.127 0.084 0.073 0.053 0.047 0.061 0.048 0.03 0.053 0.0705 0.089 Skew -0.27 -0.27 -0.37 0.474 -0.2 -0.87 -2.92 -2 0.249 0.19 0.287 -0.13 Min 51.5 43.2 45.09 57.42 65.23 65.8 61.77 72.23 82.49 74.24 67.667 55.37 Max 77.3 71.68 64.08 82.17 86.18 90.3 98.1 97.53 95.67 94.73 93.187 85.13 Wind Speed (m/s) Average 0.62 0.8 1.0 1.08 1.04 0.86 0.62 0.51 0.5 0.51 0.48 0.51 Sunshine Hours (hrs/day) Average 8.155 7.638 7 452 7.287 7.624 6.061 3.703 4.059 6.164 7.855 8.3245 8.306 CV 0.125 0.166 0.145 0.165 0.157 0.189 0.243 0.23 0.22 0 139 0.2139 0.104 Skew -0.47 -0.36 -0.27 -1.12 0.141 -0.36 0.248 -0.42 -0.27 0.138 -3.525 0.971 Min 6.05 4.905 4.592 3.304 5.428 3.364 2.277 1.6 2.622 5.778 0.1121 6.634 Max 10 9.919 9.744 9.44 10.15 8.12 5.445 6.2 9.12 10.08 10.201 11.02 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd. 27Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 4.4: Summary of Estimated Mean ETo of Arjo Dedessa Project Area May 2007 Jan Feb March April May June July Aug Sept Oct Nov Dec Daily: Estimated ETo (mm/day) Average 3.7 4.11 4.62 4.51 4.33 3.58 2.96 3.11 3.81 4.03 3.79 3.44 CV 0.05 0.06 0.05 0.07 0.08 0.08 0.08 0.08 0.09 0.06 0.12 0.05 Skew -0.47 -0.77 -0 -0.95 -0.65 -0.19 0.33 -0.51 -0.18 -0.27 -3.11 0.88 Min 3.23 3.38 3.99 3.44 3.35 2.97 2.58 2.44 2.88 3.5 1.95 3.11 Max 4.03 4.49 5.24 5.13 5.06 4.15 3.46 3.59 4.49 4.47 4.24 3.96 Monthly: Estimated ETo (mm/month) Average 115 115 143 135 134 107 91.8 96.5 114 125 114 107 CV 0.05 0.06 0.05 0.07 0.08 0.08 0.08 0.08 0.09 0.06 0.12 0.05 Skew -0.47 -0.77 -0 -0.95 -0.65 -0.19 0.33 -0.51 -0.18 -0.27 -3.11 0.88 Min 100 94.8 124 103 104 89 80 75.7 86.5 109 58.6 96.4 Max 125 126 162 154 157 125 107 111 135 139 127 123 Estimated Eto (mm/day) (form average values of data) Average 3.69 4.08 4.58 4.48 4.28 3.57 2.95 3.10 3.75 4.00 3.79 3.44 Estimated Eto (mm/month) (form average values of data) Average 114 114 142 134 133 107 92 96 113 124 114 107 Note: Total annual ETo = 1397 mm Water Works Design & Supervision Enterprise 28 In Associate with Intercontinental Consultants and Technocrats Pvt. LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 4.5j Magnitude of ETo at given non-exeedance probability level May 2007 Non-Exd (mm/day) Probalility Jan Feb Mar April May June July Aug Sept Oct Nov Dec (•/.) 55 3.72 4.14 4.65 4.56 4.37 3.61 2.99 3.14 3.85 4.06 3.84 3.46 60 3.75 4.18 4.68 4.60 4.42 3.65 3.02 3.18 3.89 4.09 3.90 3.49 65 3.77 4.21 4.71 4.64 4.47 3.68 3.05 3.21 3.94 4.12 3.96 3.51 70 3.80 4.25 4.75 4.69 4.52 3.72 3.09 3.24 3.99 4.15 4.02 3.53 75 3.83 4.29 4.79 4.74 4.57 3.77 3.12 3.28 4.04 4.19 4.09 3.56 80 3.86 4.33 4.83 4.80 4.63 3.81 3.16 3.32 4.09 4.23 4.16 3.59 85 3.90 4.38 4.88 4.86 4.70 3.87 3.21 3.37 4.16 4.28 4.25 3.63 90 3.95 4.45 4.94 4.95 4.79 3.93 3.27 3.44 4.24 4.34 4.35 3.67 95 4.02 4.54 5.03 5.07 4.93 4.04 3.35 3.53 4.36 4.43 4.51 3.74 Avg 3.70 4.11 4.62 4.51 4.33 3.58 2.96 3.11 3.81 4.03 3.79 3.44 Non-Exd 6mm/m onth) Probalility Jan Feb Mar April May June July Aug Sept Oct N ov Dec Annual (%) 55 115 116 144 137 136 108 93 97.4 116 126 115 107 1405 60 116 117 145 138 137 109 94 98.4 117 127 117 108 1412 65 117 118 146 139 138 111 95 99.5 118 128 119 109 1420 70 118 119 147 141 140 112 96 101 120 129 121 110 1428 75 119 120 148 142 142 113 97 102 121 130 123 110 1436 80 120 121 150 144 144 114 98 103 123 131 125 111 1446 85 121 123 151 146 146 116 99 105 125 133 127 112 1457 90 122 125 153 148 149 118 101 107 127 135 131 114 1471 95 125 127 156 152 153 121 104 109 131 137 135 116 1492 Avg 115 115 143 135 134 107 92 96.5 114 125 114 107 1397 Non-Exd Probalility Growth factor (Xp) Jan Feb Mar April May June July Aug Sept Oct Nov Dec Annual (%) 55 1.01 1.01 1.01 1.01 1.01 1.01 1.01 1.01 1.01 1.01 1.01 1.01 1.005 60 1.01 1.02 1.01 1.02 1.02 1.02 1.02 1.02 1.02 1 02 65 1.02 1.02 1.02 1.03 1.03 1.03 1.03 1.03 1.03 1.02 1.04 1.02 1.016 1.03 1.01 1.01 Avg 1 1 1 1 1 1 1 1 1 1 1 1 70 1.03 1.03 1.03 1.04 1.04 1.04 1.04 1.04 1.05 1.03 1.06 1.03 1.022 75 1.04 1.04 1.04 1.05 1.06 1.05 1.05 1.06 1.06 1.04 1.08 1.04 1.028 80 1.04 1.05 1.05 1.06 1.07 1.07 1.07 1.07 1.07 1.05 1.1 1.04 1 035 85 1.05 1.07 1.06 1.08 1.09 1.08 1.08 1 08 1.09 1.06 1.12 1.05 1.043 90 1.07 1.08 1.07 1.1 1.11 1.1 1.1 1.1 1.11 1.08 115 1.07 1.053 95 1.09 1.1 1.09 1.12 1.14 1.13 1.13 1.13 1.14 1.1 119 1.09 1.068 1 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 29Wind speed (m/s) Temperature (oC) Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Figure 4.1: Mean Monthly Temperature at Arjo Dedessa Project Area May 2007 Figure 4.2: Mean Monthly Relative Humidity at Arjo Dedessa Project Area Figure 4.3: Mean Monthly Wind Speed at Arjo Didesa Project Area Figure 4.4: Mean Monthly Sunshine Hours at Arjo Dedessa Project Area Water Works Design & Supervision Enterprise ’ In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 30Arjo-Dedessa Irrigation Project Meteorologic al and Hydrological Aspects May 2007 Figure 4.5: Mean Monthly ETo at Arjo Dedessa Project Area I I Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 31Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 5. RAINFALL ANALYSIS 5.1 Introduct ion The rainfall data obtained f rom B ede le, Dedessa and Jimma sta tions were found t o be the most reliable and relevant for use in th e analysis of rainfall for the Arjo Dedessa irrigation project. Bedele is geographically the closest station to the command area. Dedessa station and the c ommand a rea a re I ocated a 11 he s ame e levation (i.e, b oth 1 330 m a si). J imma s tation (which is Class I) has the longest record of all the stations within the neighbourhood of the command area so as to be index station in extrapolating and interpolating missing and shortage of rainfall data relevant to the Arjo Dedessa catchment and command area. The rainfall in the Arjo Didessa Catchment as well as in its surrounding is uni-modal type. Most of the rainfall is concentrated in the May to September covering with virtual drought from November through March. The five wettest months cover 63 percent of the total annual rainfall. The dry season, being from November to February (four months) has a total rainfall of about 7% of the mean annual rainfall. The mean monthly rainfall for stations in the project area is given in Table 5.1 and their pattern is graphically illustrated in Figure 5.3. The length of rainfall data collected from Jimma is relatively more reliable compared to the data set collected from other stations because of its long record length and shorter time interval of observation. Didessa and Bedele stations also provide more relevant rainfall data that can be adopted for the command area since Bedele is close to the project area and Didessa station is located within the same climatic zone as that of the project area. 5.2 Rainfall Internal and External Consistency Though a good data base has been established for rainfall, considering the data of the three stations, namely, Dedessa, Jimma and Bedele, it is customary in Hydro-meteorological studies to firm up the consistency with statistical analysis. The trend in the annual rainfall pattern is a relevant aspect with respect to the behavior of the rainfall and to compare such behavior with those of other relevant stations involved in the study with a view to firm up external consistency. Accordingly, a 3 year moving average analysis 32 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 was taken up for each of the 3 stations. The results are shown in the figures 5.1 (a), (b) and (c). These show similar trends. Similarly, an analysis with respect to the cross correlation structure among the 3 stations was carried out. The cross correlation matrix depicts the following status (Table 5.2) at annual time resolution level, which is not abnormal. Then, the single mass curve analysis was taken up for each of these 3 stations. (Figures 5.2. (a), (b) and (c). These also do not indicate any abnormality to reject this data set. As such, these rainfall data were used in its different forms for various spectrums of the analysis. 5.3 Estimation of Rainfall Reliability Level Using the rainfall and irrigation water available for the command area requires the magnitude and reliability level of rainfall corresponding to various rainfall time intervals. Annual, monthly and half monthly intervals are chosen durations for the Arjo-Dedessa irrigation project. Rainfall reliability level and magnitude can be analyzed by making use of theoretical distributions. In this study the Extreme Value Type III (minimum) distribution was utilized. The distribution is also known as the Weibull distribution or as Gumbel's Limited distribution of the Smallest Value. Naturally rainfalls are bound by zero or other higher values on the left. The Weibull (or EV3) distribution can be expressed as: (5.1) where Xp = E + (U-E) [-ln(1-p)]1,A Xp - magnitude of rainfall corresponding to probability level of p, The moment estimates of the parameters E (the lower limit), U and a fi.e., E, U and A) can be obtained from the following equation: U = Xm + Cv.Xm Y(a) E = U - Cv.Xm.Z(a) Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd (5.2) (5.3) 33Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects where Xm = mean value, Cv = coefficient of variation = standard deviation divided by the mean, Y(a) = (2-Cs)/6 Z(a) = [8+(3-Cs) ]/9 and A =3/(1+Cs) Cs = skew coefficient calculated from data May 2007 3 The estimated monthly and half-monthly parameters of Weibull Distribution are given in Table 5.3 and 5.5, respectively. The following algorithm were used in the derivation of annual, monthly, and half-month 55 to 95 percent reliability levels. 1. Averages, standard deviations, standard deviation, skew coefficient of annual, monthly and half-monthly averages were calculated. 2. Weibull Distribution parameters (namely U, E and A) corresponding to annual, monthly and half-monthly rainfalls were calculated from the statistics. 3. Magnitudes of rainfalls corresponding to 55 to 95 percent reliability levels were estimated. The results so obtained are given in Tables 5.4 and 5.6 for monthly and half-monthly time intervals, respectively. The half monthly rainfall magnitudes as a percentage of mean, corresponding to various reliability levels are shown in Table 5.7. 5.4 Estimation of Maximum Rainfall Frequencies For internal drains and smaller control works, the need for various return period rainfall and with different durations were found to be necessary. In general, maximum rainfall magnitudes 34 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 of intensity corresponding to various return periods (or probability levels) can be estimated by applying the following form. I T = Im [1+CV.K(T)] (5.4) where l T = rainfall intensity corresponding to return period of T years (mm), Im = mean of annual maximum intensity of rainfall (mm/hr), CV = coefficient of variation of annual intensity of rainfall, K(T) = frequency factor For Extreme Value Type I (or Gumbel) Distribution, K(T) = -0.779 (0.577 + ln.ln(T/{(T -1)]} The maximum annual 24hr rainfall service is given in Table 5.8. (5.5) The results of the maximum 24-hr and 1-hr rainfall frequencies are presented in Table 5.9 The 1-hr rainfall intensities were estimated by the formula derived for Ethiopia expressed as l h = bUO 523 + 0 15 In D) (3.6) where l h = maximum rainfall intensity corresponding to duration D (mm/hr), In = natural logarithm D = duration of lh (hr), l 24 = maximum rainfall intensity corresponding to duration 24 hours (mm/hr) The rainfall magnitudes for higher durations, 2 days & 3 days have also been analysed using the EVI frequency distribution. The results for various return periods are shown in Table 5 10 More details of the analysis are available in the annexure A "Results obtained from meteorological Analysis". 35 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects The annual rainfall available at different years are given below May 2007 Near year = 1453 mm 75 % year = 1148 mm 80 % year = 1090 mm 95 % year = 853 mm Table 5.1: Mean Monthly Rainfall Description Jan Feb March April May June Didessa 3 6 26 49 158 274 Bedele 18 23 65 105 239 291 Dembi 25 44 101 126 223 303 Agaro 24 36 88 93 149 232 Jimma 33 49 88 133 172 219 July Aug Sep Oct Nov Dec Total 312 277 209 104 28 8 1454 310 303 302 156 41 12 1864 307 367 290 145 52 29 2013 234 231 174 127 54 30 1471 208 210 182 103 68 36 1502 Table 5.2: Cross Correlation Matrix of Annual Rainfall Dedessa Jimma Dedessa Jimma Bedele 1 0.11 1 Bedele 0.24 0.48 1 Table 5.3: Parameter Estimates of Weibull Distribution Jan Feb Mar April May JuneJuly Aug Sept Oct NovDec Annual y(a) z(a) U 2.4 2.1 2.2 3.6 2.4 2.9 1.3 3.7 3.4 2.4 0.9 1.3 3.2 0.5 0.6 0.6 0.4 0.5 0.5 0.8 0.4 0.4 0.5 1.1 0.8 0.4 0.2 0.2 0.2 0.3 0.2 0.3 0.1 0.3 0.3 0.2 -0.1 0.1 0.3 E 18.3 21.9 61.2 81.5 201. -12.9-15.0-17.4-55.3 -9.8 U = Xm+Cv*Xm*y(a) E = 1267.3252.9257.7245.0131.030.013.9 I 7.3 // 154.1 *\Z_« /. 35.9 60.9 -29.9 3.8 -4.4 + 1541 575 '(-ln(1-1/T)*(1/a) Water Works Design & Supervision Enterprise ~ In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 5.4 Monthly Rainfalls Corresponding to Different Reliability Levels May 2007 Reliability Level Jan Feb Mar April May June July Aug Sept Oct Nov Dec Annuaf (%) 55 10.8 12.2 40.9 58.1 150 213 219 221 212 91.65 18.6 7.58 1353 60 8.84 9.79 35.8 51.7 137 198 211 210 203 81.66 16.3 6.12 1304 65 6.92 7.4 30.8 45.3 124 184 204 200 194 71.76 14.24.74 1253 70 5 5.03 25.8 38.6 111 169 197 190 184 61.82 12.2 3.43 1202 75 3.04 2.63 20.7 31.5 97.9 154 190 178 174 51.68 10.4 2.16 1148 80 0.99 0.1615.5 23.8 84.2 138 183 166 164 41.138.830.92 1090 85 0 0 9.97 15.2 69.4 120 177 152 152 29.86 7.36 0 1025 90 0 0 3.87 4.84 52.9 99.7 170 135 138 17.29 6.02 0 951 95 0 0 0 0 32.7 73.7 163 113 119 1.974 4.82 0 853 Avg 15.318.453.6 69.5 180.8243.0 245.9238.3228.6115.531.412.7 1453 Table 5.5: Parameter Estimates of Half-Monthly Rainfall Month Parameters of Weibull distribution 1/a y( ) a zfaj U E 1.1 1.2 2.1 2.2 3.1 3.2 4.1 4.2 5.1 5.2 6.1 6.2 7.1 7.2 8.1 8.2 9.1 9.2 10.1 10.2 11.1 11.2 12.1 12.2 0.8 0.1 1.5 8.6 -4.3 0.9 0.0 1.1 8.1 -2.6 1.2 -0.1 0.9 7.7 -4.0 0.8 0.1 1.5 11.0 -6.1 0.6 0.2 1.8 24.3 -14.8 0.6 0.2 2.0 37.7 -117 0.6 0.2 1.9 26.5 -13.5 0.5 0.2 2.4 54.5 -25.6 0.6 0.2 1.9 87.6 -11.2 0.6 0.2 2.0 112.7 7.5 0.5 0.3 2.8 134.3 -19.8 0.5 0.2 2.5 135 10.4 0.7 0.2 1.7 130 40.7 0.9 0.1 1.2 126 80.9 0.5 0.3 2.9 128 5.2 0.5 0.3 2.7 131 37.4 0.6 0.2 2.2 128 49.2 0.4 0.3 3.6 119.6 -6.2 0.5 0.2 2.4 83.5 -17.7 0.7 0.1 1.6 47.1 -11.7 0.8 0.1 1.3 21.5 -3 2 1.2 -0.1 0.9 10.3 -3.0 1.1 0.0 1.0 5.8 -3.3 1.3 -0.1 0.9 5.1 -3.7 Annual 0.4 0.3 3.2 1541.2 575.1 37 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 5.6: Half-Monthly Rainfall Magnitudes at Different Reliability Levels May 2007 Month Avg Reliability level 55% 60% 65% 70% r 75% 80% | 85% 90% 95% 1.1 1.2 2.1 2.2 3.1 3.2 4.1 4.2 5.1 5.2 6.1 6.2 7.1 7.2 8.1 8.2 9.1 9.2 10.1 10.2 11.1 11.2 12.1 12.2 7.5 7.8 8.8 9.6 20.6 33.0 22.7 46.7 78.2 102.6 119.8 123.2 122 123.9 116.5 121.8 120 108.5 73.7 41.8 19.7 11.8 6.1 6.6 1453 Annual 4.41 3.43 2.49 1.58 0.69 0 0 0 0 4 3.09 2.24 1.45 0.7 0 0 0 0 2.46 1.38 0.41 0 0 0 0 0 0 5.52 4.22 2.98 1.77 0.6 0 0 0 0 13.2 10.5 7.87 5.25 2.64 0 0 0 0 24.4 21.1 17.9 14.6 11.4 8.08 4.61 0.82 0 15.2 12.4 9.67 6.99 4.32 1.61 0 0 0 34.9 30 25.1 20.1 15.1 9.86 4.25 0 0 59.6 52.8 46.1 39.5 33 26.3 19.4 11.9 3.32 84.27 77.2 70.28 63.42 56.51 49.43 42.02 33.96 24.5 101 92.5 83.9 75.1 65.9 56.3 45.7 33.6 18.3 106 98.2 90.7 83.2 75.5 67.4 58.7 48.9 36.8 103.9 97.46 91.26 85.17 79.13 73.04 66.78 60.14 52.6 110 106 102 99.2 96 93 90.1 87.2 84.2 102 95.7 88.9 82 74.9 67.3 59 49.3 37 110 104 99 93.6 87.9 82 75.6 68.2 59.1 108 103 97.6 92.7 87.6 82.4 76.9 70.8 63.5 97.9 92.1 86.1 80 73.4 66.3 58.4 48.9 36.1 58.7 52.5 46.2 40 33.6 27 19.9 12 2.37 29.2 24.9 20.8 16.8 12.8 8.77 4.68 0.38 0 13.1 11.1 9.3 7.54 5.83 4.16 2.5 0.82 0 4.15 2.92 1.83 0.85 0 0 0 0 o 2.02 1.21 0.46 0 0 0 0 0 o 0.83 0 0 0 0 0 0 0 o 1353 1304 1253 1202 1148 1090 1025 950 5 853 . Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Table 5.7: Half-Monthly Rainfall Magnitudes in Percent of the Mean Corresponding to Different Reliability, Levels Month Avg Reliability level 55% 60% 65% 70% 75% 80% 85% 90% 95% 1.1 1.2 2.1 2.2 3.1 3.2 4.1 4.2 5.1 5.2 6.1 6.2 7.1 7.2 8.1 8.2 9.1 9.2 10.1 10.2 11.1 11.2 12.1 12.2 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 59 46 33 21 9 0 0 0 0 51 40 29 19 9 0 0 0 0 28 16 5 0 0 0 0 0 0 58 44 31 18 6 0 0 0 0 64 51 38 25 13 0 0 0 0 74 64 54 44 35 24 14 2 0 67 55 43 31 19 7 0 0 0 75 64 54 43 32 21 9 0 0 76 68 59 51 42 34 25 15 4 82 75 68 62 55 48 41 33 24 84 77 70 63 55 47 38 28 15 86 80 74 68 61 55 48 40 30 85 80 75 70 65 60 55 49 43 89 86 82 80 77 75 73 70 68 88 82 76 70 64 58 51 42 32 90 85 81 77 72 67 62 56 49 90 86 81 77 73 69 64 59 53 90 85 79 74 68 61 54 45 33 80 71 63 54 46 37 27 16 3 70 60 50 40 31 21 11 1 0 66 56 47 38 30 21 13 4 0 35 25 16 7 0 0 0 0 0 33 20 8 0 0 0 0 0 0 13 0 0 0 0 0 0 0 0 Annual 100 93 90 86 83 79 75 71 65 59 39 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 5.8 Maximum Annual 24-hr Rainfall May 2007 Year (mm/d) Year (mm/d) Year (mm/d) 1967 47.1 1980 45.6 1993 50.1 1968 47.0 1981 1994 57.8 1969 64.0 1983 50.0 1995 61.0 1970 57.0 1984 51.7 1996 60.1 1971 70.0 1985 62.2 1997 104.5 1972 45.2 1986 64.6 1998 63.5 1973 35.9 1987 58.4 1999 63.0 1974 51.8 1988 53.2 2000 47.9 1975 36.4 1989 46.8 2001 69.0 1976 47.1 1990 49.5 2002 57.0 1978 1991 87.8 2003 1979 45.0 1992 51.6 2004 39.1 Average 54.14 CV 0.306 Skew 2E-04 Table 5.9 Maximum Rainfall Magnitudes and Frequencies Return Peiod (T) Frequency Factor (K) Rainfall Magnitude (mm) 24-hr 1-hr 2 5 10 15 20 25 30 40 50 -0.16 0.72 1.30 1.64 1.86 2.04 2.20 2.40 2.61 51 27 66 35 76 40 82 43 85 44 88 46 91 48 94 49 98 51 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.ArjoDedessa Irrigation Project Meteorological and Hydrological Aspects Table 5.10 Maximum Rainfall Magnitudes for Higher Durations May 2007 Return Period, T (Years) EVI Factor K(T) Max 2day Rainfall (mm) Max. 3day Rainfall (mm) 1day Avg. of Max. 3 day Rainfall (mm) 2 5 10 15 20 25 50 100 -0.164 0.719 1.304 1.634 1.865 2.043 2.591 3.135 76.9 94.6 106.3 112.9 117.5 121.0 132.0 142.9 92.7 112.7 125.9 133.4 138.6 142.6 155.0 167.3 29.8 37.8 43.2 46.2 48.3 49.9 54.9 59.9 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd. 413-Year Rolling Mean Ji 3-Year Rolling Mea Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Year 5.1(a ): Trend Analysis of Annual Rainfall at Jimma Station Figure 5.1(b): Trend Analysis of Annual Rainfall at Bedelle Station Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt LtdCummulative Annual Rainfall (mm) Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Figure 5.1(c): Trend Analysis of Annual Rainfall at Dedessa Station Years Figure 5.2(a): Single Mass Curve of Jimma Rainfall Water Works Design & Supervisioninterprise ~ In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 43Cummulative Annual Rainfall (mm) Cummulative Annual Rainfall (mm) ArjoDedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Years Figure 5.2(b): Single Mass Curve of Bedelle Rainfall Years Figure 5.2(c): Single Mass Curve of Dedessa Rainfall Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt LtdRainfall (mm) Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 300 Figure 5.3: Mean Monthly Rainfall at Arjo Dedessa Projetct Area~ 45Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects 6. MONTHLY STREAMFLOW ANALYSIS 6.1 Hydrological Observation Stations May 2007 Hydrometric stations on the Dedessa river and the neighbouring rivers within the Abbay basin the Omo-Ghibe basin have also been identified. The hydrological data are obtained from the Hydrology Department of the Ministry of Water Resources (MoWR). There are two hydrological observation stations located on the Dedessa River. These are Dedessa near Arjo town (Station No. 114001) and Dedessa near Dembi town (Station No. 114014). Station 114001 with catchment area of 9981 km2 is located about 44 km downstream of the proposed dam site and has become operational since 1960 where as Station 114014 with a catchment area of 1806 km2 is located about 137 km upstream of the proposed dam site and has become operational since 1985. Besides the two hydrological observation stations located on the main Dedessa river, several hydrological observation stations are located on its tributaries. In addition, hydrological observation stations on the neighboring Dabana near Abasina (Station No. 1 14005), (Gilgel Ghibe near Assendabo (Station No. 091008), and Gojeb near Shebe (Station No. 091012) have been found to be relevant to the study. The list of hydrological observation stations for which data have been collected along with other details like their location and catchment area is available in Table 6.1. 6.2 Extension of records Streamflow gauging stations have been installed on the Dedessa River near Arjo town (Station 14001) since 1960 and near Dembi town (Station 14014) since 1985. Before the streamflow analysis, data obtained from Station 114001 (Didessa near Arjo) and Station 114014 (Didessa near Dembi) were checked for temporal and spatial homogeneity. The investigation of homogeneity was concentrated mainly on the outliers of the monthly data series of the record Extremely high or low values of each series, that has occurred at time T(i) in each month M(i) was checked against the records of the month M(i-1) and M(i+1) that has occurred at the same year T(i) so as to judge, whether the relation is still more or less the same as that of the other years. Whenever the outliers were rejected by this test, again another test was performed with 46 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 other data series of Station 114005 (Dabana near Abasina), Station 91008 (Gilgel Ghibe near Assendabo) and Station 91012 (Gojeb near Shebe) for the same period T(i). The data were checked for its consistency before use for different analysis. The investigation will concentrated mainly on the outliers of the monthly and daily data series. Extremely high or low values that occurred at a given time were checked against records of other near by rivers (such as Dabana). If the outliers are found to be inconsistent with others, then they were replaced by new values that were generated regionally from data set obtained from other stations. 6.3 Synthetic flows In this section, analysis of monthly flows is made with the intension of improving information required fro reservoir storage design. Reservoir storage design on the basis of generated (synthetic) flows is preassumed. It was realized that the specific sequence of historic events was a random occurrence that would certainly never occur again in the same way. To get some idea about other possible sequence within the population, in order to improve reservoir design, generating a long streamflow series is a highly accepted procedure by hydrologists. However, it has been pointed out synthetic (generated) flows do not improve poor records but merely improve the quality of designs made with whatever records are available. Mean monthly discharges, coefficient of variation of monthly flows, summary of regional monthly flow characteristics, statistics of monthly flows at Arjo Dedessa Dam Site are shown by Tables 6.2, 6.3, 6.4, 6.5 respectively. The monthly stream flows at different reliability level are available in Table 6.6. In order to maintain the historical skewness in the generated flows, the Weibull distribution has been fitted to the standardized residuals of the monthly series Accordingly, the estimated parameters of the random generator that were used in the Thomas-Fierring model are presented in Table 6.7. Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 47Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Mone details on various results are shown in the annexure B "Results obtained from hydrological analysis.” The flows at the dam site at annual level are as below. Mear year = 2328 Mm3 75 % year = 1729 Mm3 80% year = 1625 “ 90% year = 1384 “ 95 % year = 1224 “ Table 6.1: Availability of Streamflow Data in the Region SI No St. No Station name and Location Lat North Long East Area (Km2) Flow 3 (Mm /yr) Runoff (mm) 1 114001 Dedessa near Arjo 8.41 36.25 9981 3826 383 2 114014 Upper Dedessa near Dembi 8.02 36.28 1806 1221 676 3 114005 Dabana near Abasina Gilgel Gibhe near 4 091008 Asendabo 9.02 36.03 2281 1870 820 7.45 37.11 2966 1211 408 5 091012 Gojeb near Shebe 7.25 36.23 3494 1803 516 Table 6.2: Mean Monthly Flow (in Mm3/sec) St. No Jan Feb March April May June July Aug Sep Oct 'Jov Dec Annual 114001 41.9 26.7 26 33.5 63.6 216 646 1050 902 526 148 80.7 3761 114014 12.2 9.5 11.5 16.9 36.4 112.4 228.9 306.9 262.8 154.3 114005 35.4 19.8 16.3 17.0 35.1 107.0 258.8 433.0 473.4 313.9 091008 14.7 13.5 12.2 15.9 33.9 100.3 216.5 319.2 277.8 137 60.2 24.5 1211 48.4 20.5 1221 103.3 56.6 1870 901012 31.3 22.1 22.1 31.3 86.4 169.2 323.7 415.6 400.9 202.3 82.8 46.5 1803 Table 6.3: Coefficient of Variation of Monthly Discharges St. No Jan Feb March April May June July Aug Sep Oct Nov Dec 114001 0.51 0.57 114014 0.47 0.5 114005 0.28 0.42 091008 901012 0.46 0.58 0.78 0.45 0.43 0.36 0.22 0.28 0.27 0.61 0.79 0.58 0.79 0.36 0.34 0.43 0.63 0.44 0.31 0.26 0.34 0.49 0.54 0.70 Water Works Design & Supervision Enterprise In Associate with intercontinental Consultants and Technocrats Pvt. Ltd. 0.66 0.68 0.62 0.45 0.35 0.3 0.33 0.67 0.62 0.59 0.48 0.56 0.69 0.53 0.29 0.27 0.30 0.56 0.81 0.53 0.33 0.43 0 60 0.47 0.20 0.16 0.25 0.44 0.30 0.34 48Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 6.4 Summary of Regional monthly flow characteristics May 2007 Param Year Jan Feb Mar April May\june July | Aug | Sep Oct Nov Dec cv Skew R B 194 151 194 194 0.51 0.68 0.595 0.58 0.61 0.47 0.33 0.29 0.32 0.58 0.66 0.57 1.80 1.66 1.503 0.86 1.65 1.05 0.12 0.7 0.59 0.94 2.19 2.02 0.38 0.57 0.527 0.45 0.49 0.66 0.53 0.56 0.51 0.5 0.560.51 0.34 0.76 0.46 0.44 0.52 0.51 0.37 0.5 0.56 0.91 0.64 0.44 Table 6.5 Table Statistics of monthly flows at Arjo Dedessa dam site 3 (in Million m ) Param Jan Feb |Mar |Apr |May Jun |jul jAug (Sep Oct Nov Dec Annual Average Stdev Skew Max Min R B 25.00 16.97 17.86 24.21 48.26 157.2 412.8 633 540.6 299.8 105.9 46.11 12.81 9.72 11.82 16.41 29.69 70.67143.2189.6 179.2 180.5 89.35 27.17 0.626 0.743 1.067 0.937 1.629 0.891 0.126 0.037 0.254 0.585 1.866 0.96 59.09 40.3 46.01 68.61 144.9366.1 751.5 1043 905.1 661 400.8 120.1 6.806 3.462 1.775 4.586 9.685 38.71 143.8 296.2 195.6 49.32 12.69 4.808 0.446 0.828 0.889 0.59 0.298 0.785 0.45 0.529 0.436 0.431 0.796 0.704 0.21 0.628 1.081 0.819 0.54 1.868 0.912 0.701 0.412 0.434 0.394 0.214 2328 619.3 0.498 4089 1124 Table 6.6: Reliability Level Vs Monthly Streamflows at Dam Site Reliability Level Jan Feb Mar Apr May IIIIII Jun [Jul Aug Sep Oct Nov Dec ,4 nnual 20.2 12.7 14.1 19.3 37.5 131.4 371.1 568.8 480.4 239.0 75 8 35 5 19.0 11.6 13.0 17.4 34.7 122.3 348.4 542.6 454.6 216 6 69 9 33 2 17.9 10.6 12.0 15.6 32.0 113.5 325.3 516.7 429.0 194.7 64.5 31.1 16.9 9.6 11.0 13.8 29.5 104.9 301.3 490.8 403.3 173 1 59 6 29 2 2114 2019 1924 16.0 8.7 10.1 11.9 27.1 96.4 276.0 464.5 376.9 151.6 55.0 27.4 15.0 7.8 9.2 10.1 24.9 87.8 248.5 437.3 349.4 129.7 50.9 25.7 14.2 6.9 8.3 8.1 22.6 78.9 217.8 408.3 319.8 107.0 47.0 24.1 1512 13.3 6.1 7.4 6.0 20.4 69.5 181.2 376.4 286.7 82.5 43.5 22.6 1384 1828 1729 1625 12.5 5.2 6.5 3.5 18.2 59.0 132.1 337.9 246.0 54.4 40.2 21 2 1224 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 49Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 6.7 Characteristics of Random Numbers Used for Flow Generation May 2007 Param Jan Feb Mar Apr (May Jun Jul Aug jsep Oct Inov Dec Average 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 CV 0.51 0.68 0.60 0.58 0.61 0.47 0.33 0.29 0.32 0.58 0.66 0.57 Skew 1.80 1.66 1.50 0.86 1.65 1.05 0.12 0.70 0.59 0.94 2.19 2.02 0.88 1/a 0.933 7 0.834 0.620 0.883 0.683 0.373 0.567 0.530 0.647 1.063 1.007 0.05 y(a) 0.033 7 0.083 0.190 0.058 0.158 0.313 0.217 0.235 0.177 -0.032 -0.003 1.15 z(a) 1.081 6 1.262 1.978 1.162 1.713 3.543 2.241 2.444 1.860 0.948 0.993 Weibul Distribution U = Xm +Cv*Xm*y(a) *_= E + (U-E) *(-ln(1-F)(1/a> E = U - Cv'Xm'z(a) Water Works Design & Supervision Enterprise ' In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 50Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects 7 ESTIMATION OF FLOODS FOR UNGAUGED CATCHMENTS May 2007 In the hydrologic analysis for dams, weirs, bridges and drainage structures, it must be recognized that there are many variable factors that affect floods. Some of the factors that need be recognized and considered on an individual site by site basis are: o rainfall amount and storm distribution; o catchment area size, shape and orientation; o ground cover; o type of soil; o slopes of terrain and stream(S); o antecedent moisture condition; o storage potential (overbank, ponds, wetlands, reservoirs, channel, etc.); and o catchment area. In general, three types of estimation floods magnitudes (namely: the Rational Method, SCS method and Transferring Gauged Data method) can be applied for the project area. 7.1 Rational Method The Rational Method can be applied to small catchments if they do not exceed 12.8 km2 (or 5 square mile) at the most (Gray, 1971). The consequences of applying the Rational Method to larger catchments is to produce an over estimate of discharge and a conservative design. The method is nevertheless frequently used in standard or modified form for much larger catchments. This is because of its relatively simplicity. The vast majority of catchments producing floods imposed on the command drainage system lie within the validity of the Rational Method and it has been used as the principal method of estimating design discharges of dykes, culverts, drainage channels, etc. The Rational Method is based on the following formula: Qm = 0.2778 C.I.A.Fr (7j) where Qm = peak flow corresponding to return period of T years in m /sec; 3 C = a 'runoff' coefficient expressing the ratio of rate of runoff to rate of rainfall (see Annex C1 and C2); Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. "Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 I = average maximum intensity of rainfall in mm/hr, for a duration equal to the time of concentration; 2 A = drainage area in km ; Fr = is the areal reduction factor (this factors improves the catchment limitations imposed on the use of rational method). Coefficient of runoff C for the formula are given by many soil and water conservation texts (see Annex C.1). Information on rainfall intensity I in a time of concentration (time period required for flow to reach the outlet from the most remote point in the catchment) is required and can be estimated by the following formula. The selection of the correct value of 'C ' presents some difficulty. It represents a parameter that can influence runoff including: soils type, antecedent soil conditions, land use, vegetation and seasonal growth. Therefore, the value of C ' can vary from one moment to another according to changes, especially soil moisture conditions. (7.2) where Tc = (1/3080)xL1155 H'0385 (Kirpich equation) Tc = time of concentration (in hours), L = maximum length of main stream (in meters), H = elevation difference of upper and outlet of catchment, (in meters). The area reduction factor (Fr) is introduced to account for the spatial variability of point rainfall over the catchment. This is not significant for small catchments but becomes so as catchment size increases. The relationship adopted for 'Fr' is based on that developed for the East African condition (Fiddes, 1997). The relationship can be expressed as' l7 where Fr = 1 - 0.02 D’° 33 A 0 50 D = duration in hours; A = drainage area in km ; 2 This equation appi.es for storms of op to 8 hours duration. For longer durat.ons on large rqtrhmonfc tho \/ali catchments the value of D can be taken as 8 for use in the above formula id _____ ___ _ « r Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd. 52Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects 7.2 SCS Method May 2007 A relationship between accumulated rainfall and accumulated runoff was derived by SCS (Soil Conservation Service). The SCS runoff equation is therefore a method of estimating direct runoff from 24-hour or 1-day storm rainfall. The equation is: Q = (P - la) /(P-la) + S 2 (7.4) where Q = accumulated direct runoff, mm P = accumulated rainfall (potential maximum runoff), mm la = initial abstraction including surface storage, inception, and infiltration prior to runoff, mm S = potential maximum retention, mm The relationship between la and S was developed from experimental catchment area data. It removes the necessity for estimating la for common usage. The empirical relationship used in the SCS runoff equation is: la = 0.2xS (7 5) Substituting 0.2xS for la in equation 7.4, the SCS rainfall-runoff equation becomes: Q = (P - 0.2S)2 /(P+0.8S) (7.6) S is related to soil and cover conditions of the catchment area through CN. CN has a range of 0 to 100 (can be obtained from Annex C3 and ERA 2002), and S is related to CN by: S = 254x[(100/CN) -1] (7.7) Conversion from average antecedent moisture conditions to wet conditions can be done by multiplying the average CN values by Cf [where Cf = (CN/1OO)’04] Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 53Kr}o Dtdessa IrrlKitlon Project Meteorological and Hydrological Aspects 7.3 Transferring Gauged Data May 3007 Gauged data may be transferred to an ungauged site of interest provided such data are nearby (i e within the same hydrologic region, and there are no major tributaries or diversions between the gage and the site of interest) These procedures make use of the constants obtained in developing the regression equations. These procedures are adopted from the work of Admasu (1989) as follows Qu - Qg (Au/Ag)°(7.8) where Qu = mean annual daily maximum flow al ungauged site (m ’/s). Qg = mean annual daily maximum flow at nearby gauged site (m’/s), Au = ungauged site catchment area (km ). Ag = gauged site catchment area (km ), The estimate daily (or the 24-hr) annual maximum flood could be converted into a momentary peak as 2 2 Qp = Cf. Qu (7 9) Here. Cf is factor estimated as Cf = 1 + 0.5/Tc (where. Tc is time of concentration) 7.4 Estimation of Weighted Average In general, the Rational method. SCS method and Transferring Gauged Data a<-e recommended for relatively small, medium and large catchments respectively However t s very important to establish a smooth pattern of transition from small to medium and from medium to large catchments Accordingly, the recommended weighted average estimate of peak flood can be given as Qw = W,.Q, ♦ W .Q + Wj.Qj 22 (7 10) Water Works Design & Supervision Enterprise <4 In Associate with intercontinental Consultants and Technocrats Pvt LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects where: May 2007 Qi, Q , and Q are mean annual momentary peaks estimated by Rational, SCS and 23 Transferring Gauged Data methods, respectively W,,W and W3 are weighing factors of mean momentary peak estimates by Rational, 2 SCS and Transferring Gauged Data methods, respectively = 12.5/(12.5+Au) (7.11) = (Au/Ag)070 (7.12) = 1 -(W, +W3) (7.13) Where Ag and Au are gauged and ungauged site catchment areas, respectively. 7.5 Synder Method of Constructing Synthetic Hydrograph The Synder method has been used extensively to provide a means of generating a synthetic unit hydrograph. The following steps are used: Step 1: Determine the lag time, T , L of the unit hydrograph. The lag time is the time from the centroid of the excess rainfall to the to the hydrograph peak. Synder derived the following empirical equation for lag time: TL = Ct (L.Lca)0 3 (7.14) where, Tl = lag time (in hrs), L = length along the main channel from outlet to divide (in km), Lea = length along the main channel from the outlet to the point opposite the catchment area centroid in km, and Ct = an empirical coefficent ranging from 1.36 to 1.66. For Ethiopian condition, Ct can be estimated as: Ct = 1 + 0.33x S'°1 S = slope of the main stream. Water Works Design & Supervision Enterprise 55 In Associate with Intercontinental Consultants and Technocrats Pvt LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Step 2: Determination of hydrograph duration. The relationship developed by Synder for the duration of the excess rainfall, Tr in hours, is a function of the lag time computed above. T =T /5.5 rl (5.15) This results in an initial value for Tr of Ti_/5.5. However, a relationship has been developed to adjust the computed lag time for other durations. This is necessary because the equation above results in inconvenient values of unit hydrograph duration. The adjustment relationship is: T (adj) = T + 0.25(T L L rn - Tr) (7.16) where T (adj) is the adjusted lag time for the new duration, T L RN. The unit peak discharge can be determined from the following equation: Up = (1/2940)x(0.94 - la/P)x(6.08 - In Tc)3 5 where, Up = unit peak discharge (in m /s/km /mm), Tc = time of concentration (in hrs), The peak discharge Qp is computed from: Qp = Up.A. (P - 0.2S) /(P+0.8S) (7.17) 32 2 (7.18) and the time from rise of the hydrograph to the peak, Tp, is compured from: Tp = 0.5 Trn + T (adj) L (5.19) Finally, the hydrograph can be constructed using T/Tp and Q/Qp values presented in Table C5 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 56Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Tables 5.1 to 5.3 show estimated mean floods at seven relatively large catchments crossing the command area from the left and right bank directions. Table 5.1 Location of Proposed Cross Drainages and Catchment Characteristics Cachm- ent Area Stream Length Max. Elev Min. Elev. Stream Slope C :(for Rational Method) CN scs Method (km ) 2 (km) (m asl) (m asl) (%) 1 CDR-16 27. J 5 15.50 2460 1336 0.0725 0.24 71 2 CDR-19 40.25 13.50 2360 1339 0.0756 0.24 71 3 CDR-28 33.00 17.40 2480 1338 0.0656 0.23 71 4 CDL-3 29.60 9.00 1780 1340 0.0489 0.22 71 5 CDL-25 300.00 44.00 2480 1335 0.0260 0.21 70 6 CDL-28 61.00 27.00 1900 1335 0.0209 0.21 70 7 CDL-33 70.00 17.50 1990 1330 0.0377 0.22 71 Table 5.2 Characteristics of Flood Hydrographs Cachm- ent Base Flow Ct Tc (time of cone. Tr TL(adj) Tp (peak time) Tp(adj) T (km) (m /s) J (hrs) b (hrs) (hrs) (hrs) (hrs) (hrs) 1 CDR-16 0.935 1.43 1.50 0.27 6.32 6.15 6.76 90.95 2 CDR-19 1.387 1.43 1.33 0.24 5.80 5.65 6.19 89.39 3 CDR-28 1.137 1.43 1.71 0.31 6.81 6.62 7.32 92.43 4 CDL-3 1.020 1.45 1.15 0.21 4.63 4.49 4.97 85.88 5 CDL-25 10.34 1.48 4.98 0.90 12.62 12.06 14.09 109.87 6 CDL-28 2.102 1.49 3.72 0.68 9.48 9.06 10.58 100.44 7 CDL-33 2.412 1.46 2.12 0.39 7.03 6.79 7.66 93.09 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 57ArJo Dedessa Irrigation Project Meteorological and HydrologicalAspects Table 5.3 Estimated Average Floods May Cachment Q(D Rational Method Q(2) scs Method Q(3) Admasu’s Method Qavg (Weighted Average ) Unit Runoff (km) (hr) (mm/hr)) (lt/s/km ) 2 1 CDR.-16 34.94 18.98 10.35 19.10 2 CDR-19 55.45 30.37 12.32 29.74 3 CDR-28 37.95 21.15 10.72 21.02 4 CDL-3 43.25 23.20 9.93 23.11 5 CDL-25 127.43 90.45 50.25 79.28 6 CDL-28 35.63 22.24 16.48 21.93 7 CDL-33 62.30 37.56 18.14 35.94 703 739 637 781 264 359 513 Water Works Design & Supervision Enterprise " In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects 8 FLOOD FREQUENCY ANALYSIS 8.1 Introduction May 2007 In flood frequency analysis, the objective is to estimate a flood magnitude corresponding to any required return period of occurrence. The resulting relationship between magnitude and return period is referred as the Q-T relationship. Return period, T, may be defined as the time-interval (on the average) for which a particular flood having magnitude QT (also known as qunatile) is expected to be exceeded. A reliable estimate of the entire Q-T relationship cannot be obtained from small samples of at- site data. The benefits of regionalization in flood frequency analysis have been recognized at least since the work of Delrymple (1960). Nowadays, the regionalization approach to flood frequency analysis (particularly the index-flood method) is becoming more popular. An essential prerequisite for the index-flood method is the standardization of the flood data from sites with different flood magnitudes. The most common practice, used also in this study, is to standardize data by division by an estimate of the at-site mean, thus: Xi = Qi/Qm (8.1) Where Xi is the ith standardized flow, Qi is the i'n annual maximum flow, Qm is the average value of at-site annual maximum flow series. Then the quantile QT is estimated as Qt - Qm.XT (8.2) Thus, the mean annual flood is the index-flood. The parameters of the distribution of X are obtained from the combined set of regional data. In this study, two distributions have been used for flood frequency analysis. These distributions are: (a) Generalized Extreme Value (GEV) distribution (Jenkinson, 1969) (b) Log-Logistic (LLG) distribution (Ahmed et al., 1988) 59 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects 8.2 Estimation of Probability Weighted Moments May 2007 Probability weighted moments (PWM) are useful for estimating the parameters of distributions whose inverse forms can explicitly be defined such as GEV and LLG (Greenwood, et. Al., 1979; and Hosking, 1986). Accordingly, probability weighted moments (PWMs) for unbiased sample estimates can be calculated as: N m 10k = . l/N)SXi.(1-Fi)k i=1 (8.3) where Xi = flood having ranked order of / Fi = (i - 0.35)/N - plotting position of the /th ranked flood N = record length The regionally averaged probability weighted moments were computed as follows: 1. The standardized PWMs were computed for each site as: Xi = Qi/Qm where Xi is the ilh standardized flow, Qi is the i’h ranked flow and Qm is the average of the data set 2. For each annual maximum flood record the first two probability weighted moments, PWMs, i.e. m10k, k = 1 and 2) were computed using Equation (1). 3. For each k, weighted average values of PWMs over M sites included in the region were calculated as follows: M X|.Nj.(m10k)j Miok = i±L M SXi.Nj j=1 (8.4) These M10k values were then treated exactly as sample estimates of PWMs for the regional standardized annual maximum flood population. LLG and GEV were fitted to the standardized regional PWMs. ____________________________________________________________________ _________ 60 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd IArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 PWMs M1OO= 1.0000 M1O1 = 0.411964 M102= 0.250375 8.3 Generalized Extreme Value Distribution Jenkison (1969) introduced the Generalized Extreme Value (GEV) distribution for modeling floods. It has become more important in hydrology since it was recommended by NERC (1975) for modeling annual maximum streamflows of British rivers. The GEV distribution is defined as: X = u + (a/k) (1 - (-In F) ) k The shape parameter k, can be estimated as: k= 7.859 C + 2.9554 C2 where C = (Miqq — ,M10i). - In 2 (2.Mio -6.M (8.6) (8.7) (8.8) O 1o1+3.M1o2 ) In 3 the scale parameter a = k-(MiQo ~ 2.M101) (i-2’k).r(i+k) and the location parameter u = M1Oo-(a/k).{1 -r(1+k)} GEV Parameters C = -0.00061 Gama = 1.0023 (89) (8.10) u= 0.879428 a= 0.253011 k = -0.00483 8.4 Log-Logistic Distribution Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 61Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Log-Logistic (LLG) distribution was introduced for flood frequency analysis by Ahmed et al. (1988). The LLG distribution is defined as: X = a + b.{F/(1-F)}c The parameters c, b, and a can be estimated as follows. The shape parameter: c = M1QQ-6. M101+6.M 1Q2 Mioo-2.Mioi the scale parameter b = M100-2.M101 c.G and the location parameter a = M100 — b. G where G= . tt.c)/siri7t.c) LLG Paameters G= 1.051033 a= -0.01767 b= 0.968257 c= 0.173014 8.5 Regionally averaged quantiles (8.11) (8.12) (8.13) (8-14) (8.15) Generally, the differences between estimates of standardized quantiles by GEV and LLG distributions increases with increase in return periods. In all cases clear differences are observed for the large return periods where LLG distribution gives larger quantiles compared to GEV distribution. Estimated flood quantiles based on GEV and LLG distributions are presented in Tables 8.1 and 8.2, respectively. Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd. 62Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Log-Logistic (LLG) distribution was introduced for flood frequency analysis by Ahmed et al. (1988). The LLG distribution is defined as: X = a + b.{F/(1-F)}c The parameters c, b, and a can be estimated as follows. The shape parameter: c = Mioo-6.Mioi+6.Mio? M1Oo-2.Mioi the scale parameter b = Mioo:2.Mioi c.G and the location parameter a — M100 — b. G where G= . 7t.c)/sinn.c) LLG Paameters G= 1.051033 a= -0.01767 b = 0.968257 c = 0.173014 8.5 Regionally averaged quantiles (8.11) (8.12) (8.13) (8.14) (8.15) Generally, the differences between estimates of standardized quantiles by GEV and LLG distributions increases with increase in return periods. In all cases clear differences are observed for the large return periods where LLG distribution gives larger quantiles compared to GEV distribution. Estimated flood quantiles based on GEV and LLG distributions are presented in Tables 8.1 and 8.2, respectively. 62 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects 8.6 Choice of Distribution May 2007 Robustness as a criteria has received widespread attention for choice of distribution for an annual maximum flood (AMF). Robustness is assumed to test whether a distribution and method of parameter estimation, considered jointly, are insensitive to departures from assumptions made in their use. In this regard, LLG/PWM has been found to be more robust than GEV/PWM (Admasu, 1989). Often, a compromise has to be reached between flexibility and sensitivity to outliers. One may need to compromise on some kind of mid-way solution. The compromise could be to use a three-parameter distribution such as GEV and LLG. However, for this purpose, LLG has been found to be more attractive than GEV. In a ddition, L LG i s I ess s ensitive (compared 10 G EV) t o c hanges i n t he s mall v alues 0 f t he annual maximum floods. Therefore, LLG/PWM is better than GEV/PWM for modeling AM samples that display a dog-leg shape when plotted on probability paper. In general, LLG/PWM has been found to be more appropriate for modeling annual maximum floods (AMF) compared to other distributions. Therefore, LLG/PWM has been applied for estimating design floods required for the project. Thus, based on probability weighted moments method and using LLW distribution on a regional flood frequency approach, the return period floods have been arrived at for the proposed dam site. The monetary peaks discharges at various levels of probability of exceedance (return periods) are summarized below. 10 yr return period flood = 575 m /sec 20 yr return period flood = 654 m /sec 50 yr return period flood = 771m /sec 100 yr return period flood = 871m /sec 500 yr return period flood = 1155 m /sec 1000 yr return period flood = 1303 m /sec 10000 yr return period flood = 1948m /sec 3 3 3 3 3 3 3 63 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.ArjoDedessa Irrigation Project Meteorological and Hydrological Aspects Table 8.1 Estimated Flood Quantiles Based on GEV Distribution May 2007 T Return period xt Mean Max. Daily Discharge | i Momentary Peak Growth factor Gauging Site (1) ----- o' *— Gauging Wama at Site (2) Junction - Dam site Gauging ^Sitem Gauging Site (2) Wama at Junction Dam site (years) (ratio) (m /s) 3 (m /s) (m /s) 33 (m /s) 3 (m /s) 3 (m /s) (m /s) 33 (m /s) 3 2 0 95 5 1.23 10 1.42 20 1 60 50 1.83 100 2.01 200 2.19 500 2.43 1000 2.61 2000 2.79 5000 303 10000 3.22 670 214 238 354 869 278 309 460 1001 320 356 530 1129 361 402 597 1296 414 459 686 1422 455 505 752 1549 495 550 819 1716 549 610 908 1844 589 655 975 1972 631 700 1043 2143 685 761 1134 2273 727 808 1203 788 272 264 392 1022 353 342 509 1178 406 395 586 1329 458 445 661 1526 526 509 759 1674 577 559 833 1822 629 609 907 2020 697 676 1005 2170 749 726 1080 2321 801 776 1155 2522 870 842 1255 2675 923 895 1331 Average 1 707 226 251 374 832 287 278 414 Note: The analysis is based on regional flood frequency analysis based on General Extreme Value (GEV) distribution with parameters estimated by probability weighted moments method Table 8.2 Estimated Flood Quantiles Based on LLG Distribution T Return period Xt Growth factor Mean Max. Daily Discharge Momentary Peak Gauging Site - (1) Gauging Site (2) Wama at Junction Dam site Gauging Site (1) Gauging Site (2) Wama at Junction (years) (ratio) Dam site Lmjs) (m /s) 3 (m /s) 3 (m /s) 3 (m /s) 3 (m /s) 3 (m /s) 3 (m /s) 3 2 0.95 672 215 238 356 5 1.21 854 273 304 452 10 1.39 982 314 349 519 20 1.58 1118 357 397 591 50 1.86 1317 421 467 697 100 2.1 1488 476 527 787 200 2.38 1680 537 597 889 500 2.79 1972 630 700 1043 1000 3.15 2225 711 791 1177 2000 3.55 2511 803 891 1329 5000 4 17 2947 942 1047 1559 10000 4.71 3326 1063 1182 1760 Average 1 707 226 251 374 791 273 264 1005 347 336 1156 399 386 1315 454 439 1550 535 517 1751 604 584 1977 682 662 2320 800 776 2619 903 876 2956 1020 987 3468 1196 1159 3915 1350 1309 832 287 278 394 500 575 654 771 871 984 1155 1303 1471 1726 1I Q4R 414 with parameters estimated by probability weighted moments method on Log-Logistic (LLG) distribution Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd 64Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects 9. PROBABLE MAXIMUM FLOOD May 2007 The probable maximum flood is defined as the most severe flood considered reasonably possible to occur. It is customarily obtained by using unit hydrographs and rainfall information. Annex C4 gives the recommended reservoir flood standards for three main categories of reservoirs. Category A has the most stringent standards, since for such a reservoir a breach in the dam would endanger the lives of people congregated in a town or village downstream. The worst conditions are envisaged, the spillway already taking the average daily inflow when the probable maximum flood (PMF) arrives and the wave surcharge allowance must be for heights greater than 0.6 m. Categories B and C have decreasing standard requirements. In Ethiopia, the study of design floods on the basis of PMF requires further investigation. The challenging problem is particularly that of storm rainfall and the varying temporal pattern of intensities throughout a storm’s duration; the occurrence of the peak intensity is a variable to be considered for further study at national level. The initial state of the catchment is also of great significance in the generation of an extreme flood. A thorough knowledge of a catchment and of its varying responses during adverse conditions is essential for an engineering hydrologist to evaluate design floods and such situation need to be investigated at an institute level. However, in such a situation where there is maximum rainfall data, Hersfield (1961) suggests the use of following equation to estimate 24-hr PMP in region so as to superimpose it on design unit hydrograph to give the PMF PMP 4 = Pm +K.Sn = Pm (1+K.CV) 2 (9.1) Where PMP 4 - 24-hr probable maximum precipitation 2 Pm = mean of the 24-hr annual maximum over the period of record Sn = standard deviation of the 24-hr annual maximum CV = Pm/Sn = coefficient of variation K = a constant equal to 15 Water Works Design & Supervision Enterprise in Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 The mean annual maximum 24-hr rainfall for Bedele and Jimma are 55.5 mm and 51.3 mm, respectively; and also the coefficient of variation for Bedele and Jimma are 0.198 and 0.201 respectively. For the Arjo Dedessa dam catchment: Pm = (55.5+51,3)/2 = 53.4 mm CV = (0.198+0.201 )/2 = 0.20 Sn = 0.20x 53.4 = 10.68 K = 15 Then PMP24 = Pm +K.Sn = Pm(1+K.CV) = 4 01*Pm = 4.01x53.4 = 214 mm/day Total volume of daily rainfall Vp= A. PMP24 = 5310*214 = 1129.5 Mm3 Assuming runoff coefficient C that corresponds to the occurrence of continuous rainfall to be 0.68, the estimated rainfall depth that produces probable maximum flood becomes: Vpe= C.Vp = 0.68*1129.5 = 768.5 Mm3 Using the catchment characteristics given in Table 12.1 and applying the dimensionless hydrograph given by Table C4, the flood peak component due to the probable maximum rainfall becomes 3502 m /s. Assuming the a base flow of 188 m /s the total peak flood becomes: Qp = base flow + peak due to storm = 188 + 3502 = 3690 m /s Cumulative volumes of Probable Maximum Floods (PMF) derived from probable maximum 24 hr rainfall is given by Table 9.1 while design flood hydrograph derived from estimated PMF is given by 9.2. 3 3 3 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd. 66Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 9.1: Table Cumulative Volume of Probable Maximum Flood May 2007 Time (hrs) Cum. Volume Cum. Volume (Mm3) (%) Time (hrs) (Mm3) (%) Time (hrs) Cum. Volume (Mm3) (%) 0.00 0.000 0.00 4.50 0.440 0.06 9.00 2.936 0.38 13.50 9.389 1.22 18.00 21.87 2.85 22.50 42.15 5.48 27.00 71.51 9.31 31.50 110.5 14.4 36.00 157.6 20.5 40.50 210.4 27.4 45.00 266.4 34.7 49.50 322.6 42.0 54.00 376.4 49.0 58.50 426.4 55.5 63.00 471.6 61.4 67.50 511.8 66.6 72.00 546.4 71.1 76.50 576.0 75.0 81.00 601.7 78.3 85.50 623.9 81.2 90.00 643.4 83.7 94.50 660.4 85.9 99.00 675.1 87.9 103.50 687.8 89.5 108.00 698.7 90.9 112.50 708.3 92.2 117.00 716.4 93.2 121.50 723.2 94.1 126.00 729.1 94.9 130.50 734.4 95.6 135.00 739.0 96.2 139.50 743.0 96.7 144.00 746.5 97.1 148.50 749.3 97.5 153.00 751.7 97.8 157.50 753.6 98.1 162.00 755.5 98.3 166.50 757.2 98.5 171.00 758.6 98.7 175.50 759.9 98.9 180.00 761.0 99.0 184.50 762.0 99.2 189.00 762.9 99.3 193.50 763.6 99.4 198.00 764.3 99.4 202.50 764.8 99.5 207.00 765.3 99.6 211.50 765.8 99.6 216.00 766.1 99.7 220.50 766.5 99.7 225.00 766.8 99.8 229.50 767.1 99.8 234 00 767.3 99.8 238.50 767.5 99.9 243.00 767.7 99.9 247.50 767.9 99.9 252.00 768.1 99.9 256.50 768.2 100.0 261.00 768.3 100.0 265.50 768.4 100.0 270.00 768.5 100.0 274.50 768.5 100.0 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 67Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 9.2 Design Flood Hydrograph Derived from Estimated PMF May 2007 Ti Qi Ti Qi Ti Qi Ti Qi Ti Qi (hr) (m3/s) (hr) (m3/s) (hr) (m3/s) (hr) (m3/s) (hr) (m3/s) 0.00 188 2.25 216 4.50 241 6.75 339 9.00 451 11.25 573 13.50 748 15.75 958 18.00 1169 20.25 1449 22.50 1694 24.75 2009 27.00 2289 29.25 2604 31.50 2885 33.75 3095 36.00 3305 38.25 3445 40.50 3585 42.75 3655 45.00 3690 47.25 3655 49.50 3620 51.75 3515 54.00 3410 56.25 3270 58.50 3130 60.75 2990 63.00 2815 65.25 2674 67.50 2499 69.75 2324 72.00 2149 74.25 2009 76.50 1904 78.75 1764 81.00 1659 83.25 1554 85.50 1484 87.75 1379 90.00 1309 92.25 1239 94.50 1169 96.75 1099 99.00 1028 101.25 958 103.50 923 105.75 853 108.00 818 110.25 783 112.50 748 114.75 678 117.00 643 119.25 608 121.50 573 123.75 552 126.00 531 128.25 514 130.50 496 132.75 472 135.00 451 137.25 433 139.50 419 141.75 402 144.00 384 146.25 367 148.50 349 150.75 332 153.00 314 155.25 297 157.50 314 159.75 307 162.00 300 164.25 290 166.50 283 168.75 279 171.00 272 173.25 269 175.50 262 177.75 258 180.00 251 182.25 248 184.50 244 186.75 241 189.00 237 191.25 234 193.50 230 195.75 230 198.00 227 200.25 223 202.50 220 204.75 220 207.00 216 209 25 216 211.50 213 213.75 213 216.00 209 218.25 209 220.50 209 222.75 206 68 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 10 SEDIMENT ANALYSIS 10.1 Estimation of Sediment yield Suspended sediment data from Stations 14001, 14014 and 14005 were obtained. These discharges are given in Annex E5. Suspended concentration rates varying between 45 mg/lt to 1670 mg/lt were observed from Didessa river.. Relationships between water discharge and sediment loads at various sites in the region are presented in Table 10.1. At-site and regional approach has been used to to estimate sediment rates from the estimated streamflows at the dam site. Accordingly, the following relationship has been derived: Gs = 0.078Q15 (10.1) 2 Where Gs = sediment load (in gm) Q = monthly mean discharge (in lt/s/km ). Careful assessment regarding reservoir sedimentation will be required in the site as the life of the storage created by a dam is dependant of the sedimentation situation. Accordingly, reservoir p lanning will i nclude a ssessment of the p robable r ate o f s edimentation i n order t o predict the useful life of the proposed reservoir. In estimating reservoir sedimentation, materials originating as bed load will be assumed to have a density of 1.4 g m/cc and material carried in suspension will be assumed to have a density of 1.2 gm/cc. The bed load at the dam sites shall be assumed to be 15 percent of the suspended load Monthly total sediment load (suspended and bed load) and accumulated total sediment load at the reservoir site are given by Table 10.2 and 10.3, respectively. Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd 69Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects 10.2 Distribution of sediment in the reservoir May 2007 So far the sediment load likely to deposit in the reservoir has been estimated. But estimating the sediment inflow to the reservoir is not enough as how high the sediment will accumulate in the reservoir is also important. Accordingly, Area-Increment method has been used for this purpose. The method is expressed as: (10.2) Where Vs = Ao(H - Ho) + Vo Vs = sediment volume to be distributed Vo = sediment below the new zero elevation H = original reservoir depth from the stream bed level Ho height to which the reservoir is completely filled with sediment, i.e., = height of the new zero elevation Ao surface areas of the reservoir at the new zero elevation and is the = area correction factor. The results so obtained from the analysis of distribution of sediment in the Arjo-Dedessa Reservoir are given in Table 10.4. Table 10.1 Relationships between water discharge and sediment load No Station Area (km ) r 2 Module 10 t/yr 3 Loss Vales of C in: t/km2/v Qs =C.(Qwl1 5 3005 Guder at Guder 524 77 90 0.025 4007 Little Angar near Gutin 1975 176 89 0.096 4005 Dabana near Abasina 2881 453 157 0 059 4002 Anagar near Meqemte 6002 Abbay at Sudan Border 4674 702 150 0 061 172254 335170 1946 0 165 Arjo Dedessa Dam site . 5278 776 147 0.078 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Table 10.2: Monthly Total Sediment Load at the Reservoir Site Table 10.3 Accumulated Total Sediment Load at the Reservoir Site Jan Feb March April May June July Aug Sep Oct Nov Dec Annual Years 25 50 75 100 125 150 175 200 0.06 0.03 0.03 0.04 0.11 0.68 3.28 6.2 5.29 3.00 0.48 0.17 0.12 0.07 0.06 0.09 0.23 1.36 6.6 12.4 10.6 6.0 0.96 0.34 0.19 0.10 0.09 0.13 0.34 2.04 9.8 18.6 15.9 9.0 1.45 0.52 0.25 0.13 0.11 0.17 0.45 2.72 13.1 24.8 21.1 12.0 1.93 0.69 0.31 0.17 0.14 0.21 0.56 3.40 16.4 31.1 26.4 15.0 2.41 0.86 0.37 0.20 0.17 0.26 0.68 4.08 19.7 37.3 31.7 18.0 2.89 1.03 0.43 0.23 0.20 0.30 0.79 4.76 22.9 43.5 37.0 21.0 3.38 1 20 0.50 0.27 0.23 0.34 0.90 5.44 26.2 49.7 42.3 24.0 3.86 1.37 19.39 38.78 58.17 77.56 96.95 116.3 135.7 155.1 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 7)Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 10.4: Distribution of Sediment in the Arjo Dedessa Reservoir May 2007 50 years sediment load Ho = 2.03 m Ao = 1.52 Mm* 100 years sediment load Ho = 3.42 m Ao = 3.15 Mm2 Elev (m asl) Original area 2 (Mm ) Original capacit y 33 (Mm ) Depth (m) S edime nt volume 3 (Mm ) Revised area 2 (Mm ) Revised capacit y, 3 (Mm ) Original area Original capacity Depth (Mm2} jMm3) 1 2 1 4 5 6 7 Elev m asl) 1 2 3 4 Sediment volume (Mm3) 5 Revised capacity (Mm3) 7 1346 56.76 629.8 27 38.7 55.24 591.1 1343 48.13 466.4 24 34.2 46.61 432.2 1340 39.92 331.8 21 29.6 38.41 302.2 1337 32.17 224 18 25.1 30.66 198.9 1334 24.93 140.7 15 20.5 23.41 120.2 1331 18.24 79.64 12 16 16.72 63.67 1328 12.19 38.24 9 11.4 10.68 26.82 1325 6.911 13.6 6 6.88 5.395 6.724 1322 2.619 2.322 3 2.33 750 years sediment load Ho = 4.69 m Ao = 4.90 Mm2 1346 56.76 629.8 27 77.4 53.61 552.4 1343 48.13 466.4 24 68 44.98 398.4 1340 39.92 331.8 21 58.6 36.78 273.3 1337 32.17 224 18 49.1 29.03 174.8 1334 24.93 140.7 15 39.7 21.78 101 1331 18.24 79.64 12 30.2 15.09 49.4 1328 12.19 38.24 9 20.8 9.046 17.44 1325 6.911 13.6 6 11.4 3.765 2.239 1322 2.619 2.322 3 1.92 200 years sediment load Ho = 5.89 m Ao = 6.73 Mm2 Elev (m asl) Original area 2 (Mm ) 3 Original capacit y Depth (Mm ) (m) Sedime nt volume 3 (Mm ) Revised Revised capacit area y 1 (Mm ) \(Mm’) Elev (m asl) O riginal area (Mm‘) Original capacity 3 (Mm ) Depth 4 Sedime nt volume 3 (Mm ) Revised area (Mm’) Revised capacity (Mm’) 1 2 34 5 6 T? ‘ 1 2 3 5 6 7 1346 56.76 629.8 27 116 51.86 513.3 1343 48.13 466.4 24 102 43.24 364.6 1340 39.92 331.8 21 87.1 35.03 244.7 1337 32.17 224 18 72.4 27.28 151.5 1334 24.93 140.7 15 57.7 20.03 82.96 1331 18.24 79.64 12 43 13.34 36.6 1328 12.19 38.24 9 28.4 7.297 9.887 1325 6.911 13.6 6 13.7 27 24 135 41.4 331.5 331.8 21 115 33.19 217.1 224 18 94.5 25.44 129.4 155 50.02 474.7 140.7 79.64 15 74.3 18.19 66.37 12 54.1 11.5 25.52 9 33.9 5.457 4.326 6 13.7 Water Works Design & Supervision Enterprise ~~ 72 In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects 11. WATER QUALITY May 2007 The water quality status of the Dedessa river is evaluated using the data collected from MoWR database, Abbay River Basin Master Plan Study Report (1998). The samples were taken as part of the s upporting measurement for the aquatic study and appear to represent t he o nly available data on water quality within the catchment. Table 11.1 shows water quality measurements taken for Dedessa at two sites. The samples were taken as part of the supporting measurement for the aquatic study and appear to represent the only available data on water quality within the catchment. The samples shown in Table 11.1 were taken after the start of the rainy season and presumably all tributaries of the river exhibited adequate water quality at the time of sampling. Total Dissolved Solids (TDS) and Electrical Conductivity (EC) Total dissolved solids characterized mainly by major anions and cations are directly related to the electrical conductivity of the water. The low Electrical Conductivity (EC) and TDS value in general shows that the water is soft in nature and has low salinity. Moreover, the low conductivity is sign of low fertility of the water with regard to aquatic life. Electrical conductivity (EC) measurements were very low at all the sampled sites. EC is the ability of the water to conduct electric current and directly related to the amount of cations and anions in the water. pH The pH value is the measure of the concentration of hydrogen (H+) and hydroxyl (OH-) ions in the water It is to determine the acidity or alkalinity of the substance. Sodium and Potassium The Na and K reading expressed in terms of Sodium Adsorption Ratio (SAR) is the useful parameter for the evaluation of the water body for irrigation purpose. For irrigation water it is important to measure the sodium adsorption ratio as follows: SAR = ----------------------------- - (9.1) ; [(Ca’‘ + Mg~)/]° 5 Water Works Design & Supervision Enterprise 73 In Associate with Intercontinental Consultants and Technocrats Pvt LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Thehigher the SAR valueof thewater theless suitable will be for irrigation purposes.The maximum computed value among the readings is 0.29 which is less than 10. This illustrates that the water is very much suitable for irrigation purpose. Chloride The chloride concentration of the rivers stipulated in Tables 11.1 is very low (1.0 to 2.0 mg/l), at times of sampling. Hence the parameter was in conformity with the standard set by EPA (250mg/l for aquatic species). Table 11.1 Water quality results for sites on the Dedessa river Sampling at Bedele bridge at Gimbi bridge Comment Sample date Elevation (m asl) TDS (gm/l) EC (Ds/cm) pH Na~ K Ca (mg/l) ++ Mg* (mg/l) + Cl' (mg/l) SAR 13/08/96 1300 20 60 6.74 3.3 1.9 6.4 2.43 1.0 0.29 14/08/96 1200 20 50 6.97 3.0 2.5 9.6 1.4 2.0 0.25 N N N N N N N N N WQ I___________ Lilt for Maior Rivers /ArPHA/ loos o., o/-* study, 1998) Water Works Design & Supervision Enterprise 74 In Associate with Intercontinental Consultants and Technocrats Pvt. LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects 12. DESIGN FLOOD 12.1 Synthetic Hydrograph May 2007 Among several known methods of unit hydrographs, the one developed by Synder (1938) is most commonly used. The method is derived from drainage basins in the Appalachian Mountain regions in the United States ranging in areas from 25 km to 25,000 km The relations of unit hydrograph characteristics and catchment characteristics are expressed as follows: Tp = Ct((L.Lc)03 (12.1) Where Tp = lag time from the mid point of the rainfall-excess duration Tr to the peak of a unit hydrograph (hr), Ct = coefficient depending on basin characteristics Lc = river distance from the station to the point of interest nearest the centroid of the drainage area (km) L = river distance from the station to the upstream limits of the drainage area (km) The catchment characteristics (such as L, Lc, Area, Slope) of Desessa at the Arjo-Dedessa Dam Site is given by Table 12 1 The U S Soil Conservation Service (SCS) developed a dimensionless hydrograph that has its ordinate values expressed as the dimensionless ratio, Ti/Tp Qi is the discharge at any time Ti The shape of the unit hydrograph dimensionless hydrograph, and Tp is the period corresponding to peak as shown in Annex Table C5. For a given catchment, once the value of Tp is defined using Equations 12.1. the unit hydrograph can be constructed 12.2 Flood Routing Through the Reservoir The dam is located where failure may probably be confined to the irrigation command and the dam itself No excessive loss of human life would be expected For such condition, a design flood corresponding to a10.000-year return period has been proposed The volume of flow in 1000-year return period flood hydrograph is about 400fylmJ 75 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 The data used to complete surcharge storage due to the design flood and routing calculations were: inflow hydrograph for all selected design storms, elevation-storage relations for proposed storage facility, and stage-discharge relations for all outlet control structures. The step-by-step method of reservoir routing method has been used The data required for the method to construct the outflow hydrograph is: (a) the inflow hydrograph, (b) the elevation capacity relation curve of the reservoir, and (c) the outflow-elevation curve or the outflow equation. Using these data a design procedure is used to route the inflow hydrograph through the storage facility with different surcharge storage and spillway crest (outlet) geometry until the desired outflow hydrograph has been achieved A spillway with ogee shaped crested weir has been assumed The equation generally used for such broad-crested weir is where: Q =CLH15 O = discharge, in m’/sec C = broad-crested weir coefficient L = broad-crested weir length, m H = head over weir crest, m (122) If the upstream edge of a wetr is so rounded as to prevent concen.rahon and ,f the slope of the crest is as great as lhe loss of head due to Inchon. How wtll pass through critical depth at the weir crest; thus gives an average C value of 2.2. The following procedures were used to perform routing through the reservoir sis^r Developing an tnflow hydrograph, stage-discharge curve for the proposed storaoe facility. y S/SL? Selecting a -puling time period. DI, to provtde at .east five potnts on .he rtstng llmb of the inflow hydrograph Water Works Design & Supervision Enterprise ~~ In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 76Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Step 3: Using the storage-discharge data from Step 1 to develop storage characteristics curves that provide value S (+/-) (Q/2).Dt versus stage. Step 4: For a given time interval, 11 and I2 are known. Give the depth of storage or stage, H1, at the beginning of that time interval, S1 - (Q1/2).Dt can be determined from the appropriate storage characteristics curve. Step 6: Determining the value of S2 + (Q2/2).Dt from the following equation: 3 S2 + (Q2/2).Dt = [S1 - (Q1/2).Dt] + [11 + l2)/2.Dt] where S2 = storage volume at time 2, m /sec Q2 = outflow rate at time 2, m3/sec Dt = routing time period, sec S1 = storage volume at time 2, m3 Q1 = outflow rate at time 1, m3/sec 11 = inflow rate at time 1, m3/sec 12 = inflow rate at time 2, m3/sec (12.3) Step 6. Enter the storage characteristics curve at the calculated value of S2 + (Q2/2) Dt determined in Step 5 and read off a new depth of water, H2. ste P 7; Determine the value of Q2, which corresponds to a stage of H2 determined in Step 6 using the stage-discharge curve. Step_8, Repeat Step 1 through 7 by setting values of 11, Q1, S1, and H1 equal to the previous I2, Q2, S2 and H2, and using a new I2 value. This process is continued until the entire inflow hydrograph has been routed through the storage basin. Since Equation (12.3) contains two unknowns, stepwtse trial and error procedure is used Results of routed design floods based on LLG distribution. half-PMF and full PMF a presented by Table 12.2, 12.3 and 12.4. respectively. The elevation - area capactty curves of the reservoir are shown in Figure 12.1. The lOOOOyr return period design inflow and outflow hydrographs are shown in Figure 12.2. Such inflow and outflow hydrographs for smaller return Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 77Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects Ma y 2007 periods like 10, 20, 50 and 100 year return periods are shown in Figure 12.3. The average hydrograph of maximum flow at the dam site is available in Figure 12.4. 12.3 Routed Design Flood at the Coffer Dam Velocity Formula The velocity equation through the pipe outlet is given by V = (2gH ) L 05 (10.4) where A = cross-sectional area of barrel (or pipe), V = velocity through the barrel, Hl = total head loss through the barrel, H = (1.5 + f L/D) V /2g 2 l (12.5) L = length of the barrel/pipe D/4 = R = hydraulic mean radius of the barrel D = diameter of barrel/pipe V = velocity through the barrel/pipe f = coefficient of friction Manning's Formula It is one of the most common formula, which is commonly used for the analysis of problems of flow through channels, bul often used for the analysis of pipe flow problems too According to this formula the discharge Q through pipes is given by V = (F/nJ.D273 S1/2 Where V = velocity through the pipe, (12.6) n = Manning's roughness coefficient (a value of 0.065 has been selected for old concrete pipe), D = diameter of the pipe, Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 78Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects S = slope of the hydraulic gradient or energy slope = h|/L F = is constant equal to 0 39685 L = length of the pipe (m), h t = head loss through the pipe (m) Equation 12 5 can be arranged to express the relations for head loss through a pipe May 2007 h t = L ((n/F) V/D' Y v (12 7). Combined Formula Combining Equation 12 5 and 12 7 the above two expressions for velocity reduced to H, - (1 5/2g* L ((n/F)D a/’)|2} Va and also V (H /(1 5/2g * L ((n/F) D 'Y}) 2 l 0’ Q A (H,/{1 5/2g > L [(n/F)D 'Y})° 25 («D’/4) (H /{1 5/2g * L l(n/F)D t zn ]'})09 (128) (129) (12 10) Where A is cross sectional area of pipe in m2 Substituting n 0 0165, g 9 61 in Equation 12 8. can be expressed as H. (0076453* L (0 0415/7 D 'Y}Va 2 V (Ht/(O 076453* L [0 041577 D 'Y))° a 5 Q (0 7857 D') (MO 076453* L [0 041577 D" Y))°* Results of routed design flood at Coffer Dam of Arjo Didessa Reservotr are presented in Table 12 5 These results are available tor 10. 20. 50 and 100 year return penod floods According io the criteria the appropriate results could be adopted for designs Water Works Design & Supervision Enterprise In Assoclata with Intprrontinental Consultants and Terhnocrats Pvt. Ltd 79Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 12.1 Catchment Characteristics May 2007 Arjo Dedessa Catchment Characteristics Area (km2) Length (km) Centroid distance (km) Max elevation (m asl) Minimum elevation (m asl) Elevation difference (m) S (m/m) Ct Tc (hrs) Tl (hrs) Tr (hrs) Dimension 5278 199 141 3012 1315 1697 0.0085 1.53 24.00 33.00 4.40 Tuadj) (hrs) 38.00 TP (hrs) 45.00 Table 12.2 Routed Design Flood at FRL Corresponding to 1352 m (aj Based on LLG distribution L(m) Qout (m /s) 3 H (m) Max Surface Area (Km ) 2 Surcharge Storaqe (Mm ) 3 50 871 3.97 75 1031 3.39 100 1154 3.02 125 1253 2.75 150 1333 2.54 175 1399 2.36 87.06 85.20 84.01 83.14 82.47 81.91 1340.1 1288.0 1255.0 1231.4 1213.1 1198.3 Peak inflow = 1950 m3/s (b) Based on Half-PMF Qout (m /s) 3 H (mJ Max Surface Area (Km ) 2 Surcharge Storaqe (Mm ) 3 50 798 3.75 75 941 3.19 100 1051 2.84 125 1140 2.58 150 1212 2.38 175 1273 2.22 86.34 84.56 83.43 82.61 81.97 81.45 1319.8 1270.3 1239.1 1216.9 1199.7 118R n Peak inflow = 1780 m3/s Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 80Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects (c) Based on PMF May 2007 L (m) j Qout (m /s) 3 H(m) Max Surface Area (Km ) 2 Surcharge Storage (Mm ) 3 50 1668 6.13 75 2008 5.29 100 2265 4.73 125 2466 4.32 150 2626 3.99 175 2756 3.71 93.95 91.28 89.50 88.16 87.10 86.24 1539.8 1461.3 1409.5 1371.3 1341.2 1316.8 Peak inflow = 3690 m3/s Table 12.3 Routed Design Flood at FRL Corresponding to 1555 m (a) Based on LLG distribution L(m) Qout (m /s) 3 H (m) Max Surface Area (Km ) 2 3 Surcharge Storage (Mm ) 50 812 3.79 75 964 3.24 100 1083 2.89 125 1180 2.64 150 1261 2.44 175 1329 2.28 96.26 94.57 93.48 92.70 92.09 91.59 Peak inflow = 1950 m3/s 1601.8 1546.7 1511.9 1487.1 1468.0 1452 6 — (b) Based on Half-PMF L(m) Qout (m /s) 3 H (m) Max Surface Area (Km ) 2 50 746 3.58 75 881 3.06 100 988 2.72 125 1075 2.48 150 1148 2.30 175 1208 2.14 95.61 93.98 92.95 92.20 91.63 91.16 Surcharge Storaanyep IVI rn ) 1580.6 1527.9 1495.0 1471.6 1453.7 1/1QQ O Peak inflow = 1780 m3/s Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd. 81Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects (c) Based on PMF May 2007 L(m) Qout (m /s) 3 H(m) Max Surface Area (Km ) 2 Surcharge Storage (Mm ) 3 50 1540 5.81 75 1867 5.04 100 2118 4.53 125 2320 4.14 150 2483 3.84 175 2618 3.59 102.52 100.13 98.54 97.36 96.41 95.64 1811.9 1730.7 1677.1 1637.8 1606.8 1581.3 Peak inflow = 3690 m3/s Table 12.4 Routed Design Flood at FRL Corresponding to 1356m (a) Based on LLG distribution L (m) Qout (m /s) 3 H (m) j Max Surface Area (Km ) 2 Surcharge Storaqe (Mm ) 3 50 800 3.75 75 951 3.21 100 1069 2.87 125 1165 2.62 150 1246 2.42 175 1314 2.27 99.11 97.49 96.45 95.71 95.12 94.65 1693.0 1637.1 1602.0 1577.0 1557.7 1542 0 Peak inflow = 1950 m3/s (b) Based on Half-PMF U) m Qout (m /s) 3 H{m) Max Surface Area (Km ) 2 Surcharge Storaqe (Mm ) 3 50 735 3.55 75 869 3.03 100 975 2.70 125 1061 2.46 150 1134 2.28 175 1195 2.13 98.49 96.93 95.94 95.23 94.68 94.23 Peak inflow = 178 0 m3/s 1671 5 1618 2 1584 9 1561 2 1543 1 1528 5 Water Works Design & Supervision EnterprisF 82 In Associate with Intercontinental Consultants and Technocrats Pvt. LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects (c) Based on PMF May 2007 L (m) 3 Qout (m /s) H (m) Max Surface 2 Area (Km ) Surcharge 3 Storage (Mm ) 50 1515 5.75 75 1838 4.99 100 2088 4.48 125 2289 4.11 150 2453 3.81 175 2588 3.56 105.09 102.81 101.30 100.17 99.28 98.53 1905.2 1823.3 1769.3 1729.8 1698.5 1672.9 Peak inflow = 3690 m3/s Table 12.5: Routed Design Flood at Coffer Dam of Arjo Didessa Reservoir T = 10 yrs, Pea k = 654 m3/s T = 20 yrs, Peak = 654 m /s 3 DQ (m) (m3/s) Elev (m a si) D (m) Q (m3/s) Elev (m a si) 5.0 210 1337.98 5.5 223 1333.01 6.0 239 1330.00 6.5 258 1328.06 2x4.0 220 1334.18 2x4.5 243 1329.86 5.0 211 1338.22 5.5 225 1333.29 6.0 243 1330.32 6.5 263 1328.40 2x4.0 222 2x4 5 247 1334.45 1330.19 T=5C yrs, Peak = 771 m /s 3 T = 100 yrs, Peak = 871 m /s 3 D (m) Elev (m asl) D (m) Q (m3/s) Elev (m asl) 5.0 213 1338.59 5.5 229 1333.70 6.0 248 1330.79 6.5 271 1328.90 2x4.0 225 1334.86 2x4.5 253 1330.69 5.0 215 1338.89 5.5 232 1334.05 6.0 253 1331.19 6.5 277 1329.32 2x4.0 228 2x4.5 257 1335.20 1331.10 Note : Length of pipe, L = 400 m Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. S3 EArJo Dedessa Irrigation Project Meteorological and H ydrological Aspects May 2007 Elevation-Are a-Capacity Curve for Arjo Didessa Re servoir Area (Sq. Km) 125 100 75 50 25 0 Figure 12.1: Elevation-Area-Capacity Curves of Arjo Dedessa Reservoir Inflow and Outflow Hydrographs at Arjo Didessa Reservoir Figure 12.2: Inflow and Outflow Flood Hydrographs at Arjo Dedessa Reservoir Water Works Design & Supervision Enterprise 84 In Associate with Intercontinental Consultants and Technocrats Pvt Ltd Elevation (m)Discharege (m3/s) Discharege (m3/s) Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Inriow and Outflow Hydrograph* at Arjo Didessa Coffer Dam. T ■ 10 years Inflow and Outflow Hydrographs at Arjo Didessa Coffer Dam, T Inflow and Outflow Hydrographs at Arjo Dldessa Figure 12.3: Inflow and Outflow Flood Hydrographs at Arjo Dedessa Reservoir Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd 85Rainfall (mm) Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Average Hydrograph of Maximum Flows at Arjo Didessa Dam site Figure 12.4: Average Hydrograph of Maximum flows at Arjo Dedessa Dam Site Waterworks Design & Supervision Enterpri^- - - - - - - - - - - - - - - - 86 In Associate with Intercontinental Consultants and Technocrats Pvt. LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects 13. RESERVOIR SIMULATION May 2007 Determining design capacity of Arjo Dedessa reservoir required reservoir simulation study. The factors that has been considered in the analysis include the following. This particular section deals with the dam/ reservoir simulation for establishing the viability of contemplated irrigation o Useable flow between reservoir and diversion, o Spill past diversion weir, o Flow into the reservoir, o Evaporation from the reservoir, o Rainfall on the reservoir, o Total irrigation demand, and o Irrigation water release from the reservoir. The simulation sample is provided in annexure B - 8. the description of various column, referred to there in are as below: 87Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Column Abbrev Unit Description Col [1] Year Year Col [2] Month Month Col [3] Inflow Mm3 Natural inflow to the reservoir as simulated by Thomas- Feiring model (monthly flows for 1000 years) Col [4] DF Mm3 Natural flow (corresponding to 75% reliability level) between the dam site and diversion site Col [5] Eo-Rf Mm Evaporation minus rainfall over the reservoir. Eo is evaporation at 75% exceedance level as estimated from ETo and Rf is monthly rainfall at 75% reliability level Col [6] IWD Mm3 Irrigation water requirement (given by Table 13.1) Col [7] (Eo-Rf) Mm3 Col [5] converted to volume covering the entire command area Col [8] SL Mm3 Seepage loss (assumed to be 1% percent of the existing storage in the reservoir) Col [9] IWR Mm3 Irrigation water release from the reservoir (Col[6]-Col[4J) Col [10] CS Mm3 Change in storage between the ends of the previous and current months Col [11] Storage Mm3 Reservoir storage at the end of month Col [12] Area Km2 Reservoir average surface area between beginning and end of month Col [13] Level m. asl Reservoir storage at the end of month Col [14] Spill Mm3 Spill from the reservoir between beginning and end of month Col [15] STRQ Mm3 Total annual storage requirement Col [16] T.Spill Mm3 Annual spill from the reservoir (sum of Col[14] from month 1 to 12) The d etails o f s inflation i nputs a re p rovided i n t he T ables 1 3 1 a nd 1 q o detailed irrigation targeted simulation runs are provided in Table The abstrac< of the contemplated irrigation (Table 13.1) are successful at various refute k 'ciiauimies snown in Table 13 3 thGSe Para™eters (he Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd 88Ar Jo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 13.1: Irrigation Water Requirements for Various Scenarios (for 13700 ha in Mm ) May 2007 3 Phase I Phase II Month Roti Rot2 Roti Rot2 Sep 8.38 Oct 10 41 Nov 2.89 Dec 11.04 Jan 19.00 Feb 23 25 Mar 18.49 Apr 4.98 May 2.01 Jun 21.64 Jul 5.97 Aug 6.89 Total 134.93 8.43 12.43 12.45 10.69 13.19 13.72 2.90 3.16 3.29 12.49 14.02 16.07 22.18 24.64 28.61 27.87 29.98 34.92 22.15 22.99 26.41 5.21 5.09 5.30 2.01 2.01 2.01 21.64 32.42 32.42 5.97 8.95 8.95 6.89 10.33 10.33 148.43 179.22 194.49 Table13.2 Reservoir Characteristics at Dead Storage Level Description Uni) Qunatity Minimum drawdown level Minimum river bed level Area at dead storage level Dead storage m.a.s.l m.a.s.l km2 Mm3 --------- —"—~ 1350.0 1320.0 67.88 874.7 Water Works Design & Supervision Entemri^ In Association with Intercontinental Consultants and Technocrats Pvt LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 13.3 Storage Reservoir Characteristics and Reliability Levels May 2007 Description Unit Reliability level 75% 80 % 85% 90% 95% Phase I, Rot 1 Dam heightfat spillway c.l) Spillway crest level Area at normal water level Live storage Total storage Spill over the spillway Spill to live storage ratio Phase I, Rot 2 30.89 30.98 31.08 31.24 31.42 1350.89 1350.98 1351.08 1351.24 1351.42 70.797 71.094 71.424 71.952 72.546 67.3 74.4 82.3 95.1 109.4 942.0 949.1 957.0 969.7 984.1 1800.0 1799.0 1754.0 1703.0 1640.0 26.74 24.17 21.30 17.92 14.98 Dam heightfat spillway c.l) Spillway crest level Area at normal water level Live storage Total storage Spill over the spillway Spill to live storage ratio Phase II, Rot 1 m m.a.s.l km2 Mm3 Mm3 Mm3 m m.a.s.l km2 Mm3 Mm3 Mm3 31.05 31.14 31.24 31.41 31.59 1351.05 1351.14 1351.24 1351.41 1351.59 71.325 71.622 71.952 72.513 73.107 80.0 87.1 95.1 108.6 123.1 954.6 961.8 969.7 983.3 997.8 1786.0 1785.0 1740.0 1689.0 1626.0 22.34 20.49 18.31 15.55 13.21 Dam heightfat spillway c.l) Spillway crest level Area at normal water level Live storage Total storage Spill over the spillway Spill to live storage ratio Phase II, Rot 2 m m.a.s.l km2 Mm3 Mm3 Mm3 Dam heightfat spillway c.l) Spillway crest level Area at normal water level Live storage Total storage Spill over the spillway Spill to live storage ratio m m.a.s.l km2 Mm3 Mm3 Mm3 31.14 31.22 31.33 31.5 31.68 1351.14 1351.22 1351.33 1351.50 1351.68 71.622 71.886 72.249 72.810 73.404 87.1 93.5 102.2 115.9 130.4 961 8 968 1 976.9 990.5 1005.0 1755.0 1754.0 1709.0 1658.0 1595.0 20.15 18.77 16.72 14.31 12.24 31.32 31.39 31.52 31.69 31 87 1351.32 1351.39 1351.52 1351.69 1351 R7 72.216 72.447 72.876 73.437 74.031 101.4 107.0 117.5 131.2 145 7 976.1 981.7 992.1 1005.8 1020 4 1739.0 1738.0 1693.0 1642.0 1579 0 17.14 16.24 14.41 12.52 10.84 Water Works Design & Supervision Enterprise in Association with Intercontinental Consultants and Technocrats Pvt. Ltd 90ArJoDedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 14. DEDESSA SUB-BASI N MODELING 14.1. Modeling for Arjo De dessa dam for irrigat io n The simmlations discussed in previous sections is for a comprehensive analysis of Dedessa dam, which is the main focus of the TOR. A detailed Ms-Excel based model, using 1000 years of monthly data of inflows, generated synthetically, were incorporated in the various runs, to obtain the results, as indicated in the Table 13.3. As can be seen from the water requirement available at Table 13.1, for the ultimate development phase II, of the Dedessa dam, the optimal water abstraction is for RoT 2, scenario cropping pattern. Based on various combinations of the simulation runs, which are very exhaustive, it could be stated that there could be two net phases of development. The designs however need to be made for the phase II development. The firmed up geometry of the reservoir at Dedessa dam for these two phases could as below. This is for the success of irrigation at 80% reliability. The following abstracts are based on the results of simulation considering only contemplated irrigation. □ For phase I development of Dedessa dam • Irrigation command • Full reservoir level ■ Storage at full reservoir • Dead storage level • Volume at Dead stage level ■ Live storage • River bed level • Area at Dead storage level • Area at full reservoirs level ■ Irrigation Demand □ For phase II development of Dedessa dam • Irrigation command • Full reservoir level ■ Storage at full reservoir level ■ Dead storage level ■ Volumes at dead storage level 13,700 ha 1351.14 m 961.8 Mm3 1350.00 m 874.67 Mm3 87.10 Mm3 1320.00m 67.88 km2 71.14km2 148.43Mm3 13,700 ha 1351.39 m 981.7 Mm3 1350.00m 874.67 Mm3 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd 91ArJoDedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Live storage 107.00 Mm3 River bed level 1320.00 m Area at dead storage level 67.88 Km2 Area at full reservoir level 72.07 km2 Irrigation Demand 194.49Mm3 Thus both the above phases satisfy contemplated irrigation with 80% reliability. In the phase I and phase II, the cropping patterns envisaged are different. However, for the final design of Deddesa dam, it has to be based on phase II development with the above dam features if the development is for irrigation only. 14.2 The sub basin modeling When the aspect of the development of Dedessa sub basin as a whole, including the present proposal of Dedessa dam, is taken for considerations, the need for the simulation of the sub basin becomes relevant. The details and components of such sub basin simulation modeling could be for the following objectives. ■ To explore the possibility of power generation at Dedessa dam. Since only a small fraction of the total inflow is to be used for irrigation, looking at power development options at the site by raising the dam height is an important consideration ■ In such a scenario as above, that is, full scale upper optimal development of Dedessa dam, it becomes a necessity to check that this optimal water abstraction does not jeopardize future developments in the whole of the Dedessa sub-basin. This requires basin modelling at a larger scale considering contemplated developments upstream and downstream. In this report, simulation exercise has been carried out to address the first objective. A tailor made sub basin modeling was carried out by developing a Fortran source code named “Arjosim” to quickly undertake simulation exercise of various components with alternatives Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd 92Arjo-Dedessa Irrigation Project Meteo rological and Hydrol ogical Aspects May 2007 14.2.1 Power Generation in Dedessa Dam The D edessa dam with its phase II configuration, could irrigate 13 ,700ha at 80% reliability. Since, left and right bank main canals take off from the dam, no incidental power can be generated as such. Hence, power development options are sought by raising the dam height to have additional storage for separate power releases. The FRL for optimal phase II irrigation development is 1351.39 m. Two scenarios for Higher FRL values are considered with FRL of 1353 m, and 1356 m. For each FRL considered, four different power release options are taken up for the simulation as depicted in Table 14.1. It should be noted that the given releases are total monthly releases for irrigation and hydropower. That is, the given total releases less the monthly irrigation requirement shall be used for power generation. There will be a separate outlet for power at the same level as that of irrigation outlet, that is, at 1350.00m. The reservoir characteristics at the two FRLs considered for the simulation are: Full Reservoir Level = 1353 m ■ Storage at full reservoir level Live storage Dead storage level Volume at dead storage level Area at full reservoir level Full Reservoir Level = 1356 m Storage at full reservoir level Live storage Dead storage level Volume at dead storage level Area at full reservoir level 1092.51 Mm3 217.33 Mm3 1350.00m 874.67 Mm3 77.88 km2 1341.16 Mm3 466.49 Mm3 1350.00m 874.67 Mm3 87.85 km2 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd 93Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 The effective turbine center was fixed at 1322.00 m elevation. This of course, needs to be finalized as per ground condition and dam head/or otherwise, other location based powerhouse. Also, the plant factor adopted in the basin simulation runs is unity, and with unrestricted installed capacity. B ased on actual budget and power requirement analysis by Hydropower and Dam design engineer, these installed capacities could be changed or power generation could be restricted. The results presented in the Hydrological simulation are with these assumptions on turbine center level and plant factor. However, at detailed design stage, with these firmed up figures, the sub basin models could be re-run in short time. The power duration curves for the various runs are shown in Figures 14.1 (a1) to 14.1 (b4). These figures are useful to reckon the monthly power generation at various exceedance probability levels at proposed FRLs of 1353 and 1356. With respect to annual energy production the results are presented in the Table 14.2 for Dedessa dam. This piture of energy generation is after satisfying irrigation needs fully at 80% reliability. However the quantum of energy and power are of not very attractive type. 14.2.2 Optimal Power Generation With FRL upto 1956, as seen above, though irrigation is successful, the power generation scenario is not attractive. Hence the simulation model ‘AnjosinT was, slightly recoded for making simulations for increased FRL considerations and exploring the possibility of power generation at a higher level, though the exercises are beyond the scope of the present TOR A large number of runs of 'Arjosim' were undertaken under 3 different domains of preposition These are: Domain 1: k eeping t he p ower o utlet a t a I ower I evel o f 1 346 m a nd i ncreasing t he F RL i n stages, with various monthly power release patterns. Domain 2: keeping the power outlet at 1346 m and increasing the FRL in stages as above but with model in built decision support based power releases. Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd 94Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects M ay 2007 Domain 3: keeping the power outlet at the sam e level as that of irrigation outlet (of course, a separate power outlet) and increasing the FRL in stages, with decision support based power releases by the model. Domain 1 Simulations A set of 12 different runs were attempted within the FRL ranges from 1370 to 1376 m, and with different monthly power release pattern. Some of the optical ones are: i. With FRL 1370, the 97% power is 11.22 MW ii. With FRL 1372, the 97% power is 13.30MW iii. With FRL 1374, the 97% power is 13.62MW Beyond FRL 1374, there were no encouraging improvements in power generation. Domain 2 Simulations These runs totaling to 10 were made with decision support based power releases, in built in the model. This obviously increases the power generation for the set of FRLs. The optimal runs indicated the following situation. i. With FRL at 1372, the 97% power is 16.49MW ii. With FRL at 1374, the firm power is 17.20MW iii. With FRL at 1376, the firm power is 17.90MW iv. With FRL at 1378, the firm power is 19.50 MW Domain 3 Simulations Here, in addition to decision support power releases, the outlet was best at 1350W instead of 1346M adopted in the previous domains. This improved the situation. Some of the salient model runs yielded the following scenarios. i. At FRL 1370, the firm power at 97% is 17MW ii. At FRL 1372m, the 97% power is 18.1 MW iii. At FRL 1374m, the 97% power is 18.95MW iv. At FRL 1376m, the 97% power is 20MW Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd 95Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 14.2.3 Reduction In flows at Dedessa Sub-basin In either of the cases, covering 8 runs of simulation, there is no detr imental eff ect on the downstream flows of Dedessa sub basin. The maximum co nsu mptive utilization is only for irrigation, which is only 194.49Mm annually, as the additional 3 releases made for power are not 3 for consumptive uses. The power releases flows downstream. Thus, a net reduction in the sub basin flows will be up to a datum of 195mm , even without accounting for any regeneration from irrigation. The sub basin of Dedessa contributes at its end annually to Abbay a auuatum of 14,033mm3 (BCEOM Master Plan study). This will get reduced to 13,838mm3 because of the proposed arjo Dedessa project, which is only a negligible reduction of 1.39%. As such, the Arjo Dedessa Dam proposal is not going to jeopardise the overall developments of the sub basin considering various identified projects of the sub basin. 14.2.4 Conclusions The simulation runs could be made for further different scenario. At this stage, it could be said that the optimal power generation would be with FRL at 1376 m and with power outlet at 1350 m. The tail race is assumed to be at 1322 m in all the runs. With a plant factor of 0.6, the installed capacity could be around 33MW. Hydrologically, the simulations can be performed further without any constraints, provided that there are no geological, geothechnical. design, environmental, social and other constraints. The power generation at different reliability percentages are shown in the Figure 14.2 for the last run. However. Io form up power generation, even at higher FRLs, a prefeasibility study is required for exploring the possibilities ol increasing the height of dam and establishing the technical feasibility and economic viability for generation of hydro-power. Water Works Design & Supervision Enterprise ~~ 96 In Association with Intercontinental Consultants and Technocrats Pvt LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Table 14.1: Total Monthly Release (Irrigation plus Power) options for various FRL values consi dered Options FRL = 1353 m FRL = 1356 m Option I 75 Mm3 for all months Twice of monthly irrigation releases Option II 75 Mm - May to 3 September & 50 Mm - 3 Three times monthly irrigation releases Oct. to April Option III 75 Mm - May to J September & 40 Mm - 3 100 Mm3 for all months Oct. to April Option IV 150 Mm - May to August 3 75 Mm - September 3 3 & 40 Mm3 - Oct. to March, 75 Mm in Sept & April to April & 100MCM - May. to August Table 14.2: Annual Energy generations at Dedessa dam for the various options AnmJal Energy FRL Scenario Release Options Production (GWh) Probability Levels o at Exceedance Mean Level 50% 75% 90% 95% 97% 1353 m I II III IV 43.6 44.7 43.3 40.1 36.3 28.3 32.0 32.3 29.8 27.3 25.2 22 8 28.0 28.9 26.5 24.3 22.7 20 5 25.3 25.9 25.5 22.9 21.3 19 6 1356 m I II III IV 11.9 12.0 11.9 11.8 11.7 11 7 24.5 24.5 24.3 24.0 23.8 23 6 54.0 47.6 55.2 48.5 50.6 47.5 45.9 43.8 42.9 40.9 39.2 38.1 Water Works Design & Supervision Enter prise In Association with Intercontinental Consultants and Technocrats Pvt Ltd 97Ar jo Dedessa Irrigation Project Meteorological and Hydrological Aspects May ?007 Flguro 14 1 Power Duration Curvet Percent Powor I* Equalled or Exceeded. % (a. 1) Power duration curve for FRL = 1353m - Option I (a. 2) Power duration curve for FRL = 1353m - Option II (a.3) Power duration curve for FRL = 1353m - Option III Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd «>xAr jo Dedma Irrigation Project Meteorological and Hydrological Aspects May 3tXT Porcont Power Is Equalled or Excoodod , 7. (a.4) Power duration curve for FRL = 1353m - Option IV (b. 1) Power duration curve for FRL = 1356m - Option I Percent Power is Equalled or Exceeded % (b.2) Power duration curve for FRL = 1356m - Option // Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd 99Arjo Dedassa Irritation Project Meteorological and Hydrological Aspects (b.J) Power duration curve for FRL = 1356m - Option III (b.4) Power duration curve for FRL = 1356m - Option IV Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd.ArjoDedessa Irrigation Project Meteorological and Hydrological Aspects May 20 07 15. RECOMMENDATIONS ON TRAINING NEEDS It is very heartening development that the water resources exploitation f or optimal utilization towards economic stability is getting the major thrust in Ethiopia. Wit h p hase of activities, soon, the rich river basins will be impounded in different storages associated with a number of runoff the river schemes either for irrigation or power or in a multi objective sense. As such, in the present scenario, the hydrological planning and design are in the usage. However, when the basins, in the near future, become stuffed with many projects, then, the real time operation of those projects will be the dire necessity. Judicial operation of a multi reservoir /project system has a lot of benefits in combating floods, tiding over drought, reduction in water losses and others. However, such real time operation would require a complete knowledge (in the hydrological sense) of the basin system, and hydrology and simulation techniques (simulation coupled with optimization models). Such a scenario of real time operation will have to be backed up by flood forecasting networks, advance prediction of seasonal rainfall, adequate telemetry (for transfer of data), dedicated computers, telecommunication soft ware in addition to subject matter (hydrology/simulation) software. The personnel heading such operations in a basin, and those working in such a team need to be trained in the above mentioned aspect, so as t o u ndertake o peration which has i mmerse a dvantages. H ence, i t i s r ecommended t hat experts on Hydrology and Hydrological modeling should be identified for undergoing such trainings in Institutions/universities in appropriate countries. Though there could be many such institutes, the consultant feels for such multi system operation, adequate expertise is available in countries like U.S.A and India, where many institutions, Universities, River basin authorities and research stations could be identified for offering such trainings. Such trained personnel with expertise in hydrology will be able to head future river basin authorities for optimal real time operation of the systems. Water Works Design & Supervision Enterprise- - - - - - - - - - - In Association with intercontinental Consultants and Technocrats Pvt LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects REFERENCES May 2007 Admasu Gebeyehu, 1988: Regional Analysis on Some Aspects of Streamflow Characteristics in Ethiopia. (Unpublished Draft Report). August 1988. Admasu Gebeyehu, 1989: Regional flood Frequency Analysis. PhD thesis, Royal Institute of Technology, Bulletin No TRITA-VBI-148, Stockholm, Sweden. BCEOM, 1999. Abbay River Bain Integrated Development Master Plan Project. Phase 2: Data Collection, Site Investigation Survey and Analysis. Section II: Sectoral Studies Volume III: Water Resources: Part I - Climatology and Part II - Hydrology. BCEOM - French Engineering Consultants - in association with ISL and BRGM. ERA (Ethiopian Roads Authority), 2002: Drainage Design Manual, Hydrology. Fiddes D, 1977: Flood estimation for small East African rural catchments, Proceeding Institution of Civil Engineers, Part 2, 63, 21-34 (1977) Gray, D.M. Editor in Chief, 1971: Handbook on the Principles of Hydrology. Haan, C.T, 1977: Statistical Methods in Hydrology. The Iowa State University Press, Ames. Hersfield, D M., 1961: Estimating the probable maximum precipitation; ASCE, J. Hyd. Div., 87 No. Hy5, 99-116 . Matalas, N.C., 1963: Probability Distribution of Low Flows. Statistical Studies in Hydrology. Geol. Survey Prof. Paper 434-A Shaw, Elizabeth M„ 1988: Hydrology in Practice. International Van Nostrand Reinhold. USBR (United States Department of the Interior Bureau of Reclamation), 1964 Land and Water Studies of the Blue Nile Basin. Ethiopia. Appendix III - Hydrology. WAPCOS (Water and Power Consultancy Services (India) Ltd.), 1990. Preliminary Water Resources Development Master Plan for Ethiopia. Final Report. Volume III. Annex A: Hydrology & Hydrogeology. Addis Ababa. Water Works Design & Supervision Enterprise - - - - - - - - - 102 in Association with Intercontinental Consultants and Technocrats Pvt. LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 ANNEXES Annex A: Results obtained from the Meteorological Analysis Year 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Jan I Feb ,March April May June | July , Aug j Sept Oct Nov | Dec t 22.2 21.8 24.7 24 0 23.2 21.5 20.7 20.2 21.6 22.0 21.9 19 7 20.0 21 8 24.9 22.5 23.2 21.0 20.0 200 21.3 22.1 20.2 19.0 21.7 23.2 24.3 16.3 15.9 21.6 21.1 20.8 21.4 21.7 24.6 21.3 21.7 22 9 25.4 24.6 23 7 21.5 20.4 20 4 21.4 22.0 21.5 208 21.5 21.8 24.8 24.8 23.5 21.6 21.3 20.8 21.5 22.4 23.2 20.5 22.7 23.6 25 3 24.8 24.1 21.7 21.4 20.8 21.5 22.3 22.0 18.8 19.5 22.5 25.1 24.8 23.7 21.2 20.7 20 5 21.3 21.1 23.0 18.7 19.9 22.4 23 6 24.5 24.1 21.6 21.6 21.1 21.2 21.4 21.2 19.6 22 4 23.2 25.1 24 6 24.0 22.0 20.7 20.7 21.5 21.7 21 2 16.9 21.5 21.6 22.9 25.0 24 9 24.3 22.0 21.4 20.8 21.6 22.8 19.8 18.2 21.5 22.7 21.2 21.0 20.6 23.0 21.1 22 2 22.3 22 4 22.7 20.3 20 6 21.5 21.5 20.4 23.9 24.7 23.7 21.1 21.0 19.9 21.1 22.4 21.7 18.2 21.8 22.4 23.1 24.2 24.9 23.2 21.0 21.8 21.3 21.6 22.3 22.8 20 2 22.6 25.8 26 8 24.1 21.8 21.3 20.8 21.5 21.7 21.7 17.4 23.3 25.3 23.9 23.9 21.8 20 8 21.3 21.3 21.2 19.1 19.0 23.6 25.9 24 8 23.7 21.7 20.5 20.2 21.3 21 9 20.4 18.9 23 9 24.8 24.3 23.1 21.0 21.0 20.8 21.6 22.4 22.5 19.7 23.5 24.9 25.3 24.4 21 4 21.0 21 3 21.9 23.5 23.0 20.9 22.8 26.1 256 23.8 21.9 20.9 21.2 21.1 22.3 20.9 20.4 23.5 24.7 24.2 24.2 21.9 21.3 21.6 22.0 22.3 21.6 20.9 24.1 26.1 258 24 4 22.3 21.1 20.8 22.0 22.0 22.0 19.5 22.6 26 2 25.1 247 22.3 20.6 21.1 21 5 22.0 21.6 19.2 22.3 23 8 24.9 23.5 21.9 21.2 20 7 21.6 21.8 23.0 20.6 23.6 26.1 25.6 25.0 22.8 22.3 21.8 21.7 22.4 22.3 18.6 20.6 254 26.2 24.5 21 9 20.9 20.7 21.1 20.2 23.4 20.6 22.9 25.7 25.1 24.0 21.7 20.6 20 4 21.5 21.5 22.1 19.7 24.7 23.9 24 6 24.6 22.0 21.3 21.1 21.2 21.7 22.0 20.4 23.0 25.4 25.1 24.2 22.6 22.2 21.6 21.9 23.1 22.7 20.2 21.3 24.5 25.1 25 8 25.3 22.5 21.3 21.6 21 9 22.5 20.6 18.8 21.0 23.0 23.3 21.9 21.3 21.6 21.7 22.0 21.9 21.6 18.6 22.4 21.4 21.4 21.9 22.1 22.4 20.9 22.1 22.6 21.6 22.3 22.6 23.4 24.6 21.9 21.6 23.0 23.2 21.9 24.2 22.3 24.6 24 5 21.9 24.8 25.1 23.6 25.1 25.1 24.1 25.2 25.2 23.5 24.3 25.6 24.2 26.8 24.9 24.5 26.4 26.5 24.1 26.3 25.9 22.4 26 9 25.5 24 9 27.4 27.7 22 8 26.2 26.3 22 9 26.6 26.6 24.3 26.0 26.4 23.6 26.9 25.9 24 5 26.4 25.7 24.2 26.2 26.5 24.6 22.6 21.3 20.8 22.0 24.6 22.3 21.1 21.3 21.8 24.4 22.7 21.4 21.4 21.8 24.3 22.3 21.1 21.5 21.8 25.3 23.1 21.9 22.1 22 3 24.7 21.9 21.7 21 8 22 4 24 4 23 1 22.3 22.3 23.2 26.2 234 22.4 22 3 23.1 24.9 22.8 21.6 21.3 22 9 25.5 22.6 21.9 21.8 23 0 25.5 23.0 22.0 22.2 23 0 25.8 22.8 22.7 22.2 22 8 25.8 23 2 22.0 22.2 22 7 _25^__2Z8_ 21.5 22.1 22 5 21.4 21.4 18.2 22.7 21.8 21.3 22.9 21.7 19.6 22.0 23.3 20.0 23.0 23.3 22.2 22.4 22.0 20.2 24.0 25.1 22.9 24.2 22.0 19 1 23.5 21.0 19.8 24.0 23.5 20 8 24 2 23 6 21 6 23.3 23.1 22.7 23.0 23.5 20 6 Water Works Design & Supervision Eni^rto- - - - - - - - - - - - - - - - I 03 in Association with Intercontinental Consultant., and Teehnncntts Pvt. ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects A2: Estimated Minimum Temperature at Arjo Dedessa Project Area (in C) May 2007 Year 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 Jan Feb I March i April May June | July | Aug | Sept ] Oct [ Nov Dec 9.7 10.5 13.8 14.7 14.9 14.6 14.7 14.3 14.5 13.0 10.3 8.0 8.8 10.5 13.9 13.8 15.0 14.3 14.2 14.2 14.4 13.0 9.5 7.7 9.5 11.2 13.6 9.9 10.3 14.7 15.0 14.7 14.4 12.8 11.6 8.6 9.5 11.1 14.2 15.0 15.3 14.6 14.5 14.4 14.4 13.0 10.1 8.5 9.4 10.6 13.9 15.1 15.1 14.7 15.1 14.7 14.5 13.2 10.9 8.3 9.9 11.4 14.2 15.1 15.5 14.8 15.2 14.7 14.5 13.2 10.3 7.6 8.5 10.9 14.1 15.1 15.3 14.4 14.7 14.5 14.3 12.5 10.8 7.6 8.7 10.8 13.2 15.0 15.5 14.7 15.3 14.9 14.3 12.6 10.0 8.0 9.8 11.2 14.0 150 15.5 14.9 14.7 14.6 14.5 12.8 10.0 6.9 9.4 11.1 14.0 15.2 15.7 14.9 15.2 14.7 14.5 13.5 9.3 7.4 9.5 9.9 13.4 15.1 15.3 14.3 14.9 14.1 14.2 13.2 10.2 7.4 9.4 11.2 13.5 15.2 14.9 14.3 15.4 15.1 14.6 13.2 10.8 8.2 9.9 10.9 14.4 16.3 15.5 14.8 15.1 14.7 14.5 12 8 10.2 7.1 9.3 11.3 14.2 14.6 15.4 14.8 14.8 15.1 14.3 12.6 9.0 7.7 9.2 11.4 14.5 15.1 15.3 14.8 14.6 14.3 14.4 12.9 9.6 7.7 9.0 11.6 13.9 148 14.9 14.3 14.9 14.7 14.5 13.2 10.6 8.0 10.1 11.4 14.0 15.4 15.8 14.6 14.9 15.1 14.8 13.9 10.8 8.5 9.2 110 14.6 15.6 15.3 14.9 14.8 15.0 14.2 13.2 9.8 8.3 9.7 11.4 13.8 14.8 15.6 14.9 15.1 15.3 14 8 13.2 10.2 8.5 9.8 11.7 14.6 15.7 15.8 15.1 15.0 14.7 14.8 13.0 10.3 7.9 9.8 10.9 14.7 15.3 16.0 15.1 14.6 14.9 14.5 13.0 10.2 7.8 9.9 10.8 133 15.2 15.1 14.9 15.1 14.7 14.5 12.9 10.8 8.4 8.9 11.4 14.6 15.6 16.1 15.5 15.8 15.5 14.6 13.2 10 5 7.6 9.0 10.0 14.2 16.0 15.8 14.9 14 8 14.6 14.2 11.9 11.0 8.4 9.4 11.1 14.4 15.3 15.5 14.8 14.6 14.4 14.5 12.7 10.4 8.0 9.4 12.0 13.4 15.0 15.8 15.0 15.1 14 9 14.3 12.8 10.3 8.3 9.5 11.1 14.2 15.3 15.6 15.4 15.8 15.3 14.8 13.6 10.7 8.2 9.8 11.9 14.0 15.7 16.3 15.3 15.1 15.3 14.8 13.3 9.7 7.6 9.3 10.8 13.8 14.9 15.0 14 9 15.1 15.3 14.6 13 0 10 3 8.8 9.2 10.6 13.9 15.3 12.0 15.2 15.2 15.2 14.8 13.0 10.6 8.5 10.1 11.4 14.0 15.3 15.9 15.4 15.1 14.7 14.8 12.6 10.1 7.4 9.7 11.6 14.1 15.4 15.8 15.1 15.0 15.1 14.7 13.4 10.3 8 6 9.9 11.4 13.6 15.6 15.7 15.4 15.2 15.2 14.7 13.5 10.2 7.9 9.5 11.7 15.0 15.2 15.7 15.2 15.0 15.2 14.7 13.0 11.0 8.1 9.8 11.9 14.8 16.2 16.3 15.7 15.5 15.6 15.0 13.6 11.0 9.0 9.9 11.6 14.7 15.8 16.0 14.9 15.4 15.4 15.1 13.3 10.4 8 2 10.2 10.8 15.1 15.6 15.8 15.7 15.8 15.8 15.6 14.2 11.8 9 3 10 8 12.1 15.3 16.9 16.9 15.9 15.9 15.8 15.6 14.3 10.3 7 8 9.6 11.0 14.7 16.0 16.1 15.5 15.4 15.1 15.4 13 9 9.9 8 0 9.5 11.1 14.9 16.2 16.4 15.4 15.6 15.4 15.5 14 2 11 1 8 4 2002 10.1 11.8 14.6 16.1 16.5 15.6 15.6 15.7 15.5 14.3 11.1 10.2 11.4 15.0 15.8 16 6 15.5 16.1 15.7 15.4 13.8 10.9 88 2003 2004 9.6 11.8 14.8 15.7 16.7 15.8 15.6 15.7 15.3 13 6 11.0 10.6 11.7 14.7 16.2 16.5 15.5 15.3 15.7 15.2 13.4 10.9 92 84 8.8 Water Works Design & Supervision Enterprise 104Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects A3: Estimated Maximum Temperature at Arjo Dedessa Project Area (in °C) May 2007 Year Jan 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 34.7 31.2 33.9 33.9 33.6 35.4 30.4 31.1 35.0 33 6 33.7 336 35.4 33.1 32.8 32.2 35.9 32.9 34.7 34.8 35.0 35.4 31.7 32.2 33.6 33.6 34.0 35.0 33.2 32.8 35.9 34.5 35.3 33.7 34 8 35.3 36.5 38.4 34.2 33.7 35.9 36.2 34.2 37.8 Feb March! April May I June | July Aug j SeptOct ' Nov [ Dec 33.0 35.6 33.6 31.7 28 6 26.7 26 1 24.4 30.9 33.5 31 4 33.0 35.8 31 6 31.8 27.9 25.8 25 8 24.2 31.1 30.9 30.4 352 34.9 22.8 21.7 28 8 27.2 26.9 24 2 30.6 37.6 34.7 36.6 34.4 32.4 28.6 26.3 26.4 24.2 31.0 33.1 35.7 34.7 32.1 28.8 27.5 26.9 24.3 31.5 32 9 34.0 33.3 35.5 32.8 35 8 36.5 34.7 32 9 28.9 27.6 26.9 24.4 31.4 33.6 30.1 34.1 36.2 34.7 32.4 28.2 26.7 26.5 24.1 29.6 35.1 29.9 33.9 34 0 34.3 32.9 28.8 27 8 27.3 24.0 30.1 32.4 31.3 35.2 36.1 344 32.8 29.2 26.7 26.7 24.3 30 6 32.4 27.0 34.6 36.0 34.8 33.3 29.2 27.6 26.9 24.4 32.1 30.2 29.1 31.0 34.5 34.6 32.4 28.0 27.0 25.7 23.9 31.5 33.1 29.1 35 0 34.8 34.8 31.7 27 9 28.1 27 5 24.5 31.4 34.9 32.3 34 2 37.1 37.5 32.9 29.0 27.5 26.9 24.4 30.5 33.1 27.8 35.3 36.5 33.5 32.7 28.9 26.8 27 6 24.1 29 9 29 2 35.7 37.3 34.8 32.4 28.9 26.5 26.1 24.2 30 8 31.2 36.2 35.7 34.1 31.5 27.9 27.0 26.9 24.4 31.5 34.5 35.6 35.9 35.4 33.4 28.5 27 1 27.6 24 8 33.0 35.2 34.5 37.5 35.9 32.5 29.2 27.0 27.4 23.9 31.4 31.9 35.5 35.6 33.9 33.1 29.1 27.5 27 9 24.9 31.4 33.1 33.4 36.5 37.5 36.1 33.4 29.6 27.3 26.9 24.9 30 9 33.6 31.2 34.2 37.8 35.1 33.8 29.6 26.6 27.2 24.4 30.9 33.1 30.6 33.7 34.3 34.8 32.1 29.2 27.4 26.8 24.4 30.7 35.2 32.9 35.7 37.6 35.8 34.2 30.4 28.8 28.2 24.6 31.5 34.1 29.8 31.2 36.5 36.7 33.5 29.1 27.0 26.7 23.9 28 4 35.8 330 34.6 37.0 35.2 32.8 28.9 26 5 26.4 24.3 30.3 33 8 31.4 37.5 34.5 34.4 33.6 29.3 27.5 27.3 24.0 30 5 33.6 32 6 34.8 36.5 35.1 33.1 30.1 286 27.9 24.8 32 5 34.7 32 3 37.2 36.1 36.1 34 6 29.9 27.5 27.9 24.8 31.7 31.5 30.1 33.8 35.4 34.2 31 9 29.1 27.5 27.9 24.6 30.9 33.5 34 5 33.2 35.7 35.2 25.4 29.8 27 6 27.7 24.8 31.1 34 3 33.4 35.8 36.1 35.2 33.7 30.1 27.5 26.9 24.9 30.1 32.7 29.1 36.5 36.3 35.3 33.6 29 6 27.2 27 5 24.7 32 0 33.3 34.0 35.5 35.0 35.9 33.4 30.1 27.6 27.7 24.7 32.2 33.2 31.3 36.7 38.6 34.8 333 29.7 27.3 27.8 24.7 31 0 35.7 31.9 37.2 38.0 37.2 34 6 308 28 2 28.5 25.3 32.3 35.6 35.5 36.5 37.9 36.3 33.8 29.2 28.0 28.2 254 31.5 33.7 32.3 33.9 38.8 35.7 33.4 30.8 28.7 28 9 26.3 338 38.3 36.6 37.7 39.4 38.8 35.8 31.1 28.9 28.9 26.1 34.1 33.6 30.5 34.5 37.8 36.8 34.1 30.4 27.9 27 6 25.9 33.0 32.1 31.6 34.7 38.2 37.3 34.8 30.1 28.3 28.2 26.0 33.7 36 0 33.2 30 3 30 2 31 5 33 4 32.6 36.8 37.4 37.0 34.9 30.5 28.4 28.7 26.0 34 1 35.7 38.7 36.2 35.2 30.3 29.3 28.7 25.8 32 8 35.3 36 2 36 2 34 6 37.1 38.0 36.0 35.3 30.8 28.4 36.6 37.8 37.2 35.0 304 27.8 28.6 25.5 31.8 35 5 28.7 25.7 32.3 35.9 33.0 Water Works Design & Supervision Enterprise- - - - - - - - - - - 105 In Association with Intercontinental Consultants and Technocrats Pvt. Ltdlr}» Me*** nrrt<:inun Prt>|ert Mguomloghul And Hydrological Uperts w.st w * Relative Humidity it Arjo Oedeeee Project Area (in percent) /©nr J4P Feb Mm h April Muy Junta July Aug Swpt Qrt Nov 19*1 ’ 67 32 46 70 7! 78 67 87 82 82 68 */*«? t062 •• 69 •14 71 •16 65 94 M M )5 38 64 196 1 65 • < 63 62 •M 85 VI 91 19 63 •17 65 1964 ft 66 5/ 63 75 82 38 66 J2 54 71 75 1965 V 52 50 18 6‘) 76 31 85 64 82 56 *4 1966 66 S6 38 71 71 78 66 MJ 65 64 60 49 1967 55 MJ W 66 76 61 91 80 )2 85 69 73 1966 56 66 4 48 75 61 66 65 69 8! 78 72 1969 7*2 68 64 69 75 62 68 69 66 IO 77 65 1970 71 62 64 69 74 *9 66 32 69 HC» 72 66 1971 60 46 >0 64 76 61 67 90 67 87 82 78 1972 34 65 56 70 74 79 69 15 68 80 83 75 197J 55 39 57 68 76 61 82 56 39 83 rr 53 1974 54 49 33 58 76 61 90 90 93 63 63 1975 52 59 51 70 74 61 68 )3 MJ 64 1976 ry 55 56 86 57 66 79 61 92 91 91 91 1977 F» 93 66 82 58 57 66 81 69 88 87 86 62 56 74 81 36 64 75 77 8/ 68 64 1979 64 66 65 75 61 64 55 70 77 84 ’ r-. 65 86 79 50 55 53 68 76 ftO 37 61 66 67 85 79 1961 54 46 75 36 63 72 7ft 85 66 68 1962 67 83 62 55 62 65 77 75 84 60 68 MJ 1963 •MJ 66 63 61 70 87 79 66 78 79 65 1964 60 59 49 47 69 68 61 76 30 62 68 68 72 1965 38 50 51 86 6/ 74 78 60 62 90 75 1966 89 56 60 57 87 69 73 81 77 65 70 1967 87 87 50 56 63 86 60 79 82 73 81 83 .*2 1968 69 72 64 49 56 62 75 85 82 79 90 91 75 1969 63 61 60 75 93 73 87 79 73 91 66 56 1990 67 70 62 68 77 91 34 61 32 90 35 1991 MJ 66 69 60 30 91 74 33 80 ■30 30 71 1992 66 67 54 91 69 79 80 34 32 90 75 94 3d 75 1993 69 63 56 75 30 35 80 69 64 79 1994 57 53 55 67 80 78 90 66 66 3© Jft 62 80 86 1995 60 56 57 72 79 75 1996 72 43 63 73 30 90 33 1997 9ft 39 MJ 38 30 92 87 *2 73 53 53 72 76 61 66 88 74 34 81 39 74 81 69 37 34 *9 *0 19s8 74 66 62 64 79 3C 1999 61 43 53 66 76 50 8t 90 8b 38 <’ 38 72 39 •3 my 2000 55 43 45 67 77 30 rj 86 2001 67 57 58 69 8» 90 71 56 81 92 91 73 34 »j 2002 62 64 71 92 61 78 68 2003 71 oO du □6 65 50 55 70 6a 90 3ft 58 39 62 67 K' 34 54 *3 •» V 1J *8 *9 J • 66 76 61 67 39 39 9! ’8 W»«r Work., 0»,lxu 4 '•uponuiou I'uunsrlu HJt Is t<WMO t JLxXU m LuArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects A5: Estimated Mean Daily Sunshine Duration at Arjo Dedessa Project Area May 2007 Year 1961 Jan | Feb |March| April | May | June | July T Aug | Sept | Oct j Nov | Dec 8.3 7.3 7.1 6.8 5.4 6.5 4.3 6.2 9.1 9.2 8.9 7.4 1962 6.7 6.9 8.2 7.8 9.0 6.3 2.9 2.0 6.3 6.5 7.6 7.5 1963 7.2 6.2 8.4 6.8 7.3 4.4 2.8 3.8 5.8 8.0 9.1 8.3 1964 9.6 8.3 7.7 8.0 8.7 5.8 3.0 3.0 6.8 9.1 9 0 10.0 1965 9.1 8.3 8.6 6.5 83 3.4 4.3 5.5 7.9 7.4 8.4 8.1 1966 7 8 8.2 7.1 8.5 7.8 5.3 4.2 3.8 6.0 9.2 9.8 8.3 1967 7.9 9.6 8.4 7.2 9.1 8.1 4.9 5.2 8.3 8.5 7.6 9.0 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 8.1 8.0 7.7 8.1 6.8 8.2 7.6 7.5 7.3 7.6 10.0 9.5 9.7 7.8 9.4 8.2 7.6 7.5 7.3 7.6 9.2 8.8 7.4 9.4 8.3 8.5 8.9 8.5 8.4 10.1 7.9 8.1 7.3 6.7 9.1 9.4 8.3 7.5 6.4 7.1 9.0 8.7 7.8 8.7 6.8 6.2 6.3 6.6 7.2 7.4 9.4 5.8 7.5 7.6 7.8 6.3 6.6 6.0 7.0 6.7 6.1 5.3 5.8 6.5 7.4 8.5 8.6 4.6 5.9 7.9 7.4 6.0 8.3 6.5 7.1 80 7.6 7.1 8.0 6.6 8.1 9.9 8.1 8.9 6.6 8.6 7.6 7.5 6.8 6.4 6.9 6.2 6.5 5.3 7.2 8.1 7.8 6.2 8.3 5.8 8.4 7.6 9.5 8.4 8.3 8.6 8.4 7.3 7.2 9.6 9.2 4.9 6.3 3.3 5.4 8.3 7.3 7.1 6.8 5.4 6.7 6.9 8.2 7.8 9.0 7.2 6.2 8.4 6.8 7.3 9.6 8.3 7.7 8.0 8.7 9.1 8.3 8.6 6.5 8.3 7.8 8.2 7.1 8.5 7.8 7.9 9.6 8.4 7.2 9.1 8.1 8.0 7.7 8.1 6.8 8.2 76 7.5 7.3 7.6 10.0 9.5 9.7 7.8 9.4 8.2 7.6 7.5 7.3 7.6 9.2 8.8 7.4 9.4 8.3 8.5 8.9 8.5 8.4 10.1 7.9 8.1 7.3 6.7 9.1 6.8 2.3 3.2 5.7 6.5 10.1 8.3 6.1 3.7 4.1 6.2 7.9 8.3 8.3 8.0 48 4.7 7.5 7.9 8.3 8.3 6.1 3.7 4.1 6.2 6.4 5.4 4.8 8.0 7.3 3.2 4.1 7.2 5.9 4.8 4.8 5.8 5.0 3.1 1.6 4.1 7.1 3.7 4.1 5.2 5.8 3.7 4.1 6.3 6.1 2.3 3.8 5.5 5.1 2.4 3.8 4.2 5.8 3.6 3.9 5.9 5.8 3.7 4.5 2.6 6.8 3.9 3.7 6.7 7.8 5.4 3.6 5.6 6.0 4.7 4.3 7.0 5.9 2.8 3.1 5.8 3.7 3.3 4.0 4.1 5.6 4.9 4.2 7.4 7.0 2.7 4.9 5.5 7.3 3.7 5.1 6.3 4.6 3.7 3.9 5.9 7.9 8.3 8.3 8.8 9.9 7.7 9.5 9.5 9.0 8.6 0.1 8.3 7.5 8.4 9.2 6.6 6.7 8.1 6.9 8.2 83 6.8 8.9 7.1 5.8 7.8 7.5 7.9 7.8 8.6 6.5 9.6 7.9 7.5 6.6 7.3 6.6 8.4 82 6.5 4.3 6.2 9.1 6.3 2.9 2.0 6.3 4.4 2.8 3.8 5.8 5.8 3.0 3.0 6.8 3.4 4.3 5.5 7.9 5.3 4.2 3.8 6.0 8.1 4.9 5.2 8.3 68 2.3 3.2 5.7 6.1 3.7 4.1 6.2 8.0 4.8 4.7 7.5 6.1 3.7 4.1 6.2 10.1 8.6 8.1 7.6 8.7 7.8 7.4 9.4 8.2 7.6 8.3 11.0 8.5 10.2 9.1 8.3 8.2 6.6 9.5 8.9 9.2 9.2 8.9 7.4 6.5 7.6 7.5 8.0 9.1 8 3 9.1 9.0 10.0 7.4 8.4 8.1 92 9.8 8.3 8.5 7.6 9.0 6.5 10.1 8.3 7.9 8.3 8.3 7.9 8.3 8.3 6.4 5.4 4.8 8.0 7.3 3.2 4.1 7.2 5.9 4.8 4.8 5.8 7.9 8.3 8.3 8.8 9.9 7.7 9.5 9.5 9.0 8.6 0.1 Water Works Design I Supervision Enteroriw- - - - - - - - - - - - 107 in Association with Intercontinental Consultants and Technocrats Pvt LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects A6: Estimated Mean Daily ETo of Arjo Dedessa Project Area May 2007 Year Jan | Feb , March April May June July I Aug [Sept 3.73 3.93 4.49 4.26 3.73 3.64 3.04 3.54 4.43 tT oct Nov Dec 1961 1962 1963 1964 1965 1966 1967 1968 1969 4.27 3.86 3.24 3.23 3.75 4.66 4.32 4.43 3 49 2.63 2.5 3.72 3.63 3.48 3.19 3.48 3.72 4.66 3 44 3.36 3.11 2.71 3 3.63 3.98 4.22 3.56 3 95 4.18 4.65 4.66 4.52 3.45 2.72 2 79 3.87 4.25 3 86 3.82 3.84 4.13 4.83 4.25 4.43 2.97 3.1 3.43 4.13 3.88 3.92 3.45 3.68 4.22 4.47 4.73 4.35 3.4 3 07 3 3.7 4.31 4.09 3.35 3.45 4.44 4.77 4.45 4.6 3.95 3.15 3.32 4.22 4.03 3.72 3.46 3.53 4.06 4.5 4.64 4.1 3.71 2.63 2.9 3 59 3.59 4.06 3.4 3.71 4.06 4.5 4.43 4.28 3.56 2.91 3.06 3.72 3 94 3.7 3.19 1970 4 01 4.45 5 06 4.58 4.76 4.01 3.21 3.22 4.06 4.04 3.58 3.28 1971 3.66 3.9 4.49 4.49 4.24 3 49 2.93 3.01 3.69 4 3.75 3.29 1972 3.86 4.34 4.5 5.03 4.34 3.55 3.39 3.28 4.17 4.23 4.2 3.34 1973 3 81 4.3 4.87 4.92 4.91 3.84 2.81 3 09 3.97 4.32 4 01 3 34 1974 1975 1976 1977 1978 1979 1980 3.58 4 18 4.53 4.24 4.61 3.51 3.3 3.29 3.62 4.07 1.95 3.35 3.82 4.27 4.66 4.34 4.09 3.3 2.73 2.44 3.2 3.87 3.64 3.49 3.73 4.38 4.65 4.75 4.02 3.68 2.93 3.06 3.5 3.69 3.48 3.38 3.4 3.85 4.34 4.49 4.24 3.46 2.9 3.1 3.78 3 87 3.86 3.52 3.85 3.62 4.64 4.7 4.39 3.57 2 58 3.04 3.53 3.74 3.79 3 23 3.36 3.89 4.18 4.37 4.08 3 38 2.64 3.07 3.3 3.5 3.64 3.34 1981 3.29 3.63 4.21 4.39 4.32 3.56 2.93 3 05 3.7 3.98 3.66 3.44 1982 1983 1984 1985 1986 1987 3.78 4 25 3.99 4.13 4.42 3.53 2.91 3.2 2.88 3.6 3.74 4.63 4.32 4.13 3.77 2.98 2 98 3.87 3.54 4.14 4.55 4.76 4.15 4 06 3.43 3.03 3.61 3.58 4 31 4.73 5.02 4 08 3 55 3.14 3.11 3.87 3.73 4.04 4.59 4.36 3.93 3.53 2.71 2.81 3.63 3.43 3.94 4.31 4.03 4 22 3.04 2.85 3.08 3.22 1988 1989 1990 3.67 4.14 4.31 4.74 3.83 3.5 3.27 3.16 4 06 3.76 4.2 5 04 4.82 4.58 3.78 2.71 3.34 3.59 3.72 4.18 4.42 4.39 4.64 3.83 2.97 3.38 3.77 3.64 4.01 3.3 3.86 3.49 3.3 3.7 3.82 3.32 4.3 3.98 3.46 3.86 3 88 3.32 3 82 4 01 3.46 4 3 83 3.96 4 17 4.02 3.48 4.06 3.74 3 24 1991 3.82 3.38 4 31 3.57 3 35 3.25 2.92 3.07 1992 3.79 4.05 4.43 4.31 3.82 3.72 3.06 3.59 3.69 4 37 3 92 3 67 1993 1994 3.42 3.94 4.71 4.62 4.65 3.63 2.73 2.59 4 49 4.22 3.84 3.11 3.54 3.75 4.68 4.29 4.25 3.21 2.72 3.04 3.94 4.3 4.79 4.65 4.55 3.5 2.75 2.83 3.78 3.7 3.61 3 38 1995 1996 3.92 4 34 4.96 4.34 4.53 2 98 3.11 3.52 4 21 3 94 3.92 3.59 3 67 4 09 3.91 3.4 3 91 4 26 4 06 3 75 1997 3.68 4 29 4.57 4.88 4.37 3.35 3.09 3.03 3 77 4.31 4.09 3.46 1998 3.91 4.33 4 8 4.93 4.24 3.85 2.66 3.77 4 43 4.95 4.46 4.65 4.07 3.23 3.46 2.96 3 74 3.11 3 83 4 41 4.32 3.9 3 85 1999 3.68 4.07 4.67 4.57 4.36 3.63 2.98 2000 2001 4.03 4.45 5.24 4.79 4.86 4.15 3.31 3.78 4 21 4.66 4.64 4.42 3.65 2 98 3.35 4 19 2002 4 4.39 4.75 5.13 4.59 3.71 3.46 3.16 3 84 2003 3.75 4.49 4.92 4.82 5.06 3.88 2.85 3.4 4 29 2004 3.84 4.28 4.58 4.51 4.83 3.6 3.22 3.16 4 08 0.00 3.72 4.21 2 06 3.61 3.83 4.12 3.36 4.11 3.7 3.42 4.16 3.92 3.5 4 19 3.92 3.57 4.34 4 24 3 54 4.47 4.19 3 63 Water Works Design & Supervision Enternrise In Association with intercontinental Consultants and Technocrats Pvt. 108 - Ltd.Arjo -Dedessa Irrigation Project Meteorological and Hydrological Aspects A7: Estimated Mean Monthly ETo of Arjo Dedessa Project Area (in mm/month) May 2007 Year 1961 116 110 139 128 1962 100 105 144 130 1963 108 104 145 103 1964 122 117 144 140 1965 119 116 150 128 1966 114 118 138 142 1967 107 124 148 133 1968 109 114 140 139 1969 115 114 140 133 1970 124 124 157 137 1971 113 109 139 135 1972 120 122 140 151 1973 118 120 151 148 1974 111 117 140 127 1975 118 120 144 130 1976 116 123 144 143 1977 105 108 135 135 1978 119 101 144 141 | May | June I July Auq Sept Oct Nov DecJ Annual 1979 104 109 130 131 126 101 81.9 95.3 98.9 109 109 104 116 109 94.2 110 133 132 116 100 1403 137 105 81.6 774 112 112 104 99 1308 104 93 2 84 92.9 109 124 127 110 1303 140 104 84.3 86.6 116 132 116 119 1420 137 89 96.2 106 124 120 118 107 1410 135 102 95.1 93.1 111 134 123 104 1408 143 118 97.7 103 127 125 111 107 1444 127 111 81.4 89.9 108 111 122 105 1358 133 107 90.1 94.8 112 122 111 99 1369 148 120 99.4 99.7 122 125 107 102 1466 132 105 90.8 93.2 111 124 113 102 1366 135 106 105 102 125 131 126 104 1466 152 115 87.2 95.9 119 134 120 104 1464 143 105 102 102 109 126 58.6 104 1346 127 99 84.7 75.7 96 120 109 108 1332 125 111 90.8 94.8 105 115 104 105 1375 132 104 90 96 113 120 116 109 1362 136 107 80 94.2 106 116 114 100 1359 1980 102 102 130 132 134 107 90.9 94.5 1981 117 119 124 124 137 106 90.1 99.2 86.5 1982 112 105 144 129 128 113 92 3 92.5 116 111 123 113 110 107 120 102 1983 110 116 141 143 129 122 106 94 108 115 115 103 1984 111 121 146 151 127 107 97.4 96.6 1985 116 113 142 131 122 106 84.1 87.1 1986 106 110 134 121 131 91 3 88.2 95.6 116 109 120 105 102 133 120 107 120 116 103 1987 114 116 134 142 119 105 101 98 122 124 115 123 1988 117 118 156 145 142 113 84.2 103 108 129 121 108 1989 115 117 137 132 144 115 92 105 113 126 112 100 96.5 118 120 107 1990 118 94.8 133 107 104 97.4 90.6 1991 117 113 137 129 118 112 94.8 95 111 135 111 136 117 114 1992 106 110 146 139 144 109 84.5 80.3 1993 110 105 145 129 132 96.4 84.4 94.3 1994 122 120 149 139 141 105 85.2 87 8 117 132 122 116 113 110 131 115 96.4 115 108 105 127 117 105 1995 122 121 154 130 140 89.4 96.4 1996 114 120 142 147 135 101 95.8 94 113 134 123 107 1997 117 124 153 134 144 122 100 107 132 134 117 119 1998 121 121 149 148 132 115 82.6 91.9 112 119 124 104 109 126 122 118 111 1999 114 114 145 137 135 109 92.4 96.3 2000 125 124 162 144 151 125 103 104 126 129 118 109 2001 117 118 144 139 137 110 92.4 98 115 130 118 111 2002 124 123 147 154 142 111 107 106 129 135 127 110 2003 116 126 153 145 157 117 88 2 98 122 139 126 112 2004 119 120 142 135 150 108 100 104 112 130 61.7 112 115 127 111 106 1299 1343 1338 1358 1401 1432 1349 1320 1412 1443 1408 1318 1411 1360 1355 1437 1439 1425 1505 1419 1402 1518 1429 1515 1498 1393 Water Works Design & Supervision Enterorise in Association with Intctconllnental Consultants and Technocrats Pvt. ltd. 109Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects A8: Estimated Mean Monthly Rainfall at Arjo Dedessa Project Area in mm) May 2007 Year Jan Feb1 March April May June July | Aug Sept Oct Nov Dec Annual 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1978 1979 1980 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 15.6 0 96.3 21 7 172 172 140 220 220 111.5 151 0.12 0 57 6 0.75 36.4 93.8 169 186 207 192 90.97 21.7 14.5 37.7 359 53.7 140 121 144 159 212 165 56.39 7.39 0 29 2 30 51.3 21.2 149 154 249 162 256 107.2 4.44 4.04 11.3 0.32 20.7 30.8 142 193 180 135 262 188.2 32.3 14.1 15.6 11.1 15 89 1 53 166 186 157 170 49.48 69 9.24 0 9.97 5.66 294 236 155 186 233 143 58.82 12.2 5.77 38.7 7.98 31.8 5.14 287 205 242 168 212 72.78 4.62 167 23 5 55.1 21.1 60.4 116 124 189 159 141 131.3 11.5 12.5 23.7 16 2 90.3 55.8 154 154 192 215 273 88.66 36 5.37 3 3.5 66.5 103 122 154 206 206 181 122.6 0.58 12.5 15.6 8.89 17 25.6 97 5 202 235 159 154 64.94 31.2 12.5 15.6 17.8 57.3 118 164 100 136 176 246 49.87 28.7 0 15.6 8 23 27.6 35.6 149 213 296 270 177 113.9 57.2 0 15.6 0 31 6 69.8 234 249 443 198 230 8.716 26.8 5.77 2.79 0 12.3 105 257 341 242 212 315 48.2 32.5 37.7 0 39.2 46.9 56.4 37 5 315 274 244 191 103.8 35.9 0.46 2.89 17.2 88.6 79.9 123 282 488 328 183 116.4 42.3 34.3 14.1 42.7 74.3 15.3 335 325 177 297 343 259.9 15.4 3.87 25 6 26 7 76.3 108 245 284 316 332 297 189.3 61.3 47 1 8.77 37 8 50.4 83 3 90.6 438 228 319 241 73.89 33 4 3.12 26.4 7.91 68.2 74.4 139 106 364 309 222 98.59 35 13 24.8 32.8 106 105 222 225 267 291 250 104 7 53.6 15.8 1.04 31 69.5 100 213 313 217 347 166 149.4 2 03 0 11.2 1.15 20.1 53.9 127 227 255 228 279 8.467 13.7 0 0 22.9 75.5 109 222 195 229 310 279 86.46 11.2 22.3 45.5 19.1 162 71.7 338 225 245 197 215 74.57 44.6 7.56 1645 39.6 0.97 56.6 139 293 314 205 291 234 213 40.4 2.54 1830 1320 1070 1132 1217 1210 990.6 1075 1292 1045 1303 1181 1024 1110 1362 1514 1607 1345 1785 1903 2008 1607 1464 1697 1609 1223 1563 Average CV Skew Max Min 13 84 81.1 15.2 162 280 264 272 239 235.9 67 2 1.04 31.7 2.91 15 92.3 393 427 257 239 309 197.3 8 89 42.1 0 0 3.69 105 195 345 222 260 274 255 34.4 7.39 0 32 65.5 60.3 327 346 298 292 312 206 3 19.9 24.1 17.7 2.19 39.7 42 2 106 252 274 153 224 59 11 1.84 53.1 5.84 53.5 117 121 58.9 358 232 300 155 51.59 11.5 1.86 4 96 2.1 61.2 51.5 150 353 326 243 249 193.9 40.7 13 1 75.3 18.4 53.6 69.5 180.8 243.0 245.9 238.3 228.6 115.5 31.4 12.7 0.85 0.96 0.68 0.55 0.49 0.37 0.31 0.25 0.24 0.591 0.9 1.13 0.62 0.78 0. 74 0.1 0.62 0.38 1.44 0.07 0.17 0.635 2.31 1.48 45.5 57.6 161.7 139.9 392.7 437.6 487.6 346.6 343.1 259.9 150.7 53.1 0.0 0.0 0.8 5.1 37.5 100.3 136.2 135.3 141.3 8.5 0.6 0.0 Water Works Design & Supervision Enterprise —~ In Association with Intercontinental Consultants and Technocrats Pvt Ltd 1638 2014 1702 1983 1226 1466 1 6RQ 1452 9 0.209 0.26 2014 5 990.6 1 10Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects A9 May 2007 1.1 1.2 2.1 2.2 3.1 3.2 4.1 4.2 j 5.7 5.2 6.1 6.2 7.1 7.2 8.1 8.2 9.1 9.2 10 10 11.1 11 12.1 12 Total Year 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1978 1979 1980 1983 1984 1985 1986 1987 1988 1989 1990 1991 1 1992 7.8 7.79 0 0 22 4 73.9 0 21.7 75.2 96.97 112 60.8 68.4 71.7 110 110 132 87.7 110 1.92 75.7 75 0.12 0 0 0 57.3 0.29 0 0.75 1.27 35.1 31 62.8 81.4 87.4 82.5 104 121 86.1 76.5 115 76.8 14 2 0 21.7 10.3 4.25 26.1 11.6 14.7 21.2 37.6 16.1 6.75 133 18 103.1 72.3 71.9 55.2 103 106 106 83.6 81.7 36 20.4 3.46 3.92 0 0 2.1 27.1 7.27 22.7 23.6 27.7 1.73 19 5 34.3 114.3 49.4 104 127.4 122 81.7 79.8 94.4 162 50 57.3 4.44 0 0 4.04 11 0.27 0.32 0 4.62 16 30.4 0.46 42.1 99.86 62.2 131 63.4 116 61.4 73.9 125 137 104 84.3 26.8 5.48 3.17 11 7.8 7 79 4.31 6.84 0 15 36 5 52.6 25.5 27.53 78.1 87.9 87.2 99 89.7 67.2 94.2 75.8 25.7 23.8 61.3 7.69 0 9 24 0 0 9.97 0 0 5.66 25.4 4.04 140 96.39 96.2 58.9 91.6 94 2 108 125 78.8 64.1 57.1 1.73 12.2 0 0 5.77 30.6 8 12 2.26 5.72 19.9 11.9 0.29 4 85 188 98.87 102 103 119.5 123 101 67.5 102 110 44.4 28.3 0 4.62 4.62 12.1 0 23.5 47.7 7.4 0.69 20.4 5.14 55.2 67 5 48 89 80.8 43.3 75.2 113 62.1 96.9 92.5 48.8 86.9 44.4 11.5 0 6.06 6.46 23.7 0 10.3 5.89 57.9 32.4 32.2 23.5 78.8 74.81 72 81.8 102.9 89.1 51.9 163 198 74.2 40.1 48.6 32 3.98 2.89 2 48 3 0 3.5 0 56.4 10.1 12.4 90.9 49.1 73.14 87.8 66 79.7 127 71.2 134 84.8 96.5 72 50.5 0.58 0 6.06 6.46 7.8 7.79 8.89 0 0.46 16.5 11.6 14 57.2 40.35 99.6 102 145 90.3 85.5 73 6 97.2 57 40.4 24.5 15.6 15.6 6.06 6.46 7.8 7.79 8.89 8.89 27.7 29.6 28.6 89.8 64.2 100.3 41.6 58.7 65.6 70.6 99 76.5 138 109 26.3 23.5 11.9 16.9 0 0 7.8 7.79 7.98 0.25 18.7 8.89 20.7 14.9 54.3 94.53 89.7 123 168.1 128 134 136 89.9 86.7 78.7 35.2 44.2 13 0 0 7.8 7.79 0 0 4 73 26.9 17.3 52.5 53.9 180.3 138 111 232.6 211 51.8 147 66 7 163 7.16 1.56 15.2 11.6 4.96 0.81 0.3 2.49 0 0 1.5 10.8 57.5 47.8 121 136.6 168 173 94.1 148 82.6 130 160 155 37.2 11 24.9 7.58 36.9 0.81 0 0 2.75 36.4 15.2 31.7 28.1 28 3 1.24 36.22 195 119 147 6 127 110 134 114 77.1 85 18.9 28.2 7.68 0.23 0.23 0 2.89 0 17.2 48.1 40.5 6.93 72.9 19.2 104.3 158 124 224.5 263 215 112 116 66.8 81.4 35 31.2 11 34.3 0 9.4 4.73 2.66 40 57 17.3 0.98 14.3 145 190.2 172 154 75.1 102 175 122 179 164 155 104 15.4 0 0 3.87 18.6 7.03 26 0.7 43.9 32.5 65.3 42.7 148 96.74 182 102 208.4 107 186 145 194 104 91.5 97.8 29.5 31.8 19.8 27.3 0 8.77 13.1 24.7 21.6 28.8 0 83.3 60.3 30.3 253 185 123.1 105 108 211 98.1 143 53.4 20.4 32.4 1.03 3.12 0 14.2 12.2 0 7.91 37.6 30.6 1.27 73.2 89.9 49.04 13.3 93.1 195.1 169 179 131 144 77.9 97.3 1.27 10.5 24.5 12.7 0.29 0 24 8 17.7 152 25.2 80.6 3.34 102 152 70.12 82.1 143 161.3 106 159 131 102 148 81.4 23.3 29 24.6 1.15 14.7 1320 1070 1132 1217 1210 990.6 1075 1292 1045 1303 1181 1024 1110 1362 1514 1607 1345 1785 1903 2008 1607 1464 1697 111Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 1.1 12 2.1 2.2 3.1 3.2 4.1 4.2 [ 5.1 5.2 6.1 6.2 7.1 9.1 9.2 11.1 11 12.1 12 Total Year 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 0 1.04 6.64 24.4 3.06 66.4 63.6 36.6 93.7 119.7 86.2 227 79.7 11.2 0 0 1.15 1.3 18.8 29.2 24.7 55 71.64 105 122 109 7 0 0 5.6 17.3 0 75.5 0.52 109 116 105.9 63.4 131 123 9 9.2 36.3 4 09 15 78.8 82.9 26.6 45.1 146 192.4 159 66.1 84.7 2.1 37.5 0 0.97 28.1 28.5 72.8 66 6 71.7 221.5 152 161 78.6 11.2 1 84 1.94 6.46 24.6 56.5 8.89 6.33 69.7 92.18 142 138 141.7 28.3 3.35 0 2.91 0 15 19 73.3 227 166 209 217 99.2 0 0 0 0 2.31 1.39 28.4 76.2 76.9 118.6 215 129 99.4 0 0 23.7 8.3 1.24 64.3 36.9 23.3 96.3 230.8 122 224 118.2 12.5 5.19 0 2.19 8.37 31.3 37 7 4.49 19.8 86 64 139 114 156.4 2 3.84 17 8 35.7 39.2 77.6 68.8 52.3 20.3 38.67 165 193 127.5 0.2 4.76 1.4 0.7 10.6 50.6 9.7 41.8 28.5 121 9 148 204 256.7 137 149 197 104 61.9 83.9 65.5 1.39 0.65 0 0 1609 145 116 111 166 112 7 24 1.23 9.52 4.16 0 0 1223 105 177 133 125 154 40.8 45.7 5.95 5.3 1.96 20.4 1563 160 100 96.6 93.2 122 58.2 16.4 8.48 36.1 0.69 6.87 1645 127 165 126 148 85.8 119 94.2 25.3 15.1 0.06 2.48 1830 122 131 142 118 121 92.9 143 62.3 4 92 0 1.04 1638 158 141 98.2 146 162 148 48.9 8 89 0 26.6 15.5 2014 Average 123 149 112 139 135 168 87.1 25.2 9.15 2.89 4.5 1702 180 126 165 187 124 96.4 110 7.27 12.7 14.4 9.75 1983 118 51.7 102 954 129 35.3 23.8 0 1 84 3.29 49.8 1226 105 133 166 85.9 69.1 23.7 27.9 6.64 4.91 1.4 0.46 1466 69.6 91.1 152 132 117 168 25.7 11.3 29.4 9.24 3.88 1689 7.5 7.8 8.8 9.6 20.6 33.0 22.7 46.7 78.2 102.6 119.8 123.2 122.0 123.9) 117 121.8 120.0 108.5 73.7 41.8 19.7 11.8 6.1 6.6 1452.9 CV [1.18 1.28 1.48 1.21 1.03 0.74 0.95 Skew 11.27 1.82 2.47 1.27 0.95 0.83 0.95 0.72 0.68 0.511 0.46 0.41 0.31 0.36 0.29 0.3 0.32 0.58 0.86 0.94 1.26 1.57 1.5 0.209 0.63 0.94 0.84 0.41 0.57 1.039 1.64 0.36 0.47 0.72 0.1 0.63 1.11 1.42 2.61 2.15 2.9 0.26 30.6 37.5 57.3 40.0 78.8 82.9 72.8 133.1 226.7 230.8 252.9 226.8 256.7 263.1 216 210 9 198.4 164.1 168.3 143.0 75.7 75.0 36.9 49.8 2014.5 Max Min 0.5 1.2 27.5 13.3 43.3 55.2 69.6 1.2 0.0 0.0 0.0 0.0 990.6 0.0 0.0 0.0 0.0 0.0 09 0-0 51.7 67.2 66.7 48.8 7.2 H2Aijo-Dedessa Irrigation Project Meteorological and Hydrological Aspects Annex B: Results obtained from the Hydrological Analysis B1: Estimated Monthly Flows at Arjo Dedessa Dam Site (in AUllion rnJ___ May 2007 Year Jan Feb i* ___ Mar Apr |May ]jun Jul Aug Sep Oct Nov Dec LAnnual 1961 30.74 28 02 25.73 68.61 49.78 207.7 751.5 972.5 900 661 291.8 101.4 4089 1962 34.68 18 98 19.47 5.073 21.39 157.2 397.6 560.6 700.8 512.2 64.92 31.95 2525 1963 22 72 12.3 12.28 30.86 111.6 235.3 429.5 826.3 622.8 223.9 111.8 97.23 , 2736 1964 7642 24.32 17.86 24.21 41.69 167 670 784.4 705.4 621.4 307 42.03 3413 1965 33.05 16.1 11.28 34.56 21.07 122.1 532.7 633.6 410.3 573.5 194.6 90.12 2673 1966 1967 42.41 40.3 39 61 53.61 47.41 134.3 547.5 654.6 726.3 49 32 25.38 11.62 2372 6.806 5.364 15.57 14 73 19.24 82.14 452.6 764.7 719.5 634.8 400.8 120.1 30.4 29.71 46.01 28.69 55.55 253.9 607 857 565.3 174.2 53.81 26.41 3236 1969 2728 1970 20.38 5.351 9.245 24.21 34.36 209.3 593.4 635.7 673.2 121.1 110.2 35.46 2472 1971 1972 22.1 10.44 7.454 9.019 40.6 175.5 525.6 708.6 568.4 450.3 184.8 60.15 2763 31.3 18.92 13.43 25.78 42.79 85 61 512.9 746.2 430.7 125.4 71.09 29.98 2134 1973 15.44 7.121 3.221 4.586 82.96 181.5 156.2 633 839.1 354.5 90.45 37 1974 1979 1980 1981 1982 21.79 10.31 9.887 6.561 71.15 190 409.5 770.6 195.6 83.73 72.32 27.9 10 27 7.805 6.815 16.56 35.18 94.19 340.6 497.5 371 157.1 57.07 25.13 10.73 9.737 6839 49.56 144.9 366.1 584.3 777 745 235.5 62.71 52.8 47.75 27.57 29 73 25.58 40.74 38.71 412.8 633 540.6 315.2 19.85 7.138 2405 1869 1619 3045 2139 35.71 19.2 19.63 13.95 34.68 180 3 451.6 571.2 414.6 455.6 107.4 53.96 2358 1983 25.9 20.13 23 4 16.88 39.8 111.5 361.4 687 668.2 617.6 282.5 69.26 2924 23.01 10.61 8.146 6.854 21.69 134.7 449.2 401.2 311.8 78.36 12.69 4.808 1463 7.152 3.462 1.775 8.54 47.33 123.1 280 559 504.1 155.7 48.31 25.72 1764 10.49 6.052 11.02 9.993 9.685 86.35 288.9 296.2 438.4 132.9 50.52 28.15 1369 7.756 3.775 8.501 12.5 27.82 157.2 412.8 633 402.9 231.4 97.47 38.7 2034 24.16 17.49 14.79 5.553 28.08 203.6 354.6 689.1 905.1 315.2 114.9 46.11 2719 25 14.84 13.97 24.24 20.58 87.63 174.3 301.1 651.3 315.2 65.15 70.31 31.93 19.11 23.19 44 03 31 91 114.4 219.3 1043 669.7 280.5 46.23 23.01 1764 2546 0 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 | 23.32 12.45 10.62 11.34 45.32 160.1 341.3 736 3 514 93.66 41.38 21.09 2011 1995 12.16 7.787 10.15 14.06 29.04 60.34 143.8 343.1 291 93.56 36.44 82.8 1124 16.3 12.32 10.51 18.94 44.17 113.8 517.4 964.2 486 9 310.9 29.61 21.7 2547 14.62 15.23 9.435 14.96 42.85 116.8 235.1 497.2 338.1 482.9 99.78 41.9 1909 25.4 17.72 16.74 39.56 79.86 226.9 383.1 698.7 377 8 243.8 107 6 36.17 2253 I 1 1996 29.25 18.44 26.36 21.96 107.7 271.3 462.2 515.2 358 225.1 71.87 508 37.86 45.32 41.35 97.36 291.4 49.76 2157 2001 473.1 630.3 602 2 403.8 130.5 63.78 286R 2002 59.09 36.38 37.91 45.85 35.1 127 292.1 356.4 346 126.2 70.05 47.88 1580 2003 33.66 23.05 38.53 53.75 36.41 87.39 347.2 393.2 540.6 315.2 90.27 46.11 2005 2004 31.2 25.55 20.76 20.73 4947 146 8 336.3 385 2 384.9 322.3 85 26 46.11 1855 I I Water Works Design & Supervision Enterprise ~ 113 In Association with Intercontinental Consultants and Technocrats Pvt LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 B2: Regional monthly coefficient of variations (CV) ---------- r Station Year Jan | Feb Mar Aoril\Mav\ June] July] Aug Sep | Oct Nov Dec 114001 114014 114005 114004 114003 91008 91012 35 20 23 22 21 38 35 0.51 0.57 0.66 0.68 0.62 0.45 0 35 0.3 0.33 0.67 0 62 0.59 0.47 0.46 0.48 0.56 0.69 0.53 0.27 0.33 0.28 0 56 0.81 0.53 0.28 0.41 0.33 0.43 0.6 0.47 0.2 0.16 0.25 0.44 0.3 0.34 0.33 0.42 0.45 0.55 0.56 0.43 0.57 0.38 0.43 0.64 0.35 0.33 0.51 0.83 0.57 0.71 0.66 0.58 0.35 0 25 0.36 0.56 0.46 0.55 0.68 1.3 0.7 0.6 0.61 0.46 0.29 0.32 0.28 0.64 1 0.86 0.61 0.49 0.76 0.49 0.57 042 0.3 0.29 0.32 0.52 0.8 0.59 B3: Regional monthly coefficient of skewness Station Year Jan Feb | Mar April\May\june\ July \ Sep Oct Nov Dec 114001 114014 114005 91008 91012 35 20 23 38 35 0.63 0.74 1.07 0.94 1.63 0.89 0.13 0.04 0.25 0.99 1.37 0.96 1.35 0.31 0.47 0.81 0.85 1.03 -0.5 0.93 0.89 0.67 2.6 1 98 0.33 1.48 0.59 -0.1 2.18 1.54 0.07 0.45 0.81 0.42 0.52 1.09 2.73 0.29 3.26 0 77 1.14 0.81 0.17 1.14 1.13 0.77 3.14 2.85 3.17 4.94 1.22 1.5 2.34 1.15 0.43 0.94 0.05 1.6 2.86 2.79 B4: 16 Rec ional monthly coefficient of correlations (R) Station 1 Year Jan Feb I Mar April May\June July] Aug Sep Oct Nov Dec 114001 35 114014 114005 114004 114003 91008 91012 20 23 22 21 38 35 -0.1 0.83 0.89 0.59 0.3 0.78 0.45 0.53 0.44 0.45 0.74 0.78 0.36 0.5 0 77 0.56 0.62 0.81 0.46 0.54 0.28 -0.04 0.65 0.78 0.84 0.5 0.35 0.3 0.64 0.38 0.48 0.68 0.8 0.83 0.25 0 16 0.8 0.52 0.21 0.52 0.6 0.58 0.58 0.69 0.61 0.77 0.37 0.14 0.84 0.3 0.18 0.52 0.45 0.73 0.68 0 66 0.58 0.82 0.56 0 1 0.27 0.33 0.37 0.27 0.53 0.59 0.54 0.55 0.46 0.45 0.77 0 62 0.12 0.83 0.72 0.48 0.41 0.72 0.53 0.41 0.48 0.31 044 0.65 Water Works Design & Supervision Enterpri^--------------- 114 Id Association with Intercontinental Consultants and Technocrats Pvt LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects B5: Standardized probability weighted moments i May 2007 Station Name of Station Location PWMs Deg N. I Deg E. Area (km2) Record Length,N mi 10 m2 10 1 114001 Dedessa near Arjo Upper Dedessa near 2 114014 Dembi 3 114005 Dabana near Abasina 4 91008 Gilgel Ghibe 5 91012 Gojeb near Shebe Angar Gutin near 6 114007 Neqemte 7 114004 Wama near Neqemte 8 114003 Siffa near Neqemte 9 115008 Aleltu at Nejo 10 101001 Sor at Metu 11 91013 Ghibe-Limu near Limu 12 91001 Great Ghibe near Abelti 8.41 36.25 8.02 36.28 9.02 36.03 7.45 37.11 7.25 36.23 8.53 36.47 8.52 35.45 9.30 35.3 8.19 35.36 8.35 37.13 8.14 37.15 9981 1806 2881 2966 3494 1975 844 951 155 1622 663 15460 29 15 18 37 34 20 21 20 7 17 10 19 0.40739 0.420504 0.414042 0.400025 0.408619 0.421145 0.419805 0.416527 0.400261 0.401323 0.425296 0.424754 0.243171 0.262951 0.253945 0.240847 0.248091 0.254033 0.254029 0.251324 0.247582 0.244658 0.261749 0.260656 Weighted Average 255 0.411964 0.250375 Waterworks Design & Supervision Enterori^-------------------- 115 In Association with Intercontinental Consultants and Technocrats Pvt LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects B6: Mean Monthly Total (Suspended and Bed) Sediment Load 3 at Arjo Dedessa Dam Site (in 1000 m ) May 2007 Year Jan Feb March April May June July Aug Sep Oct Nov Dec Annual 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1979 1980 1982 1983 1984 1985 1986 1987 1988 1989 1990 1992 1993 1994 1995 1996 2001 2002 2003 2004 2.11 1.75 1.27 5.73 3.11 33.4 315 523 476 372 32.3 15.3 2.56 0 94 0.81 1.07 3.18 22.4 114 216 319 189 6.92 2.41 1.3 0.47 0.39 1.6 11.3 40.8 129 403 264 50.4 16.5 14.3 1 78 1.32 0.71 1.07 2.34 23.6 262 370 322 387 19.7 3.74 2.37 0.72 0.34 1.91 0.79 14.3 182 263 135 227 40.1 12.7 3.54 3.13 2.54 3.86 2.88 22.4 190 277 338 102 40.8 9.14 0.64 0.57 0.57 0.49 3.18 22.4 140 356 333 352 71.4 20.1 5.73 2.22 0.52 0.22 2.26 2.27 123 265 299 102 10.4 2.97 2.07 1 92 3.22 1.42 3.71 46.1 224 427 205 102 5.13 1 78 1.09 0.75 0.4 0.23 1.72 33.8 216 246 205 102 16.1 2.85 1.25 0.36 0.18 0.22 2.25 25.5 178 315 228 154 36.9 6.64 2.17 0 88 0.45 1.2 2.44 8.09 171 342 146 19.9 8 2.18 0.7 0.2 0.05 0 08 7.04 26.9 123 246 425 105 11.8 3.05 1.22 0.35 0.28 0.13 5.51 29 119 360 205 102 8 23 1.94 1.91 1.29 0.65 0.59 1.79 9.43 88.9 179 115 28.6 5 63 1.64 0.39 0.3 0.15 3.41 17.2 82.8 211 365 352 54.6 6.55 5.39 2.69 0.96 0.83 0.45 1.74 26.7 140 223 138 157 15.5 5 58 1.61 1.03 1.09 0.61 2.18 12.3 97.7 300 296 339 29.6 8 32 1.33 0.35 0.2 0.14 0.82 16.7 138 127 87.3 9.39 15.5 5.24 0.2 0.06 0.02 0.2 2.87 14.5 65 216 188 28.2 4.31 1.71 0.38 0.15 0.33 0.26 0.23 8.21 68.3 78 151 21.9 15.5 5.24 0.23 0.07 0.22 0.38 1.23 22.4 91.7 301 132 53.1 13.3 3.28 1.44 0.78 0.52 0.1 1.24 32.4 94.8 246 205 102 17.3 1.31 2.38 0.63 048 1.08 0.76 8.4 30.4 80.1 284 102 6.96 8.52 2.24 0 95 1.08 2.82 1.53 12.9 44 246 205 102 15.5 5.24 0.64 0.62 0.26 0.5 2.45 13.3 49.1 179 99.4 172 13.8 3.72 1.56 0.84 0.64 2 37 6.63 38.5 107 308 119 57 7 15.5 2.94 1.36 0.48 0.31 0.32 2.68 22 89.2 335 194 12.5 3.37 1.24 0.48 0 23 0.29 0.45 1.31 4.63 22.4 98.7 78.2 12.5 2.75 5 24 1 78 0.87 0.71 0.93 10.7 51.2 145 189 109 102 15.5 4.9 4.72 2.83 3.15 2.55 9.1 57.5 150 261 250 129 21.1 6.01 2.66 2.37 3 01 1.78 15.2 69.5 105 103 20.1 7 2Q 2.44 1.28 2.43 3.88 1 89 8.37 123 123 205 102 15.5 5.24 2.16 1.43 0.9 0.84 3.08 19 2 87.1 119 122 90.2 10.7 5.24 7.82 4 A1 1781 878.9 932.5 1397 880.6 995.4 1300 815.6 1024 826.7 948.3 704.9 949.6 833.7 434.5 1098 711.7 1089 402.1 520.8 349 618.6 703 4 525.4 639.8 534 7 660 6 662 4 297 631 5 oyy.j 341.1 594 5 461.9 Water Works Design & Supervl^Enterpri^------------------ “ 116 in Association with Intercontinental Consultants and Technocrats Pvt LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 B7: Eleveation-Area -Capacity Relationships of Arjo Dedessa Rest Elevetion Area Volume (m asl) (km ) (Mm ) 23 Elevetion Area Volume (m asl) (km2) (Mm3) 1320 0.54 0.0 1321 0.99 0.8 1322 2.39 2.5 1323 3.78 5.5 1324 5.11 10.0 1325 6 64 15.9 1326 8.03 23.2 1327 9.46 31.9 1328 10.87 42.1 1329 12.67 53.9 1330 14.40 67.4 1331 15.89 82.5 1332 17.74 99.4 1333 19.46 118.0 1334 23.59 139.5 1335 26.66 164.6 1336 29.05 192.5 1337 31.73 222.9 1338 34.24 255.8 1339 36.62 291.3 1340 39.45 329.3 1341 41.97 370.0 1342 44.25 413.1 1343 47.05 458.8 1344 49.95 507.3 1345 53.11 558.8 1346 56.31 613.5 1347 59.15 671.2 1348 61.56 738.8 1349 63.97 808.7 1350 67.88 874.7 1351 70.62 943.9 1352 74.35 1016.4 1353 77.88 1092.5 1354 81.28 1172.1 1355 84.51 1255.0 1356 87.85 1341.2 1357 90.75 1430.5 1358 94.18 1522.9 1359 97.23 1618.6 1360 100.54 1717.5 1361 103.64 1819.6 1362 106.39 1924.6 1363 109.00 2032.3 1364 111.91 2142.8 1365 115.05 2256.3 1366 117.68 2372.6 1367 120.20 2491.6 1368 122.76 2613.0 1369 125.28 2737.1 1370 127.69 2863.5 1371 130.25 2992.5 1372 133.03 3124.2 1373 135.45 3258.4 1374 138.08 3395.2 1375 142.38 3535.4 1376 145.27 3679.2 1377 148.00 3825.8 1378 150.75 3975.2 1379 153.73 4127.5 1380 156.02 4282.3 1381 159.09 4439.9 1382 162.13 4600.5 1383 166.96 4765.0 1384 173 01 4935.0 1385 178.58 5110.8 1386 183.38 5291 8 1387 188.10 5477 5 1388 193.28 5668 2 1389 197.36 5863 6 1390 201.96 6063.2 I Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 B8: Sample ! r'Year Simulation Results of Arjo Dedessa Reservok Reservoir Status Inflow (Mm3) 3 OF (m3/s) 4 Eo-Rf IWD (Eo-Rf) (mm) (Mm3) (Mm2) f rn r SL (Mm3) 5 6[7[8 IWR (Mm3) 9 cs (Mm3) 10 Storage (Mm3) 11 Area (km2) 12 Level (m asl) 13 Spill 'Mm3) 14 STRQ (Mm3) 15 T. Spill (Mm3) 16 577.4 0.0 0 0.0 333.3 102.7 47.7 22.5 12.3 16.3 16.8 40.1 160.9 400.3 0.0 111 0.0 0.0 143 0.0 135 0.0 146 0.0 147 0.0 164 0.0 146 0.0 80 0.0 0 0.0 0 46.2 60.0 74.0 85.0 50.4 7.4 0.0 0.0 0.0 0.0 8.2 10.6 10.0 10.7 10 4 10.9 9.4 5.1 0.0 0.0 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.8 0.8 0.8 1.0 0.0 0.0 46.2 60.0 74.0 85.0 50.4 7.4 0.0 0.0 0.0 576.4 1006.3 74.1 1351.9 576.4 324.1 1006.3 74.1 1351 9 324 1 44.9 1006.3 74.1 1351.9 44.9 -23.4 982.9 73.1 1351.5 0.0 -63.2 919.7 70.4 1350.7 0.0 -84.0 835.8 66.7 1349.4 0.0 -45.9 789.9 64.6 1348.7 0.0 -0.9 789.0 64.6 1348.7 0.0 34.1 823.1 66.1 1349.2 0.0 160.1 983.2 73.1 1351.5 0.0 399.3 1006.3 74.1 1351.9 376.3 Aug Sep Oct 647.4 717.9 0.0 0.0 0 0 777.8 0.0 111 0.0 0.0 0.0 0.0 0.0 82 1.0 1.0 1.0 0.0 0.0 0.0 646.4 1006.3 74.1 1351.9 646.4 789 716.9 1006.3 74.1 1351.9 716.9 768.6 1006.3 74.1 1351.9 768.6 118 Water Works Design & Supervision Entp.rnricpArjoDedessa Irrigation Project Meteorological and Hydrological Aspects B8: (........ continued) May 2007 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 405 Nov 405 Dec 405 Jan 405 Feb 405 Mar 405 Apr 405 May 405 Jun 405 Jul 405.1 193.8 70.5 48.7 46.9 31.3 43.5 149.4 466.8 0.0 143 46.2 10.6 1.0 0.0 135 60.0 10 0 1.0 0.0 146 74.0 10.8 1.0 0.0 147 85.0 10.8 1.0 0.0 164 50.4 11.7 0.9 0.0 146 7.4 10.3 0.9 0.0 80 0.0 5.7 09 0.0 0 0.0 0.0 1.0 0.0 0 0.0 0.0 1.0 46.2 60.0 74.0 85.0 50.4 7.4 0.0 0.0 0.0 347.3 1006.3 74.1 122.8 1006.3 74.1 -15.3 990.9 73.5 -48.1 942.8 71.4 -16.2 926.6 70.7 12.6 939.2 71.3 36.9 976.1 72.8 148.4 1006 3 74.1 465.8 1006.3 74.1 1351.9 347.3 1351.9 122.8 1351.7 0.0 1351.0 0.0 1350.8 0.0 1350.9 0.0 1351.4 0.0 1351.9 118.3 1351.9 465.8 405 Aug 406 Sep 406 Oct 406 Nov 406 Dec 406 Jan 406 Feb 406 Mar 640.7 516.8 402.5 166.2 71.5 31.7 24.8 17.0 13.5 0.0 0 0.0 0.0 0 0.0 0.0 111 0.0 0.0 1.0 0.0 1.0 8.2 1.0 0.0 143 46.2 10.6 1.0 0.0 135 60.0 10.0 1.0 0.0 146 74.0 108 1.0 406 Apr l 0.0 147 85.0 0.0 164 50.4 0.0 146 74 10.6 1.0 11.3 0.9 9.7 0.8 0.0 0.0 0.0 462 60.0 74.0 85.0 50.4 7.4 639.7 1006.3 74.1 515.8 1006.3 74.1 393.3 1006.3 74.1 108.4 1006.3 74.1 0.5 1006 3 74.1 -54.1 952.1 71.8 -71.7 880.5 68.7 -45.6 834.9 66.7 -4.5 830 4 66.5 1351.9 639.7 926.6 1351.9 515.8 1351.9 393.3 1351.9 108.4 1351.9 0.5 1351.1 0.0 1350.1 0.0 1349.4 0.0 1349.4 0.0Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects B8: (..^....continued) May 2007 2 3 4 5 6 7 8 5.3 0.0 0.0 0.0 0.0 8.2 10.6 10.0 10.8 10.6 11.3 9.8 5.4 0.0 0.0 0.0 9 10 11 12 13 14 15 16 406 May 406 Jun 406 Jul 406 Aug 407 Sep 407 Oct 407 Nov 407 Dec 407 Jan 407 Feb 407 Mar 407 Apr 407 May 407 Jun 407 Jul 407 Aug 45.8 135.6 403.5 668.9 564.2 387.5 160.8 73.1 32.4 23.5 23.1 24.7 44.2 130.6 359.7 565.6 0.0 80 0.0 0.0 0 0.0 0.0 0 0.0 0.0 0 0.0 0.0 0 0.0 0.0 111 0.0 0.0 143 46.2 0.0 135 60.0 0.0 146 74.0 0.0 147 85.0 0.0 164 50.4 0.0 146 7.4 0.0 80 0.0 0.0 0 0.0 0.0 0 0.0 0.0 0 0.0 0.8 0.9 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.8 0.9 1.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0 46.2 60.0 74.0 85.0 50.4 7.4 0.0 0.0 0.0 0.0 39.6 870.0 68.2 134.7 1004.7 74.0 402.5 1006.3 74.1 667.9 1006.3 74.1 563.2 1006.3 74.1 378.3 1006.3 74.1 103.0 1006 3 74.1 2.1 1006.3 74.1 -53.5 952.8 71.8 -73.0 879.8 68.7 -39.5 840.3 66.9 6.7 847.0 67.2 38.0 885.1 68.9 129.7 1006.3 74.1 358.7 1006.3 74.1 564.6 L_ 1006.3 74.1 1349.9 0.0 1351.8 0.0 1351.9 401.0 1351.9 667.9 830.4 1351.9 563.2 1351.9 378.3 1351.9 103.0 1351 9 2.1 1351.1 0.0 1350.1 0.0 1349.5 0.0 1349.6 0.0 1350.2 0.0 1351.9 8.5 1351.9 358.7 1351 9 564.6 840.3 2087 1978 WatPF Wnrfrc n. lArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Annex C: Standards C1: Commonly used values ofjunoff coefficients Class Description of catchment May 2007 Runoff percentage A Flat, cultivated and blck cotton soils B Flat, partly cultivated stiff soils C Average catchment D Hills and plains with little cultivation E Very hilly and steep, with little or no cultivation 10 15 20 35 45 C2: Runoff coefficient for pervious surfaces by selected hydrologic soil groupings and slope Ranges Terrain Type Soil Type A B C D Flat, <2% 0.04-0.09 0.07-0.12 Rolling, 2 - 6% 0.09-0.14 0.12-0.17 Mountain, 6-15% 0.13-0.18 0.18-0.24 Escarpment, >15% 0.18-0.22 0.24 - 0.30 0.11 -0.16 0.15 - 0.20 0.16 - 0.21 0.20 - 0.25 0.23 - 0.31 0.28 - 0.38 0.30 - 0.40 0.38 - 0.48 Note: Where A, B. C, and D are defined as shown in C3: Water Works Design & Supervision Enterpri^-------------- — In Association with Intercontinental Consultants and Technocrats Pvt Ltd 121ArjoDedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 C3: SCS Curve Numbers for Various Conditions' Cover Description Curve numbers for ydrologic soil grout Cover type i Hydrologi c condition A B C D Fallow Bare soil Crop residue cover (CR) Pasture, grassland, or range- continuous forage for grazing2 Meadow-continuous grass, protected from grazing Brush-weed-grass mixture with brush the major element3 Woods-grass combination5 Woods6 Farms—buildings, lanes, driveways, and surrounding lots - Poor Good Poor Fair Good — Poor Fair Good Poor Fair Good Poor Fair Good — 77 86 91 94 76 85 90 93 74 83 88 90 68 79 86 89 49 69 79 84 39 61 74 80 35 59 72 79 48 67 77 83 35 56 70 77 304 48 65 73 57 73 82 86 43 65 76 82 32 58 72 79 45 66 77 83 36 60 73 79 304 55 70 77 59 74 82 86 Arid and semi-arid rangelandse Hyd ------------------------------------------------------- J_ cond7 A B c Lnz Mixture of grass, weeds, and low- Poor growing brush, with brush the minor element Fair Good __ 80 87 — 71 62 81 Mountain brush mixture of small trees and brush Poor Fair Good 74 74 57 41 93 89 85 — Small trees with grass understory 66 48 30 Poor Fair Good — Qrnch lA/ith nrasQ undorQtnrv 75 58 41 85 73 61 79 63 4o 89 80 71 Desert shrub brush Fair Good Poor Fair Good Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt.May 2007 Other combinations of > 11 lay u/c ii^uiuu ii win v> iv, — i— ArjoDedessa Irrigation Project Meteorological and Hydrological Aspects (C^.3co: ntinued^ 1------- Average runoff condition, and la = 0.2S 2 Poor: < 50% ground cover or heavily grazed with no mulch Fair: 50 to 75% ground cover and not heavily grazed Good: > 75% ground cover and lightly or only occasionally grazed 3 Poor: < 50% ground cover Fair: 50 to 75% ground cover Good: > 75% ground cover 4 Actual curve numberJ is Cllelss ^> tIhCaOnO30II; IuQseI ICN = 30 fo’ Wr rWuno. f—- f co--m---p-u--t-a-t-i-o--n-s. -- , 5 CNs shown were ( computed for areas with 50% grass ' (pasture) cover. r conditions may be computed from CNs for woods and pasture. . Forest litter, small trees, and brush are destroyed by heavy grazing or regular 6 Poor __ ______ _____ . . ’’ ' - --------- burning. Fair Woods grazed but not burned, and some forest litter covers the soil. Good . Woods protected from grazing, litter and brush adequately cover soil. 7 Poor: < 30 % ground cover (litter, grass, and brush overstory) Fair: 30 to 70 % ground cover Good: > 70 % ground cover So/7 Groups Group A: Sand, loamy sand or sandy loam. Soils having a low runoff potential due to high infiltration rates. These soils primarily consist of deep, well-drained sands and gravels. GrouP 5: Silt loam' or loam- Soils having a moderately low runoff potential due to moderate infiltration rates. These soils primarily consist of moderately deeo to deer> moderately well to well drained soils with moderately fine to moderately coarse textures G^C: Sandy clay loam. Soils having a moderately high runoff potential due to slow infiltration rates. These soils primarily consist of soils in which a layer exists opL th fine textim1 m °Vement of water °r soi|s with moderately fine to Group_D; Clay loam, silty clay loam, sandy clay, silty clay or clav Snik ho,/ runoff potential due to very slow infiltration rates These soils nrimarii S hav ng a hl9h with high swelling potential, soils with permanently-high wateMables YSo ils < SISt.hf C'ayS a*layer al or near ,he surface'and shaii°” Pa as 123 Water Works Design & Supervision Enterprise------------------ in Association with Intercontinental Consultants and Technocrats Pvt LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects C4: Reservoir Flood Standards May 2007 1 Dam design flood inflow Category of reservoir Initial condition Spilling long term av. General Min. standard, Rare overtopping Wind speed, Min. wave surcharge A: Breach endangers in Daily lives in commentary inflow PMF Larger of 0.5 PMF or 10,000 year flood B: Breach may endanger lives not in a community, Larger of 0.5 PMF or Larger of 0.3 Average annual max. hourly wind Wave surcharge 10,000 year PMF or 1,000 allowance > 0.6 extensive drainage Full flood year flood m Av. Annual C: Breach with negligible risk to life and causing limited damage Larger of 0.3 PMF or Larger of 0.2 max. hourly wind. Wave surcharge 1,000 year PMF or 150 allowance > 0.4 Full flood year flood m Note: For the purpose of PMF, the ordinates of the computed PMF hydrograph are multiplied by the proportion indicated. Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd 124Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects ji ay 2007 - C5: Ratios of the basic dimensionless hydrographof the St TfTp Qi/Qp Ti/Tp Qi/Qp Ti/Tp Qi/Qp 00 0.05 0.008 0.1 0.015 0.15 0.043 0.2 0.075 0.25 0.11 0.3 0.16 0.35 0.22 0.4 0.28 0.45 0.36 0.5 0.43 0.55 0.52 0.6 0.6 0.65 0.69 0.7 0.77 0.75 0.83 0.8 0.89 0.85 0.93 0.9 0.97 0.95 0.99 11 1.05 0.99 1.1 0.98 1.15 0.95 1.2 0.92 1.25 0.88 1.3 0.84 1.35 0.80 1.4 0.75 1.45 0.71 1.50 0.66 1.55 0.61 1.6 0.56 1.7 0.49 1.8 0.42 1.9 0.37 2.0 0.32 2.1 0.28 2.2 0.24 2.3 0.21 2.4 0.18 2.5 0.16 2.6 0.13 2.7 0.11 2.8 0.098 2.9 0.088 3 0.075 3.2 0.056 3.5 0.036 3.7 0.027 4 0.018 4.2 0.014 4.5 0.009 4.7 0.007 5 0.004 Water Works Design & Supervision Enterprise"---------------~~ In Association with Intercontinental Consultants and Technocrats Pvt Ltd 125Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects C6: Guidelines for Interpretations of Water Quality for Irrigation May 2007 Water parameter Symbol Unit1 Usual range in irrigation water SALINITY Salt Content Electrical Conductivity (or) Total Dissolved Solids Cations and Anions Calcium Magnesium Sodium Chloride NUTRIENTS- Potassium MISCELLANEOUS Acid/Basicity Sodium Adsorption Ratio- ECW dS/m TDS mg/l Ca*+ me/l Mg++ me/l Na* me/l cr me/l K* mg/l pH 1-14 0-3 0 - 2000 0-20 0-5 0-40 0-30 0-2 6.0-8.5 0-15 dS/m mg/l me/l me/l me/l me/l mg/l SAR (me/l) 12 , - Ssslce^AO. 1994: Water OuaMy fcMgricatore. Wgatten and Dra/nage Paper No. Nov 1, Reprinted. 1994. Water Works Design & SupenistoJtoteSST,------------------ ------------------ 126 in Association with Intercontinental Consonants and Technocrats Pn LtaArjoDedessa Irrigation Project Meteorological and Hydrological Aspects Annex D: Meteorological Data D1: Details of Meteoroloqical Observation Stations May 2007 Longitude East S.No. Latitude Station Name North Deg. Min. Deg | Min. Altitude (m) Class Period 1 Agaro 07 51 36 36 2030 1980-2004 1 2 Arjo 08 45 36 30 2565 1972-2004 3 3 Bedelle 08 27 36 20 2030 1967-2004 1 4 Dedessa 09 23 36 06 1200 1971-2004 1 5 Dembi 08 04 36 27 1950 1954-2004 3 6 Gimbi 09 10 35 47 1970 1978-2004 1 7 Jimma 07 40 36 50 1725 1952-2004 1 8 Kone 08 41 36 47 2000 1979-2004 4 9 Meko 08 41 36 02 2000 1980-1989 4 10 Nekemte 09 05 36 28 2080 1971-2004 1 11 Wama 08 59 36 40 1450 1980-1987 3 D2: Types of Climatic Data available at the various Meteorological Observation Stations S.No. Station Name Altitude . ( m) Yrs JRF TM ----------------- 1 Agaro 2030 25 X X X X X X 2 Arjo 2565 33 X X RH WS SD EP 3 Bedelle 2030 38 X X X 4 Dedessa 1200 34 X X X X 5 Dembi 1950 51 X X Xx Y zx 6 Gimbi 1970 27 X X X X X 7 Jimma 1725 53 X X X x x Y A 8 Kone 2000 26 X 9 Meko 2000 10 X 10 Nekemte 2080 34 X X X x Y zx 11 Wama 1450 8 X X RF monthly rainfall SD sunshine duration Tm average temperature 1 hr maximum 1-hour rainfall RH relative humidity 1 day maximum 1-day rainfall WS wind speed Rday number of rain days Data length refers to Rainfall and Temperature data Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects D3: Mean Monthly Rainfall at Bedele Station May 2007 Water Works Design & Supervision Enternrisp in Association wlth Intercontinental Consultants ana Technocrats Pvt. Ltd 1;Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects D4: Mean Monthly Rainfall at Jimma Station May 2007 (in mm) Year Jan Feb March April 1953 1954 1955 1956 1957 1958 1959 1960 1961 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 33 49 88 133 8 49 88 133 33 49 88 135 91 25 100 109 29 4 83 290 0 52 117 215 43 86 53 138 81 140 86 138 11 39 104 145 0 86 98 225 40 57 131 116 43 4 39 203 21 73 100 153 4 15 198 82 3 74 63 105 55 61 199 91 78 135 91 188 18 3 58 81 12 74 127 115 28 11 7 149 5 56 76 103 4 65 100 171 36 85 107 112 73 56 54 16 5 71 42 138 32 118 111 23 23 42 100 301 1 7 136 62 105 43 61 136 20 40 97 161 24 11 32 83 25 20 77 147 0 48 82 115 26 89 158 60 81 59 31 87 28 47 138 179 25 46 133 56 79 81 62 169 28 56 56 162 May June July iAug Sept 172 283 399 211 256 93 210 194 214 152 94 298 235 244 169 96 183 288 254 215 142 226 169 195 249 225 278 185 189 82 141 292 203 215 288 103 170 272 138 151 284 219 135 210 212 197 237 272 262 243 106 206 221 206 225 102 249 205 191 58 122 161 307 172 139 157 273 207 283 250 154 233 173 248 210 109 165 189 185 104 103 288 197 263 148 267 153 205 204 201 101 161 159 193 167 148 180 297 160 181 320 165 221 265 240 120 198 252 194 151 189 324 211 233 190 130 197 203 268 191 204 222 184 215 203 116 232 153 164 115 108 189 96 164 141 252 114 193 250 164 211 223 141 192 157 228 166 174 229 299 191 183 211 166 187 203 136 268 168 128 151 256 233 134 163 188 204 186 180 136 182 165 185 294 220 102 179 232 213 204 194 320 280 280 245 110 223 200 246 140 144 287 212 344 175 Oct Nov Dec Annual 116 1 3 27 68 36 103 36 23 50 16 96 118 3 3 68 25 11 87 16 42 130 68 32 38 68 28 97 221 73 164 24 109 107 116 25 56 17 13 132 215 2 31 59 55 85 35 5 149 68 36 124 107 44 58 183 0 57 10 10 25 1 1 98 7 55 93 118 25 229 61 15 64 57 38 75 9 22 109 27 28 31 127 1 94 212 37 141 54 7 12 138 50 63 50 12 89 14 47 116 46 52 172 2 0 107 28 170 23 93 19 51 8 78 _ 180 70 36 1743 1270 1507 1523 1508 1446 1604 1509 1494 2012 1606 1341 1333 1819 1408 1283 1743 1465 1350 1237 1479 1414 1723 1491 1442 1169 1328 1337 1611 1614 1288 1297 1331 1440 1477 1627 1712 1445 1749 Water Works Design & Supervision Enternris’e---------------- In Association with Intercontinental Consultants and Technocrats Pvt Ltd. 129Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 D4 : (■ . continued) i Year Lian iPah M^rch Anril iMav iJune July Aug Sept Oct Nov Dec 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 9 81 110 237 237 225 189 263 164 17 3 0 33 28 87 153 213 274 255 155 177 11 18 11 8 27 74 193 115 163 181 216 141 54 30 96 35 22 135 203 175 183 231 91 245 24 93 40 65 49 69 178 274 237 122 276 148 337 243 36 103 22 97 93 174 223 248 307 200 201 47 1 30 1 84 72 214 575 136 102 131 198 1 2 0 1 39 194 238 154 266 159 255 244 47 25 16 13 86 117 341 299 312 161 183 163 76 4 69 5 11 90 137 242 150 235 165 80 8 138 29 61 87 111 12 272 187 151 239 92 30 15 51 28 46 131 162 128 216 219 210 133 67 89 1534 Annual 1410 1298 1476 2034 1713 1546 1622 1772 1330 1285 1482 Avg CV Skew Max Min 33 49 88 133 172 219 208 210 182 103 68 36 0.86 0.71 0.48 0.43 0.39 0.34 0.24 0.26 0.26 0.67 0.96 1.06 0.95 0.68 0.55 0.41 0.41 2.53 0.11 0.12 0.04 1.10 1.32 1.74 105 140 199 301 341 575 312 344 299 337 243 170 0 1 7 16 12 114 96 91 58 11 1 0 1502 0.13 0.83 2034 1169 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd 130Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects D5: Mean Monthly Rainfall at Dedessa Station May 2007 \iii i iniiy Year Jan |Feb March April May (June |july Aug ISept Oct 1971 1972 1973 1976 1977 1978 1979 1980 1981 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 152 11 6 5 90 187 283 497 219 181 123 0 0 3 41 266 273 203 289 146 00 0 0 0 83 80 217 196 184 121 49 0 0 0 0 0 191 245 197 289 193 0 0 2 13 228 285 272 240 130 96 0 48 39 88 150 205 39 0 0 35 11 244 207 00 334 625 401 196 107 0 0 9 20 221 306 297 309 123 0 1 0 47 89 219 316 373 296 158 146 0 5 12 73 90 184 339 259 221 94 4 3 25 29 141 399 428 296 215 97 1 9 32 8 275 341 370 442 380 241 0 0 160 38 243 289 337 289 305 120 4 10 39 2 11 280 402 245 152 53 7 17 33 74 101 215 355 304 132 5 4 0 0 0 84 197 153 207 171 183 0 8 26 95 141 224 307 264 170 132 0 0 1 79 0 0 34 19 81 112 265 241 177 89 21 4 79 60 239 311 380 380 370 0 13 0 13 154 184 203 277 247 147 0 0 0 13 14 251 399 196 371 254 191 18 0 0 47 178 306 151 274 351 141 0 0 0 154 241 448 136 347 300 192 0 11 27 31 143 214 196 224 254 128 6 15 30 31 77 203 252 126 102 17 0 35 50 0 73 366 417 302 193 67 0 5 6 35 106 252 427 318 140 147 Average CV Skew Max Min 3 6 26 49 158 274 312 277 209 104 1.91 1.87 1.28 0.88 0.51 0.29 0.37 0 25 0.38 0 64 2.18 2.78 2.75 0.94 -0.25 0.25 0 64 0 35 0.87 -0 04 21 48 160 154 275 448 625 442 380 241 0 0 0 0 0 112 136 126 102 0 40 65 60 20 14 7 68 32 8 27 5 54 3 22 19 1 65 15 10 12 60 29 17 22 40 0 36 36 28 0.76 0.59 68 0 0 14 5 0 0 4 0 0 14 23 1 1 0 76 0 10 6 0 5 0 0 0 11 0 29 8 6 0 8 2.05 3 66 76 0 Annual 1679 1222 784 1128 1278 1695 1306 1695 1284 1691 2101 1880 1216 1251 1069 1382 1032 1856 1299 1717 1494 1842 1296 865 1544 1470 1426 0.23 0.05 2101 784 Water Works Design Supervision Enterpri^----------------------------------- ---------- '3 In Association with Intercontinental Consultants and Technocrats Pvt. LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects D6: Mean Temperature at Bedele Station (in oC) Year T Jan | Feb | Mar I Apr May | Jun Jul May 2007 I Aug I Sep Oct [ Nov | Dec 1971 175 19.9 21.2 208 21.5 20.4 18.2 16.7 16.6 15.5 15.4 17.2 1972 19.5 20.9 18.4 17.9 19.8 18.3 15 8 15.9 1973 179 18.7 21.5 21.5 19.4 17.9 14.3 16.4 18.0 17.3 17.4 24.9 1974 17.7 198 19.3 20.2 18.7 18.2 16.9 15.7 172 17.1 17.9 17.0 1975 1976 1977 1978 1979 1980 1981 17.3 19.3 19.7 198 19.4 17.7 16.7 16.2 17.7 18.1 17.2 179 18.1 19.1 18.8 17.8 17.6 17.2 17.1 17.7 17.0 16.7 18.2 19.0 17.3 18.4 19.3 18.9 18.5 17.5 168 16.0 16.1 19.7 16 0 16.5 21.0 20.5 19.7 19.5 7.9 16.6 17.3 17.3 17.5 19.2 19.1 17.6 17.2 16.9 17 4 17.0 17.6 174 17.3 17.5 17.1 170 1982 1983 1984 1985 1986 1987 7.5 19.1 20.1 17.6 17.4 17.8 18.3 18.7 190 19.4 20.8 21.4 21.2 22.0 19.7 18.0 16.9 17.3 17.4 18.6 18.9 19.6 20.5 20.5 21.4 20.5 18.6 18.0 17.2 17.1 17.3 17 7 18.8 18.9 199 20.6 20.8 20.9 21.4 18.1 17.4 17.8 17.7 18.2 18.7 18.4 19.4 20.8 20.4 1988 1989 1990 1991 19.3 20.6 20.7 21.0 20.4 18.3 19.7 20.3 20.8 21.6 19.6 18.1 170 17.3 17.5 18.3 18.2 17.9 17.8 18.7 19.1 193 19.0 17.8 15.0 17.3 17.7 17.5 18.0 17.8 18.1 18.7 19.5 20.2 19.3 18.5 17.4 17.4 17.8 18.2 18.9 19.1 18.1 18 2 18.3 19.0 1992 1993 1994 19.1 20.1 21.3 20.6 20.7 19.5 18.4 17.4 18.2 18.4 18.7 20.0 180 19.6 19.1 18.8 20.6 1995 1996 1997 1998 1999 2000 20.5 20.8 21.3 21.4 19.9 19.4 17.6 19.2 21.0 20.6 20.7 19.1 18.4 17.8 192 19.9 21.5 19.9 19.3 18.6 17.8 19.6 21.7 21.7 21.8 19.1 18.7 17.3 20.9 20.9 220 21.3 19.5 17.8 17.7 18 2 19.0 19.6 19.5 13.9 21.2 21.2 23.2 21.0 19.3 18.1 18.3 18.9 19.2 18.6 19.2 18.1 18.5 18.8 18.9 19.5 18.0 18.3 18.3 18.5 18.7 18.0 188 17.7 18.6 17.9 18.4 19.2 2001 17.7 17.9 18.5 18.9 18.6 18.9 19.1 20.9 20.7 21.2 19.9 18.0 17.5 17.7 18 6 19.4 18.7 19.2 2003 20.0 21.5 21.1 21.2 21.9 18.7 17.6 2002 19.2 21.1 21.6 21.8 21.2 18.5 18.3 17.5 18.1 18.1 186 18.9 2004 20.8 21.0 22.1 21.5 20.8 18.3 17.8 Average 18.7 19.7 20.6 20.6 19.6 18.0 17.3 CV 9.08 0.13 0.05 0.05 0.06 0.12 0.05 Skew 1.21 3.96 ■1.19 ■0.08 0.00 -4.24 -2.06 Min 13.9 7.5 17.1 18.4 17.0 7.9 14.3 Max >0.9 21.7 22.1 23.2 21.9 20.4 18.4 -0.86 18.1 18.6 19.0 19.6 19.6 18.1 18.6 18.7 19.1 19 6 17.4 17.9 18.0 18.3 18.9 0.04 0.05 0.05 0.06 0.09 -0.58 -0.94 15.7 16.0 15.5 15.4 15 9 18.3 19.6 19.4 19.7 24.9 -1.35 1 44 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects D7: Relative Humidity at Bedele Station (in%) May 2007 Year Jan Feb Mar Apr May Jun | Jul 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 63 80 58 52 70 78 89 51 53 67 62 68 80 83 59 62 56 60 70 79 82 55 46 56 67 78 80 82 68 65 58 62 66 75 77 53 48 48 57 78 83 85 46 50 51 59 72 75 85 59 54 63 62 75 82 83 63 65 55 64 59 50 49 55 76 76 84 58 82 62 62 65 65 73 83 84 69 60 66 65 67 81 85 62 55 63 60 57 81 88 61 54 56 62 66 81 85 Average 60 57 58 61 70 78 84 80 80 69 58 84 83 76 63 50 85 84 72 64 75 80 80 70 69 60 84 77 71 65 65 81 74 72 69 64 72 81 61 66 61 83 78 69 69 67 84 80 72 68 64 84 80 78 64 63 84 82 80 74 70 84 83 80 74 67 86 83 86 84 73 69 61 84 82 74 70 69 83 81 69 63 60 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd 133Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects D8: Wind Speed at Jimma Station May 2007 Year Jan ^Feb March April |May jjune ljuly lAug Sept Oct Nov Dec 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 0.8 0.8 0.9 0.9 0.8 0.9 0.9 1.1 1.2 0.9 1.1 0.9 0.9 0.8 0.9 1.1 0.9 0.9 0.9 1.2 0.8 1.3 1.4 0.9 0.8 0.8 0.9 0.8 0.8 0.8 0.8 0.7 1.0 1.0 09 0.9 0.8 0.9 0.9 0.9 0.8 0.7 0.7 0.8 09 0.9 1.0 0.8 0.8 0.9 0.9 0.8 0.7 0.8 0.7 0.8 1 2 1.1 0.9 0.9 0.7 0.8 0.8 0.8 1.0 0.7 0.9 0.8 0.8 0.9 0.6 0.9 0.7 0.8 0.8 0.7 0.6 0.7 0.7 0.8 0.9 0.9 0.8 0.7 0.7 0.7 0.7 0.6 0.6 0.6 0.7 08 0.9 0.7 0.8 0.8 0.6 0.7 0.6 0.6 0.5 0.6 0.7 0.8 0.8 0.8 0.8 0.7 0.6 0.6 0.7 0.6 0.6 0.5 0.6 0.6 0.8 07 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.6 *•• 0.6 0.6 0.5 0.6 0.6 0.6 0.5 0.6 0.5 0.8 0.7 0.6 0.6 0.5 0.5 0.5 0.5 0.4 0.3 0.3 0.5 0.5 0.6 0.6 0.5 0.5 0.5 0.4 0.4 0.3 0.2 0.3 0.1 0.1 0.2 0.2 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.5 0.6 0.6 0.6 0.6 0.6 0 5 0.6 0.6 0.6 0.6 0.5 0.1 0.1 0.1 0.1 0.1 0.2 0.1 0.1 0 1 0.1 0.1 0.1 0.6 06 0.7 07 0.7 0.6 0.5 0.5 0.6 0.5 0.5 0.5 0.5 0.5 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.5 0.6 0.5 0.1 0.1 0.4 0.2 0.3 0.1 0.1 0.1 0.2 0.1 0.1 0 1 0.4 0.6 0.6 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0 5 0.4 0.5 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0 4 0 4 0.4 0.5 0.5 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.3 0.4 0.4 0.4 0.5 0.5 0.4 0.5 0.3 0.3 0.4 0.4 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.2 0.2 0.2 0.2 0 2 0.2 0.3 0.3 0.3 0.3 0.3 0.2 0.3 0.3 0.2 0.2 0 2 0.2 0.3 0.3 03 0.3 0.3 0.2 0.2 0.1 0.2 0.2 0.2 0.3 0.2 0.1 0.2 0.1 0.1 0.2 0.2 0.1 0.3 0.10 0.11 0.09 0.18 0.19 0.18 0.3 0.2 0.2 0.1 0.2 0.1 02 0.1 Average CV Skew Max Min 0.52 062 0.72 0.73 0 75 0.74 0.71 0.76 0.82 0.82 0.83 0 89 0 52 -0.04 0.16 0.1 0.29 0.63 0.5 0.44 0.44 0.42 0.36 0.36 0.35 0.33 0.34 0 32 0.29 -0 -0.1 -0 0.9 1.2 1.2 1 3 1.4 0.02 0.9 09 0.9 0.9 0.1 0.1 0.3 0 31 0 08 0.1 0.1 0.1 0.1 0.1 0.1 0.1 1.1 0.1 1.0 0.1 0.9 0.1 Water Works Design & Supervlsio^EmeTSiTn-------------------------- in Association with Intercontinental Consnlunu and TecLocL Wt Ltd 134E ■ ■ ■ N ■ 1 I I I I I Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects D9: Sunshine Duration at Bedele Station (in hrs/davi May 2007 Year Jan Feb Mar Apr May Jun Jul LAu9 Sep I Oct Nov Dec ---------------------- ------------------------ --------- 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 L. 7.9 7.2 6.9 8.5 5.6 6 6.3 5.7 8.4 8 8.3 8.3 9.3 7.1 6.5 8.2 7.9 6.4 2.6 4.2 5.1 9.7 9.5 8.5 8.2 7.9 7.9 7.4 6 3.8 5.1 6.5 7.9 8.8 6.4 8.9 5.6 7.7 6.4 8.2 6.4 3.8 4.8 6 9.6 8.7 9 79 8.1 6.8 6.3 7.1 4.5 2.7 3.4 5.9 8 8.4 7 5.7 7.7 7.1 8.3 6.1 3.4 2.2 6.7 6.2 6.2 8.3 7.6 6.6 7.5 5.5 7.7 7.5 7.7 7.6 w*•*•*•♦ ♦ 2.4 3.4 5.8 9.5 8.4 9.3 8.8 6.6 7.7 6.6 ** ♦*♦ 7.9 3.7 4.3 6.7 9 7.9 7.8 7.2 9.2 7.5 6.8 7 6.1 4.1 4.6 8.4 7.6 6.7 8.3 7.5 7.7 6.4 8.7 6.4 6.7 2.9 3.3 4.7 5.4 8.4 9.2 8.1 9.1 8.8 7.6 7.6 6.6 3.5 4.6 6.6 5.8 9.8 8.8 9 8.8 9 6.1 7.8 8 ♦* ♦ 5.5 6.4 ** * 8.2 7.5 9.1 8.4 6.1 5.6 3.1 6.9 8.8 8.3 7.6 7.9 86 7.3 8.8 9.6 5.7 2.9 3.6 6.1 9.5 8.7 8.6 7.5 7.9 6 5.7 7.4 4.3 4.2 4.5 3.5 8.2 8.3 7.7 Average 8.2 7.6 7.5 7.3 7.6 6.1 3.7 4.1 6.2 7.9 8.3 8.3 Water Works Design & Supervision Enterprise ~ In Association with Intercontinental Consultants and Technocrats Pvt Ltd 135Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Annex E: Hydrological Data May 2007 E1: List of Selected Hvdroloaical Observation Stations_____________________________________________ _______ Latitude, N Longitude, E S. No Station No. Station Name Deg. Min. Deg. Min. Catch. Area (km ) Period 2 1 114001 Dedessa near Arjo 08 41 36 25 9981 1960-2004 2 114002 Angar near Nekemt 09 30 36 35 3742 1994-2004 3 114005 Dabana near Abasina 09 02 36 03 2881 1962-1984 4 114007 Angar near Gutin 29 1999-2003 5 114008 Yebu at Yebu 07 48 36 42 47 1979-2004 6 114009 Urgessa near Gembe 07 50 36 39 19 1979-2004 7 114013 Dabana near Bunno Bedelle 08 24 36 17 47 1984-2003 8 114014 Dedessa near Dembi (Toba) 08 03 36 27 1806 1985-2003 9 114016 Loko near Nekemt 09 22 36 36 375 1997-2004 10 114019 Temssa near Agaro 07 51 36 35 47.5 1989-2004 11 113004 Melke near Guder 08 51 37 44 38 1998-2004 12 08 56 37 45 111 1986-2004 13 101006 Uka at Uka 08 10 35 22 52.5 1980-2004 14 113038 Indris near Guder 091008 Gilgelghibe near Asendabo 07 45 37 11 2966 1967-2004 15 091012 Gojeb near Shebe 07 25 36 23 3577 1970-2004 Water Works Design & Supervision Enternrise ~ In Association will. Intercontinental Consonants and Technocrats Pvt ltd 136Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects Annex E2: Mean Monthly Streamflow at Dedessan near Arjo Station May 2007 ■ Year (Million m3) ---------------------------------------------------------- ------------------- --------------------- -------------------------- 1------------------------ Jan | Feb | Mar | Apr May Jun Jul Aug 1 Sep i Oct Nov^ Dec 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1054 1124 51.5 44.0 37.5 94.9 65.6 286 1176 1613 1503 1304 280 177.5 58.1 29.8 28.4- - - 622 930 1170 855 107 55.9 38.1 19.3 17.9 42.7 147.1 324 672 1370 1040 374 184 170.3 - 38.2- - 54.9 230 1049 1301 1178 1337 205 73.6 55.4 253 16.4 47.8 278 168 834 1051 685 957 320 157.8 71.0 63.4 57.7 74 1 62.5 - 857 1086 1212 - - - 22.7 20.4 708 1268 1201 1260 459 210.4 96.0 529 21.4- -- 138 63.7 50 9 46.7 67.1 39.7 73.2 349 950 1421 944 291 89 46.2 34.1- - - 45.3 288 929 - - - 181 62.1 37.0 16.4 10.9 12.5 53.5 241 823 1175 949 752 304 105.3 52 4 29.8 19.6 35.7 56.4 118 803 1237 719 209 117 52.5 25.9 11.2 4.7 63 109.3 250 36.5 16.2 14.4 9.1 93.7 261 641 1278 24.5 21.9 11.5- 48.3 37 8 24 7- - 25.9 18.1 12.7 55.5 20.1- 12.4 80.1 - 1401 592 149 64 8 119 48.9 151 89 5 324 128 7 - - 22.9 46.4 130 533 825 619 262 94 44 0 18.0 15.3 10.0 68.6 190 9 504 914 1288 1244 393 103 92.5 80.0 43.4 43.3 35.4 53.7 53 598 30.2 28.6 19.3 45.7 248 707 947 692 761 177 94 5 43.4 31.7 34.1 23.3 52.4 153 38.5 16.7 11.9 9.5 28.6 185 703 665 521 131 12 0 5.4 2.6 11.8 62.4 169 438 927 842 260 79 566 1139 1116 1231 265 1 9 1 9 1 ZL I .J 17 6 9.5 16.1 13.8 128 119 452 491 13.0 5.9 12.4 17.3 36.7 732 222 40.5 27.5 21.6 7.7 37.0 280 555 233 20.4 33.5 27.1 121 273 499 1087 - 53.5 30.0 338 60.9 42.0 157 343 673 386 160 67.8 189- 107 123.1 - ---- 543 1143 42.5 279 24.4 54 7 105.2 312 24.5 23.9 13.8 20.7 56.5 161 368 824 564 806 164 39.1 19.6 15.5 15.7 59.7 220 600 1159 534 1221 631 858 407 177 156 68 38.1 734 63.3 36 9 _____________________________________ 1 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Year Jan Feb Mar Apr May E2: (.... Continued) Jul Aug Jun Sep Oct Nov Dec 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 20.4 12.2 14.8 19.4 38 3 83 225 569 486 156 60 - - - 30.4 141.8 373 723 854 598 - 87.2 41.4 19.0 - - - - - - • - --- --- - - -- - - - -- -- -- 242 135.7 85.1 59.5 66.1 57.2 128.3 401 740 1045 1005 674 215 111.7 99.0 57.2 55.3 63.4 46.2 175 457 591 578 211 115 83.9 56.4 36 2 562 74.3 48.0 120 652 - - 52.3 40.2 30.3 28.7 65.2 202 526 639 643 538 140 - Avg CV Skew Max Min 46.2 28.7 26.0 33.2 66.5 223 654 1007 889 581 177 90.9 0.47 0.52 0.66 0.71 0.59 0.46 0.34 0.30 0.32 0.68 0.51 0.50 0.66 0.65 1.14 0.94 1.54 0.74 0.22 -0.16 0.43 0.73 1.26 1.00 99.0 63.4 67.1 94.9 190.9 503.5 1176.1 1612.8 1502.5 1337.4 459.2 210.4 12.0 5.4 2.6 6.3 12.8 53.2 225.0 491.1 485.9 Mean annual flow = 3821 Mm3) 130.8 59.9 36.9 Water Works Design & Supervision EnternrisT ----------------------------- -- ---------- - 138 in Association with Intercontinental Consultants and Technocrats Pvt LtdArjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects E3: 41 Mean Monthly Stream flow at Dedessan near Dembi Station May 2007 Year IVIIIIIVII Jan mo; Feb Mar Apr May Jun Jul Aug Sep | Oct | Nov | Dec 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 6.4 3.7 4.2 78 26.8 92 83 165 302 272 70.2 21.9 8.5 5.5 9.7 8.4 9.4 58 262 208 299 67 22.9 11.5 5.9 4.5 9.7 9.2 18.6 105 243 342 218 104 44.1 27.1 17.9 157 12.5 6.4 23.9 153 217 392 489 142 52.0 18.8 11.0 7.6 4.5 11.5 8.2 31 167 253 272 142 24 8 13.8 18.3 5.8 5.6 22.7 9.9 52 252 564 362 126 20.9 9.4 7.2 6.3 6.6 12.5 29 5 76 305 522 263 140 13.4 8.9 7.8 15.3 12.9 8.8 36.6 78 138 269 183 218 45 2 17.1 11.2 17 2 16.6 376 80 8 252 334 378 204 110 48.7 14.7 12.3 13.5 168 22.5 37.8 112 274 381 282 59 26.6 16.4 12.9 12.1 16.5 23.8 48.7 87 190 272 331 101 32.5 33.7 12.9 94 16.5 23.8 48.6 87 190 272 331 101 32.5 33.7 21.2 13.8 23.2 30.1 55.2 142 219 343 204 262 188 56.1 28.1 13.6 20.3 12.7 31.1 110 272 415 299 329 88.8 21.1 13.0 6.5 8.3 9.5 54.9 148 242 245 214 302 48 4 18.3 10.2 5.6 4.5 9.7 41.2 119 290 309 242 209 82 0 21.9 12.7 9.6 11.2 14.5 55.5 226 330 322 296 212 59.6 22.5 6.5 6.9 6.6 9.0 6.5 63 192 255 195 68 27.7 14.9 7.4 4.0 9.2 24.0 6.7 59 241 223 324 82 20.3 10.0 130 13.0 13.7 33.0 98.5 198 208 208 145 39 18.8 18 8 Average CV Skew Max Min 12.2 9.47 11.5 16.9 36.4 112.4 232.4 316.9 273 154.3 48.4 20.5 0.47 0.46 0 48 0.56 0.69 0.526 0.27 0.326 0.28 0.561 0.81 0.53 1.35 0.31 0.47 0.81 0.85 1.028 -0.47 0.927 0.89 0.668 2.6 1.98 28.1 17.2 23.2 37.6 98.5 252 334 564 489 329 187 9 56.1 5.9 3.7 4 2 6.4 6.5 31 83 165 145 39 13.4 8.9 Mean annual flow = 1255 Mm3) Water Works Design & Supervision Enterprise-------------------------- In Association with Intercontinental Consultants and Technocrats Pvt Ltd 139Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Annual Maximum Floods (in m3/s) Year Dedessa near Arjo Upper Dedessa near Dembi Dabana near Abasina Gilgel Ghibe near Asendabo Gojeb ne arShebe Angar near neqemte Angar near Gutin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 633 1173 893 789 850 951 814 1165 781 634 896 721 490 645 554 1083 369 480 502 574 771 750 646 804 353 525 525 744 312 601 213 206 212 243 354 228 200 151 189 262 164 175 226 175 211 244 271 300 370 267 467 264 434 449 247 196 257 180 314 341 238 202 248 151 132 198 272 130 176 330 127 151 231 167 110 205 116 168 129 148 151 223 135 149 119 92 96 127 143 85 121 247 86 106 192 237 159 255 100 174 339 188 185 258 186 241 284 217 214 140 249 177 288 138 297 314 184 150 203 226 132 245 366 164 164 261 164 150 282 132 193 199 439 236 335 361 209 247 256 157 271 252 128 141 73 55 124 107 134 105 125 142 136 142 149 1 ro 172 109 106 79 181 128May 2007 E5: Measured Sediment Concentration at Gumara Gauging Station ' “T No. Field V samplelLab.No. River / Stream Station l Date & Time No | | of Sampling Time (Sec) G/height (m) Flow 3 (m /s) Depth (m) Width i (m) Sediment Concen (mg/l) Remarks AV 484 1 Dedessa Toba 15-Mar-90 485 2 Dedessa Toba 15-Mar-90 486 3 Dedessa Toba 15-Mar-90 664 1 Dedessa Toba 21-Mar-90 665 2 Dedessa Toba 21-Mar-90 666 3 Dedessa Toba 21-Mar-90 0.43 4.16 0.26 6.9 51.56 _ _ 0.43 4.16 0.70 13.8 0.43 4.16 0.36 20.7 0.50 5.41 0.54 7.0 0.50 5.41 0.80 14.0 0.50 5.41 0.39 6.1 1057 1 40.00 42.81 59.69 173.13 90.63 Dedessa Toba 2-Jul-90 1058 2 Dedessa Toba 2-Jul-90 1059 3 Dedessa Toba 2-Jul-90 1190 1 Dedessa Toba 22-Dec-90 1.81 9.14 8.40 6.6 — 1.81 9.14 8.00 13.3 — 1.81 9.14 7.00 19.9 215.31 135.62 190.00 1191 2 Dedessa Toba 22-Dec-90 1192 3 Dedessa Toba 22-Dec-90 50 0.40 , 4.37 0.43 7.0 90.94 1223 1 Dedessa Toba 18-Sep-90 1224 2 Dedessa Toba 18-Sep-90 1225 3 Dedessa Toba 18-Sep-90 50 0.40 4.37 0.74 14.0 50 0.40 4.37 0.46 21.0 2.46 I 98.50 2698 1 2699 2 2700 3 2704 1 2705 2 2706 3 Dedessa Toba 16-May-93 Dedessa Toba 16-May-93 Dedessa Toba 16-May-93 Dedessa Toba 12-Apr-93 Dedessa Toba 12-Apr-93 Dedessa Toba 12-Apr-93 45 45 0 46 2.89 0.61 6. 2.46 98.50 2.46 98.50 0.46 2.89 0.66 19. ! 99.37 63.13 141.56 187.82 124.69 5 87.90 40 0.46 2.89 0.71 13. 5 108.63 - 0.64 0.64 8.01 8 01 0.64 I 8.01 - - 0 8140 73.05 64.61 61.59 59.20 Water Works Design & Sn npHrin? ~- III Ascnnin*:----------- • -E5: (... continued) No. Field sample No Lab.No. River / Stream Station ______ 541 1 179/04 Dedessa Arjo 10-Aug-04 30 2.45 542 2 Dedessa Arjo 10-Aug-04 26 2.45 543 3 Dedessa Arjo 10-Aug-04 28 2.45 544 1 180/04 Dedessa Arjo 11-Aug-04 32 2.56 545 2 Dedessa Arjo 11-Aug-04 28 2.56 546 3 Dedessa Arjo 11-Aug-04 27 2.56 559 1 185/04 Dedessa Arjo 1-Sep-04 29 3.61 560 2 Dedessa Arjo 1-Sep-04 28 3.61 561 3 Dedessa Arjo 1-Sep-04 29 3.61 Date & Time of Sampling Time (Sec) G/height (m) Flow (m /s) 3 Depth (m) Width (m) Sediment Concen (mg/l) Remarks AV 143.12 9.05ft 17.5 143.12 9.1ft 35.0 143.12 9.5ft 52.5 196.11 11ft 18.0 196.11 9.6ft 36.0 196.11 96ft 54.0 611.23 137ft 18.0 611.23 14.3ft 37 0 611.23 1.46ft 55.0 1417.50 1739.74 1740.74 1652.86 1718.12 1639.31 1360.22 1328.81 1438.44 142 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Annexure - 8 HYDROGEOLOGICAL STUDIESArJoDedessa Irrigation Project Hydrogeological investigations May 2007 TABLE OF CONTENTS TABLE OF CONTENTS I LIST OF TABLES II LIST OF FIGURES II 1. INTRODUCTION 1.1 General 1.2 Location 1.3 Physiography‘ 1.4 Methodology and approaches 2. PHYSICAL HYDROGEOLOGY.. 1 6 2.1 Hydrogeological setup........................................................................................................................................ 6 2.2 Hydrogeologic units7 2.2.1 Fractured and/or weathered volcanic rocks 8 2.2.2 Alluvial sediments8 2.2.3 Delluvial sediments 2.3 Inventory and well data8 2.4 Hydrodynamic parameters of aquifers9 3. GROUNDWATER POTENTIAL 3.1 Groundwater recharge estimation 3.1.1 Base flow analysis 3.1.2 Water balance method 4. WATER QUALITY 4.1 Water samples 4.2 Sampling techniques and analysis 4.3 Pictorial representations of water quality analysis . 4.3.1 Piper diagram 4.3.2 Schoeller diagrams 4.3.3 Stiff diagram 4.4 Agricultural/irrigation water quality 5. PIEZOMETERS OBSERVATION WELLS AND WELL FILED 5.1 Distribution of Piezometers/Observation Wells 5.2 Future well field’’’’’ 6. WATER LOGGING AND DRAINAGE 6.1 Topographic features and soil characteristics 6.2 Existing groundwater table” ’ * 6.3 Future groundwater table and recharge from irrigation 7. SALINITY AND SODICITY 8. EXSITING AND FUTURE PROSPECT OF GROUNDWATER 8.1 Existing groundwater development 8.2 Future groundwater prospect 8 11 ,.27 27 .28 .30 30 30 31 .39 ..41 41 Water Works Design & Supervision Enterprise—------------------ In Association with Intercontinental Consultants and Technocrats Pvt LtdArjo-Dedessa Irrigation Project Hydrogeological investigations May 2007 LIST OF TABLES Table 2.1 Details of boreholes in the study area Table 3.1 Monthly total flow, and Minimum flow of Dedessa river near ArjoI Table 4.1 SAR and EC values in terms of irrigation water suitability23 Table 4.2 SAR and EC values for surface and groundwater in Arjo-Dedessa area24 Table 5.1 Locations of the Proposed Piezometers27 Table 6.1 Annual gross crop water requirement at primary canal head31 Table 6.2 Estimation of wetted area for Arjo- Dedessa irrigation canal33 Table 6.3 Seepage loss from unlined Arjo- Dedessa irrigation canal33 LIST OF FIGURES Figure 1.1 Location map of Arjo- Dedessa irrigation project Figure 1.2 A map showing 3- D view of Dedessa river Catchment Figure 2.1 A map showing hydrogeologic units of Dedessa river cathment Figure 4.1 Location of water sample points Figure 4.2 Piper Trilinear Diagram for Water Samples Figure 4.3 Schoeller diagram for water samples 3 5 10 17 20 21 Figure 4.4 Figure 4.5 Figure 4-6a Figure 5.1 Stiff diagram for water samples............................................................ 22 Electrical conductivity (EC) in Rs/cm and Total Dissolved Solids (TDS) in mg/Lfor Map Showing Contour for TDS Figure 6.1 Proposed Piezometers/Observation wells 26 29 Figure 6.2 Profiles along different lines in the command area.. Figure 8.1 A map showing lines of profiles in the command area A map showing groundwater potential areas 37 38 42 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt LtdArjoDedessa Irrigation Project Hydrogeological Investigations 1. INTRODUCTION 1.1 General May 2007 Hydrogeology refers to the occurrence, movement, chemistry (quality), etc of groundwater in general. It has a diversified application in developing, utilizing and managing groundwater. Furthermore, different aspects of groundwater such as recharge-discharge condition, aquifer type and set up, its interaction with surface water, etc are treated under this discipline. The nature of groundwater and how it behaves, when subjected to nature or man-made activities is studied for different purposes such as for water supply (domestic, agriculture and industry) and construction of surface and sub surface engineering structures (e.g., dam, tunnels, drainages, etc). In order to develop and manage groundwater, one has to know its potential, quality and movement. Ethiopia has diversified hydrogeological features that are attributed to its geology, structure, hydrometeorology, topography, etc. The hydrogeology of the country has not been studied thoroughly so far. With the exception of few areas such as Rift valley that has been mapped at scale of 1:250,000, the country has only small scale (1:2,000,000) hydrogeological map. Hydrogeology is usually applied for locating borehole sites in light of water supply. Groundwater has been used without detail understanding of the resource. In spite of ample groundwater resources of the country, very little been studied and used so far. Currently, however, not only groundwater development and/or utilization but also its management is getting an attention. Since any development relies generally on proper utilization of natural resources, the government has also given focus on water resource development both for domestic water supply and irrigation. As part of this water resource development. Integrated Master Plan Study of various River basins has been undertaken in the country since some years The Abay River basin is one of them. Arjo-Dedessa irrigation project has been identified as one of the projects during the Abay River Basin Master Plan study. Hydrogeological investigation and study that mainly focuses on groundwater occurrence movement, chemistry, etc has been included as one of the components of the^eaXliN study and design of the project. Accordingly, this study at Feasibility Study level has been undertaken. Water Works Design & Supervision Enterpri^" In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo-Dedessa Irrigation Project Hydrogeological investigations 1.2 Location May 2007 The project area is located within Dedessa River sub-basin which is in turn located in Abay River basin. It is within the Western Oromia National Regional State; particularly at tri junction of East Wollega, llubabor and Jima zones. The sub basin of the irrigation project is bordered byOmo-Gibe River basin on eastern side and Baro Akobo River basin on SW side. The total area of the catchment at the proposed dam is about 5,632.64 km2. The project location is shown in Fig. 1.1 The project area can be reached from Addis Ababa through two alternative high ways that take either to Bedele or Nekemt. The all- weather gravel road that takes from Nekemt to Bedele passes through the project area. Hence, in general the project area is about 480km from Addis Ababa through Jima and Bedele. 2Fig. 1‘1 Location map of Arjo-Dedessa Irrigation project 109000 7*10000 JOCOY) T50TW —_—y u— j.—............. — --------- v Warn a Boneya ______h Kumba I •- )/ \J Llmu Seka Rtver/Stream Setema A qh » o Command >f»a Wo'»da BoundaryArJoDedessa Irrigation Project Hydrogeological investigations May 2007 1.3 Physiography The basin drains a part of Jima high lands including Goma (Agaro), Setema, Sigimo, Limu Saka, and part of llubabor including Borecha, Dedessa, Gachi and Bedelle Woredas above the proposed dam. Arjo, Nunu Kumba, Sibu Sire and Wama Bonaya woredas are also within the catchment. The command area is drained by river Dedessa and other tributaries such as Wama River. The general slope of the basin/or catchment is toward NE, E and NW directions. The area has generally a rugged topography with the highest and lowest elevation is about 2890 a nd 1 030 m amsl respectively located at S igimo-Gera area and Dedessa river valley. The river basin has mainly a dendritic drainage pattern. 3- D view of Dedessa river catchment is shown in Fig. 1.2. 1.4 Methodology and approaches In order to undertake the hydrogeolgoical investigation of Arjo-Dedessa irrigation project area, the following methodology and approaches have been used: . Reviewing of the previous works and data available with different institutions such as MoWR, Institute of Geological Survey. Regional Water Resources Bureau and Offices, Regional Water Works Construction Enterprises. . Field survey to collect primary information on geology, hydrogeology, geomorphology, and other physical features of the area. . preparations of inventory for water supply schemes and fixing their location with GPS; measurement of water level for wells; estimation of discharge for springs; water sampling from springs, wells and streams/rivers for physicochemical analysis. . Interpretation of aerial photos, satellite images and Topo maps (1:50,000 & 1: 250,000); applications of various GIS and remote sensing software to identify and delineate lithology and geological structures, and finally to analyze, and compile the spatial data; and to incorporate them as maps for various themes. . in-situ measurement of physical parameters of water quality indicators by using field water quality test kits (Ph, EC, TDS and Temperature meter). . Finally, preparations of hydrogeological maps with different thematic layers such as hydrogeologic units, depth to groundwater table, water quality, groundwater yield based on all the collected and analyzed data. Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Fig. 1-2 A map showing 3-D view of Dedessa river catchmentArjo Dedessa Irrigation Project Hydrogeological Investigations 2. PHYSICAL HYDROGEOLOGY 2.1 Hydrogeological setup May 2007 The basin comprises volcanic lava flows mainly basalts and ignimbrite as well as pyroclastic falls on Jima side; where as on llubabor and Wollega sides, the outcrop is mainly basaltic lava flows except within the Dedessa River Valley, where the outcrop is crystalline basement of various granites, gneisses and pegmatite. The volcanic rocks on Jima side are referred to as Lower part of Jima volcanics comprising flood basalt with minor salics on the western, southwestern, eastern and southeastern part of the river catchment; especially on the high land. However, at the lowland part of the catchment along the Dedessa River, the outcrop is referred to as Alghe group comprising biotite and horn blende gneisses, granulite and migmatite with minor Meta-sedimentary gneisses. The volcanics are of Late Eocene- Late Oligocene age; where as the gneisses are of Archean age. The volcanic rocks (basaltic lava flow) in Bedele area is referred to as Makonnen basalt comprising flood basalts. It directly overlies the crystalline basement that shows the unconformable relation for the two outcrops. It is Oligocene-Miocene age. Similarly, Arjo area is comprised by such flood basalts of the so-called Makonnen basalt. Based on the Investigations made in the area, various aquifer set up exist The main aquifers are weathered and /or fractured basaltic lava (lows and other acidic volcanic rocks such as rhyolite and Ignimbrite. The aquifers of volcanic origin have both confined and unconfined character: for example the volcanic rocks In Agaro area show both characters. The confining layer in this particular area is highly weathered volcanic ash of clay size revealed from existing welt drilling data There are aquifers that are attributed to sect 7 especially alluvial sediments along over valley and streams, and colluvial sediment " ' mountains and escarpment, tn addition to these, there are also minor aquifers attributedT weathered basement recks (granges and granitic pegmatalites). This last aqu.fer tvnos t, ....... Si9™licance to their limited areal extent and limited aquifer The presence of thermal springs, cold groundwater and saline springs in the„ diversification ol the hydrogeological set up of the river catchment tk and weathered basemen. recks origtn are on conbned. tn Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd. Sh °WS 'he 6ArJo-Dedessa Irrigation Project Hydrogeological investigations May 2007 diversification, geological structures mainly faults play significant role on groundwater dynamics and quality of the area. Within Dedessa River valley, deep penetration of groundwater may be hindered by the underlying massive basement crystalline rocks except where they are controlled by geological structures as revealed by the presence of thermal springs in the river valley. The volcanic ash a nd clay form the confining I ayer for water-bearing formation (aquifer). Aquifer in Agaro area can be mentioned as an example. The volcanic lava flows are highly weathered (fractured) enhancing the infiltration of precipitation (mainly rainfall) for groundwater recharge. Groundwater recharge in the area is very maximal due to different reasons; among them are the high precipitation, dense vegetation cover, and highly weathered and/or fractured volcanic lava flows. The main groundwater recharge of the area is the SE, SW and the N E part of the river catchment. The pyroclastic falls of mainly volcanic ash composition is found at most parts of the river catchment such as in Setema and Atnago area. The intercalations of the volcanic ash with fractured and/or weathered volcanic lava flows cause the emergency of many springs in the river catchment of the area. However, the presences of thermal springs with in the Dedessa river valley are attributed mainly to geological structures, faults. The physicochemical characteristics of the thermal springs highly vary from upstream to down stream along Dedessa River within the project area Although it needs further investigation to verify the physico-chemical variation, the longer residence time of rock-water interaction while groundwater flows from upstream to down stream could be one possible reason. The topography of the area along with the prevailing hydro-meteorological conditions favor. the existence of well demarcated groundwater recharge and discharge area 2.2 Hydrogeologic units Groundwater occurrence, movement and quality are mainly governed b th hydrogeologic units. The phrase hydrogeologic unit refers to the rocks < . . r__ ii j_______ x i . avuio ’ * eX'Stln9 unconsolidatedArjo Dedessa Irrigation Project Hydrogeological investigations May 2007 The hydrogeologic units in Dedessa river catchment have been categorized into the following units. They have been shown on map available at Fig. 2.1 and have been discussed here under in brief. 2.2 .1 Fractured and/or weathered volcanic rocks This comprises basaltic lava flows, acidic lava flows and falls such as ignmbrites and pyroclastic falls. In this category of hydrogeologic unit, secondary porosities such as fractures produced due to weathering and geological structures play immeasurable role as compared to the primary porosity/permeability. The areal coverage of this hydrogeologic 2 unit in Dedessa river catchment is 8,189.35 Km (79.56%). 2.2.2 Alluvial sediments As t he n ame implies t hese are c oncentrated a long r ivers a nd s treams; a nd it c omprises various sediments ranging in size from clay through sand and gravel to boulders. The areal 2 coverage of this hydrogeologic unit in Dedessa river catchment is 1651 05 Km (16 04%). 2.2.3 Delluvial sediments These sediments exist at the transition zone from the mountains/or plateaus to the river valley They are derived from down slope moving earth materials from mountains mainly due to gravitational force From hydrogeological point of view, there are no as such demarcated properties between alluvial sediments and delluvials. However for the convenience of description, this hydrogeolog.c unit has been described separately' Dellu J 2 sediments with in the project area have coverage of 452.91 Km (4 40 %) 2.3 Inventory and well data in order Io undertake detailed investigation of the groundwater of the area, water supply ■hemes have been inventoried and their geographical locations have been identified using GPS Borehole data have been collected for detailed analysis of hydrodynamic parameters though complete well data are not available in the area Some of the measurements that have been undertaken for water supply sources during the field survey are physical parameters of water quality by using field test kits such as TDS, PH and temperature meter Water Works Design & Supervision Enterprise " 8 In Association with Intercontinental Consultants and Technocrats Pvt LtdArjo-Dedessa Irrigation Project Hydrogeological investigations May 2007 In addition to these primary data, secondary data have also been collected on both water quality a nd other Well d ata. S atellite images a nd a erial p hotos h ave b een i nterpreted t o identify geological structures and other lithological boundary demarcation that have been verified by field work. 2.4 Hydrodynamic parameters of aquifers As it has been mentioned previously, the main aquifers in Arjo-Dedessa project area are fractured and/or weathered volcanic lava flows (basaltic and acidic lava flows) and sediments (alluvial and colluvial).The boreholes in the fractured volcanic rocks and sediments are either with partial well data or totally without well data. Table 2.1 shows the boreholes drilled previously in the study area and their depths: Table 2. l Details of boreholes in the study area No Well No PA/village Depth (m) SWL 1 Well 1 Metta 55.75 16 2 Well 2 Metta 43.4 12 3 Well 3 Metta 43.5 17 4 HT-2 Qollo Siri 27 5 HT-6 Chilalo Bildima 72 6 HT-7 Chafe Anani 57 7 Well 1 Chuli 52 1.3 8 Well 2 Chuli 41 1.7 9 Well 3 Chuli 26 2.1 10 Well 4 Chuli 30 2.1 11 Well 5 Chuli 25.5 1.5 12 Well 6 Chuli 42.5 2.2 13 Mada Talila Bakalcha Biftu 52 14 Iftu Biftu Bakalcha Biftu 35.55 Water Works Design & Supervision Enterorise to Asooelalo. with c.nsu,Unt5 „„ TXXU 9Fig. 2-1 A map showing hydrogeologic units of Arjo-Dedessa river catchment 0 80000 Meters 1(7X00 150000 xcnoo ;*nooo Xco*-- itoocrr 1 osccoo Hkx.00 tSCC’.V ecaxz ’Vxuv lUMXtf*Arjo Dedessa Irrigation Project Hydrogeological investigations 3. GROUNDWATER POTENTIAL 3.1 Groundwater recharge estimation May 2007 In order to develop groundwater of an area, its potential including its annual replenishment, which is usually referred to as groundwater recharge, has to be known. Groundwater recharge of an area can be estimated based on different approaches. One of the best approaches is through water balance method. In order to employ this method of groundwater potential estimation, the necessary data have been acquired for analysis. In supplementary to this method, base flow analysis for River/stream flow (Dedessa River) have been undertaken to derive some coefficients for water balance. Hence, in the groundwater potential estimation of Dedessa River catchment both methods have been employed in order to come up with concrete result as much as possible. 3.1.1 Base flow analysis In order to employ base flow analysis approach for groundwater recharge estimation, the monthly discharge of Dedessa River from 1961 - 2002 for a total of 15 years have been used. The river flow data is not consecutive due to some missing data for some years. Accordingly, the mean monthly minimum flow of Arjo-Dedessa on annual base is shown in Table 3.1. The difference between the total flow and the Minimum monthly flow is supposed to be the surface runoff. Accordingly, the surface runoff for Dedessa river catchment at the gauged station is 2,105,796,874 m3. Where as the total minimum monthly flow of the river is 1 962 092,938 m3 as shown in the Table 3.1. The basic assumption in deriving groundwater recharge from base flow analysis is that the monthly minimum stream discharge is equal to the base flow. This approach has been mentioned by Wundt (1978) that the monthly minimum stream discharge best approximates the base flow, especially, for humid climate. Therefore the base flow that is supposed to correspond to the groundwater recharge is found to be 196.6mm. This value is obtained by dividing 1,962,092,938m3 by the area of the gauged catchments, which is 9,981 km . This amount of ground water recharge is very Water Works Design & Supervision Enterprise In Association with intercontinental Consultants and Technocrats Pvt Ltd. 2Arjo Dedessa Irrigation Project Hydrogeological investigations May 2007 minimal as it amounts to only about 13.53% of the total annual precipitation of the area which is 1452.9mm. Furthermore, based on the same method, the surface runoff of the River catchment has been estimated as the difference between the total river flow of Dedessa and the minimum flow on annual base and works out to 2,105,796,874 m3 that is attributed to surface runoff. This value is used to derive the run off coefficient of the river catchment to asses the surface run off for the entire Dedessa catchment that will be used in the water balance approach of the groundwater recharge estimation in the next section. Table 3.1 Monthly total flow, and Minimum flow of Dedessa river near Arjo Parameters Months Qtot______________ M^month ___________Qmln ___________________ Diffe rence M’/se c 1764 12.4 10.44 I 47238048 ‘ 29994209 * 27973924 M’/sec M3/month 4,473 2.25 0.966 M’/se M /month _c 11980483 5443200 2587334 13.16 35257565 1564 40527302 4 557 11811744 29.14 78052326 98.47 263 37 423.39 343.82 218.67 58.32 35 65 255236832 ; 705408958 2134009026 891191981 585697513 177074554 95485139 10.364 27758938 45.433 117762336 137.365 ; 367918416 ! 220.652 217.777 58.377 26.258 13.792 590994317. 564477984 156356957 68060736 J36940493 ♦ 53.04 126 202.74 126 05 160.3 I 42.06 ’ 21 86 " 24551009 25386589 28715558 50293388 _137474496 337490542 543014709 326713997 429340556 u 1O9O13818 58544646 4.067,889,811 Qi0(= T __ __________ , , 2,105,796,874 T total monthly discharge (m ). Min Q = Minimum monthly discharge (fvF/S), Diff = difference between the total monthly discharge 3.1.2 Water balance method By water balance it is meant equating or balancing the amount of water inflowing and out flowing for a given system, such as hydrogeologic system, over a given duration for a given area Hence it is a dynamic system, (Delay, 1 997). The hydrogeologic system can be a drainage basin/or catchment, groundwater basin, soil layer, or any surface water reservoir (natural or artificial). Water balance is a valuable tool in the analysis of water availability in a region. The method can be employed for different purposes: computation of • ' "" ------------- Water Works Design & Supervision Enterprise -■ groundwater recharge, evapo- In Association with Intorrnntu—- _ _ —a-iUVVJL pl ItSC In Association with Intercontinental Consultants and Technocrats Pvt Ltd 12Arjo Dedessa Irrigation Project Hydrogeological investigations May 2007 transpiration, continuous record of soil moisture, and stream flow from a meteorological record and a few observations on the soil and vegetation, seasonal and geographic patterns of irrigation demand, the flux of water to lakes, prediction of human effect on hydrologic cycle. (Leopold and Dunne, 1978). In this study the water balance method is aimed at estimation of groundwater recharge. The basic assumption that is considered in this case is that the surface water divide coincides with the subsurface drainage basin. Accordingly, other than the water that is percolated within the limit of the surface water divide, there is no inter-aquifer flow (inflow or out flow) of groundwater. The basic equation of water balance is: Inflow = outflow +AS Where AS is change in storage For the study area, the main inflow component is precipitation, but the outflow components are evapotranspiration and surface runoff assuming all other components such as water abstraction by human for other purposes to be negligible. Besides this, the change in storage, can be considered to be zero if the water balance is made by taking water year /or hydrologic year. Hence, the value of AS will be negligible/or zero since the calculation is to be made on annual basis. Since rainfall record can be obtained from meteorological stations in the area, the mam task left is to estimate /or calculate the potential evapo-transpiration from which the Actual Evapotranspiration (AET) can be derived for the catchment. In addition to this the surface runoff has also to be estimated/or calculated since there is no actual measurement of Z component in the study area. The surface runoff for Arjo- Dedessa river catchment has been derived (estimated! follows: 1 1 The monthly minimum stream flow has been considered as a base flow as mentioned previously' and this value has been subtracted from the monthly total runoff to get the component that forms over land flow from which the runoff coefficient, Rc, is calculated. Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd. 13Arjo-Dedessa Irrigation Project Hydrogeological investigations Rc = D/PA Where: Rc= Runoff coefficient D = overland flow = 2,105,796,874 m3 P = annual precipitation =1452.9 mm = 1.452m May 2007 3 2 2 3 2 A = drainage area = 9,981.000.000 m (drainage area at the river gauging station. But this does not mean that the total drainage area of the studied basin). Hence, Rc = 2.105.796.874 m /1.4529 m x 9.981.000.000 m = 0.1453 This Runoff coefficient is used to estimate the surface runoff for the river basin (Dedessa River) under study. In order to estimate the surface runoff of Dedessa area, the mean annual precipitation 1452 9mm has been used. Hence, the surface runoff for the entire Dedessa River catchment becomes 0.1452 X 1.452m X 10,293,303,358.08 m = 2,170,141,264.31 m . Thus the surface runoff works out to 210.83mm This value is only about 14.51% of the total annual precipitation in the area. Note that the total area of the studied river catchment at the out let of the command 2 area is 10,293,303,358.08 m . By assuming, the coincidence of groundwater basin with that of surface water divide and also by assuming that there is no artificial or natural intra-basin subsurface or surface flow the groundwater recharge of Dedessa river catchment can be estimated as follows- GWr = P - (Sr + AET) Where. GWr = Groundwater recharge P = Annual precipitation= 1452.9mm AET = Actual Evapo-transpiration Sr = Surface runoff = 210.83mm The Actual Evapotranspiration, (AET), can be estimated based on different methods; one of th em is the empirical Turc method Turc method is represented by the following formula: Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd 14Arjo Dedessa irrigation Project Hydrogeological Investigations May 2007 2 AET = P/V[0.9 + (p/L) ] Where, P = annual mean precipitation in mm - 1452.9mm T = annual mean air temperature in C - 20 L = 300 + 25T + 0.05T3 [mm] = 1200mm Hence, for Dedessa river catchment, AET = 944.57mm Therefore, in order to estimate groundwater recharge for Dedessa River catchment, the value (AET = 944.57mm) obtained by Turc method is used in the water balance method of groundwater recharge estimation. Hence, groundwater recharge in the Dedessa river catchment becomes as follows: GWr = P - (Sr + AET) = 1452.9mm - (944.57+ 210.83) mm = 297.5mm This value is about 20.48% of the total annual precipitation in the area. This high recharge rate may be attributed possibly to the relatively better vegetation cover and to the highly fractured rock prevailing in the area. Finally, an average value from the two methods, the base flow analysis method (196.6mm) and the water balance method (297.5mm), which is 247.05 mm, has to be used as annual groundwater recharge of the area. This value is about 17% of the total annual precipitation in the area. ISArjo-Dedessa Irrigation Project Hydrogeological investigations 4. WATER QUALITY 4.1 Water samples May 2007 Natural water interacts with environment, and also it is affected by anthropogenic process changing its chemical, physical and biological constituents. The utilization of this water requires an understanding of such constituents. Hence, the water should meet certain quality standard that is set mainly based on its purpose in order to use it. Some important physical and chemical parameters have been determined for the water of the study area to compare its quality with certain standards set by different Organization such as WHO for specific water uses. Water samples from different sources have been taken for physicochemical and microbiological analysis based on the actual/existing geology, hydrogeology and geomorphology of the area. Accordingly, a total of thirteen samples have been taken from springs and Wells. Fig. 4.1 shows the location of the water sample points. All the samples have been submitted to the laboratory of WWDSE for analysis. In addition to these water samples collected during the field work, previously analyzed water quality by different institutions have been used for hydrogeological interpretation of the area. Among the collected water samples, four samples were taken from springs and nine were from boreholes. The numbers of samples have been determmed based on various conditions such as geological and hydrogeological setup of the area and availability of previously analyzed physico-chemical and microbiological data in the area Water Works Designi &S?perv^ionEnt er prise ' In Association with Intercontinental Consultants and Technocrats 16 Pvt Ltd.Fig. 4.1 A map showing water sample points in Arjo- Dedessa project area 0 40 Kj/ometersArjo-Dedessa Irrigation Project Hydrogeological investigations 4.2 Sampling techniques and analysis May 2007 A total of thirteen samples have been collected from different sources. One duplicate sample is collected from spring in order to see the reproducibility of the laboratory results. Natural water is sampled in view of carrying out various analyses on it. In order to undertake water quality analysis water samples have been collected for physicochemical analysis. The collected water samples were from ground water (springs and Wells) sources. The samples have been taken with one liter capacity plastic bottles. In order to compare some physicochemical parameters, some physical parameters such as TDS (Total Dissolved Solids), Temperature and PH have been measured at field in order to compare the result with that of Laboratory. 4.3 Pictorial representations of water quality analysis 4.3.1 Piper diagram The Piper diagram plots the major ions as percentages of milli-equivalents in two base triangles. The Piper trilinear diagram for water samples in Arjo- Dedessa is available at Fig. 4 2. The total cations and the total anions are set equal to 100% and the data points in the two triangles are projected onto an adjacent grid. This plot reveals useful properties and relationships for large sample groups. The main purpose of the Piper diagram is to show clustering of data points to indicate samples that have similar compositions. The Piper diagram can be used to plot all samples in the open database or selected sample groups. In addition, the symbols representing the sample values can be customized according to shape and color. Other options include individual multiplication factors for each selected ion to prevent data point accumulation along a base line. The highlighted sar^ I points indicate samples that are selected in the database and are also highlighted^ other open graphical displays. According to the water samples plotted in Piper t T diagram for Arjo-Dedessa area, samples can be categorized based on their cla t ' Ad-01, AD-10, AD-12 and AD-13 as one category; AD-02, AD-03 AD 04 AD 05 and AD-11 as second category; AD-07 and AD-03 as third category; and finally AD 03 fourth category. However, if we refine further the water type based composition, they can be categorized in to five categories 00 Chemical Water Works Design & Supervision Enterprise--------------------- In Association with Intercontinental Consultants and Technocrats Pvt Ltd 18Arjo Dedessa Irrigation Project Hydrogeological Investigations May 2007 • Na- HCO3 type (Sample AD-01, AD-07, AD-08, AD-10, AD-12 and AD-13). • Ca- HCO3 type (Samples AD- 02 and AD- 11) • Ca- Mg- HCO3 type (AD-03, AD- 06 and AD- 09) • Ca- Mg- Na- HCO3 type (Sample AD- 04) • Ca- Na- HCO3 type (Sample AD-06) The cation to anion ratio also varies for the different samples indicating various conditions of rock-water interaction. 4.3.2 Schoeller diagrams These semi-logarithmic diagrams were developed to represent major ion analyses in meq/l and to demonstrate different hydrochemical water types on the same diagram. This type of graphical representation has the advantage that unlike the trilinear diagrams, actual sample concentrations are displayed and compared. The Schoeller diagram in AquaChem can be used to plot all samples in the open database or selected sample groups only. Up to 10 different parameters can be included along the x-axis and the symbols representing the sample points can be customized according to shape and color. The highlighted lines indicate specific samples that are selected in the database and are also highlighted on all other open graphical displays. The Schoeller diagram for the water samples of Arjo- Dedessa area is available in Fig. 4-3. Water of similar source (type) shows a similarly shaped curve; where as water of different types show differently shaped curves. Accordingly, two major types of water can be identified from the graph; Calcium bicarbonate types (Samples AD-02, AD- 03, AD- 04, AD- 05, AD- 06, AD- 09 and AD- 11) and the sodium bicarbonate types (Samples AD- 01, AD- 07, Ad- 08, AD- 10, AD- 11 and AD- 13). 4.3.3 Stiff diagram The Stiff diagram method of water quality representation uses a scale for concentration of ions in meq/L along the x-axis. The ions are arranged along y-axis in such a way that the cations (Na*. Ca *, Mg *) are to the 22 left of the center of the plotting scale and the anions are to the right of it. It is shown for some of the analyzed samples in Fig.4 4. According •>-- 1940 40 20 SO4 O AC-01 □ ADO2 ♦ AC-03 * AC-04 X AC-05 ♦ AC-06 o AD-07 A AD-03 V AC-O9 * AD-10 X AD-11 ♦ AD-12 AC-13 ao « —'............................... \ X =» i • JO ♦ AC-06 • AD-12 - •- • 3) « ao « <o 20 •* ""**— 20 Ca Na-KHCO3 Fig 4-2 A map showing Piper trilinear diagram for water samples in Arjo- Dedessa area >Concentration (meq/1) Legend: AD-01 AD-02 -e - —M— —«----- - -e — -a- AD-03 AD-04 AD-05 AD-06 AD-07 AD-08 AD-09 AD-10 AD-11 AD-12 \ HCO3Na CI N»~------ Cl z1X X Ca HC03 HC03 Ca ✓ S04 Mg S04 Mg 1 T 1 C03 K CC3 i/ 10 5 AD- 02S Na 10 Ca - > Mg \l Cl HCC3 S04 C03 5 C -5 2.5 5 5 ~ AD- 03 1 K 5 25 25 AD- 04 5 3 AD- 05 3 Cl HC03 S04 C03 a Na Cl X1 \ Ca ‘ HC03 Mg V V; SO4 K 1 CO3 30 30 ’^D-071’ Fig 44 A map shwing Stiff diagram for water samples in Ago- Deaessa Project area (Concent. meq/L)X x Cl HCO3 K 1 C03 Na Ca Mg K J SO4 CO3 AD- 08 10 AD- 09 i 10 Cl HC03 SC4 C03 Na Ca Mg K Cl HCO3 SO4 CO3 to to 50 AD-11 Na x X \ I X Cl to Cl HCO3 S04 Ca Xs HCO3 to Mg SO4 I 'I/ CO3 K 1 CO3 I 40 40 40 20 AD- 13 20 40 IArjo Dedessa Irrigation Project Hydrogeological investigations 4.4 Agricultural/irrigation water quality May 2007 Agricultural suitability of water depends on crop type, climate, soil type, and amount of irrigation water use, (Davis 1966). The main parameters to be analyzed to evaluate irrigation water quality are Boron, Sodium hazard, and Salinity. These parameters affect plants either directly (e.g. by causing an adverse physiological effects) or indirectly (e.g by limiting plant root nutrient or moisture uptake). Salinity is best estimated based on Electrical Conductivity (EC) value. Other direct indicator of salinity is Total Dissolved Solids (TDS). The two parameters, TDS & EC are related by the following equation: TDS (mg/L) = 640 x EC (dS/m), where mg/L = milligram per litre, dS/m = deci Siemens per meter. According to U.S. Department of Agriculture, water with an EC greater than 4dS/m is considered as saline. Sodium hazard is assessed by the so-called Sodium Adsorption Ratio (SAR). It is caused by sodic water. Sodic water is water that has high sodium concentration relative to the concentration of calcium and magnesium. Water is said to be sodic if its SAR is greater than 12. SAR is calculated as follows: SAR= [Na*]No.5[Ca * + Mg *] Where, the concentration of each cation is expressed in meq/L. If the concentration is expressed in mmol/litre, SAR = [Na*]/ [Ca2* + Mg2*] According to Todd (1980 and references there in), the water quality evaluation for irrigation based on SAR and EC are as shown in Table 4.1. Table 4.1 SAR and EC values in terms of irrigation water suitability 22 Water class Excellent Good Fair r SAR < 10 10- 18 Poor 18- 26 >26 ------ Water class EC (ps/cm) Excellent Good Permissible Doubtful <250 250- 750 Unsuitable 750- 2000 2000- 3000 1dS/m = io fis/cin ---------- -------------------- — >3000— In order to evaluate water quality for irrigation from Salinity and Sodium hazard oi for Arjo-Dedessa area, the parameters have been measured and calculated aTd^ shown in Table 4-2. an theV are Water Works Design & SupervisionE^^ri 7----------------------------- ------ ------ - S In Association with Intercontinental Consuitants and Technocrats Pvt. LtdArjo-Dedessa Irrigation Project Hydrogeological investigations May 2007 Table 4.2 SAR and EC values for surface and groundwater in Arjo-Dedessa area -------------------- Sample code - --------------- AD-1 ----M---- AD-2 -------- AD-3 --------- AD-4 -------- AD-5 -------- AD-6 --A--D---7----- --AM AD AD-8 -9ADA-9D- 1A0DA-1M0 I [ "AAdD--1lZ1 Ad-12 AD-13 EC (ns/cm) 4^10 604 436 439 496 418 2660 2370 665 4450 515 3160 3160 SAR 38 4 0.7 04 0.7 0.5 1.6 128 10 8 04 37 1 0.4 21.6 21 6 According to SAR values obtained for the water samples, AD-01, AD-07, AD-10, AD-12 and AD-13 are all sodic water and AD-08 is slightly sodic, where as, the remaining water samples are all non sodic. From irrigation water quality point of view, they range from excellent quality to poor quality. But from salinity point of view, the quality varies from excellent to unsuitable; i.e., from 418 ^is/cm to 4450 ps/cm. In other words, it can be said the salinity ranges from medium salinity to very high salinity. Fig. 4.5 shows values of TDS and EC for different water samples in the project area. Figure 4-5 Electrical conductivity (EC) in ps/cm and Total Dissolved Solids (TDS) in mg/L for water samples in Arjo-Dedessa area —•— TDS(m&L) A EC (mcro SienYcm) This graph clearly indicates the extent of salinity for different water of for the EC and the TDS. Contour map of the TDS is available area For description one the water samples may be categorized 4 6 based on their Electric conductivity and TDS values Acc d __________________________________________ r in9ly’ seven samples (AD-02, 'nt° Pr °jeCt Cate9°ries Association with ■ot.rcootlo.oui Coosotaou aod tX ' c 1b Ud 24Arj o-Dedessa Irrigation Project Hydrogeological investigations May 2007 AD-03, AD-04, AD-05 and AD-06) have low salinity, four samples (AD-07, AD-08, AD-12 and AD-13) have high salinity ; and two samples (AD-01 and AD-10) are extremely saline. This qualitative description doesn’t follow the standard procedure of water quality classification based on TDS and/or EC, but it is simply for the sake of description. Water samples coded as AD-01, AD-10, AD-12 and AD-13 are all from springs; all other water samples are from boreholes (drilled shallow Wells). Hence, it is possible to conclude that even if they are all from groundwater, they are from different aquifers. The more saline water (having high TDS values) are mainly from weathered basement rocks (granite and granitic pegmatite), and deep-seated volcanic aquifers, especially along fault lines (e.g. thermal springs). 25□□2 Fig. 4-6 A map showing the contour for Total Dissolved Solids (TDS - mg/L) for Arjo- Dedessa Project area MW 0 i?W*fArjo Dedessa Irrigation Project Hydrogeological investigations 5.PIEZOMETERS OBSERVATION WELLS AND WELL FILED 5.1Distribution of Piezometers/Observation Wells May 2007 In order to monitor groundwater quality and quantity of the area both before and after the construction of the dam under investigation, a total of fourteen Piezometers/Observation wells have been proposed and their sites have been located. The geographic configuration/distribution of the piezometers/Observation wells is selected based on geology, hydrogeology, topography, groundwater flow direction, etc of the area. Since the depth of the piezometers to be constructed rarely exceeds 100 meters, PVC casing is recommendable. In some cases the existing well depth at the immediate down stream of the proposed dam axis are 50 - 70 meters depth Table 5.1 shows the geographical coordinates of the proposed piezometers Table 5.1 Locations of the Proposed Piezometers Geographical coordinates (UTM) Ser.No. Piezometer code Easting Northing Altitude (m) 1 Pao-1 241283 945079 1332 2 Pao-2 239578 942443 1348 3 Pad-3 +-x---- :------------- 239229 948568 1354 4 Pad‘4 232368 945622 1345 5 Pao-5 237407 951746 1391 6 Pad*6 228492 944575 1374 7 Pad-7 230198 952870 1386 8 P*d-8 225779 947133 1324 9 Pad-9 220119 954111 1341 10 Pad- 10 217677 951707 1319 11 Pad-11 217135 961437 1332 12 Pad 12 - 212716 952444 ----------------- _ 1354 13 Pad-13 214654 956087 1323 14 Pad" 14 213336 961320 1320 ----------------------- ------ ____ The construction of these piezometers shall follow the standard procedur site-specific conditions such as hydrogeological set up will also matter proposed Piezometers is available on the map shown in Fig 5.1 6 IOCa,IOn of the Water Works Design & Supervision EWnri^- - - - - - - - - - - - - - - - - - - - - - - in Association with Intercontinental Consultants and Technocrats Pvt Ltd ?Arjo Dedessa Irrigation Project Hydrogeological investigations 5.2 Future well field May 2007 The potential aquifers for groundwater storage in the area are basaltic lava flows with minor salics including rhyolite and ignimbrite, and alluvial deposits in the river valley of Dedessa. This can be verified by existing boreholes data in the area. For example, Borehole data in Agaro area show this situation. Well field sites on which detail geophysical investigation shall be undertaken have been identified based on geological, hydrogeological and geomorphological setting/or approaches. Test wells drilling and construction shall follow the detail geophysical investigation. 28WXm JdCOZ 3WOOO irxxui pcmoc > opc*«*<l P4axneU<»>‘Vdno<rij *♦» *■<«•< pcir» A*t»f River.’Swajr. ■ -'->v -.Vf kVama Boneya i.W»iOO TTw-mi) l(zto/i IXOXX5 Ljmu Seka ciSCVzj &X<O0Arjo Dedessa Irrigation Project Hydrogeological investigations May 2007 6.WATER LOGGING AND DRAINAGE 6.1 Topographic features and soil characteristics The undulating and rolling topography in upper part of the project area gradually acquires gentle slope of flat land in the bottom valley of Dedessa, especially the lower part where the command area becomes almost flat. This flat land is covered with sediments mainly of colluvial/delluvial and alluvial origin. This sediment is underlain mainly by basement rocks. The topography and land characteristics of the command area can be said to fall u nder level (0- 1%), nearly level (1- 2% slope), very gentle (2- 4% slope), and gentle (4- 6% slope), categories as about 35% of the command area falls under first two categories and about 23% of the command area falls under the last two categories. Though the command area is plain, it has a rolling topography and there are several small hills dispersed in the command. There are rising hills also on the outer boundaries of the command area on both banks of river Dedessa. The major part of the area is comprised of vertisol (47% of the command area) that has very low permeability. Next to vertisols are cambisols and luvisols covering 15% and 8.68% of the area respectively. Hence, this soil type hinders the infiltration of the most incoming rainfall during rainy season. On one hand this helps to restrain the rise of the groundwater table through reducing infiltration, on the other hand the plain nature of the land wouldn’t allow the surface run off to flow out easily. 6.2 Existing groundwater table Groundwater level in the project area varies from 2 to 20m b.g.l. |n the command area the groundwater table is 2 meters below surface during rainy season except in few exceptional cases of surface water logging. During dry season the groundwater table was found dee than 5 meters below natural ground surface. The rise of the groundwater table can h due to different natural conditions and man made activities. The application f A practice is the major human interferences for rise of groundwater table The lrr'9atl°n irrigation (drip, furrow, etc) that is practiced and the crops oronn^a » i_ • . / meU'°d °f m “u io bo qrown win determine the extent to which it may affect the rise in groundwater level of th uie 3T63. Water Works Design & Supervision Enternrisp — Id Association with Intercontinental Consultants and Technocrats P 3°Arjo-Dedessa Irrigation Project Hydrogeological investigations May 2007 6.3 Future groundwater table and recharge from irrigation Whenever there is a major irrigation project with continued and intensive irrigation activity, there is always an apprehension of rise of groundwater table. If the rise of the groundwater table is significant, and it continues unabated, it may cause serious adverse impact on the fertility of the land. Some of the factors that affect the rise of groundwater are: • Topographic features • Land characteristics • Natural drainage system • Intensity and amount of rainfall • Existing groundwater table • Soil characteristics • Crops and its water requirement • Seepage and other losses from canal system • Surface drainage system implemented and its effectiveness The estimated annual crop water requirement at primary canal head, for various crops to be cultivated in the command area of the proposed Arjo- Dedessa project comprises four set of values categorized under two phases each phase having two rotations. This has been shown in Table 6.1. Table 6.1 Annual gross crop water requirement at primary canal head Ser. No Phase Rotation GCWR (mm) 1 I I 987.40“ 2 I II 1086.14 3 II I 4 II 1311.47 II 1423 234 In order to assess groundwater recharge from irrigation water, the maximum Gross C rop Water Requirement (GCWR) in t he second □ ha^ nf , Va 'Ue °f *he Hiia&e or second rotation that 1423 234 mm/yr has been used. Therefore, the groundwater recharge from of irrigation has been estimated under two main situations as follows- 'S S aPPl'CatlOn Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd 31Arjo-Dedessa Irrigation Project Hydrogeological investigations May 2007 , therefore, may be neglected. Seepage loss to the groundwater from the canals (main canals tertiary canals) has also been estimated. According to United States (U.S.B.R.), seepage loss from unlined irrigation canal is 1.5 m3/sec meter of wetted area for clay and clay loam soils. Based on this from Arjo- Dedessa irrigation canal is shown in Table 6.2 and 6 3 1. According to groundwater recharge estimation made in this report, out of the total annual precipitation in the area, only 17% is going for recharging the groundwater. If the same scenario is considered, the annual groundwater recharge from the application of irrigation in the command area becomes 241.95 mm. This value is a crude estimation since various factors among which the irrigation method can affects the groundwater recharge. 2. Along with other crops, cultivation of paddy has been proposed in the command area. Paddy is the only crop that requires constant standing water in the field for its growth and development. Thus paddy cultivation results into percolation loss, and only that quantity of water which is lost through percolation has the chance and tendency of reaching groundwater. It may be noted that about 330 mm of water is estimated to be lost through percolation, and only this quantity of water has the scope of reaching groundwater, which may add to the rise of the groundwater The intensity of paddy is only 30% in phase- I, which will increase finally to 45% in phase- II. Considering the entire command on average, the annual contributions of irrigation water to the groundwater would be 99mm in the Phase- I, which will increase to 148.5 mm under phase- II. Regarding other crops, they are all dry irrigated i.e., no standing water is required The irrigation water applied to the field in case of all other crops except paddy will be contained as soil moisture within the root zone. Very small amount of water, which will be lost below the root zone, will reach the groundwater. Other losses will be in form of surface runoff which will be taken care by surface drainage system. As such the addition to groundwater due to irrigation of all other crops except paddy may be considered verv nPmi k, y "egnQiole and secondary canals and Bureau of Reclamation Per one million square approaches, seepage loss Water Works Design &Super^l^^ —-- - - - - - - - - - - - - - - - - - - - - - - - - _ tn Association with Intercontinental Consultants and Technocrats P 32Arjo Dedessa Irrigation Project for Ario- Dedessa irrigation canal 2 Area (m ) Total length (m) Total Area Canal category Estimation of wetted a Average wetted perimeter 2 (m /m) Right Left Right Main canal 87115 10.211 42.800 00 Secondary canal Tertiary canal 2.795 2.795 1 49.370.00 199.464.00 47.190.00 239,100.00 137.989 00 203.453.00 836,651.05 the total area has been considered for the main canal from unlined Arjo- Dedessa irrigation canal Table 6.3 Seepage loss f T No Command area (wing) 2 Wetted area of Canal (m ) Main canal Secondary canal Tertiary canal Total wetted 2 area (m ) Total seepage loss (mm) 279.639.00 203.453.00 621,081.00 1 Right Bank Left Bank "j 460,873.00 137\989?0d" 'm896?05 243,882 00 836.651 05 2 3 7 Total area (m ) 740,512.00 269,885.05 447.335.00 226.26 z Total Seepage (ST 23.320,796.31 e seepage loss calculation from the Main canal, only 75%. of the total area has been considered. The duration of the seepage loss is considered to be eight months (October - nd twenty four hours a day for the main canal; where as for six months of twenty four for secondary and tertiary canal. The command area on which the seepage loss has averaged out is the gross command area, i.e., 17,825 hectares (178, 250, 000 m ), P the total seepage loss of 40,330,960.80 n, is spread in the gross command area, which gave a„„noavpveraioayce seepaqe loss of 226.26mm from the irrigation canal. 2 “ Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd. 33Arjo-Dedessa Irrigation Project Hydrogeological in vestigations May 2007 Therefore, the total annual groundwater recharge from the application of irrigation becomes the sum of the seepage loss from the canals (226.26 mm) and from the paddy irrigation (148.5 mm) that is 374.76 mm. Although detail aquifer and soil sampling and analysis is required to come up with actual result of the porosity, its value has been estimated to be 35% in the command area by considering a range from clay to sand soils. This parameter will be used to estimate groundwater level rise due to the application of irrigation. Finally, by knowing the groundwater recharge from the application of irrigation, and the porosity of the aquifer and the soil materials above it, the extent of the groundwater level rise due to the application of irrigation has been estimated under different scenarios as follows: Scenario I: No groundwater flows out of the catchment (stagnant condition) Annual groundwater recharge from application of irrigation, GR = 241 95mm Effective porosity of aquifer (sand) in command area, n = 0.35 (35%) e Groundwater level rise due to application of irrigation, GWLr = GR/n =241,95mm/0.35 = 0,691 m. e However, it should be noted that groundwater is always in a dynamic condition; hence the stagnant groundwater condition never prevails in the area. Therefore, the stated value of groundwater level rise (0.691m) will never happen. Scenario II: Groundwater flows out of the catchment (dynamic system) Annual groundwater recharge from application of irrigation, GR = 241 95mm Effective porosity of aquifer (sand) in command area, n = 0.35 (35%) e According to base flow separation method, the ratio of groundwater y unuwater outflow from the entire river catchment to the groundwater recharge of the catchment from precipitation i Hence, the remaining 20.42% of the groundwater recharge contributes to 0 3 6' rise. Similarly, if we apply such dynamicity to the groundwater recharge from ^^ '^ 'e* application, the groundwater outflow from the irrigation application becnm 'rr'9atlon Water °mes 192.54 mm. t — Water Works Design & Supervision Enterprise tn Association with Intercontinental Consultants and Technocrats Pvt. Ltd. 34ArJo Dedessa Irrigation Project Hydrogeological Investigations May 2007 Hence, if we reduce this amount from the recharge due to the application of irrigatio mentioned above (241.95mm), the net recharge that contributes to the groundwater level rise becomes only 49.4mm. Therefore, under this scenario the groundwater level rise due to the application of irrigation will be: Groundwater level rise due to application of irrigation. GWLr =GR/ne = 49.4 mm/0.35 = 0,141m. Scenario III: According to the paddy cultivation and seepage loss from canals, the annual groundwater recharge from the application of irrigation is 374.76 mm as mentioned before. If this is the case, the groundwater level rise due to the application of irrigation under stagnant groundwater condition becomes: Groundwater level rise due to application of irrigation, GWLr = GR/n =374.74 mm/0.35 = e 1070.74mm= 1.07m. Scenario IV: (Scenario III under dynamic condition): This Scenario assumes that groundwater is continuously flowing out of the catchment. Hence, only 20.42% (76.53 mm) of the groundwater recharge from irrigation water will contribute to the groundwater level rise. Therefore, the groundwater level rise under this Scenario becomes, GWLr = GR/n = 76.53 mm/0.35 = 218.66mm = 0.219m, In conclusion, the assumption of stagnant groundwater condition Scenarios (scenario I and III), over estimates the groundwater level rise due to the application of irrigation Because it assumes static/or stagnant groundwater condition that is not the vi me case in reality since groundwater is usually in a dynamic condition. The second . according to this Q that works best is Scenario IV. Hence, the annual groundwater ...... However, it has to be noted that the existing soil in the command area is mainly clay and loam soils as revealed from soil survey (sampling and analysis) under the — • the same projectArjo-Dedessa Irrigation Project Hydrogeological investigations May 2007 The s oil h as an a verage hydraulic conductivity o f 0.0000056 m /s, i .e. 0.482 m/day. T his value is very small inhibiting the infiltration of any water (precipitation or irrigation) to Groundwater. Hence, the contribution of groundwater recharge from the application of irrigation should be less than the amount stated here. Therefore, the groundwater level rise due to the application of irrigation cannot exceed 0.219m/year. Another factor that can reduce the contribution of irrigation application to groundwater recharge is the presence of number of creeks that are transversal to the trend of the command area and Dedessa River. Some infiltrated water from the irrigation application will come out as regeneration through the creeks before reaching the groundwater table. Profile across some creeks and Dedessa river in the command area is available in Fig. 6.1 (a, b, c, d and e). The lines along which the profiles have been taken are also shown in the map Fig. 6.2. Although there is no well documented well completion data in the command area, the depth to groundwater in the area is below 5 meters during dry seasons except in some creeks such as Chuli area (eastern part of command area) where the water table is about 2 meters below ground surface. Only few boreholes and their data exist in the Dedessa River valley of project area since it is inhabited mainly through resettlements only 2- 4 years ago Hence, construction of contour map depicting depth to groundwater is hardly possible under such data limitation since they are entirely constructed for emergency purposes 36From Pos: 232335.077, 944187.179 fig 6 f A map showmg praties atong dfoeni ires in file commend area a) Prufie from upstream to downstream on fed bent ofDedessa river To Pos: 213587.927, 956965.088 1380 m 1370 m i 15.0 km 20.0 kmFrom Pos: 219184.091. 943954.006 To Pos: 226412.470. 954446.814From Pos: 223707.657, 939756.8B3 To Pos: 230189.880, 953187.677 d)PrvUe wross Oedessi river from Id Mt to right M 1 400 m 1375 m 1350 m 1325 mM&?$ 1300 m r—- •----'~ / L______________________________ 2.5 km —*— 5.0 km ■ 10.0 km 12.5 km 14.99 kmFrom Pos: 210789.844, 952208.348 e) Prtfie xrcm fedesst river hm ti bri to right bvi To Pos: 218531.206, 957198.261Fig. 6.2 A map showing lines of profiles in the command area 210000 21(000 220CCC 225000 230000 235000 245000 coxoo S OS5COO Legend Profile line Dedessa river CD Command area *t«00 / — v- D 10000 o 10000 Meter*Arjo Dedessa Irrigation Project Hydrogeological investigations May 2007 7. SA LINITY AND SODICITY Sa linity of soils/water can be defined in terms of electr ical conductivity. Particularly for soils it i s the e lectrical conductivity of the s at uration ex tract. How ever, sodicity is defined in terms of exchangeable sodium percentage. Salinity may be categorized in to two based on its sources: primary (inherent) salinity and secondary salinity. Primary (inherent) salinity is derived from the weathering/degradation of primary rocks/minerals. It usually occurs when evaporation exceeds precipitation. Where as secondary salinity is derived from the upward movement of salts from saline groundwater through capillary size under the situation of in adequate leaching. This situation happens mainly under shallow groundwater. Mass flow to the soil surface through capillary rise is known to cease when the water table is below 2 meters in a clay and silty clay; where as the same value is 1.6 meters in coarse textured soil. Water and soil salinity occur due to different reasons. Among them are over irrigation that causes groundwater level rise due to in appropriate provision of drainage and/or crop water requirement calculation, poor method of irrigation, capillary rise of groundwater due to naturally high groundwater level below surface, etc. When such raised groundwater level is subjected to evaporation loss, the chemical constituents of the water will be left over and becomes concentrated on the surface leading to soil and/or water salinity. The leaching of some existing nutrients in soil is also the potential source of salinity of water and soil in irrigation. In order to assess the possibility of salinity for the project area in the future, data have been collected and have been evaluated. Among them are the existing groundwater quality (physicochemical characteristics of groundwater), and soil chemistry. Other Parameters that have been given emphasis here is the meteorological parameters that cause high evapotranspiration. However, the high rate of precipitation (rainfall) in the area can counteract the problem by leaching the highly soluble salts such as chlorides, sulphates and carbonate salts. The distribution of relatively saline water is sporadic in the area It is highl basement (crystalline) rocks and thermal springs. Cold groundwate dSS°Ciated with volcanic rocks in the area has very low TDS; and hence vnn, i™. ' er7 low salinity, a man cr Total Dissolved Solids of the project area is available at Fig 45 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd , or'9lna,e^ from p snowing 39Arjo-Dedessa Irrigation Project Hydrogeological in vestigati ons May 2007 — Hence, the hazard soil/wat er sa linity during the design period of the pr oject can be controlled naturally (through high precipitation and topogra phy of the area) or artifici ally through appropriate irrigation water management.Arjo Dedessa Irrigation Project Hydrogeological investigations May 2007 . 8. EXSITING AND FUTURE PROSPECT OF GROUNDWATER 8.1 Existing groundwater development Presently, the majority of the Woredas’ capital town and the rural community in the river catchment are supplied potable water from groundwater, either through borehole construction or from spring development with the exception of Bedele town that get water from Dabana River through the treatment of raw water. The yield of groundwater from some volcanic lava flow shows very promising result both for current and future water supply from groundwater for different purposes. Can be mentioned as examples are boreholes for Agaro town where the yield is about 30lit/sec from a single borehole. Furthermore, the aquifer in this particular area has multilayer system attributing to a confined aquifer. Here, it is vital to discuss Agaro town as an example. The town is entirely supplied water from groundwater through boreholes. There are three new boreholes and two old boreholes. Among these boreholes, four boreholes are currently functional, one from the old and three of the new boreholes. In addition to this, the Quaternary sediments in the river valley are the potential aquifers for groundwater development, particularly shallow groundwater. Other Woreda towns that are supplied potable water from groundwater are Arjo Atnago Gatira and Atnago. 8 2 Future groundwater prospect The existing geologica. ml, eteorological, hydrogeological and geomorphological conditions catchment indicate there are areas that can be developed in light of groundwater 10 the nVer water supply purposes. Accordingly, potential well field sites have been identified f inorovardreioruto develop grounmowdwaiac te■r These identified well field sites have to be verified based I investigations and test well drilling before being entirely developed. The on 96 likelv limitation in me iuiunyroundwater development in the area is not the quantity but the . ,ho fllture quality (relatively highiron concentration). The map of potential groundwater areas for 7 future desert Is available al F,g. 8.1 Water Works Design & Supervision Enterprise —~~~- - - - - - - - , hinh Io Association with Intercontinental Consultants and Technocrats Pvt Ltd 4'I Fig. 8-1 A map showing Groundwater potential areas for future development 0 80000 Meters 154X00 200000 1190000 1100000 River/Stream 1050000 lOCOCOO Piopuwtd PMZon>el«i&MaiiitQ(rg «*«lte 1300000 IOOOOOG 95000C 8SOTOO 500000 •00000 750000 xxjoro *00000I I DATE DUE BORROWER'S NAME AUTHOR TITLE CALL NO. EDITION VOLUME CAcc. NO.
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