<h'1 -8 Acc~^ IKE FEDERAL DEMOCRATIC REPIRUC IF 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 J a t 10^^ WATER WORKS DESIGN & SUPERVISION ENTERPRISE IN ASSOCIATION WITH INTTRCONTIMf NTA! CONSOITANTS AND HCHN9CRATS INDIA PVT LTD I’0 Box 2561 Addis Ababa Ethiopia Tel (251)1 614501/6*1189U Fax (1251)1 6l5171E-inail w w d s c alclccom net clARJO-DEDESSA IRRIGATION PROJECT FEASIBILITY STUDY REPORT CONTENTS OF THE REPORT SERIAL NO. 1 2 3 VOLUME NO. PARTICULARS EXECUTIVE SUMMARY MAIN REPORT Pan I - Report Part II - Maps & Drawings ANNEXURES VOLUME -1 SURVEY AND INVETIGATION (ANNEXURES - 1 to 3) 4 Volume -1 (a) Topographic Survey, Geomorphological Studies & Geological & Geotechnical Investigation Part l - Report 5 Volume -1 (b) Part II - Appendices 6 VOLUME -II NATURAL RESOURCES (ANNEXURES - 4 to 6) Forestry. Energy & Catchment Development Plan VOLUME - III WATER RESOURCES (ANNEXURES - 7 to 11) Volume - III (a) Meteorological & Hydrological & Hydrogeological Studies Dam & Appurtenant Works Part I - Report 8 Volume - III (b) 9 10 Volume-III (c) 11 12 Volume - III (d) 13 Part II - Drawings irrigation & Drainage Part I - Report Part II - Drawings Hydraulic Structures Part I - Report Part II - Drawings VOLUME IV AGRICUTLRUE (ANNEXURES - 12 to 18) 14 Volume - IV (a) Soil Survey & Land Evaluation 15 Volume - IV (b) Agricultural Planning 16 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 LIST OF TABLES Ill LIST OF ANNEXE RE-................................................ LIST OF FIGL RES 1. INTRODUCTION................................................................................... --—1 I I The Nile Basis .... 1.2 abbay Basin 1 I 3 The dedessa Catchments-....................... ....................................................................... 3 2. REVIEW OF PREVIOUS STUDIES-5 2 I LaHMAYER 1962 STUDY 5 2.2 Land and Water Resources of the Blue Nile Basin Ethiopia 5 23 Country wide Master Plan studies - EVDSA'WAPCOS (1988-90) .................................................... 8 2 4 STUDY BY BCEOM - IN ASSOCIATION WITH ISL AND BRG 1999 2 5 Study by ministry of Water resourcesfor Lower Dedessa (2001; 9 15 2.o Utility of Earlier Studies....................................................................................................................... 16 3. 3 l Climatological Data.................................................................................................................. I5 6 7 8 3.2. Rainfall......................................................................................................................................- 17 3.3 River Discharge............................................................................................................................. 17 3 4 SedmentData.................................................................................................................................. 18 4. ESTIMATION OF REFERENCE EVAPOTRANSPIRATION 4.1 Introduction...................................................................................................................................... 19 4.2 Meteorological Data............................................................................................................ ................. 20 4.2.1 Meteorological Observation Stations 20 4 2.2 Air temperature.................................................................................................................. 21 4.2.3 Air humidity 22 4.2.4 Wind speed............................................................................................................................................ 23 4 2 5 Solar radiation.......................................................................... ........................................... 23 4 3 Penman-Monteith Arjo Didesa Project Area Arjo Dedessa Project Area 5. RAINFALL ANALYSIS 5 I Introduction32 5.2 Rainfall Internal and External Consistency32 53 Estimation of Rainfall Reliability Level 33 5 4 Estimation of Maximum Rainfall Frequencies 6. MONTHLY STREAMFLOW ANALYSIS Equation24 JO .34 6.1 Hydrological Observ ation Stations............................................................................... 6.2 Extension of records 6 3 Synthetic flows........................................................................................’’ 7 ESTIMATION OF FLOODS FOR UNGaUGED CATCHMENTS 7 1 Rational Method.............................................................................................. 7 2 SCS METHOD 7.3 Transferring Gauged Data 7 4 Estimation of Weighted average* 7.5 Synder method of Constructing Synthetic Hydrograph 8 FLOOD FREQUENCY ANALYSIS _____________________________________________________ ____________________________ _______ 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 INTRODUCTION 8 2 Estimation of Probability Weighted Moments .. May 2007 59 60 8 3 Generalized Extreme v alue Distrjbl tion................................................................................... 61 8 4 Log-Logistic Distribution ..................................................................................................................... ol 8 5 Regionally a veraged quantiles.......................................................................................................... 62 8 6 Choice of Distribution ...........................................................................................................................63 9. PROBABLE maximum flood 10 SEDIMENT ANALYSIS 10 1 Estimation of Sediment yield............... 10.2 Distribution of sediment in the reservoir ................................................................................ 70 il. Water QUALITY............. 12. 65 69 o9 73 12.1 Synthetic Hydrograph ........................—............................................................................................. 75 12 2 Flood Routing Through the Reservoir............................................................................................... 75 i 2.3 Routed Design F_ood at the Coffer Dam............................................................................................78 13. RESERVOIR SIMULATION 14. DEDESSA SUB-BASIN MODELING.......... 87 91 14 i Modelinc for arjo Dedessa dam for irrigation ................................... ...... -............................................ 91 14 2 The sub basin modeling....................................................... -........................................................................ 92 /4.2 / Power Generation tn Dedessa Dam.......................................................................... -.......................... 93 /4.2.2 Optimal Power Generation ............................................................... ............ ................................... 94 J4.2.3 Reduction inflows at Dedessa Suo-oasin ........................................................................ ................. 96 14 2 4 Conclusions ...... ........ .......................... ................................................... .... 15. RECOMMENDATIONS ON TRAINING NEEDS REFERENCES 96 II Water Works Design & Supervision Enterprise Id Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 LIST OF TABLES Table i i Break up of Abbay Basin Area.......................................................................................... 4 Table 4 1 Table Details of meteorological Observation Stations located in and around the PROJECT area .................................................................................................... 26 Table 4 2 Types of Climatic Data available at the various Meteorological Observation Stations ........................................................................................................................................... 26 Table 4.3: Summary of Meteorological Characteristics at Project area Table 4 4 Summary of Estimated mean ETo of Arjo Dedessa Project area 27 28 Table 4.5. Magnitude of ETo at given non-exeedance probability level............................................. 29 Table 5 1 Cross Correlation Matrix of annual Rainfal^ ..................................................................... 36 Table 5.2: mean Monthly Rainfall .............................................................................................................. 36 Table 5 3 Parameter Estimates of weibulx 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 Table 5 7 Half-Monthly Rainfall Magnitudes in Percent of the Mean Corresponding to 38 Different Reliability levels......................................................................................................... 39 Table 5.8: Maximum Annual 24-hr Rainfall ..............................................................................-.................. 40 Table 5.9: maximum Rainfa^ Magnitudes and Frequencies...................................................................... 40 Table 5.10: Maximum Rainfag. Magnitudes for Higher Durations........................................................... 41 Table 6.1 Availability of Streamflow Data in the Region.................................................................... .48 Table 6.2. Mean Monthly Flow (in Mm3/seC).............................................................................................. 48 Table 6.3 Coefficient of Variation of Monthly Discharges................................................................. 48 Table 6 4 Summary of Regional monthly flow characteristics......................................................... .49 Table 6 5 Table Statistics of monthly flows at arjo Dedessa dam site .... 49 Table 6.6 Reliability level Vs Monthly Streamflows at Dam Site ...................................................... 49 Table 6.7 Characteristics of Random numbers Used for Flow Generation..................................... 50 Table 8 i Estimated Flood Quantiles Based on GEV Distribution......................................................<>4 Table 8.2 Estimated Flood Quantiles Based on llG Distribution 64 Table 9 i Table Cumulative volume of Probable Maximum F^ood....................................................... 67 Table 9.2: Design Flood hydrograph Derived from Estimated PMF ................. Table 10 1 Relationships between water discharge and sediment load .... ........ . 68 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 Reservoir.....................................................72 Table 11 1 Water quality results for sites on the Dedessa river....................................................... 74 Table 12.1: Catchment Characteristics....................................................................................................... 80 Table 12.2: Routed Design Flood at FRl Corresponding to 1352 m Table 12.3. Routed Design Rood at frl Corresponding to 1555 m go si Table 12 4 Routed Design Flood at FRL Corresponding to 1356m................................................. 82 Table 12.5; Routed Design Rood at Coffer Dam of arjo Didessa Reservoir Table 13 1 irrigation Water Requirements for various Scenarios 83 88 Tablei3.2 Reservoir Characteristics at Dead Storage level.............................................................. 89 Table 13.3: Storage Reservoir Characteristics and Reliability Levels............................................... 90 Table 14 1 Total monthly Release (Irrigation plus Power) options for various frl values considered.................................................................................................................................. 97 Table 14.2: Annual Energy generations at Dedessa dam for the various options ........ 97 _______________________________________________ ______________ HI Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.ArJoDedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 LIST OF ANNEXURE annex A Results obtained from the Meteorological Analysis ........................................................ 103 Al: Estimated Mean Temperature at Arjo Dedessa Project area (in°C).................................... .103 A2 Estimated Minimum Temperature at arjo Dedessa Project area (in°C)................................... i04 A3 Estimated Maximum Temperature at Arjo Dedessa Project Area (in°C) A4 Estimated Relative humidity at arjo Dedessa Project Area (in percent/ A5 Estimated Mean Daily Sunshine Duration at arjo Dedessa Project area. I05 I06 107 A6 Estimated mean Daily ETo of arjo Dedessa Project area........................................................108 A7 Estimated Mean Monthly ETo of arjo Dedessa Project Area A8 Estimated mean monthly Rainfall at Arjo Dedessa Project Area i 09 ho A9 Estimated Mean half-monthly Rainfal at the Project area (in mm/hr)..................................... ill Annex B Results obtained from the hydrological Analysis .....................................................................H3 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) .................................................... H 4 B5 Standardized probability weighted moments ............................................................................... 115 B6 Mean monthly Total (Suspended and Bed) Sediment load ..................................................... 11 o B7 Eleveation-area-Capacity Relationships of arjo Dedessa Reservoir B8. Sample Simulation Results of Arjo Dedessa Reservoir i 17 118 Annex C Standards............................................................................................................................................ 121 C1 Commonly used values of runoff coefficients......................................................................... 121 C2 Runoff coefficient for pervious surfaces by selected hydrologic soil I2! 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 ............... ........................... ) 27 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 .................................................................................................................................. 136 E1 list of Selected hydrological Observation Stations............................... ..................... 136 E2 Mean Monthly Streamflow at Dedessan near arjo Station E3 Mean Monthly Stream flow at Dedessan near Dembi Station i 37 139 E4 Annual Maximum Floods................................................................................................................... 140 E5 Measured Sediment Concentration at Gumara Gauging Station.......................................... .141 __________________________________________________________________ ________ IV Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arj o-D edess a Irrigation Project Meteorological and Hydrological Aspects May 2007 LIST OF FIGURES Figure 4 1 mean monthly Temperature at Figure 4.2: Mean monthly Relative humidity at so 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 Figure 5 1(a): Trend Analysis of Annual Rainfall at jimma Station Figure 5.1(B). Trend Analysis of Annual Rainfal*. at BedellE Station Figure 5.1(C). Trend Analysis of Annual Rainfall at Dedessa Station ... 31 42 42 43 Figure 5.2(a). Single Mass Curve of jimma Rainfall......................................................................................43 Figure 5.2(B): Single mass Curve of BedeluE Rainfall............................................................................... 44 Figure 5.2(c): Single Mass Curve of Dedessa Rainfall Figure 5.3; mean Monthly Rainfall at arjo Dedessa Projetct Area Figure 12 1 Elevation-Area-Capacity Curves of Arjo Dedessa Reservoir Figure 12.2: inflow and Outflow Flood hydrographs at arjc Dedessa Reservoir Figure 12.3: inflow and Outflow Flood hydrographs at arjo Dedessa Reservoir Figure 12 4 Average hydrograph of maximum flows at Arjc Dedessa Dam Site 44 45 84 84 85 86 Figure 14 1 Power Duration Curves .................................................................................................... 98 _____________________ ____________________________________ ___________ _______ V 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 tne world It drains a total drainage area of 2.96 M.Krrf, with its annual total flow of about 84 Bm As one could appreciate, the discharge per Km 3 2 is small when compared J 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 ano 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 AODay and the Tekeze -Atbara System. 1.2 Abbay Basin The ADbay 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 kmz The Aobay nas an average annual run off of about 50 B m The rivers of Abbay contribute on an average 62% of Nile over 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 not/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 mghiand climate, it is perhaps better to describe it using the local climatic zones, that have bean established witn 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 Woma 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 1O°C to 16°C The major portion of the population inhabit in the more climatically pleasant ano nealthier upper two zones, whicn leaves the lower Qolla zone sparsely populated. Water Works Design & Supervision Enterprise I In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.ArjoDedessa 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 winas 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 wnich clear skies are associated with maximum sunshine hours, high daily temperature vanation and low relative humidity F inally the minor 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 nours 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 aDout 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 ano West Wellega, Jimma and lllubabor Zones with relatively hign rainfall (1400-2200 millimeters) and a iong wet season. ii) A central area covering most of Western Gojam ano Darts of neignooring zones as well, charactenzed 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 ano South Wello, Eastern part of East Gojam and South Gondar and much of North and North West Snewa 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 In Associate with Intercontinental Consultants and Technocrats Pvt Ltd. 2Arjo Deaessa Irrigation Project Meteorological and Hydrological Aspects May 2007 iv) The West and North West area covenng North Gondar region. The rainfall is about 1200 millimeters, falling predominantly, in the mam 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 AbDay the main river flows north from its source near Sekela into the wide and shallow Lane Tana The take 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 oasin 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 over o nginates in the Mt.Vennio and Mt.Wache ranges, flowing in an easteny direction for about 75 kilo meters, then turning rather sharply to the north until it reaches the AbDay 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 tne 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 iowest 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 SeptemDer period with virtual drought from November througn 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 or the catchments in the Abbay basin Examination of the rainfall records from this area shows that this is due to a longer (May through OctoDer) rainy season rather than heavier maximum monthly quantities 2 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd. 3R R R ■I Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects The mean annual flow of Dedessa nver at Arjo station is about 3,800 million m naving 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 descnption 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 May 2007 3 System Tributary Joining Catchment From Area (Km ) 2 Lake Tana — 15,054 North Gojam Right side Beshilo Weieka Jemma Left side tf M South Gojam Rignt side Muger Guder Fincha Deaessa Angar Wonoera Dabus Beles Dinder Rahad Left side M * M M Right side Left side Right side — — Total 14,389 13,242 6,415 15,782 16,762 8,188 7,011 4,089 19,630 7,901 12,957 21.032 14,200 14,891 8.269 199,812 >1 il d d d Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd. 4Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 2. REVIEW OF PREVIOUS STUDIES 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 suo basin exclusively, all the studies under taken, pertaining to Abbay or the country as a whole, spoke of Dedessa development. Hence thougn 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 Scneme 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 ano 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 taxen 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 Dasin is wortn 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 nyoroiogicai studies In fact, the pioneering works undertaken during that time, has made ADbay basin in Ethiopia, to be proud of a possessing a good net work of hydrometric stations for making reliaDle estimates. The hydrological aspects nave been covered in Appendix III of the report. In 4 different sections of this Appendix, the various facets of hydroiogical analysis nave been put forth as below: • Section I: A general cescnption 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 5 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 low sodium hazard; most of them showed low to medium salinity hazard, 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 tne 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 ot analysis available at tne time In the study period 59 gauging stations were established, including 14 stations with automatic stage records By the various analysis including grapnicai 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 Deoessa at Arjo, the correlated flows were established for 8 years (1911 to 1917 and 1932j. 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 (catcnment area 3080 Square Kilometers) For the Angar near Nekemte, the flow estimate at annual mean level was 2523.33 Mm3 (Catcnment area 4350 square Kilometersj 6 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Ar Jo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 3 For the proposed Deaessa 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 iIo meters (AG-6 Dam). The mean annual flows estimated respectively at these two locations were, 983 125 and 2251 26 Mm3 The section ill, addresses the causative factors of floods in Abbay The design rainfall for the basin was estimated Daseo on 6 representative station s data. These are presented below, which are forming a qata base, worth for review and up dating for adoption. 1 day design rainfall = 87 Midi meters 2 day design rainfall = 126 " 5 day design rainfall = 185 “ 10 day design rainfall = 251 “ 15 day desigr rainfall = 321 “ 3 The design flood was estimated by physical approach using unit hyorograpn, storm analysis and design flood nydrograpn convolution for 21 dam sites F or the others, flood frequency analysis based statistical return period floods were estimated For the Deoessa DD-2 reservoir, the PMF was computed as 5390 m3/sec with a base period of 99 hours. For the Dabana storage reservoir, the PMF estimate was at 4860 m /sec with a Dase penod of 91 hours. For the Angar-2 reservoir with a catchment area of 1780 square Kilometers the PMF ano the duration of the nydrograph 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.Arjt> Dedessa Irrigation Project Meteorological and Hydrological Aspects May_2Qo^__ The section IV, as indicated in the beginning deals with the water use studies. The 1960 water use status was reviewed along with such water uses in villages. Then, the run off estimates have been adopted considering the envisaged irngation and power developments in respective simulation study. Due to Dedessa dam USBR study, estimated a reduction of about 139 M mJ 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 of 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 resources development, covering all nver basins. These were primarily desK studies for identifying potential irrigation and hydropower sites based on country wide data collection and analysis, coupled with detailed map studies. The study was addressing the Abbay basin also, along with other basins. The USBR studies were reviewed in detail for the Abbay basin, and subsequently this study came out with modifications in the USBR sites in some cases and proposed many other sites as well. Though desk study, the data base available to this study, on nydrological and hydro meteorological aspects were fairly adequate because of the earlier 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 were collected ano analyzed even though elaborate consistency checks were not under taken. The data gaps filling and extrapolation of data have been done using statistical regression analysis, using mostly oi-variate linear as well non linear correlations. In certain major dams, synthetic 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 has been earned 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 the 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 have been transferred to the dam site by empirical formula. For deriving the shape of the complete design inflow hydrograph at the dam site the procedure as indicated below has been followed. 8 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 aft’ and QP is the peak discharge Using this pattern of relationship the cam 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 cntena based reliability levels. Climatic data otner than rainfall have also been documented, though without detailed processing or elaborations. The sediment rates as quoted by various previous studies of different Dasins 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 hydroiogicai and hydro meteorological data were also not put into rigorous analysis, which is called for design of identified projects. However, this study aiong with USBR study back up gave a very good data base/ inventory of all possible exploitable cam sites in Abbay Dasin. This EVDSA/WAPCOS study has cameo 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 nght side. The project envisaged irrigation over 139.00C nectares with 160% irrigation intensity The inflow in a 75% reliaDle year was estimated to oe 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 3 3 2.4 Study by BCEOM - in association with ISL and BRG 1999 The study entitled "Abbay River Basin integrated development Master Plan Project” has Deen carried out with the following water resources onented objectives. 9 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrol ogical Aspects May 2007 • Preparation of the nver basin development m aster pla n 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 ill of the Master Plan Study report. The Dasic 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 availaDle for 108 stations. The field verification of these stations and equipments has also been under taken The data is said to nave been subjected to analysis and some errors connected with observations or processing were laentified. The study has perhaps not attemDted to improve the quality of sucn data on the plea that it was outside the consultant's capacity or responsibility As such, tne data base after screening and omitting such erroneous data is stated to be good. With respect to Hydrology in the part 2 of the aoove volume III, the following aspects nave been covered systematically. • Basic Hydrograpmc Features • The Hydrometric net work • Review of orevious studies • Data collection ana 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 10 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, tneir locations, and drainage areas controlled have been well documented in T ables, appendices and maps The master plan has found that the spatial distribution of the stations is not even or equitable The parts of Besnilo, 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 tneir installations • In many gauges stations the cables of bank operated cable way were missing • On tne other hand most staff gauges were in good condition and water level data was considered to De 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 hydroiogicai net works are concerned, optimality vanes depending upon the purpose of the net work. It could De 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 catcnment, it seems they have been ignored by the master plan study. Measurement of discnarges 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 catcnments does not seem to be Dased on analysis of vivid concepts. Subsequently, the Master Plan has made a very brief review of hydroiogicai 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 Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 more elaoorate manner. The review could have brought out each aspect of hydrological and hydro meteorological and simulation studies attemptea 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 oe 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 have been fitted, wmch is common practice in Hydrology It is a good thing that Master Plan has used both analytical ana 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 discnarges 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 witn earlier studies ana the results did not nave major variations. Again it is felt that better appreciation could have been made, if the concept of major variation had been spelt out. 12 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological AspectsMay_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 c omprehensive 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 prepareo 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 couid De of use just for a preliminary estimate of annual flows at pre-feasibility level The water availability has Deen further estimated by aetailed water balance model. In this in the first run, tne present scenario has been in built and for 18 net work stations, and water availability has Deen estimated. The salient findings of this run are as Deiow which are in order. • The annual average volume flowing across the border from Abbay River is 50.30 Bm3 • Adoui 83% of tne average annual volume at border is flowing in 4 months (July - October), while tne 4 montns from FeDruary to May account for less than 4% of the mean annual flow • The average annual flow at the out let from Tana represents aDoui 7% of the above annual flows at border. Floods: The highest flood nydrographs recorded at each of the water balance net work stations have Deen put to analyses to establish the relation Detween time and Q/Qm ratios. Then flood frequency analysis of the annual maximum discharges has been carried out by Gumbei's EV1 distribution to estimate the return period flood peaks (It is not clear wnetner the annual maximum oDservec peaks were converted in to instantaneous peaks). Further another relationship connecting catchment size to flood peak has been derived for 2 groups of catcnment 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 _____________________________________ _____________ _________ Water Works Design & Supervision Enterprise 13 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 catchments with flood discharge rates, which a*so 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 teve' 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)° linking water level with flow QS = aQLp linking sediment discharge QS with liquid discharge QL with a and 0 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 nas 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 ano water resources modeling seem to be in order Software WATBAL has been used in the modeling for vanous scenanos 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.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 • present situation • Future situation encompassing o Scenario N° 1 (identified projects 1) g Scenario N° 2 (identified projects 2 including Tana Beles) o Scenario N° 3 (identified projects in main stream) o Scenario N° 4 (F ull d evelopment ) The results could De utilized for comparing the results of specific sub basin oriented modeling 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. This gives a vivid analysis of the data and the Hydrological features of the Dedessa sub basin The aam site controlling a catchment area of 18,200 square Kilo meters, has the following water 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 gives annual sediment load of 9 1 million tons per year. The 50 year sediment volume of 329 Mm3 had been accounted for reservoir sizing. 15 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.ArjoDedessa Irrigation Project Meteorological and Hydr ological Aspects May 2007 The study had analyzed the energy generation with a net head of 133 meters and with tne assumption of regulation of 70% of the mean annual flow T he energ y 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 ano modeling studies are warranted with modern tools of analysis. This sectoral report narrates these specific studies. 16 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.ArjoDedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 3. DATA BASE 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 ano 'A 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 penods) 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 senes of observed annual maximum 1 day rainfall or as monthly / fortnightly totals as per analysis at different stages The analysis has to under take tne 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 tne 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 througn synthetically generated time senes (mostly generated Dy a stochastic generation scheme); where as, the same flow data nas 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. 17Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 3.4. Sedment Data The s ediment data is obv iously req uired to pian the si ze of the storages, for app ortion ing the activ e and inactive storag e spaces and for determin in g the revi sed geometry of the stor age after certain design life, (revised elevat ion - area - c apa city relationship); as this revi sed relation is used in the simulation modeling The water quality is another aspect, which needs to De a daressed i n H ydrological s tudy along with I ow f low a nalysis f or m andatory d ownstream releases, closely associated with the concerns of environmental and ecological aspects. With sucn appreciation of the frame work of nyarological 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 brougnt to analysis desk and appropriately included. Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. 18Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 4. ESTIMATION OF REFERENCE EVAPOTRANSPIRATION 4.1 Intro duction The climate of the Aqo Didessa catchme nt results from its lo cation and e levation (1 300 to 3012 mete rs). The Iist of stations for observations of m eteorological dat a along with iength 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 Deen 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 (ET ) from meteorological data. This section 0 describes how the monthly ETO is determined from temperature, numidity, wind-speed and sunshine hours data collected at Banir Dar station. The ET calculation nas been carried out by 0 means of a computer The FAO Penman-Monteith equation determines tne 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 pnysical parameters. Some of the data are measured directly in Banir Dar meteorological station. Other parameters are related to commonly measured data and can be derived with tne nelp of a direct or empirical relationship. This section discusses the source and computation of all aata 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 which 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 Beoele, Dedessa and Jimma stations are assumed directly applicable to the Arjo Dedessa 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 Bedeie 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 imgation 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 ciass 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 Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 whicn 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 nave Deen used in addition to the aata obtained from Jimma station for estimating rainfall and evapotranspiration at the proposed irrigation command. in summary, climatologicall data obtained from Bedele, Deoessa 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 De index station in extrapolating and interpolating missing and snort 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 tnroughout the year are minor, oeing 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 Deen jsed in estimating evapotranspiration rates from reference crops. Agrometeorology is concerned with the air temperature near the level of the crop canopy In traditional and modem 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 a nd maximum air temperature over a 24-hour penod. 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 penod The daily maximum air temperature (Tmax) and daily minimum air temperature (Tmjn) 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 aTK4 (Stefan-Boltzmann law). The soiar 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 Marcn 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 Detween the amount of water the ambient air actually holds ana the amount it could nold at the same temperature. It is dimensionless and is commonly given as a percentage. Although tne 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 cnanges during the day, the relative humidity also cnanges 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 ana the surrounding air is the determining factor for the vapour removal. Well-waterea fields in hot dry arid areas consume large amounts of water due to the aDundance of energy and the desiccating power of the atmosphere. In numid tropical regions, notwithstanding tne 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 and regions. 22 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 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 aata 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 wnich the wind is blowing. For the computation of evapotranspiration, wino speed is the relevant vanable. Wind speed is measurea with anemometers. The anemometers commonly usea in weather stations are composed of cups or propellers which are turned by the force of the wino By counting the number of revolutions over a given time period, the average wind speed over the measunng 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 sunsmne duration is 8.3 hours in December and is reduced to 3.7 hours during July The mean monthly sunsmne 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. Ltd.Arjo 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 De zero. In the absence of a direct measurement of R , 5 the relative sunsnme duration, n/N, is often used to derive solar radiation from extraterrestnal 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 Soiar 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 reacnmg the evaporating surface depends on the turbidity of the atmosphere and the presence of clouds whicn 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 ano 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 = 0 408 A (P nOry [900/(T -r 273)1 v - £=) (2.1) A + y (1+ 0.34 bj) where ET0 = reference evapotranspiration [mm day ], 1 R = net radiation at the crop surface [MJ nrf n 2 day ], 1 G = soil heat flux density [MJ m z day' ], 1 1 s a 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 mean. Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd. 24Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects e 5 - e = saturation vapour pressure deficit [kPa], a A = slope vapour pressure curve [kPa °C ], y = psychrometric constant [kPa C ] RH = relative humidity divided by 100 and Rn — Rns " Rnl (2.2) Rns = 0 77 Rs (2.3) R = (0.25 + 0.50 n/N) R (2 4) s a R = ctT (0.34 -0.14 e ) (0 135 Rs/Ro - 0.35) nl k a 4 05 (2 5) R = [0.75 + 2 (Altitude)/100000] R so a (2.6) The calculation procedure consists of the following steps 1. Derivation of some climatic parameters from the daily maximum (Tmax) and minimum (Tmin ) air temperature, altitude (z) and mean wind speed (u ). 2 2. Calculation of the vapour pressure deficit (es - e ). The saturation vapour pressure (e ) a s is denved from Tmai< and Tmtn , while the actuai vapour pressure (e ) can be denved from a the dewpoint temperature (Taew), from maximum (RHma,) and minimum (RHmin) relative humidity, from the maximum (RHmax), or from mean relative humidity (RHmean). 3. Determination of the net radiation (Rn) as the difference between the net shortwave radiation (Rns) and the net longwave radiation (Rm). 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 m'2 day ’, 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 Irngation and drainage paper 56). o Psychomemc 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, o oTk (Stefan-Boltzmann law) at different temperatures (T) 4 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 ano 4 4. respectively ano 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 Period (m) 1 Agaro 07 51 36 36 2 Beaelle 08 27 36 20 3 Dedessa 09 33 36 06 4 DemDi 08 04 36 37 5 Jimma 07 40 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 1 Dioessa 30 2 Bedele 28 3 Dembi 20 4 Agaro 21 5 Jimma 50 Yrs refer to rainfall series No Station name Yrs RF Tm RH ws SD 1 hr 1 day Rday Class XXX X 1 XXX X 1 XX XX 3 3 XXXXXXXX1 RF monthly rainfall Tm average temperature RH relative numidity WS wind speed SD sunshine duration 1 hr maximum 1-hour rainfall 1 day maximum 1-day rainfall Rday number of rain days 26 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. LtdArjo Dedessa Irrigation Project Meteorologica l 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 (%) i 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 i 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 0.51 048 0.51 Sunshine Hours (hrs/oay) 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 27 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorologic al and Hydrological Aspects May 2007 Table 4.4: Summary of Estimated Mean ETo of Arjo Dedessa Project Area Jan Feb March April May June July Aug Sept Oct Nov Dec Dailv: 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 -047 -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 005 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) 1 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 mrr. 28 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 4.5: Magnitude of ETo at given non-exeeaance probability level May 2007 1 Non-Exd (mm/day) Probaiility 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 84 346 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 I I 70 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 75 3 3 . . 8 83044..229544..7795 44.7649 44..5572 33.7772 33.0129 33..2248 43.0949 44..1195 44..0029 33..5563 Non-Exd (mm/month) Probaiility Jan Feb Mar April May JuneJuly Aug Sept Oct Nov 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 Growth factor (Xp) Probaiility Jan Feb Mar April May JuneJuly Aug Sept Oct Nov Dec Annual 90 (%) 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 1 03 1.01 1.01 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 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 1.07 1.08 1.07 1.1 1 11 1.1 1.1 95 1.09 1.1 1.1 1.11 1 09 1.08 1.15 1.07 1.053 1 12 1 14 1.13 1.13 1.13 1.14 Avg 1 1 1 1.1 1 19 1 09 1.068 1 1 1 1 11 1 11 1I ---------------------------------------- ------------------------------------------------ ------------- 29 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Wind speed (m/s) Temperature (oC) ArjoDedessa 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 30 Figure 4.3: Mean Monthly Wind Speed at Arjo Didesa Project Area Figure 4.4: Mean Monthly Sunshine Hours at Arjo Dedessa Project Area 30 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.ETo (mm) Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Figure 4.5: Mean Monthly ETo at Arjo Dedessa Project Area 31 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Ar Jo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 5. RAINFALL ANAL YSIS 5.1 I ntroduction The rainfall data obtained from B edel e, Dedessa and Jimma sta tions were found t o be the most reliable and relevant for use in the analysis of rainfall for the Arjo Dedess a ir riga tion project. Bedele is geographically the closest station to the command area. Dedessa station ana the command a rea a re I ocated at the s ame e levation (i.e. b oth 1 330 m a si). J imma station (whicn 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 tnrougn 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 Deen established for rainfall, considering the data of the three stations namely Dedessa. Jimma and Bedeie, it is customary in Hydro-meteoroiogical studies to firm up tne 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 Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 200? 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 matnx 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 ana 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 distnbution 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 probaoility level of p. The moment estimates of the parameters E (the lower limit), U and a fie., 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. (52) (5 3) 33Arjo Dedessa Irrigation Project Meteorologic al and Hydrological Aspects May 2007 where Xm = mean value, Cv = coefficient of variation = standard deviation dividea by the mean, Y(a) Z(a) = (2-Cs)/6 = [8+(3-Cs) ]/9 3 and A = 3/(1+Cs) Cs = skew coefficient calculated from data The estimated monthly and half-monthly parameters of Weibull Distribution are given in Table 5.3 ana 5.5, respectively. The following algorithm were used in the denvation 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 naif-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 penod 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 l 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/hrj, 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. I h = I24 (0.523 + 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). I24 = maximum rainfall intensity corresponding to duration 24 hours (mm/hr) i he 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" Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects The annual rainfall available at different years are given below 200Z 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 July Aug Sep Oct Nov Dec Total Didessa 3 6 26 49 158 274 312 277 209 104 28 8 1454 Bedeie 18 23 65 105 239 291 310 303 302 156 41 12 1864 Dembi 25 44 101 126 223 303 307 367 290 145 52 29 2013 Agaro 24 36 88 93 149 232 234 231 174 127 54 30 1471 Jimma 33 49 88 133 172 219 208 210 182 103 68 36 1502 Table 5.2: Cross Correlation Matrix of Annual Rainfall Dedessa Jimma Bedeie Dedessa Jimma Bedeie 1 0.11 1 0.24 0.48 1 Table 5.3: Parameter Estimates of Weibull Distribution Jan Feb Mar April May June July Aug Sept Oct Nov Dec Annual y(a) 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 z(a) 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 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 E 18.3 21 9 61 2 81.5 201.1 267.3252.9257 7245.0 131 0 30.0 13.9 1541 -12.9-15.0-17 4-55.3 -9.8 7.3 154 1 35.9 60.9 -29 9 3 8 -4 4 575 U = Xm +Cv'Xm'y(a) E = U- Cv'Xm'z(a) X = E + (U-E)'(-ln(1-1/T)*(1/a) 36 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. LtdArjo 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 Annua/ (%) 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 16.36.12 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 16 15.5 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 69.5 180.82431)245.9238.3228.6115.531.412.7 1453 Table 5.5: Parameter Estimates of Half-Monthly Rainfall Month Parameters of Weibull distribution 1.1 1.2 2.1 2.2 3.1 3.2 4.1 1/a y(a) W I u | E 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 -11.7 0.6 0.2 1.9 26.5 -13.5 4.2 0.5 0.2 2.4 54.5 -25 6 5.1 0.6 0.2 1.9 87.6 -11.2 5.2 0.6 0.2 2.0 112.7 7.5 6.1 0.5 0.3 2.8 134.3 -19.8 6.2 7.1 7.2 8.1 8.2 9.1 9.2 10.1 10.2 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 2.7 131 374 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 -117 11.1 0.8 0.1 1.3 21.5 -3 2 11.2 12.1 12.2 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 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.ArjoDedessa Irrigation Project Meteorological and Hydrological Aspects Table 5.6: Half-Monthly Rainfall Magnitudes at Different Reliability Levels Month Avg 7.5 1.1 7.8 1.2 8.8 2.1 9.6 2.2 20.6 3.1 33.0 3.2 22.7 4.1 46.7 4.2 78.2 5.1 102.6 5.2 119.8 6.1 6.2 7.1 7.2 123.2 Reliability level 55% 60% 65% 70% 75% 80% 85% 90% 95% 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 6342 56.51 49 43 42.02 33.96 24.5 101 92 5 83 9 75.1 659 56.3 45.7 33.6 183 | 106 98.2 90.7 83.2 75.5 67.4 58.7 48.9 36 8 122 103.9 97 46 91.26 85.17 79.13 73.04 66.78 60.14 52.6 1 123.9 110 106 102 99.2 96 93 90.1 87.2 84.2 116.5 102 95.7 88.9 82 74.9 67.3 59 49.3 37 8.1 121 8 110 104 99 936 87.9 82 75.6 68.2 59.1 8.2 120 108 103 97 6 92.7 87.6 82.4 76.9 70.8 63.5 9.1 108.5 979 92.1 86 1 80 73.4 66.3 58.4 48.9 36 1 9.2 73.7 58.7 52.5 46.2 40 33.6 27 19.9 12 2.37 10.1 41.8 29.2 24.9 208 16.8 12.8 8.77 4.68 0.38 0 10.2 19.7 13.1 11.1 9.3 7.54 5.83 4 16 2.5 0 82 0 11.1 118 4.15 2.92 1.83 0.85 0 0 0 0 0 11.2 6.1 2.02 1.21 0.46 0 0 0 0 0 0 12.1 6.6 0.83 0 0 0 0 0 0 0 0 12.2 1453 1353 1304 1253 1202 1148 1090 1025 950.5 853 Annual 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 LeveIs Month Avg Reliability level _____ ________] — 1.1 100 1.2 100 2.1 100 2.2 100 3.1 100 3.2 100 4.1 100 4.2 100 5.1 100 5.2 100 6.1 100 6.2 100 7.1 100 7.2 100 8.1 100 8.2 100 9.1 100 9.2 100 10.1 100 10.2 100 11.1 100 11.2 100 12.1 100 12.2 100 557. 607. 657. 707. 757. 807. 857. 907. 957. --------- 1 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 I 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 6^ 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 LtdAr Jo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 5.8 Maximum Annual 24-hr Rainfall Year (mm/d) Year (mm/d) May 2007 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 584 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 Frequency Peiod (T) 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 4(1 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 EVI Factor (Years) K(T) Max 2day Rainfall (mm) Max. 3day 1day Avg. of Max. 3 day Rainfall Rainfall (mm) (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 92.7 29.8 94.6 112.7 37.8 106.3 125 9 43.2 112 9 1334 46.2 117.5 138 6 48.3 121.0 142 6 49.9 132.0 155 0 54 9 142.9 167.3 59.9 41 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Figure 5.1(a ): Trend Analysis of Annual Rainfall at Jimma Station Figure 5.1(b): Trend Analysis of Annual Rainfall at Beaelle Station Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 1970 1975 1980 1985 Year 1990 Figure 5.1(c): Trend Analysis of Annual Rainfall at Dedessa Station E E c « a c c < © 8© 3 E E 3 o 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Years Figure 5.2(a): Single Mass Curve of Jimma Rainfall 43 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa 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 44 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt LtdArJoDedessa Irrigation Project Meteorological and Hydrological Aspects Ma > 2007 45 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May ZOO? 6. MONTHLY STREAMFLOW ANALYSIS 6.1 Hydrological Observation Stations Hydrometric stations on the Dedessa river and the neighbouring rivers withi n the Abbay b asin the Omo-Ghibe basin have also been identified The hydrological data are o btained 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, hydroiogicai observation stations on the neighboring Dabana near Abasina ( Station No. 1 14005), (Gilgei Ghibe near Assendabo (Station No. 091008), and Gojeb near Shebe (Statior 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 Ago town iStation 14001) since 1960 and near Dembi town (Station 14014) since 1985 Before the streamflow analysis, data obtained from Station 114001 (Didessa near Arjo) ano Station 114014 (Didessa near DemDi) were checked for temporal and spatial homogeneity The investigation of nomogeneity was concentrated mainly on the outliers of the monthly data senes of the record Extremely hign 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() 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 ------------------------------------------------------------------------------------ - ------------------- 4b Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects other data series of Station 114005 (Dabana near Abasina), Station 91008 (Gilgei Gnibe 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 mghly accepted procedure by hydrologists. However, it has been pointed out synthetic (generated) flows do not improve poor records out 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 Deaessa 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 tne standardized residuals of the monthly series Accordingly, the estimated parameters of the random generator that were used in the Thomas-Fiernng model are presented in Table 6.7. 47 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects 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 Mean 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 Nc St. No Station name and Location Lat North Long East Area 2 JKm ) Flow (Mm’/yr) Runoff lT L m 1 114001 Dedessa near Arjo 841 36.25 9981 3826 383 2 114014 Upper Dedessa near Dembi 8 02 36.28 1806 1221 676 I 3 114005 Dabana near Abasina Gilgel Gibhe near 4 091008 Asenaabo 5 091012 Gojeb near Shebe Table 6.2: Mean Monthly Flow (in Mm’/secj 9.02 36.03 2281 1870 820 7 45 37.11 2966 1211 408 7.25 36.23 3494 1803 516 I 1st No Jan Feb March April May June July Aug Sep Oct Nov Dec 1 114001 114014 114005 091008 901012 Annual I 41.9 26.7 26 33 5 63.6 216 646 1050 902 526 148 80.7 3761 12.2 9.5 11.5 16.9 36 4 112.4 228 9 306.9 262.8 154.3 48.4 20.5 1221 1 35.4 19.8 16.3 17.0 35.1 107.0 258.8 433.0 473.4 313.9 103 3 56 6 1870 14.7 13.5 12.2 15.9 33.9 100.3 216.5 319.2 277.8 137 60.2 24 5 1211 | 31 3 22 1 22 1 31 3 86.4 169.2 323.7 415 6 400.9 202.3 82.8 46.5 J___________________ — i 1803 J Table 6.3: Coefficient of Variation of Monthly Discharges St. No Jan Feb March April May June July Aug Sep Oct Nov Dec 114001 114014 114005 091008 901012 0.51 0.57 0.66 0.68 062 0.45 0.35 0.3 0 33 0.67 0 62 0.59 0.47 0.5 0.48 0.56 0 69 0 53 0.29 0.27 0 30 0.56 0.81 0.53 0.28 0.42 0.33 0.43 0.60 0 47 0.20 0 16 0.25 0 44 0 30 0 34 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 34 049 0 54 0 70 48 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.ArJoDedessa 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 Jujy Aug Sep Oct | Nov Dec_| cv 194 Skew 151 0 51 0.68 0.595 0.58 0 61 0 47 6.33 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 R B 194 0 38 0.57 0.527 0.45 0 49 0 66 0 53 0.56 0.51 0.5 0.56 0.51 194 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 Table 6.6; Reliability Level (%) 55 60 65 70 75 80 85 90 95 Avg Reliability Level Vs Monthly Streamflows at Dam Site (in Mm3j Jan Feb Mar Ap£ May |jun Ju| Aug Sep Oct Nov Dec A nnual 20.2 12.7 14.1 19 3 37.5131 4 371 1 568.8 480.4 239.0 75.8 35.5 2114 19.0 11.6 13.0 17.4 34 7122.3 348 4 542.6 454.6 216.6 69.9 33.2 2019 17.9 10.6 12.0 15.6 32.0 113.5 325.3 516.7 429.0 194 7 64 5 31.1 1924 16 9 9 6 11.0 13.8 29 5104.9 301 3 490.8 403 3 173.1 59.6 29.2 1828 16.0 8.7 10.1 11.9 27 1 96.4 276.0 464.5 376.9 151.6 55.0 27.4 1729 15.0 7 8 9.2 10.1 24 9 87 8 248.5 437 3 349.4 129 7 50.9 25 7 1625 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 12.5 5.2 6.5 3.5 18.2 59 0 132.1 337.9 246 0 54440.221.2 1224 49 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 6.7 Characteristics of Random Numbers Used for Flow Generation May 2007 aram Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec werage 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 0.58 066 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 00^ 0.05 y(aj 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 I Weibul Distribution X = E + (U-E) *(-in(1-F)(1/a) U = Xm +Cv'Xm*y(a) E = U - Cv'Xm'z(a) 50 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects 7 ESTIMATION OF FLOODS FOR UNGAUGED CATCHMENTS May — In the hydrologic analysis for dams, weirs, bridges and drainage structures, it must oe 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 t ypes of estimation f loods magnitudes (namely: t he Rational Method, SCS methoa 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 exceeo 12.8 kmz (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 metnod is nevertheless frequently used in standard or modified form for much larger catcnments. This is because of its relatively simplicity. The vast majority of catchments producing flooas imposed on the commana 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 Methoa is Dasea on the following formula: Qm = 0.2778 C.I.A.Fr where Qm - peak flow corresponding to return period of T years in m /sec. = a 'runoff coefficient expressing the ratio of rate of runoff to rate of rainfall (see Annex C1 and C2), 3 51 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.ArjoDedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 2 I = average maximum intensity of rainfall in mm/hr, for a duration equal to the time of concentration. 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 (72) where Tc = (1/3080)xL’ 155 h ° 385 (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; where Fr = 1 - 0 02 D'033 A 050 D = duration in hours, A = drainage area in km ; (73) 2 This equation applies for storms of up to 8 hours duration. For longer durations on large catchments the value of D can be taken as 8 for use in the above formula. 52 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hyd rological Aspects . 7.2 SCS Method A relationship Detween accumulated rainf all and ac cu mulated ru noff was derived Dy SCS (Soil Conservation Service). The SCS runoff equation is therefore a method of es timating direct runoff from 24-hour or 1-day storm rainfall The equation is: Q = (P - la) /(P-la) + S 2 (7.4) wnere 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 Detween 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) /(P-»-0.8S) 2 (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 De obtainea 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] 53 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May_20Q7_^_ 7.3 Transferring Gauged Data 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 tnbutaries 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 Aomasu (1989) as follows. Qu = Qg.(Au/Ag)°70 (7.8) where: Qu = mean annual daily maximum flow at ungaugeo site (m /s), 3 2 Qg = mean annual oaily maximum flow at nearDy gauged site (rrr/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 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 are recommended for relatively small, medium and large catchments respectively However, it is 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 De given as. Qw = WiQ, + W .Q + W .Q 22 33 (710) 54 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.ArjoDedessa Irrigation Project Meteorological and Hydrological Aspects where. May 2007 Qi, Q2, and Q are mean annual momentary peaks estimated by Rational SCS ano 3 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 and W, = 12.5/(12.5+Au) (711) W3 =(Au/Ag)°70 (7 12) W = 1 - (Wi + W ) 23 (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 7 Determine the lag time, T , of L 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)03 (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. 55 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects M «y 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 TL/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. Tjadj) = T *0.25(T l rn-Tr) (7.16) wnere T (adj) is the adjusted lag time for the new duration. T L RN. (7 17) 32 The unit peak discharge can be determined from the following equation; Up = (1/2940)x(0.94 - la/P)x(6.08 - In Tc)35 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)2 /(P+0 8S) and the time from rise of the hydrograph to the peak, Tp, is compured from Tp = 0.5 Trn + T (adj) L (7.18) (5.19) Finally, the hydrograph can be constructed using T/Tp and Q/Qp values presented in Table C5 56 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt LtdArjo Dedessa Irrigation Project Meteorological apd 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 Caclim- ent Area Stream Max. Elev Min. Length Elev. Stream Slope C :(for Rational Method) CN scs Method (km') (kmj (m asb (m asl) (%) l CDR-16 27. J 5 15.50 24o0 1336 0.0725 0.24 71 2 CDR-19 40.25 13.50 2360 1339 0 075t> 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 021 70 6 CDL-28 61.00 27.00 1900 1335 0 0209 0.21 70 7 CDL-33 70.00 17.50 1990 1330 00377 0.22 71 Table 5.2 Characteristics of Flood Hydrographs Cachm- ent Base Flow Ct Tc (time of cone. Tr T L(adj) Tp (peak time) Tp(adj) Tb (km) (m'7s) (hrs) (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 4.63 449 4.97 85.88 5 CDL-25 10.34 1 48 4 98 0.90 12.62 12.06 14.09 10987 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 6.79 766 93 09 57 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 5.3 Estimated Average Floods May 2007 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 58 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 8 FLOOD FREQUENCY ANALYSIS 8.1 In troduction In flood frequency ana lys is, the objecti ve is to estim ate a flood magnitude correspon ding to any required return period of occurrence. Th e 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 whicn a particular flooa having magnitude Q- (also known as qunatile) is expected to be exceeded. A reliable estimate of the entire Q-T relationship cannot be obtained from small samples ot 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 trequency analysis (particularly the inaex-flooa metnod) 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,h annual maximum flow. Qm is the average value of at-site annual maximum flow senes. Then the quantile QT is estimated as Qt = Qm.Xj (8.2) Thus, the mean annual flood is the moex-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 Probaoility 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)ZX,.(1-F,)k i=1 (8.3) where Xi = flood having ranked order of i Fi = (i - 0.35)/N = plotting position of the rth ranked flood N = record length The regionally averaged proDability weighted moments were computed as follows: 1. The standardized PWMs were computed for each site as: Xi = Qi/Qm where Xi is the i“' standardized flow, Qi is the ith ranked flow and Qm is the average of the data set 2. For eacn annual maximum flood record the first two probability weignted moments, PWMs, i.e. m10k. k = 1 ana 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 E X,.Nj.(m10k)) MWk = _Ei__________________ _ M Z X,.Nj J=1 (8 4) These M,Ok 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.Arjo Dedessa Irrigation Project Meteorological and Hy drological Aspects May 2007 PWMs M1OO= 1OOOO M1O1 = 0.411964 M102 = 0.250375 8.3 Generalized Extreme Value Distribution Jenkison (1969) introauced the Generalized Extreme Value (GEV) distribution for modeling floods. It has become more important in hydrology since it was recommenced by NERC (1975) for modeling annual maximum streamflows of Bntisn rivers. The GEV distribution is defined as: X = u + (a/k) {1 - (-In F) } k The snape parameter k, can be estimated as: k= 7 859 C + 2.9554 C2 where C = (Miqq — .Midj________ L - In 2 (2.M1oo-6.Mioi-t-3 M102) In 3 the scale parameter a = k.(M,oo - 2.M_wi) (1-2*).r(1-rk) and the location parameter u = Mi00-(a/k).{1-r(1+k)} GEV Parameters C = -0.00061 Gama = 1 0023 u = 0.879428 a= 0.253011 k = -0.00483 8.4 Log-Logistic Distribution (8.6) (87) (88) (8.9) (8.10) 61 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Log-Logistic (LLG) distribution was introduced for flood frequency analysis by Anmed et ai (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 snape parameter c = Mioo-6.M_ioit6.Mio2 Mioo"2.M 101 the scale parameter D = Miqq-2.Miqi c.G and the location parameter a = Mioo — b G where G= ncj/sinn cj LLG Paameters G= 1.051033 a= -0.01767 b= 0.968257 c= 0.173014 8.5 Regionally averaged quantiles < 811> (8.12) (813) (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 penods where LLG distribution gives larger quantiles compared to GEV distribution Estimated flood quantiles oased 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 May 2007 8.6 Choice of Distribution 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 addition, LLG is less sensitive (compared to GEV) to changes in the small values of the annual maximum floods Therefore, LLG/PWM is better than GEV/PWM for modeling AM samples that display a dog-ieg shape when plotted on probability paper In general, LLG/PWM nas been found to be more appropriate for modeling annual maximum floods (AMF) compared to otner distributions. Therefore, LLG/PWM has been applied for estimating design floods required for the project. Thus, Dased 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 exceeaance (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 = 87lm /sec 500 yr return period flood = 1155 m /sec 1000 yr return period flood = 1303 m /sec 10000 yr return period flood = I948m /sec 3 3 3 3 3 3 3 03 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Lta.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 8.1 Estimated Flood Quantiles Based on GEV Distribution May 2007 T Return period Xt Growth factor Mean Max. Daily Discharge Gauging Gauging Wama at Site (1) Site (2) Junction Dam site Momentary Peak Gauging Wama at Site (2) Junction Dam site (years) (ratio) (m /s) 3 (m /s) 3 (m /s) 3 (m /s) 3 Gauging S.i*t 5e (1) (m7s) (m3/s) (m3/s) 2 0.95 670 214 238 354 788 272 264 392 5 1.23 869 278 309 460 1022 353 342 509 10 1 42 20 1 60 50 1 83 100 2 01 200 2.19 500 2.43 1001 320 356 530 1178 406 395 586 1129 361 402 597 1329 458 445 661 1296 414 459 686 1526 526 509 759 1422 455 505 752 1674 577 559 833 1549 495 550 819 1822 629 609 907 1716 549 610 908 2020 697 676 1005 1000 2.61 1844 589 655 975 2170 749 726 1080 2000 2.79 1972 631 700 1043 2321 801 776 1155 5000 3.03 2143 685 761 1134 10000 3.22 2273 727 808 1203 Average 1 707 226 251 374 2522 870 842 1255 2675 923 895 1331 832 287 278 414 Note The analysis is basea on regional flood frequency analysis based on Gene distribution with parameters estimated by probability weighted moments method Table 8.2 Estimated Flood Quantiles Based on LLG Distribution Value (GEV) T Return period (years j 2 5 10 20 50 Xt Growth factor Mean 1 Max. Daily Discharge Momentary Peak Gauging Site i Gauging Site (2) Wama at Junction Dam site Gauging Site (1) Gauging Site (2) Wama at Junction Dam site (ratio) (m /s) J (m /s) 3 (m /s) 3 (m /s) 3 (m /s) 3 .m/s, (m /s) 3 m /s 0 95 672 1 21 854 1 39 1 58 1.86 982 1118 1317 100 200 500 1000 2000 5000 10000 Average 3.55 4.17 4Z1 1 707 1488 1680 1972 2225 2511 2947 3326 215 238 356 273 304 452 314 349 519 357 397 591 421 467 697 476 527 787 537 597 889 630 700 1043 2320 800 711 791 1177 2619 903 803 891 1329 2956 1020 942 1047 1559 3468 1196 1063 1182 1760 3915 1350 791 273 1005 347 1156 399 1315 454 1550 535 1751 604 1977 682 226 251 374 264 394 336 500 386 575 439 654 517 771 584 871 662 984 776 1155 876 1303 987 1471 1159 1726 1309 1948 832 287 64 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo 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 aam 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 proDable maximum flood (PMF) arrives ana the wave surcharge allowance must be tor heights greater than 0.6 m. Categories B ana 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 De 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, Hersfieid (1961) suggests the use of following equation to estimate 24-nr PMP in region so as to superimpose it on design unit hydrograph to give the PMF PMP24 = Pm +K.Sn = Pm (1+K.CV) Where PMP24 - 24-hr probable maximum precipitation Pm - mean of the 24-hr annual maximum over the period of record Sn = standard deviation of the 24-nr annual maximum CV = Pm/Sn = coefficient of variation K = a constant equal to 15 Water Works Design & Supervision Enterprise (9.1) 65 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 20 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 0l*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 charactenstics 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 Dase 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 66 Water Works Design & Supervision Enterprise In Associate with intercontinental Consultants and Technocrats Pvt Ltd.Ar]o Dedessa Irrigation Project Meteorological and Hydrological Aspects TaDle9 1 Table Cumulative Volume of Probaole Maximum Flood May 2007 Time Cum. Volume Time Cum. Volume Time I Cum. Volume (hrs) (Mm3) (%) (hrs) (Mm3) (%) _ (hrs) ' (Mm3) 1%) J| 0.00 0 000 0 00 103 50 687 8 89 5 207.00 765 3 99 6 4.50 0440 0 06 108 00 698 7 90.9 211.50 765 8 99.6 900 2 936 0 38 112.50 708.3 92 2 216 00 766.1 99 7 13 50 9 389 1.22 117.00 716 4 93 2 220.50 766.5 99 7 18 00 21.87 2 85 121 50 723.2 94.1 225.00 766.8 99.8 22 50 42 15 5.48 126.00 729 1 94 9 229.50 767.1 99 8 27 00 71.51 9.31 130 50 734 4 95 6 234 00 767 3 99.8 31 50 110.5 14 4 135.00 739 0 96 2 238.50 767 5 99.9 36 00 157.6 20.5 139 50 743 0 96 7 243 00 767 7 99 9 40.50 210 4 27 4 144.00 746.5 97 1 247.50 767 9 99 9 45 00 266.4 34 7 148.50 749.3 97 5 252.00 768 1 99.9 49.50 322 6 42 0 153.00 751 7 97 8 54.00 376 4 49 0 157 50 753 6 98.1 58.50 426.4 55.5 162.00 755.5 98.3 256.50 768.2 100.0 261 00 768.3 100 0 265.50 768.4 100 0 63 00 471 6 61 4 166 50 757.2 98 5 270.00 768 5 100 0 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 85.9 171.00 758.6 98.7 274 50 768 5 WOO 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 I I 99 00 675.1 37 9 202.50 764.8 99 5 67 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 9.2 Design Flood Hydrograph Derived from Estimated PMF May 2007 Tl 0/ Ti ------- ~r Qi Ti Qi Ti Qi Ti ■4----------------------- (hr) ------------■ Q> J (hr) (m3/s) (hr) I im3/s) Uli ^3/S) (hr) (m3/s) 0.00 188 45.00 3690 90.00 1309 135 00 451 180.00 251 2 25 216 47.25 3655 92 25 1239 137.25 433 182.25 248 4.50 241 49 50 3620 94.50 1169 139 50 419 184 50 244 6.75 339 51 75 3515 96.75 1099 141 75 402 186.75 241 900 451 54 00 3410 99.00 1028 144.00 384 189.00 237 11.25 573 56.25 3270 101 25 958 146.25 367 191.25 234 13.50 748 58.50 3130 103.50 923 148.50 349 193.50 230 15.75 958 60 75 2990 105 75 853 150.75 332 195 75 230 1800 1169 63.00 2815 108.00 818 153.00 314 198 00 227 20.25 1449 65 25 2674 110 25 783 155.25 297 200 25 223 22.50 1694 24 75 2009 27 00 2289 67.50 2499 112 50 748 157.50 314 202.50 220 69.75 2324 114.75 678 159 75 307 204 75 220 7200 2149 117 00 643 162.00 300 207 00 216 29.25 2604 74 25 2009 119 25 608 164.25 290 209.25 216 31 50 2885 76.50 1904 121.50 573 166.50 283 211 50 213 33.75 3095 78 75 1764 123.75 552 168 75 279 213.75 213 36 00 3305 81 00 1659 126 00 531 171.00 272 216 00 209 38.25 3445 83.25 1554 128 25 514 173.25 269 40.50 3585 85 50 1484 130 50 496 42 75 3655 87.75 1379 132.75 472 175.50 262 218.25 209 220.50 209 177.75 258 222 75 206 b8 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects 10 SEDIMENT ANALYSIS 10.1 Estimation of Sediment yield May 2007 Suspended sediment data from Stations 14001, 14014 and 14005 were obtained These discharges are given in Annex E5. Suspended concentration rales 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 nas been derived Gs = 0 078 Q15 C0 1) ? 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 piannmg will include assessment of the probable rate of sedimentation in order to predict the useful life of the proposed reservoir in estimating reservoir sedimentation matenals onginating as oed load will be assumed to have a density of 1 4gm/cc and matenal cameo in suspension will be assumed to have a density of 1.2 gm/cc. The oed loaa at the dam sites shall be assumea to be 15 percent of the suspended load Monthly total sediment load (suspenaed and bea load) and accumulated total sediment load at the reservoir site are given py Table 10.2 and 10.3 respectively 09 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. 2 Distribution of sediment in the reservoir So far the sediment load likely to deposit in the reservoir nas been estimated But estimating the sediment inflow to the reservoir is not enough as how h igh the sediment will accumulate in the reservoir is also important According ly Area-Incremen t method has been used for this purpose. The method is expressed as: Vs = Ao(H - Ho) * Vo Where (102) Vs = sediment volume to be distributed Vo = sediment beiow the new zero elevation H = original reservoir depth from the stream bed level Ho neight to wnicn the reservoir is completely filled with sediment, i.e , = neight of the new zero elevation Ao surface areas of the reservoir at the new zero elevation ano 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 ana sediment load No Station Area (km ) 2 Module 103Vyr Loss t/km2/y Vales of C in; Qs =C.(Qw)1 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 Meqemie 4674 702 150 0.061 6002 Aboayjat Sudan Border 172254 335170 1946 0.165 Arjo Dedessa Dam site 5278 776 147 0.078 ____________ 70 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May_2007___ 3 Table 10.2: Monthly Total Sediment Load at the Reservoir Site (in lOOOjn } _____________________________________ _____ ______ Jan Feb March April May June July Aug Sep Oct Nov Dec Annual Avg 2 487 33 1 14 1 71 4 51 27.2 131 1 248.5 211 5 720 7 19 29 6 87 775.6 Stddev 1 711 01 1 11 1 72 4.2 17 6 62 72 98 19 92 6 99 01 14 7 4 95 304.5 CV 3.634 01 5.75 5 31 4 91 3 42 2 526 2.086 2.311 4 349 4.024 3.8 2.07 Skew 7.366.29 8.83 7 54 11 4 7 48 3.696 0 678 3.509 7 051 10.92 8.77 4.57 Table 10.3 Accumulated Total Sediment Load at the Reservoir Site Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 10.4: Distribution of Sediment in the Arjo Dedessa Reservoir May 2007 r 50 years sediment load Ho = 2.03 m A - 4 C*) U-2 — 100 years sediment load Ho = 3 42 m Ao = 3.15 Mm2 tm asJL Original area Mm') Original capacit y 1 Mm ) — • Depth imj Sedime nt volume 3 (Mm ) Revised area (Mm’) Reviseu capacit Mm ) Eiev m asl) Original area 1 (Mm ) Original capacity Depth Sediment volume (Mm') Revise d area | (Mm1 Revised capacity 12 3456712 3. L5 6 7 _. 1346 56.76 629.8 27 38 7 55 24 591 1 1346 56 76 629 8 27 774 53.61 5524 I 1343 48 13 466.4 24 34.2 46 61 432 2 1343 48.13 466.4 24 68 44 98 398.4 1340 39 92 331 8 21 29 6 38 41 302 2 1340 39 92 331 8 21 58.6 36 78 273 3 1337 32.17 224 18 25 1 30 66 198.9 1337 32 17 224 18 49.1 29 03 174 8 1334 24 93 140.7 15 20 5 23 41 120.2 1334 24.93 140 7 15 39 7 21 78 101 1331 18.24 79 64 12 16 16 72 63 67 1331 18.24 79 64 12 30.2 15 09 49 4 1328 12.19 38 24 9 114 10 68 26.82 1328 12 19 38.24 9 20 8 9.046 17 44 1325 6.911 13.6 6 6.88 5 395 6.724 1325 6.911 13.6 6 114 3.765 2.239 1322 2.619 2.322 3 2.33 150 years sediment load Ho = 4.69 m Ao = 4.90 Mm2 1322 2.619 2.322 3 1.92 - 200 years sediment load Ho = 5.89 m Ao = 6.73 Mm2 Etor Original Original capacit area Depth Sedime Revised nt Rewsed capacit D riginal Original 1 Sedime Revised Revised (Mm’j 17 > __ volume area (Mm^) (Mm2) W) Elev area capacity (m asl) (Mm1) (Mm’] Depth volume area r capacity 333 (Mm ) (Mm ) (Mm ) 1234 567123 4 ------- F 1346 56.76 629.8 27 116 51.86 513.3 1346 56.76 629 8 27 155 50 02 474 7 1343 48 13 466 4 24 102 43.24 364.6 1343 48 13 466.4 24 135 41 4 331.5 1340 39.92 331.8 21 87 1 35 03 244 7 1340 39.92 331 8 21 115 33 19 217 1 1337 32.17 224 18 72.4 27.28 151 5 1337 32.17 224 18 94.5 25 44 129.4 1334 24 93 140 7 15 57 7 20.03 82.96 1334 24.93 140 7 15 74 3 18 19 66 37 1331 18 24 79.64 12 43 13.34 36 6 1331 18.24 79.64 12 54.1 11.5 25.52 1328 12 19 38.24 9 28 4 7 297 9 887 1328 12 19 38.24 9 33.9 5 457 4 326 1325 6.911 13 6 6 13.7 1325 6 911 13 6 6 13.7 72 Water Works Design & Supervision Enterprise 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 MoVVR database Abbay River Basin Master Plan Stuoy Report (1998). The samples were taken as part of the supporting measurement for tne aquatic study and appear to represent the only 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 snown in Table 111 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 ana cations are directly related to tne electncal 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 or 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*’)/]0 5 73 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants ana Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrologic al A spects May 2007 The higher the SAR value of the water the I ess suitable will be for irriga tion purposes The maximum computed value am ong the re adin gs is 0.29 which is less than 10 This illustrates that the water is very much suitable for irrigation purpose. Chloride The chlonde 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 Sample date Elevation (m asl) at Bedele bridge at Gimbi bridge Comment 13/08/96 1300 14/08/96 1200 TDS (gm/l) 20 20 N EC (Os/cm) 60 50 N pH 6.74 6.97 N Na” 3.3 3.0 N K* 1.9 2.5 N Ca” (mg/l) 64 9.6 N Mg” (mg/l) 2 43 1.4 N Cl (mg/l) 1.0 2.0 N SAR 0.29 0.25 N WO Result for Major Rivers (BCEOM 1996, Cited By BCEOM Abbay River basin study 1998) Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.I I I IArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects ___ May 200,------------------------ 12. DESIGN FLOOD 12.1 Syntheti c Hydrograph Among several known methoas of unit hydrograp hs, the one de velop ed by Synder (1938) is most commonly used. The method is derived fro m drainage bas ins in the Ap palachian Mountain region s in the United States ranging in are as from 25 km to 25,000 km The relations of unit hydrograph characteristics and catchment characteristics are expressed as follows (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 = nver distance from the station to tne point of interest nearest the centroid of the drainage area (km) L = nver distance from the station to the upstream limits of the drainage area (km) The catchment characteristics (sucn 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 discnarge 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 or human life would be expected For sucn condition, a design flood corresponding to al0,000-year return period has been proposed The volume of flow in 1000-year return perioa flood hydrograph is about 400Mm3 75 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 data used to complete surcharge storage due to the design flood and routing calculations were inflow hyorograph 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 hydrograpn 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 surcnarge storage and spillway crest (outlet) geometry until the desired outflow hydrograph nas been achieved A spillway with ogee shaped crested weir has been assumed The equation generally used for such broad-crested weir is where: Q= Q = CLH15 discharge, in m /sec (12.2) 3 C = broad-crested weir coefficient L = broad-crested weir length, m H = head over weir crest, m If the upstream edge of a weir is so rounded as to prevent concentration ana if the slope of the crest is as great as the loss of head due to fnction, flow will 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 SteP 7 Developing an inflow hydrograph, stage-discharge curve for the proposed storage facility Step 2: Selecting a routing time period, Dt, to provide at least five points on the rising limb of the inflow hydrograpn 76 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Step 3. Using the storage-discharge data from Step 1 to develop storage characteristics cu 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 Qi = outflow rate at time 1 m3/sec 11 = inflow rate at time 1, m3/sec 12 = inflow rate at time 2. m3/sec (123) Step 6. Enter the storage characteristics curve at the calculated value of S2 f (Q2/2).Dt determined in Step 5 and read off a new depth of water, H2 Step 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 througn 7 by setting values of 11 Q1. S1, and H1 equal to the previous l2, Q2, S2 and H2, and using a new I2 value This process is continued until the entire inflow hydrograph has been routed througn the storage basin. Since Equation (12.3) contains two unknowns, stepwise trial and error procedure is used Results of routed aesign floods based on LLG distribution, half-PMF and full-PMF are presented by Table 12.2, 12.3 and 12.4, respectively Tne elevation - area capacity curves of the reservoir are snown in Figure 12.1 The 10000yr return period design inflow and outflow hydrographs are shown in Figure 12.2 Such inflow and outflow hydrographs for smaller return -------------------------------------------------------------------------------------------------------------------------------------- 77 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 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 < 1O4J where V = (2gHl)05 A = cross-sectional area of barrel (or pipe), V = velocity through the barrel. Hl = total nead loss through the barrel, Hl = (1.5 + f L/D) V /2g L = length of the barrel/pipe D/4 = R = hydraulic mean radius of tne barrel D = diameter of barrel/pipe V = velocity througn the barrel/pipe f = coefficient of friction 2 (12.5) Manning's Formula It is one of the most common formula, which is commonly used for the analysis of problems of flow through cnanneis. but often used for the analysis of pipe flow problems too According to this formula tne discharge througn pipes is given by V = (F/n).D S M 1/2 (12.6) Where V = velocity through the pipe n = Manning s rougnness 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.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects S = slope of the hydraulic gradient or energy slope = h /L. May 2007 t F = is constant equal to 0 39685 L = length of the pipe fm). h L = head loss through the pipe (m) Equation 12 5 can be arranged to express the relations for head loss through a pipe. h L = L [(n/F).V/D ' 232 ] (127). Combined Formula Combining Equation 12.5 and 12 7 the above two expressions for velocity reduced to Hl = {1,5/2g+L [(n/F) D ' 23 22 )] } V and also V = (H /{1 5/2g + L. [(n/F) D' l 273]2})05 Q = A. (H /{1 5/2g + L. [(n/F) D l 273]2})°5 = (kD /4). (H /{1 5/2g + L. [(n/F) D' 2 273 2 05 l ] }) (12.8) (12.9) (12.10) Where A is cross-sectional area of pipe in m2 Substituting n = 0 0165, g = 9 81 in Equation 12.8 can be expressed as. Hl = {0 076453+ L. [0 041577 D' 273 2 ] }^2 V = (H /{0.076453-L [0 041577 D’ L 273]2})0 5 Q = (0 7857 D ).(H /{0.076453+ L. [0 041577 D’ 2 L 273 2 ] }) 05 Results of routed design flood at Coffer Dam of Ago Didessa Reservoir are presented in Table 12.5. These results are available for 10, 20 50 and 100 year return period floods. According to the criteria, the appropriate results could be adopted tor designs Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.I I I p pArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Table 12.1 Catchment Characteristics Arjo Dedessa Catchment May 2007 Characteristics Dimension Area (km2; 5278 Length (km) 199 Centroid distance (km) 141 Max elevation (m asl) 3012 Minimum elevation (m asl) 1315 Elevation difference (m; 1697 S (m/m) 0.0085 Ct 1.53 Tc (hrs) 24.00 Tl (hrs) 33.00 Tr (hrs) 4.40 Tuadj) (hrs) 38.00 TP (hrs) 45.00 Table 12.2 Routed Design Flood at FRL Corresponding to 1352 m (a) Based on LLG distribution Max Surface Surcharge Ljmj Qout (m /S) 3 H m Area (km ) Storage (Mm ) 2 3 50 871 75 1031 100 1154 125 1253 3.97 3.39 3.02 2.75 Peak inflow = 1950 m3/s 87 06 85 20 84.01 83.14 1340 1 1288.0 1255 0 1231.4 150 1333 2.54 82.47 1213.1 175 1399 2.36 81.91 1198.3 (b) Based on Half-PMF L(m) Qout (m3/s) Hm () Max Surface Area (Km ) 2 50 75 798 941 100 1051 125 1140 150 1212 175 1273 3 75 3.19 2 84 2.58 2.38 2.22 Peak inflow = 1780 m3/s 86 34 84.56 83 43 82.61 81.97 81 45 Surcharge Storage (Mm 13198 1270 3 1239 1 1216.9 1199 7 1186.0 80 Water Works Design & Supervision Enterprise In Associate with intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects (c) Based on PMF Qout (m /s) May 2007 Max Surface Surcharge 2 Storage (Mm ) 3 H (m) Area (Km ) 50 1668 75 2008 100 2265 125 2466 150 2626 175 2756 6 13 5.29 4 73 4 32 3 99 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 Max Surface Surcharge Limy Qout(m /si 3 Area (Km . Storage iMm ) 2 3 50 75 812 964 100 1083 125 1180 150 1261 1329 175 (b) Based on Half-PMF 3.79 3.24 2.89 2.64 2 44 2.28 Peak inflow = 1950 mis 96.26 94 57 93 48 92.70 92 09 91.59 1601.8 1546 7 1511.9 1487.1 1468.0 1452 6 Max Surface Surcharge L(m) Qout (m /s) 3 H (m) Area (Km ; 2 Storage (Mm ) 3 50 746 3.58 95.61 1580.6 75 881 3.06 93 98 1527.9 100 988 2.72 92.95 125 1495.0 1075 2 48 92.20 150 1148 1471.6 2.30 91 63 175 1208 1453.7 2.14 91.16 ----------11439.2 Peak inflow = 1780 m3/s ---------------------------- 1 ------------------------------------------- --------- --------------------------------------------------------------- 81 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.u IN IN M N N N N Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects (c) Based on PMF ------------------------------------------------------------ —r--------------------------------------------------------------- - --------------- -I L (mj 3 Qout (m /s) Surcharge Storage (Mm3) r--------- 1 ------- 50 1540 75 1867 100 2118 125 2320 150 2483 175 2618 H (m) 5.81 5 04 4.53 4 14 3 84 3 59 Max Surface Area (Km2) 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 LLC distribution L(m) Qout (m /s) H (mj 3 Max Surface Area (Km ) 2 3 Surcharge Storage (Mm ) 50 800 3.75 99.11 75 951 3.21 97 49 100 1069 2.87 96 45 125 1165 2.62 95.71 150 1246 2 42 95 12 175 1314 2.27 94.65 1693.0 1637 1 1602.0 1577.0 1557 7 1542.0 Peak inflow = 1950 m3/s ri (b) Based on Half-PMF N 1 L(m) Qout (m /sj H(m) 3 Max Surface Area (Km ) 2 — Surcharge Storage (Mm ) 3 ri 50 735 75 869 100 975 125 1061 150 1134 175 1195 3.55 3.03 2.70 2 46 2 28 2 13 il 9849 96 93 95.94 95.23 94 68 94.23 1671.5 1618.2 1584.9 1561 2 1543 1 1528 5 Peak inflow = 1780 m3/s 82 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects (c) Based on PMF May_2007___ i------------ r L (m) Qout (m /s) 3 H (m) Surcharge Storage (Mm --------------- — 11 50 1515 5.75 75 1838 4 99 100 2088 4.48 Max Surface Area IKm2) 105.09 102.81 101.30 1905.2 1823.3 1769.3 125 2289 4 11 100 17 1729.8 150 2453 3 81 99.28 1698.5 98 53 1672.9 Peak inflow = 3690 m3/s Table 12.5. Routed Design Flood at Coffer Dam of Arjo Didessa Reservoir 175 2588 3.56 T= 1C yrs, Peak = 654 m /s , —“1 3 T = 20 yrs, Peak = 654 m /s D (m) 0 Elev D (m) Q Elev (m3/s) (m asl) im3/s) (m asl) 5.0 210 1337.98 5.0 211 1338.22 5.5 223 1333 01 5.5 225 1333.29 6.0 239 1330.00 6.0 243 1330.32 6.5 258 1328.06 6.5 263 1328.40 2x4 0 220 1334 18 2x4.0 222 1334.45 2x4.5 243 1329.86 2x4.5 247 1330.19 3 T = 50 yrs, Peak = 771 m /s 3 T = 100 yrs, Peak = 871 m /s ("v L D Q Elev D Q Elev (m3/s> (m asl) (m) (m3/s) (m asl) 5.0 213 1338.59 5.0 215 1338.89 5.5 229 1333.70 5.5 232 1334.05 6.0 248 1330 79 6.0 253 1331 19 6.5 271 1328.90 6.5 277 1329.32 2x4 0 225 1334 86 2x4.0 228 1335.20 2x4.5 253 1330.69 2x4.5 257 1331.10 Note Length of pipe, L = 400 m S3 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.I feg Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 I I I M M 4 M 4 1 4 ri ri J J 4 Elevation-Arca-Capacity Curv® for Arjo Dtacssa Reservoir Area (Sq. Km) Figure 12.1 Elevation-Area-Capacity Curves of Arjo Dedessa Reservoir Inflow and Outflow Hydrographs at Arjo Didessa Reservoir Time (hrei Figure 12.2: Inflow and Outflow Flood Hydrographs at Arjo Dedessa Reservoir 84 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd. Elevation (m)□ischarege (m3/») Dischir.ge (m3/») Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 inflow and Outflow Hydrograph* at Arjo Dlde»*a Coffer Dam. T inflow and Outflow Hydrograph* at Arjo Didessa Co FT ar Dam. T • 20 year* O 25 50 75 100 125 150 t75 200 Tww(hr*| Inflow and Outflow Hydrograpns at Arjo Didessa Collar Dam. T ■ 50 year* inflow and Outflow Hydrograpns at Arjo Didessa Coffer Dam. T = 100 years Tima (hr*) Figure 12.3: inflow and Outflow Flood Hydrographs at Arjo Dedessa Reservoir 85 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Average Hydrograph of Maximum Flows at Arjo Didessa Dam site 15 20 25 Tmm tmonlht) 30 35 Figure 12.4: Average Hydrograph of Maximum flows at Arjo Dedessa Dam Site 86 Water Works Design & Supervision Enterprise In Associate with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo 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 Fiow into the reservoir, o Evaporation from the reservoir. o Rainfall on the reservoir o Total irrigation demand, and o Irrigation water release from tne reservoir The simulation sample is provided in annexure B - 8 the description of various column, referred to there in are as below 87 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorologi cal and Hy drologic al 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] convened to volume covering the entire command area Coi [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 ano 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 imulation i nputs a re p rovided i n t he T abies 1 3.1 a nd 1 3.2. The a Dstract o f t he detailed irrigation targeted simulation runs are provided in Table 13 3. With these parameters the contemplated irrigation (Table 13.1) are successful at various reliabilities shown in Table 13 3 88 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Table 13.1: Irrigation Water Requirements for Various Scenarios 3 (for 13700 ha in Mm ) Phase I Phase II Month Roti Rot2 Roti Rot2 Sep 8.38 843 12.43 12.45 Oct 10.41 10 69 13 19 13.72 Nov 2.89 2.90 3.16 3.29 Dec 11.04 12.49 14 02 16 07 Jan 19 00 22 18 24 64 28 61 Feb 23.25 27.87 29.98 34 92 Mar 18 49 22 15 22 99 26.41 Apr 4.98 521 5 09 5.30 May 2.01 2.01 2.01 2 01 Jun 21 64 21 64 32 42 32 42 Jul 5.97 5.97 8.95 8 95 Aug 6.89 6.89 10 33 10.33 Total 134.93 148.43 179.22 194.49 Tabie13.2 ReservokCharacteristics at Dead Storage Level Description Minimum drawdown level Minimum nver bed level Area at dead storage level Dead storage Uni) Qunatit•fy 1 m.a.s.l 1350.0 m.a.s.l 1320.0 | km2 67.88 Mm3 874.7 89 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Table 13.3 Storage Reservoir Characteristics and Reliability Levels Description Unit i n] 75% I Reliability level 80 % 85% 90% Phase I, Rot 1 Dam heighqat spillway c.l) Spillway crest level m mas.I 30.89 30.98 31.08 31.24 I I 95% I 31.42 Area at normal water level km2 Live storage Total storage Mm3 Mm3 Spill over the spillway Mm3 Spill to live storage ratio Phase I. Rot 2 Dam heightfai spillway c.l) m m.a.s.l Spillway crest level km2 Area at normal water level Mm3 Live storage Mm3 Total storage Mm3 Spill over tne spillway Spill to live storage ratio Phase II. Rot 1 Dam height(ai spillway |C.I) Spillway crest level m m.a.s.l Area at normal water level km2 Live storage Total storage Mm3 Mm3 Spill over the spillway Mm3 Spill to live storage ratio Phase II, Rot 2 Dam heighqat spillway c.l) m Spillway crest level Area at normal water level m.a.s.l km2 Live storage Total storage Spill over the spillway Spill to live storage ratio Mm3 Mm3 Mm3 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 1094 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 I 31.05 31.14 31.24 31.41 31.59 I 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 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 87 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 90 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa irrigation Project Meteorological and Hydrological Aspects May 2007 14. DEDESSA SUB-BASIN MODELING 14.1. Modeling for Arjo Dedessa dam fo ri rrigat ion The simmlations discussed in previous sectio ns is fo ra com prehens ive ana lysis of Dedessa dam. which is the main focus of the TOR A de tailed Ms-E xcel based mod el, 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 pnase I development of Deaessa dam ■ Irrigation command ■ Full reservoir level ■ Storage at full reservoir ■ Deaa storage level ■ Volume at Dead stage level ■ Live storage 13,700 na 1351 14 m 961.8 Mm3 1350.00 m 874.67 Mm3 87 10Mm3 ■ River bed levei 1320.00m ■ Area at Dead storage level 67 88 km2 ■ Area at full reservoirs level 71 14km2 ■ Irrigation Demand 148 43Mm3 □ For phase II development of Dedessa dam ■ Irrigation command 13 700 ha ■ Full reservoir levei 1351 39 m ■ Storage at full reservoir level 981 7 Mm3 • Dead storage level 1350.00m • Volumes at dead storage level 874 67 Mm 91 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa 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 pnases satisfy contemplated irrigation with 80% reliability, in the phase I and phase II, the cropping patterns envisagea are different However, for the final design of Deadesa dam, it has to be based on phase II development with tne above aam 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 wnole, 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 oam 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 tn 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 Deen 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 undertaxe simulation exercise of various components with alternatives. 92 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants ana Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects 14.2.1 Power Generation in Dedessa Dam May 2007 The Deaessa aam 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 irngation 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 i rrigation r equirement shall b e u sed f or power g eneration. T here will b e a s eparate 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 oead storage level • Area at full reservoir level Full Reservoir Level = 1356 m ■ Storage at full reservoir level ■ Live storage ■ Deaa 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 93 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorologic al and Hydrol ogical Aspe cts May 2007 The effective turbine cente r was fixed at 1322.00 m eleva tion. This of cours e, needs to be finalized as per ground condition and dam head/or otherwise, other location based powerhouse Also, tne plant factor adopted in the basin simulation runs is unity, and with unrestncted i nstalled c apacity. B ased o n a ctual b udget a nd p ower requirement a nalysis d y 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 vanous runs are shown in Figures 14 1 (a1) to 14 1 (b4). These figures are useful to reckon the monthly power generation at various exceeoance 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 Anjosim' was, slightly recoded for maxing simulations for increased FRL considerations and exploring the possibility of power generation at a higher levei. though the exercises are beyond the scope of the present TOR. A large number of runs ot 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 basea power releases 94 Water Works Design & Supervision Enterprise In Associauon with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo-Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 Domain 3: keeping the power outlet at the same 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 ni. 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 n With FRL at 1374, the firm power is 17.20MW in. 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 n At FRL 1372m, the 97% power is 18.1 MW ni. Al FRL 1374m, the 97% power is 18 95MW lv. At FRL 1376m, the 97% power is 20MW 95 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects 14.2.3 Reduction In flows at Dedessa Sub-basin May 2007 In either of the cases, covering 8 runs of simulation, there is no detrimental effect on the downstream flows of Dedessa sub basin. The maximum consumptive utilization is only for irrigation, which is only 194.49Mm annually, as the additional 3 releases made for power are not 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 3 of 14,033mm3 (BCEOM Master Plan study). This will get reduced to 13,838mm because of 3 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 furtner different scenario. At this stage, it could be saia 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 De at 1322 m in all the runs. With a plant factor of 0.6, the installed capacity could be arouno 33MW. Hydroiogically, the simulations can be perrormea funner without any constraints, provided that there are no geological, geothechmcal, 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 to form up power generation, even at higher FRLs, a prefeasibility study is required for exploring the possibilities of increasing the height of dam and establishing the technical feasibility and economic viability for generation of hydro-power 96 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects ______ May_20Qj__ Table 14.1: Total Monthly Release (Irrigation plus Power) options for various FRL values considered Options FRL = 1353 m __________________ FRL = 1356 m Option i 75 MmJ for all months Twice of monthly irrigation releases Option II L 75 Mm - May to 3 September & 50 Mm - 3 Three times monthly irrigation releases Oct. to April Option III L 75 Mm - May to 3 100 Mm3 for all September & 40 Mm - months 3 Oct to April Option IV 150 Mm - May to August 3 & 40 Mm3 - Oct. to March, 75 Mm3 in Sept & April 75 Mm3 - September to April & 100MCM - May. to August Table 14.2: Annual Energy generations at Dedessa dam for the various options FRL Release Scenario i Options Mean Level Annual Energy Production (GWh) at Exceedance ___ Probability Levels of__________ 50% 75% 90% 95% 97% 1353 m I II 28 0 28.9 26.5 24.3 22.7 20.5 III 25.3 25.9 25.5 22.9 21 3 19.6 IV 436 44.7 433 40.1 36.3 28.3 32.0 32.3 29.8 27.3 25.2 228 1356 m I II 24 5 24.5 24.3 24.0 23.8 23 6 III 540 55.2 50 6 45 9 42 9 39.2 I IV 47.6 48.5 47.5 43.8 40 9 38.1 11.9 12.0 11.9 11.8 11.7 11.7 Water Works Design & Supervision Enterprise 9-> In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 (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 98 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 (a.4) Power duration curve for FRL - 1353m Option IV (b.1) Power duration curve for FRL = 1356m - Option I (b.2) Power duration curve for FRL = 1356m - Option II Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 21X77 (b.3) Power duration curve for FRL = >3560, - Option III (b.4) Power duration curve for FRL = 1356m - Option /V lot) Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.ArjO'Dedessa Irrigation Project Meteorological and Hydrological Aspects 15. RECOMMENDATIONS ON TRAINING NEEDS May W7 It is very heartening development that the wafer resources exploitation tor optima* ut uza. towards economic stability is getting the major thrust in Ethiopia With phase of actrv soon, the rich river basins will be impounded in different storages associated with a number o runoff the river schemes either for irrigation or power or in a multi objective sense As suet the present scenano. the hydrological planning and design are in the usage However wr.e' 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 ndertaxe o peration which has i mmerse a dvantages H ence. 111 s r ecommenaec t hat expens on Hydrology and Hydrological modeling should be identified for undergoing such trainings in Institutions/umversities 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, wnere many institutions. Universities. River basin authonties ano research stations could be identified for offering such trainings Such trained personnel with expertise in hydrology will be able to head future river basin authonties for optimal real time operation of the systems 101 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt LtdArjo Odessa Irrigation Project Meteorological and Hydrological Aspects M«y 2907 references Admasu Gebeyehu 1988 Regional Analysts or- Some Aspects o< Stream' uw .naracte' «9C* m Ethiopia (Unpublished Draft Report) August’988 Admasu Gebeyehu 1989 Regional flood Frequency Analysis PhD them P • Technology. Bulletin No TRlTA-VBI 148. Stockholm Sweden BCEOM 1999 Abbay River Bam Integrated Development Master Plan Project Pheae 2 Data Collection Site Investigation Survey and Analysis Section n Sectora Shx>es Volume III Water Resources Part I - Climatology and Part II - Hydrology BCE OAZ French Engineering Consultants - in association with ISL and BRGM ERA (Ethiopian Roads Authority). 2002 Drainage Design Manua' Hydrology Fiddes D, 1977 Flood estimation for small East African rural catcnments Proceetf.ng Institution of Civil Engineers. Pari 2. 63 21-34 (1977) Gray. D M Editor in Chief. 1971 Handbook on the Pnnciples 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 Drv 8' No Hy 5. 99-116 Matalas N.C 1963 Probability Distribution of Low Flows Statistical Studies in Hydroiog. Geol Survey Prof Paper 434-A Shaw Elizabeth M 1988 Hydrology in Practice International Van Nostrand Reinhold USBR (Unitea States Department ot 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 Wate* Resources Development Master Plan tor Ethiopia Final Report Volume III Annex A Hydrology & Hydrogeology Addis Ababa I'V Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Fn tMArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects ANNEXES Annex A: Results obtained from the Meteorological Analysis A1: May 2007 I I M °i Year May June July__ Aug ; Sept _ Oc_I___ Nov_ Dec 1961 222 21 8 24 7 24 0 23 2 21 5 20.7 20 2 21 6 22 0 21 9 19 7 1962 20 0 21 8 24 9 22 5 23 2 21 0 20 0 20.0 21 3 22 1 20.2 190 Jan Feb March April 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 21 7 23 2 24 3 16.3 15.9 21 6 21 1 20 8 21 4 21 7 24 6 21 3 I 21 7 22.9 25 4 24 6 23 7 21 5 20 4 20 4 21 4 22 0 21 5 20 8 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 N 195 22.5 25 1 24 8 23 7 21 2 20 7 20 5 21.3 21 1 23 0 18 7 19.9 224 23 6 24 5 24 1 21 6 21 6 21 1 21.2 21 4 21.2 19 6 224 23.2 25.1 24 6 24 0 22 0 20 7 20 7 21 5 21 7 21 2 169 18.2 N N 21.5 22.9 25 0 24 9 24 3 22 0 21 4 20 8 21 6 22.8 22.4 19 8 21 6 20.4 23 9 24 7 23.7 21 1 21 0 19.9 21 1 21.7 18 2 21 5 23 1 24.2 24 9 23 2 21 0 21 8 21 3 21.6 22 3 22 8 20 2 22 7 22 6 25.8 26 8 24 1 21.8 21 3 20 8 21 5 21 7 21 7 17 4 21 2 23 3 25 3 23.9 239 21 8 20 8 21.3 21.3 21.2 19 1 19.0 21 0 23 6 25.9 24 8 23 7 21 7 20 5 20 2 21.3 21 9 20 4 18 9 20 6 23 9 24 8 24 3 23.1 21 0 21 0 20 8 21.6 22 4 22.5 23.0 23.5 24.9 25 3 24 4 21 4 21 0 21.3 21.9 23.5 22.3 23 0 197 20.9 21 1 22 8 26.1 25.6 23.8 21.9 20 9 21.2 21 1 20 9 20 4 22.2 23 5 24 7 24 2 24 2 21 9 21.3 21.6 22 0 22 3 21 6 20 9 22 3 24 1 26.1 25 8 24 4 22.3 21 1 20 8 22.0 22 0 22 4 22 6 262 25 1 24 7 22.3 20 6 21 1 21 5 22 0 19.5 19.2 22 7 22.3 23 8 24 9 23 5 21.9 21.2 20.7 21.6 21 8 22.0 21.6 23.0 22.3 20 6 20 3 23.6 26 1 256 250 22.8 22 3 21.8 21 7 22 4 18 6 20 6 20 6 25.4 26.2 24 5 21.9 20 9 20 7 21.1 20.2 21.5 23 4 20.6 21.5 22 9 257 25 1 24.0 21.7 20 6 20 4 21.5 22.1 19 7 21 5 24 7 23 9 24 6 24.6 22 0 21 3 21 1 21.2 21 7 22 0 20 4 21 8 23 0 25 4 25 1 24 2 22 6 22.2 21 6 21.9 23.1 22.7 20.6 20.2 22 4 24 5 25.1 25 8 25.3 22 5 21 3 21.6 21 9 22 5 18 8 21.3 22.3 24 6 24 5 23.3 21.9 21 3 21 6 21 7 22.0 21 9 21.6 21 0 21 9 24 8 25.1 186 224 21 4 21 4 21 9 22 1 22 4 20 9 ri 23.0 236 25 1 25 1 24 6 226 21.3 20.8 22 0 21 4 21 4 22 1 24 1 252 252 23 5 24.3 256 24.2 26.8 24 9 24 5 26 4 26 5 24 1 26 3 25.9 224 26 9 25.5 24 9 27 4 27 7 22 8 26.2 26 3 22 9 26 6 266 24.3 26.0 264 23 6 26.9 25.9 24 5 26 4 25.7 24 2 26.2 26 5 182 22 6 21.6 22 3 226 23 4 24 6 21 9 21 6 23 0 23.2 21 9 24.2 24 6 22 3 24 4 22.7 24.3 22.3 25.3 23 1 24 7 21 9 24 4 23.1 262 23 4 249 22.8 255 22.6 25.5 230 25 8 22 8 25.8 23.2 25.6 22.8 21 1 21.3 21.8 21 4 21 4 21.8 21.1 21 5 21 8 21 9 22 1 22.3 21 7 21.8 22 4 22.3 22.3 23.2 22 4 22 3 23.1 21 6 21.3 22 9 21.9 21 8 23.0 22.0 22.2 23.0 22 7 22.2 22.8 22 0 222 22 7 21 5 22 1 22.5 22 7 22 9 22.0 23 0 22 4 24 0 24 2 23 5 24 0 24.2 23.3 23 0 22 6 21 8 21.7 23 3 23.3 22.0 25.1 22 0 21 0 23 5 23.6 23 1 23 5 23 2 21.3 196 20 0 22.2 202 22 9 19 1 19.8 20 8 21 6 22 7 206 21 8 4 4 103 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects A2: Estimated Minimum Temperature at Arjo Dedessa Project Area (in C) Year Jan Feo March April Ma? June July Au£ Sept 1 Oct Nov Dec 1961 97 ' 10 5 13 8 14 7 14 9 14 6 14 7 14 3 14.5 13 0 10 3 8 0 1962 88 10 5 13 9 138 150 14 3 14 2 14.2 14 4 13 0 9 5 7 7 1963 95 112 136 99 10 3 14 7 15 0 14 7 14 4 12.8 11 6 8 6 1964 95 11 1 142 150 153 14 6 14 5 14 4 14 4 13 0 10 1 8 5 1965 9 4 106 139 15 1 15 1 14 7 15 1 14 7 14 5 13 2 10 9 8 3 1966 99 11 4 14 2 15 1 15 5 14 8 15 2 14 7 14 5 13 2 10 3 76 1967 85 109 14 1 15.1 15 3 14 4 14 7 14.5 14.3 12 5 10 8 7 6 1968 8 7 108 132 150 15.5 14 7 153 14 9 14 3 12 6 10 0 8 0 1969 98 11 2 14 0 150 15 5 14 9 14 7 14 6 14 5 12 8 10 0 6 9 1970 94 11 1 14 0 152 15 7 14 9 15 2 14 7 14 5 13 5 9 3 74 1971 95 99 134 15 1 15 3 14 3 14 9 14 1 14 2 13 2 10 2 7 4 1972 94 11.2 135 15.2 14 9 14 3 15 4 15 1 14 6 13 2 10 8 8 2 1973 9.9 10 9 14 4 163 155 14 8 15 1 14 7 14 5 12 8 10 2 7 1 1974 9 3 11 3 142 14 6 154 14 8 14 8 15 1 14 3 12 6 90 7 7 1975 1976 1977 1978 1979 1980 9.2 11 4 14 5 15 1 15 3 14 8 14 6 14 3 14 4 12 9 96 7 7 90 11 6 13.9 14 8 14 9 14 3 14 9 14 7 14 5 13 2 10 6 80 10 1 11 4 14 0 154 158 14 6 14 9 15 1 14 8 13 9 108 8 5 92 110 14 6 156 15.3 14 9 14 8 15 0 14.2 13.2 98 8 3 97 11 4 138 14 8 156 14 9 15 1 15 3 14 8 13 2 10.2 8.5 9.8 11 7 14 6 157 158 15 1 15.0 14 7 14 8 13 0 10 3 79 1981 98 109 14 7 15 3 160 15 1 14 6 14 9 14 5 13 0 102 78 1982 99 108 13 3 152 15 1 14 9 15 1 14 7 14 5 12 9 10.8 84 1983 89 11 4 14 6 156 16 1 15.5 15 8 15 5 14 6 13.2 10 5 7.6 1984 90 100 14.2 16 0 15 8 14.9 14 8 14.6 14 2 119 11 0 84 1985 94 11 1 14 4 15.3 155 14 8 14 6 14 4 14 5 12 7 104 80 1986 94 12 0 134 150 158 150 15 1 14 9 14 3 12 8 10 3 8.3 1987 95 11 1 14 2 153 156 154 158 15.3 14 8 13 6 10 7 8.2 1988 98 119 14 0 157 163 153 15 1 153 14 8 13 3 9 7 76 1989 9 3 108 13 8 14 9 15 0 14 9 15.1 15 3 14 6 13 0 10 3 8.8 1990 9.2 10 6 13 9 153 12 0 152 15.2 15 2 14 8 13 0 106 8 5 1991 10 1 11 4 14 0 15.3 159 154 15 1 14 7 14 8 12 6 10 1 7 4 1992 9 7 11 6 14.1 15.4 15.8 15.1 150 15.1 14 7 134 10 3 8 6 1993 9.9 11 4 136 156 15 7 15.4 15.2 152 14 7 13 5 10 2 7.9 1994 9.5 11 7 150 152 15 7 15.2 150 152 14 7 13 0 11 0 8.1 1995 9.8 11 9 14 8 162 16 3 157 15 5 15 6 150 13.6 11.0 9 0 1996 99 11 6 14 7 158 160 14.9 154 15.4 15 1 13 3 10 4 8 2 1997 10 2 10 8 15 1 156 158 157 158 15.8 15.6 14 2 11 8 9 3 1998 10 8 12.1 15 3 169 16.9 159 15 9 15.8 156 14 3 10.3 7 8 1999 96 11.0 14 7 16.0 16.1 15.5 154 15.1 154 13 9 9 9 8 0 2000 95 11 1 14 9 162 164 15 4 156 154 15 5 14 2 11 1 8 4 2001 10 1 11 8 14 6 16 1 16 5 15.6 15 6 15 7 15 5 14 3 11 1 2002 | 102 11 4 15.0 15 8 166 15.5 16 1 15 7 154 13 8 10 9 98 28 2003 9.6 118 148 15 7 16.7 158 156 15 7 15.3 13 6 11 0 8 4 2004 10 6 11.7 14 7 16.2 16.5 15.5 15 3 15.7 15.2 134 10 9 88 Water Works Design & Supervision Enterprise 104 In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa IrrigaiIod Project Meteorological and Hydrological Aspects A3: Estimated Maximum Temperature at Arjo Dedessa Project Area (in ) Year Jan Feb March 1961 34 7 33 0 35 6 April May June July _ A4 33 6 31 7 28 6 26 7 26 1 1970 33 6 34 6 36 0 34 8 33 3 29 2 27 6 26 9 24 4 32.1 30 2 29 1 1971 33.7 31 0 34 5 34 6 32 4 28 0 27 0 25 7 23 9 31 5 33 1 29 1 1972 33 6 35 0 34 8 34 8 31 7 27 9 28 1 27 5 24 5 31 4 34 9 32 3 1973 35 4 34 2 37 1 37 5 32 9 29 0 27.5 26 9 24 4 30 5 33 1 27 8 1974 33 1 35 3 36 5 33 5 32 7 28 9 26 8 27 6 24 1 29 9 29 2 30 3 1975 32 8 35 7 37 3 34 8 32 4 28 9 26 5 26 1 24 2 30 8 31 2 30 2 1976 32.2 36 2 35 7 34 1 31 5 27 9 27 0 26 9 24 4 31 5 34 5 31 5 1977 35 9 35 6 35 9 35 4 33 4 28 5 27 1 27 6 24 8 33 0 35.2 33 4 1978 32 9 34 5 37 5 35 9 32 5 29 2 27 0 27 4 23 9 31 4 31 9 32 6 1979 34 7 35 5 35 6 33 9 33 1 29 1 27 5 27 9 24 9 31 4 33 1 33 4 1980 348 36 5 37.5 36 1 33 4 29 6 27 3 26 9 24 9 30 9 33.6 31 2 1981 35 0 34 2 37 8 35.1 33 8 29 6 26 6 27 2 24 4 30 9 33 1 30 6 1982 354 33 7 34 3 348 32 1 292 27 4 26 8 24 4 30 7 352 32 9 1983 31 7 35 7 37 6 35 8 34 2 30 4 28 8 282 24 6 31 5 34 1 29.8 1984 32 2 31 2 36 5 36 7 33 5 29 1 27 0 26 7 23 9 28 4 35 8 33 0 1985 336 34 6 37 0 352 32 8 28 9 26 5 26 4 24 3 30 3 33 8 31 4 1986 33 6 37.5 34 5 34 4 336 29 3 27 5 27.3 24 0 30.5 33 6 32.6 1987 340 34 8 36 5 35 1 33 1 30 1 28 6 27 9 24 8 32 5 34 7 32 3 1988 35.0 37 2 36 1 36 1 346 29 9 27 5 27 9 24 8 31 7 31 5 30 1 1989 332 33 8 35 4 342 31 9 29 1 27 5 27 9 24 6 309 33.5 34 5 1990 32 8 33 2 35 7 352 25 4 29 8 27 6 27 7 24 8 31 1 34 3 33 4 1991 35 9 35 8 36 1 352 33 7 30 1 27.5 26 9 24 9 30 1 32 7 29 1 1992 34 5 36 5 36 3 353 336 29 6 27 2 27 5 24 7 32 0 33 3 34.0 I 1993 35 3 35 5 35 0 35 9 33 4 30 1 27 6 27 7 24 7 32.2 33 2 31 3 1994 33 7 36 7 38 6 34 8 33 3 29 7 27 3 27 8 24 7 31 0 35 7 31 9 1995 34 8 37 2 38 0 372 34.6 30 8 282 28 5 25 3 32 3 35 6 35 5 1996 35 3 36 5 37 9 36 3 33 8 29.2 28 0 28.2 25 4 31 5 33 7 32 3 1997 36 5 339 38 8 35 7 33 4 30 8 28 7 28 9 26 3 33 8 38 3 36 6 1998 38 4 37 7 39 4 38 8 358 31 1 28 9 28 9 26 1 34 1 33 6 30 5 1999 34 2 34 5 37 8 36 8 34 1 30 4 27 9 27 6 25 9 33.0 32 1 31 6 2000 33 7 34 7 38 2 37 3 348 30 1 28 3 28 2 26 0 33 7 36 0 33 2 1962 31 2 33 0 35 8 31 6 31 8 27 9 25 8 25 8 1963 33 9 35 2 34 9 22 8 21 7 28 8 27.2 26 9 1964 33 9 34 7 36 6 34 4 32 4 28 6 25 3 26 4 1965 I 33 6 33 1 35 7 34 7 32 1 28 8 27 5 26 9 1966 35 4 35 8 36 5 34 7 32 9 28 9 27 6 26 9 1967 30 4 34 1 36 2 34 7 32 4 28 2 26 7 26 5 1968 31 1 33 9 34 0 34 3 32 9 28 8 27 8 27 3 1969 35.0 35 2 36 1 34 4 32 8 29 2 26 7 26 7 Sept Oct Nov Dec 24 4 30 9 ' 33 5 31 4 24 2 31 1 30 9 30 4 24 2 30 6 37 6 34 0 ' 24 2 31 0 32 9 33 3 24 3 31.5 35.5 32 8 j 24 4 31 4 33 6 30 1 24 1 29 6 35 1 29 9 I 24 0 30 1 32 4 31.3 24 3 30 6 32 4 27 0 2001 35 9 36 8 37 4 37 0 34 9 30 5 284 28.7 26 0 34 1 36.2 346 2002 36 2 35.7 38 7 36.2 35 2 30 3 29 3 28 7 25 8 32 8 35 3 36 2 2003 342 37 1 38 0 36 0 35 3 30 8 28 4 28 7 25 7 32 3 35 9 33 0 | 2004 37 8 366 37 8 37 2 350 30 4 27 8 28 6 25 5 31 8 35 5 34 8 | 105 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedrssa Irrigation Project Meteorological and Hydrological Aspects A4 Estimated Relative Humidity at Aqo Dedessa Pro/ect Area (tn percent) Year Jan Feb March April M ?y »June Aug Sept Oct m*j :ao-. Dec 1961 67 52 46 70 71 78 87 87 82 82 72 1962 77 69 64 73 86 85 94 94 96 95 88 M 1963 65 72 63 82 84 85 89 91 89 83 87 85 1964 71 66 57 63 75 82 88 88 92 84 73 75 1965 67 52 50 68 69 78 83 85 84 82 86 ’4 1966 65 68 58 71 73 78 86 90 85 84 80 69 1967 65 50 57 66 76 81 91 89 92 85 89 73 1968 55 66 54 68 75 81 88 85 89 81 76 72 1969 72 68 64 69 75 82 88 89 88 8u 77 65 1970 71 62 64 69 74 79 86 92 89 86 72 66 1971 60 48 50 64 76 81 87 90 87 87 82 76 1972 64 65 56 70 74 79 89 85 86 80 83 75 1973 65 59 57 68 76 81 62 88 89 83 77 63 I 1974 54 49 53 58 78 81 90 90 93 83 72 63 1975 52 59 51 70 74 83 86 93 90 84 73 66 1976 55 55 57 68 79 81 92 91 91 91 93 82 1977 72 66 58 57 66 81 89 88 87 86 82 74 1978 58 61 58 64 75 77 87 86 84 84 75 55 1979 68 65 61 64 70 77 84 85 86 79 69 67 1 1980 59 55 53 68 76 81 86 87 85 79 75 65 j 1981 54 46 56 63 72 76 88 88 83 82 77 64 1982 67 62 55 65 75 80 88 90 90 87 86 79 1983 66 63 61 70 79 78 85 89 89 88 82 72 1984 59 49 47 61 76 80 88 88 86 74 82 75 1985 68 50 51 67 78 80 90 89 87 81 77 70 1986 58 60 57 69 73 85 87 87 88 82 73 72 1987 59 56 63 69 79 81 83 89 86 85 79 75 1988 72 64 49 62 75 82 90 91 93 87 73 66 1989 63 61 60 75 73 79 91 88 91 84 82 35 1990 67 70 62 68 77 81 90 90 91 80 80 71 1991 68 69 60 80 74 83 90 91 89 82 75 75 1992 68 67 54 69 79 84 90 94 88 89 84 79 1993 69 63 56 75 80 85 89 89 90 86 82 69 1994 57 53 55 67 78 86 86 98 89 75 80 72 1995 60 58 57 72 79 90 98 90 92 84 81 79 1996 72 43 63 73 80 83 89 98 87 81 69 70 1997 73 53 53 72 76 81 86 89 87 88 89 80 1998 74 66 62 64 79 66 74 74 93 92 78 6? 1999 61 48 53 65 76 80 90 89 89 92 73 68 2000 55 48 45 67 77 81 89 72 89 93 84 74 2001 67 57 58 69 81 90 91 92 89 88 82 75 2002 71 56 62 64 71 81 85 88 87 84 78 79 2003 71 60 60 66 65 78 90 89 90 84 77 73 2004 66 59 55 70 76 81 87 89 89 91 78 78 It* Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects A5 Estimated Mean Daily Sunshine Duration at Arjo Dedessa Project ea May W (in hrs/day) Year Jan Feb March 1961 83 7 3 7 1 1962 6 7 69 82 1963 72 6.2 8 4 1964 96 8 3 7 7 1965 9 1 8 3 86 1966 78 82 7 1 1967 79 96 84 1968 8 1 80 7 7 1969 82 76 7 5 1970 100 95 97 1971 82 76 7 5 1972 92 88 74 1973 8.5 89 85 1974 79 8 1 73 1975 94 8.3 75 1976 90 8 7 78 1977 62 63 66 1978 94 58 7 5 1979 6.3 66 60 1980 6 1 53 58 April May_ June Jij»y 68 54 6 5 4 3 7 8 90 63 29 20 6 3 6 5 7 6 7 $ Aufl Sep* • Mcv Dec 6 2 9 1 9 2 fl 9 7 4 68 7 3 4 4 2 8 3 8 58 8 0 9 1 8 3 80 8 7 58 30 30 6 8 9 1 9.0 100 6 5 8 3 34 4 3 5 5 7 9 74 84 8 1 8 5 7 8 53 4 2 3 8 60 92 98 8 3 8 1 68 68 2 3 3 2 5 7 65 10 1 83 72 9 1 8 1 4 9 e 1 *- 8 3 8 5 76 90 73 76 6 1 3 7 4 1 62 7 9 8 3 83 78 94 8 0 4 8 4 7 7 5 7 9 8 3 83 . 73 76 6 1 3 7 4 1 62 7 9 8 3 83 94 8 3 64 54 4 a 8 0 8 fl 99 7 7 84 10 1 7 3 32 4 1 7 2 95 9 5 90 67 9 1 5 9 4 8 4 8 58 8 6 0 1 83 64 7 1 50 3 1 1.6 4 1 7 5 84 92 8 7 68 7 1 3 7 4 1 52 66 6 7 3 1 72 7 4 58 3 7 4 1 6 3 6 9 82 83 76 7.8 6 1 23 38 55 68 89 7 1 70 6 7 5 1 24 3 8 42 5 8 78 7 5 6 5 74 5.8 36 3 9 59 79 78 86 1981 8.5 86 46 59 79 58 3.7 45 26 65 96 79 1982 74 60 83 65 71 68 39 37 67 75 66 73 1983 80 76 7.1 80 66 78 54 36 56 66 84 82 1984 8 1 99 81 8.9 66 60 47 43 70 10 1 86 3 1 1985 86 76 75 68 64 59 28 31 58 76 8 7 78 1986 69 6.2 65 53 72 37 3.3 40 41 74 94 82 1987 8 1 78 62 83 58 56 49 42 74 76 83 110 1 1988 84 76 95 84 83 70 27 49 55 85 102 9 1 1989 86 84 73 7.2 96 73 37 5.1 63 83 82 66 1990 92 49 6.3 33 54 46 3.7 39 59 95 89 92 1991 83 73 71 68 54 65 43 62 91 92 89 74 1992 6 7 69 82 78 90 63 29 20 63 65 76 7 5 1993 72 62 84 68 7.3 44 28 38 58 80 9 1 83 1994 96 8.3 77 80 87 58 30 30 68 91 90 10 0 1995 9 1 83 86 65 83 34 43 55 79 74 84 8 1 1996 78 82 71 85 78 53 42 38 60 92 98 83 1997 79 96 84 72 91 81 49 52 83 85 76 90 1998 8 1 80 77 81 68 68 23 3.2 57 65 10 1 83 1999 82 76 75 73 76 61 37 41 62 79 83 8 3 2000 10 0 95 97 78 94 80 48 47 75 79 83 83 2001 82 76 75 73 76 61 37 4.1 62 79 83 83 2002 92 88 74 94 83 64 54 48 80 88 99 7 7 2003 85 89 85 84 10 1 73 3.2 41 72 95 95 90 2004 7 9 81 73 67 91 59 48 48 58 86 01 83 IO Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt ltdArjo Dedesea Irrigation Project Meteorological and Hydrological Asp?< ts A6: Estimated Mean Daily ETo of Arjo Dedessa Project ee Ma? M (in mm/day) Year Jan Feb March April 1961 3 73 3 93 4 49 4 26 373 3 64 •.J * J 54 4 43 427 386 3 24 Maj JijfWl J '6 Aug Sept Oct Nov Dec 1963 3 48 3 72 4 66 3 44 3 36 3 1 *. 2 71 3 3 63 3 98 4 22 3 56 1962 3 23 3 75 4 66 4 32 4 43 3 49 2 63 2 5 3 72 3 63 • 4 3 19 1964 3 95 4 18 4 65 4 66 4 52 1965 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 45 2 72 4 79 3 87 4 25 3 86 3 82 1966 3 68 4 22 4 47 4 73 4 35 3 4 307 3 3 7 4 31 4 ‘ 3 35 1967 I 3 45 4 44 4 77 4 45 4 6 3 95 3 32 4 22 4 03 3 72 3 46 1980 3 29 3 63 4.21 4 39 4 32 3 56 2 93 3 05 3 ’ 3 98 3 66 3 44 1981 3 78 4 25 399 4 13 4 42 3 53 2 91 3 2 2 88 364 4 01 3 3 1982 36 3 74 4 63 4 32 4 13 3 77 2 98 2 98 3 87 3 86 3 49 33 1983 354 4 14 4 55 4 76 4 15 4 06 3 43 3 03 3 61 3 7 3 82 3 32 1984 358 4 31 4 73 5 02 4 08 3 55 3 14 3 11 3 87 4 3 398 34b 1985 3 73 4 04 4 59 4 36 3 93 3 53 2 71 281 3 63 3 86 3 88 332 1986 3 43 394 4 31 4 03 4 22 3 04 2 85 3 08 3 22 3 82 4 01 ! 4- 1968 3 53 4 06 4.5 4 64 4 1 1969 I 3 71 4 06 4 5 4 43 4 28 1970 4 01 4 45 5 06 4 58 4 76 1971 3 66 39 4 49 4 49 4 24 1972 3 86 4 34 4 5 5 03 4 34 1973 3 81 4 3 4 87 4 92 4 91 1974 3 58 4 18 4 53 4 24 4 61 1975 3 82 4 27 4 66 4 34 4 09 1976 ’ 3 73 4 38 4 65 4 75 4 02 1977 I 34 3 85 4 34 4 49 4 24 1978 3 85 3 62 4 64 4 7 4 39 1979 ' 3 36 3 89 4 18 4 37 4 08 3 71 2 63 2 9 3 59 3 59 4 06 3 4 3 56 2 91 306 3 72 3 94 3 7 3 19 4 01 3 21 3 22 4 Ob 4 0-4 3 56 328 3 49 2 93 301 3 69 4 3 75 329 3 55 3 39 3 28 4 17 4 23 4 2 3 34 3 84 2 81 3 09 3 97 4 32 4 01 3 34 3 51 3 3 3 29 3 62 4 07 1 95 3 35 3 3 2 73 2 44 3 2 3 87 3 64 3 49 3 68 2 93 3 06 3 5 3 69 3 48 3 38 3 46 29 3 1 3 78 3 87 3 86 352 3 57 2 58 3 04 3 53 3 74 3 79 3 23 3 38 2 64 3 07 3 3 3 5 3 64 3 34 1987 367 4 14 4 31 4 74 3 83 35 3 27 3 16 4 06 4 3 83 396 1988 3 76 4.2 5 04 4 82 4 58 3 78 2 71 3 34 3 59 4 17 4 02 ! 48 1989 3 72 4 18 4 42 4 39 4 64 3 83 2 97 3 38 3 77 4 06 3 74 3 24 1990 3 82 3 38 4 31 3 57 3 35 3 25 2 92 3 07 3 69 4 37 3 92 3 67 1991 3 79 4 05 4 43 4 31 382 3 72 3 06 3 59 4 49 4 22 3 84 3 11 1992 3 42 3 94 4 71 4 62 4 65 363 2 73 2 59 3 78 37 361 3 38 1993 ' 3 54 3 75 4 68 4 29 4 25 3 21 2 72 304 3 67 4 09 3 91 34 1994 3 94 4 3 4 79 4 65 4 55 35 2 75 2 83 3 91 4 26 4 06 3 75 1995 3 92 4 34 4 96 4 34 4 53 2 98 3 11 3 52 4 21 3 94 3 92 3 59 1996 3 68 4 29 4 57 4 88 4 37 3 35 3 09 3 03 3 77 4 31 4 09 3 46 1997 3 77 4 43 4 95 4 46 4 65 4 07 3 23 3 46 4 41 4 32 39 3 85 1998 391 4 33 4 8 4 93 4 24 3 85 2 66 296 3 74 3 83 4 12 3M 1999 3 68 4 07 4 67 4 57 4 36 3 63 2 98 3 11 3 83 4 11 37 3 42 2000 4 03 4 45 5 24 4 79 4 86 4 15 3 31 3 35 4 19 4 16 3 92 35 2001 3 78 4 21 4 66 4 64 4 42 3 65 2 M 3 16 3 84 4 19 3 92 3 57 2002 4 4 39 4 75 5 13 4 59 3 71 3 46 34 4 34 4 24 3 54 2003 3 75 4 49 4 92 4 82 5 06 3 88 2 85 3 16 4 08 4 47 4 19 363 2004 384 4 28 4 58 4 51 4 83 36 3 22 3 35 3 72 4 21 2 lk> 36* S Water Works Design &. Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects A7: Estimated Mean Monthly ETo of Arjo Dedessa Project Area May 20C7 (in mm/month) Year Jan Feb March April May 1961 116 110 139 128 116 1962 100 105 144 130 137 105 81 6 77 4 112 112 104 June 'July Aug Sept Oct Nov 109 94 2 110 133 132 116 1963 108 104 145 103 104 1964 122 117 144 140 140 1965 119 116 150 128 137 1966 114 118 138 142 135 102 95.1 93 1 111 134 123 93 2 84 92.9 109 124 127 104 84 3 86 6 116 132 116 89 96 2 106 124 120 118 Dec Annual 100 1403 99 1308 110 1303 119 1420 107 1410 104 1408 1967 107 124 148 133 143 118 97 7 103 127 125 111 107 1444 1968 109 114 140 139 127 1969 115 114 140 133 133 107 90 1 94 8 112 122 111 99 1369 111 81 4 89 9 108 111 122 105 1358 1970 124 124 157 137 148 120 99 4 99 7 122 125 107 102 1466 1971 113 109 139 135 132 105 90 8 93.2 111 124 113 102 1366 1972 120 122 140 151 135 106 105 102 125 131 126 104 1466 1973 118 120 151 148 152 115 87 2 95 9 119 134 120 104 1464 1974 111 117 140 127 143 105 102 102 109 126 58 6 104 1346 1975 118 120 144 130 127 99 84 7 75 7 96 120 109 108 1332 1976 116 123 144 143 125 111 90 8 94 8 105 115 104 105 1375 1977 105 108 135 135 132 104 90 96 113 120 116 109 1362 1978 119 101 144 141 136 107 80 94 2 106 116 114 100 1359 1979 104 109 130 131 126 101 81 9 95 3 98.9 109 109 104 1299 1980 102 102 130 132 134 107 90.9 94 5 111 123 110 107 1343 1981 117 119 124 124 137 106 90 1 99 2 86.5 113 120 102 1338 1982 112 105 144 129 128 113 92 3 92 5 116 120 105 102 1358 1983 110 116 141 143 129 122 106 94 108 115 115 103 1401 1984 111 121 146 151 127 107 97 4 96 6 116 133 120 107 1432 1985 116 113 142 131 122 106 84 1 87 1 109 120 116 103 1349 1986 1987 1988 106 110 134 121 131 91.3 88.2 956 96.5 118 120 107 1320 114 116 134 142 119 105 101 98 122 124 115 123 1412 117 118 156 145 142 113 84 2 103 108 129 121 108 1443 1989 115 117 137 132 144 115 92 105 113 126 112 100 1408 1990 118 94 8 133 107 104 97 4 90 6 95 111 136 117 114 1318 1991 117 113 137 129 118 112 94 8 111 135 131 115 96 4 1411 1992 106 110 146 139 144 109 84 5 80 3 113 115 108 105 1360 1993 110 105 145 129 132 96 4 84 4 94 3 110 127 117 105 1355 1994 122 120 149 139 141 140 135 105 85.2 87 8 117 132 122 116 1437 1995 122 121 154 130 894 96 4 109 126 122 118 111 1439 1996 114 120 142 147 101 95 8 94 113 134 123 107 1425 1997 117 124 153 134 144 1998 121 121 149 148 132 122 100 107 132 134 117 115 82.6 91.9 112 119 124 119 1505 104 1419 1999 114 114 145 137 135 109 92 4 96.3 115 127 111 106 1402 2000 125 124 162 144 125 103 104 126 129 118 109 1518 2001 117 118 144 139 110 92 4 98 115 130 118 111 1429 2002 124 123 147 154 151 137 142 111 107 106 129 135 127 110 1515 2003 116 126 153 145 157 150 117 88 2 98 122 139 126 112 1498 2004 119 120 142 135 108 100 104 112 130 61 7 112 1393 ____________________ ______________________________ Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd. 109Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects w A8: Estimated Mean Monthly Rainfall at Arjo Dedessa Project Area (in mm) N I I N I ri I I I i l I l i I I rVear Jan Feb March April May_ June July 1967 156 0 96 3 21 7 172 172 140 1968 0 57 6 0 75 36 4 93 8 169 186 I 1969 37 7 35 9 53 7 140 121 144 159 Auq Sept Oct Nov Dec Annual 220 220 111 5 151 0 12 1320 207 192 90 97 21 7 14 5 1070 212 165 56 39 7 39 0 1132 1970 1971 29 2 30 51.3 21 2 149 154 249 162 256 107 2 4 44 4 04 1217 11 3 0 32 20 7 30 8 142 193 180 1972 156 11 1 15 89 1 53 166 186 135 262 188 2 32 3 14 1 1210 157 170 49 48 69 9.24 990.6 1973 0 9 97 5 66 29 4 236 155 186 233 143 58 82 12.2 5.77 1075 1974 38 7 7 98 31 8 5 14 287 205 242 168 212 72 78 4 62 16 7 1975 23.5 55 1 21 1 60 4 116 124 189 159 141 131 3 115 12.5 1976 23 7 162 90 3 55 8 154 154 192 215 273 88 66 36 5.37 1978 3 35 66.5 103 122 154 206 206 181 122.6 0 58 12.5 1979 156 8 89 17 256 975 202 235 159 154 64.94 31.2 12.5 1980 156 17.8 57.3 118 164 100 136 176 246 49 87 28 7 0 1292 I 1045 1303 1181 1024 1110 '983 156 8.23 27 6 356 149 213 296 270 177 113 9 57.2 0 1362 1984 156 0 31 6 69 8 234 249 443 198 230 8 716 26 8 5 77 1514 1985 2 79 0 12.3 105 257 341 242 212 315 48.2 32 5 37 7 1607 1986 0 392 46 9 56 4 37 5 315 274 244 191 103 8 35.9 046 1345 1987 2 89 17 2 886 799 123 282 488 328 183 1 16 4 42.3 34 3 1785 1988 14 1 42 7 74 3 15.3 335 325 177 297 343 259.9 154 3.87 1903 1989 25 6 26 7 76 3 108 245 284 316 332 297 189.3 61 3 47 1 2008 1990 8 77 37 8 50 4 83.3 90 6 438 228 319 241 73 89 33 4 3.12 1607 I 1991 264 791 68 2 74 4 139 106 364 309 222 98 59 35 13 1464 1992 24.8 32 8 106 105 222 225 267 291 250 104 7 53.6 158 1697 1993 1994 1995 1 04 31 69.5 100 213 313 217 347 166 149 4 2.03 0 1609 11 2 1 15 20 1 53.9 127 227 255 228 279 8 467 13 7 0 1223 0 22 9 75.5 109 222 195 229 310 279 86 46 11.2 22 3 1563 1996 45 5 19 1 162 71 7 338 225 245 197 215 74 57 44 6 7 56 1645 1997 396 0 97 56.6 139 293 314 205 291 234 213 40 4 2 54 1830 1998 13 84 81 1 15.2 162 280 264 272 239 235 9 67.2 1 04 1638 1999 31 7 2.91 15 92.3 393 427 257 239 309 197 3 8.89 42 1 2014 2000 0 0 3 69 105 195 345 222 260 274 255 34 4 7 39 1702 2001 0 32 655 60 3 327 346 298 292 312 206.3 19.9 24.1 1983 I 2002 17 7 2.19 39 7 42.2 106 252 274 153 224 59 11 1 84 53.1 1226 2003 5 84 53 5 117 121 58 9 358 232 300 155 51 59 11.5 1 86 2004 4 96 2.1 61.2 51 5 150 353 326 243 249 193 9 40 7 13 1 1466 1689 I Average 15.3 18 4 53 6 69.5 180 8 243.0 245.9 238.3 228 6 115.5 31 4 12.7 CV 0.85 0 96 0 68 0.55 0.49 0 37 0.31 0 25 0.24 0.591 0.9 1 13 1452.9 0.209 Skew Max 0.62 0.78 0 74 0 1 0.62 0.38 1 44 45.5 57 6 161 7 139 9 392 7 437 6 487 6 Min 00 0.0 08 5.1 37 5 100 3 136.2 0.07 0.17 0 635 2.31 1 48 0 26 346 6 343.1 259 9 150 7 53 1 2014.5 135.3 141.3 8.5 06 0 0 990.6 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects A9: Estimated Mean Half-Monthly Rainfal at the Project Aiea (in mm/hr) May 2007 □ 11 1 2 2 1 2 2 3 1 3 2 4 1 4 2 51 52 6.1 6 2 7.1 7 2 8 1 9 1 9 2 10 10 12 1 I-- — 12 Total Year | 1967 ’ 1968 | 1969 1970 1971 1972 1973 1974 1975 1976 1978 1979 1980 1983 1984 1985 1986 1987 1988 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 1320 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 1070 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 1132 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 1217 11 0 27 032 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 1210 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 24 990 6 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 1.73 122 0 0 5 77 1075 30 6 8 12 2 26 5 72 199 119 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 1292 0 23 5 47 7 74 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 4 115 0 6 06 6 46' 1045 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 1303 3 0 35 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 1181 78 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 5 156 156 6 06 6 46 1024 78 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 9 169 0 0 1110 7 8 7 79 7 98 0 25 187 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 1362 78 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 56 152 11 6 4 96 1514 03 2 49 0 0 1 5 108 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 1607 0 0 2.75 36 4 152 31 7 28 1 28 3 1 24 36 22 195 119 147 6 127 110 134 114 77 1 85 189 28 2 7 68 0 23 0 23 1345 0 2 89 0 172 48 1 40 5 6 93 72 9 192 104 3 158 124 224 5 263 215 112 116 66 8 81 4 35 31.2 11 34 3 0 1785 94 4 73 2 66 40 57 173 0 98 14 3 145 190 2 172 154 75 1 102 175 122 179 164 155 104 154 0 0 3 87 1903 1989 186 7 03 26 07 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 31.8 198 27 3 1990 1991 1992 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 2008 j 1607 , 14 2 122 0 7 91 37 6 30 6 1 27 73 2 89 9 49 04 133 93 1 195 1 169 179 131 144 77 9 97 3 1 27 10 5 24 5 12 7 0 29 1464 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 | 1697 1 Hi Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd. 00 oo Ob --------Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 (in mm/hr) 1.1 | 1.2 2.1 2.21 3.1 | 3.21 4.1 I 4.2 5.1 5 2 6.1 6 2 7 1 7.2 \ 8.1 8.2 9.1 9.2 10 10 111 11 12 1 12 Year 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Average CV Skew Max Min 0 1 04 6 64 24 4 3 06 66 4 63 6 36 6 93 7 119 7 86 2 227 79 7 137 149 197 104 61 9 83 9 65 5 1 39 0 65 0 0 11 2 0 0 1 15 1 3 18 8 29 2 24 7 55 71 64 105 122 109 7 145 116 111 166 112 7 24 1 23 9 52 4 16 0 0 0 0 5 6 17 3 0 75 5 0 52 109 116 105 9 63 4 131 123 9 105 177 133 125 1 54 40 8 4 5 7 5 95 5 3 1 96 20 4 9 2 36 3 4 09 15 78 8 82 9 266 45 1 146 192 4 159 66 1 84 7 160 100 966 93 2 122 58 2 16 4 8 48 36 1 0 69 6 87 2 1 37 5 0 097 28 1 28 5 72 8 66 6 71 7 221 5 152 161 78 6 127 165 126 148 85 8 119 94 2 253 15 1 0 06 2 48 11 2 1 84 1 94 646 24 6 56 5 889 633 69 7 92 18 142 138 141 7 122 131 142 118 121 92 9 143 62 3 4 92 0 1 04 283 3 35 0 291 0 15 19 73.3 227 166 209 217 99 2 158 141 98 2 146 162 148 48 9 8 89 0 26 6 15 5 0 0 0 0 2 31 1 39 28 4 76 2 76 9 118 6 215 129 99 4 123 149 112 139 135 168 87 1 252 9 15 2 89 4 5 0 0 23 7 8 3 1 24 64 3 36 9 23 3 96 3 230 8 122 224 118 2 180 126 165 187 124 96 4 110 7 27 12 7 14 4 9 75 12 5 5 19 0 2 19 8 37 31 3 37 7 4 49 19 8 86 64 139 114 156 4 118 51 7 102 95 4 129 35 3 23 8 0 1 84 3 29 49 8 2 3 84 17 8 35 7 39 2 77 6 68 8 52 3 20 3 38 67 165 193 127 5 105 133 166 85 9 69 1 23 7 27 9 6 64 4 91 1 4 0 46 0 2 4 76 1 4 0 7 10 6 50 6 9 7 41 8 28 5 121 9 148 204 256 7 69 6 91 1 152 132 117 168 25 7 11 3 29 4 9 24 3 88 168 7 5 7 8 8 8 9 6 20 6 33 0 22 7 46 7 76 2 102 6 119 8 123 2 122 0 123 9 117 121 8 120 0 108 5 73.7 41 8 197 11 8 6 1 66 1 18 1 28 1 48 1 21 1 03 0 74 0 95 0 72 0 68 0 511 0 46 0 41 0 425 0 31 0 36 0 29 0 3 0 32 0.58 0 86 0 94 1 26 1 57 1 5 1 27 1 82 2 47 1 27 0 95 0 83 0 95 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 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 I 00 00 00 0.0 0.0 03 00 05 12 27 5 133 433 552 69 6 51.7 67 2 66 7 43 3 7.2 1 2 00 00 00 00 990.6 Total 1609 1223 1563 1645 | 1830 j 1638 2014 1702 1983 1226 I 1466 9 1452.9 0.209 0 26 3 2014 5 112 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt LtdArj Dedessa Irrigation Project 0 Meteorological and Hydrological Aspects Annex B: Results obtained from the Hydrological Analysis B1: Estimated Monthly Flows at Arjo Dedessa Dam Site May 200/ ___ _Jin Million m )____ ___________ _____________ . _. 3 .— f Year Jan Feb Mar Apr May Jun Jul Aug Sep JOct jNov Dec Annual T I I I I I I I I I 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 1947 5.073 21.39 157.2 397 6 560 6 700 8 512 2 64.92 31.95 \ 2525 11963 22 72 123 12.28 30.86 111 6 235.3 429 5 826.3 622 8 223 9 111 8 97.23 | 2736 1964 7 642 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 j 2673 1966 42 41 40.3 39 61 5361 4741 134 3 547.5 654 6 726 3 49.32 25.38 11.62 2372 1967 6.806 5.364 15.57 14 73 19 24 82.14 452 6 764 7 719 5 634.8 400 8 120.1 3236 1969 30 4 29 71 46.01 28.69 55 55 253.9 607 857 565 3 174.2 53 81 26 41 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 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 1972 31.3 18 92 1343 25.78 42.79 85.61 512 9 746.2 430 7 125 4 71.09 29.98 2134 1973 1544 7 121 3.221 4 586 82.96 181.5 156.2 633 839 1 354 5 90 45 37 2405 1974 21 79 10 31 9.887 6561 71 15 19C 409.5 770.6 195 6 83 73 72.32 279 1869 1979 10.27 7 805 6815 16 56 35 18 94 19 340.6 497 5 371 157 1 57 07 25.13 1619 1980 1073 9 737 6.839 49.56 144 9 366.1 584 3 777 745 235.5 62.71 52 8 I 3045 1981 47 75 27 57 29.73 25 58 40.74 38.71 412.8 633 540 6 315.2 19 85 7 138 2139 1982 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 88 398 111.5 361 4 687 668 2 617 6 282 5 69.26 2924 1984 2301 10 61 8.146 6 854 21 69 134 7 449.2 401.2 311 8 78.36 12 69 4 808 1463 1985 7 152 3 462 1 775 8.54 47.33 123 1 280 559 504 1 155 7 48 31 25 72 1764 1986 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 1987 7 756 3.775 8.501 12.5 27 82 157 2 412 8 633 402 9 231 4 97 47 38.7 2034 1988 24 16 1749 1479 5.553 28.08 203.6 354.6 689 1 905.1 315.2 114.9 46.11 2719 1989 25 14 84 13.97 24.24 2058 87 63 174 3 301 1 651.3 315.2 65 15 70.31 1764 1990 31.93 19 11 23 19 44 03 31 91 1144 219 3 1043 669 7 280.5 46.23 23.01 2546 1991 ' 16 3 12 32 10.51 18.94 44 17 113.8 5174 964 2 486.9 310.9 29 61 21 7 2547 1992 14 62 1523 9 435 14.96 42.85 116 8 235 1 497.2 338.1 482.9 99 78 41.9 1909 1993 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 1994 23.32 12.45 1062 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 1996 29.25 18 44 26.36 21 96 107 7 271 3 462.2 515.2 358 225 1 71 87 49 76 2157 2001 ( 50 8 37.86 45 32 41.35 97 36 291 4 473 1 630 3 602 2 403.8 130.5 63.78 2868 2002 59 09 36 38 37 91 45 85 35 1 127 292.1 356 4 346 126.2 7005 47.88 1580 0 0 0 2003 33 66 2305 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 75 20 73 49 47 146 8 336 3 385 2 384 9 322.3 85.26 46 11 1855 0 0 113 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 B2: Regional monthly coefficient of variations (Cv) Station 114001 /earl Jan Feb Mar April >MayTjune July i Aug | Sep ' Oct^Nov_iDec 35 051 0 57 0.66 0 68 0 62 0 45 0 35 0 3 0.33 0 67 0 114014 114005 114004 114003 . 20 0 47 0 46 0 48 0.56 069 0 53 23 0.28 041 0 33 0 43 0.6 0 47 62 0 59 0 27 0 33 0 28 0.56 0 81 0.53 0.2 0 16 0.25 0 44 0.3 0 34 I 22 0 33 0 42 0.45 0 55 0.56 0 43 0 57 0.38 0 43 0.64 0 35 0.33 1 21 0 51 0 83 0 57 071 0 66 0 58 0 35 0.25 0 36 0 56 0 46 0 55 B3: FRegional mon 91008 38 0.68 1.3 0 7 0 6 0 61 0 46 0 29 0.32 0 28 0.64 1 0.86 91012 35 0 61 0 49 0 76 0 49 0 57 0 42 03 0 29 0 32 0 52 08 0.59 thly coefficient of skewness Station Year Jan Feo Mar April MaypJune July Aug Sep Oct i Nov Dec 114001 35 0.63 0 74 1 07 0.94 1 63 114014 20 1.35 0 31 0.47 0.81 0.85 114005 23 0 33 1 48 0.59 -0 1 2.18 0.89 0.13 0 04 0.25 0 99 1.37 0 96 1 03 -0.5 0.93 0.89 0.67 26 1 98 1.54 0 07 0 45 0 81 0 42 0 52 1.09 91008 38 2 73 0.29 3.26 0 77 1 14 0 81 0 17 1 14 1 13 0 77 3.14 2 85 91012 35 3 17 4 94 1.22 1.5 2 34 1 15 0 43 0.94 005 1.6 2.86 2.79 B4: 16 Regional monthly coefficient of correlations JRj Station Year Jan Feb Mar Apnl May June July Aug Sep Oct Nov Dec 114001 35 -0 1 0 83 0 89 0.59 0.3 0.78 045 0 53 0.44 0.45 0 74 0 78 114014 20 0.36 0 5 0.77 0.56 0.62 0 81 0 46 0 54 0.28 -0 04 0 65 0 78 114005 23 0 84 0.5 0 35 0.3 0 64 0.38 0.48 0 68 08 0 83 0.25 0 16 114004 22 0.8 0 52 0.21 0 52 0.6 0.58 0 58 0 69 0 61 0 77 0.37 0.14 114003 21 0.84 0 3 0 18 0.52 0 45 0 73 0.68 0 66 0.58 0.82 0.56 0.1 91008 38 0.27 0 33 0.37 0.27 0 53 0.59 0 54 0.55 046 0.45 0 77 0 62 91012 35 0 12 0 83 0 72 0 48 0.41 0 72 0 53 0 41 0 48 0.31 0 44 0 65 ____ I 14 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 B5: Standardized probability weighted moments Location Deg N. Deg E. Area (km 2) Record Length,N PWMs________ _ Station Name of Station Whoi mio2_ t i 1 Dedessa near Arjo 8 41 36 25 9981 29 0 4073 9 0.243171 114001 Upper Dedessa near 0.262951 2 114014 114005 91008 91012 Dembi 8 02 36 28 9.02 36.03 1806 2881 2966 3494 15 18 37 34 0 420504 3 4 5 Dabana near Abasina 0 414042 7 45 37.11 0 400025 0 253945 0.240847 Gilgel Ghibe Gojeo near Shene 7.25 36 23 0.408619 0 248091 6 7 8 9 114007 Angar Gutin near Neqemte 1975 I 20 0 421145 0 254033 t 114004 Wama near Neqemte 114003 115008 Siffa near Neqemte Aleltu at Nejo 8.53 8 52 9.30 844 951 155 21 0 419805 20 0 416527 7 10 101001 SoratMetu 8 19 35.36 1622 17 11 91013 Ghibe-Limu near Limu 8.35 37 13 663 10 12 91001 Great Grube near Abelt 8 14 37 15 15460 Weighted Average 19 0 400261 0 401323 0 425296 0 424754 0.254029 0.251324 0.247582 0 244658 0 261749 0 260656 255 0.411964 I 15 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects B6. Mean Monthly Total (Suspended and Bed) Sediment Load 1 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 2 11 1.75 1.27 5.73 3 11 33 4 315 523 476 372 32.3 15.3 1781 1962 2.56 0.94 081 1.07 3.18 22 4 114 216 319 189 6.92 2 41 878.9 1963 13 0 47 0.39 1.6 11 3 40 8 129 403 264 50 4 16 5 14.3 932.5 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 07 0.2 0 05 0.08 7 04 26.9 123 246 425 105 11 8 3.05 949.6 1974 1 22 0 35 0.28 0 13 5.51 29 119 360 205 102 8 23 1 94 833.7 1979 1.91 1 29 0.65 0 59 1 79 9 43 88.9 179 115 28 6 5 63 1.64 434.5 1 78 1 32 0.71 1.07 2.34 23.6 262 370 322 387 19.7 3.74 1397 2.37 0 72 0 34 1.91 079 14 3 182 263 135 227 40 1 12 7 880.6 354 3 13 2.54 3.86 2 88 224 190 277 338 102 40 8 9 14 995.4 0 64 0 57 0.57 0.49 3 18 22 4 140 356 333 352 71 4 20 1 1300 5 73 2 22 0 52 0.22 2.26 2.27 123 265 299 102 104 2.97 815.6 2.07 1 92 3.22 1 42 3.71 46.1 224 427 205 102 5 13 1 78 1024 1 09 0 75 04 0.23 1 72 33.8 216 246 205 102 16 1 2 85 826.7 1 25 0.36 0 18 0 22 2.25 25.5 178 315 228 154 36 9 6 64 948.3 2.17 0 88 0 45 1 2 2.44 8.09 171 342 146 19.9 8 2 18 704.9 1980 1982 1983 1984 1985 1986 1987 0.39 0.3 0 15 341 172 82.8 211 365 352 54.6 6 55 5.39 1098 2.69 0.96 0.83 0 45 1 74 26.7 140 223 138 157 15.5 5 58 711.7 1 61 1 03 1 09 0 61 2 18 12.3 97 7 300 296 339 29 6 8 32 1089 1.33 0 35 02 0.14 0.82 16 7 138 127 87.3 9 39 15 5 5.24 402.1 0.2 0.06 0 02 0.2 2.87 14.5 65 216 188 28.2 4 31 1 71 520.8 0.38 0 15 0 33 0.26 0 23 8.21 68.3 78 151 21 9 15.5 5 24 349 023 0 07 0.22 0.38 1.23 224 91 7 301 132 53.1 13.3 3.28 618.6 1988 1 44 0 78 C 52 0 1 1 24 32 4 94 8 246 205 102 17 3 1 31 703.4 1989 2 38 0.63 0 48 1.08 0 76 8.4 30 4 80.1 284 102 6 96 8.52 525.4 199C 2 24 0 95 1 08 2 82 1.53 12 9 44 246 205 102 15 5 5 24 639.8 1992 0 64 0.62 0 26 0.5 245 13.3 49 1 179 99 4 172 13.8 3.72 534 7 1993 1 56 0 84 0.64 2.37 6.63 38.5 107 308 119 57 7 15.5 2.94 660.6 1994 1 36 0 48 0.31 0.32 2 68 22 89 2 335 194 12.5 3.37 1.24 662.4 1995 0 48 0.23 0 29 0.45 1.31 4.63 224 98 7 78.2 12.5 2.75 5.24 227 1996 1 78 0 87 071 0 93 10 7 51.2 145 189 109 102 15.5 4.9 631 5 2001 4.72 2 83 3 15 2 55 91 57 5 150 261 250 129 21 1 7 29 899 3 2002 601 2 66 2.37 3 01 1 78 15.2 69 5 105 103 20 1 7 82 4 61 341.1 1 2003 2 44 1.28 2.43 3.88 1 89 8 37 123 123 205 102 15.5 5.24 594.5 2004 2 16 1 43 09 0 84 3.08 19.2 87 1 119 122 90 2 10.7 5 24 461.9 116 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects B7:Eleveation-Area-Capacity Relationships Elevetion Area Volume Elevetion (masl) (km2) (Mm3) (mas!) May 2007 of Arjo Dedessa Reservoir Arcs Volume (km ) 2 (Mm ) 3 1321 0.99 0.8 1357 90.75 1430 5 1320 0 54 00 1356 87 85 1341.2 1323 3 78 5.5 1324 5.11 100 1322 2.39 2.5 1358 94 18 1522 9 1359 97.23 1618 6 1325 6.64 15.9 1361 103 64 1819 6 1360 100 54 1717.5 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 1925 1337 31 73 222.9 1338 34.24 255 8 1339 36.62 291.3 1340 3945 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 10164 1353 77 88 1092.5 1354 81 28 1172.1 1355 84 51 1255 0 I 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 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Meteorological and Hydrological Aspects Sample Simulation Results of Arjo Dedessa Reservoir Year 1 Eo-Rf (mm) 5 IWD (Mm3) 6 (Eo-Rf) (Mm2) 7 SL (Mm3) ( 8 T IWR Mm3) 9 - " T" Month 2 DF (m3/s) 4 cs Reservoir Status (Mm3) 10 Storage (Mm3) 11 Area (km2) 12 Level (m as!) 13 Spill (Mm3) 14 STRQ (Mm3) 15 -----~---- T. Spill (Mm3) 16 404 Sep 404 Oct 404 Nov 404 Dec 404 Jan 404 Feb 404 Mar 404 Apr 404 May 404 Jun 404 Jul 404 Aug 405 Sep 405 Oct Inflow (Mm3) 3 577 4 333.3 102 7 47.7 22.5 12.3 16 3 16.8 40.1 160 9 400.3 00 0 0 0 0 0 111 00 00 1 0 82 10 00 00 576 4 00 143 46 2 10 6 1 0 46 2 00 135 60 0 100 1 0 00 146 74 0 10 7 1 0 00 147 85 0 10 4 09 60 0 74 0 85 0 50 4 74 00 0.0 00 576 4 1006 3 74 1 324 1 1006 3 74 1 44 9 1006 3 74 1 -23 4 982 9 73.1 63 2 919 7 70 4 -84 0 835 8 66 7 459 789 9 64 6 1351 9 00 164 50 4 0.0 146 7 4 00 80 00 00 0 00 00 0 00 00 0 00 0.0 0 00 00 111 00 109 08 94 08 51 08 00 08 00 1 0 1351 9 324 1 1351 9 44 9 1351 5 00 1350 7 0 0 1349 4 0 0 1348 7 00 -0 9 789 0 64 6 1348 7 0 0 34 1 823 1 66 1 1349 2 0 0 647 4 717 9 777.8 00 1 0 00 1 0 82 10 00 00 00 160 1 983 2 73 1 399 3 1006 3 74 1 646 4 1006 3 74 1 1351 5 0 0 1351 9 376 3 1351 9 6464 789 716 9 1006 3 74 1 1351 9 716 9 768 6 1006 3 74 1 1351 9 768 6 i Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Ar jo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 1n 405 Nov 405 Dec 405 Jan 405 Feb 405 Mar 405 Apr 405 May 405 Jun 405 Jul 405 Aug 406 Sep 406 Oct 406 Nov 406 Dec 406 Jan 406 Feb 406 Mar 406 Api 3 405.1 193.8 70.5 48.7 46 9 31.3 43.5 149.4 466.8 .] 5 6 7 00 143 46 2 00 135 60 0 0.0 146 74 0 00 147 85 0 0.0 164 50 4 00 146 74 00 80 0.0 00 0 00 00 0 00 00 0 00 00 0 00 00 111 00 00 143 46 2 00 135 60 0 00 146 74 0 00 147 85 0 00 164 50 4 00 146 74 8 9 « 106 1 0 100 1 0 108 1 0 10 8 1 0 11 7 09 10 3 09 57 09 00 1 0 0.0 1 0 10 46 .2 60 0 74 0 85 0 50 4 74 00 00 00 .. n 13 347 3 1006 3 74 1 122 8 1006 3 74 1 -153 990 9 73.5 -48 1 942 8 71 4 162 926 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 14 15 1351 9 347 3 1351 9 122 8 1351 7 00 1351 0 00 1350 8 0.0 1350 9 00 1351 4 00 1351 9 118 3 1351 9 465 8 640.7 516.8 402.5 166.2 71.5 31.7 24 8 17 0 13.5 00 1 0 00 1 0 82 1 0 106 1 0 100 1 0 108 1 0 106 1 0 11 3 09 97 08 00 00 00 46 2 60 0 74 0 85 0 50 4 74 639 7 1006 3 74 1 5158 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 G39 7 1351 9 5158 1351 9 393 3 1351 9 108 4 1351 9 05 1351.1 00 1350 1 00 1349 4 00 1349 4 0.0 926 6 _____________________________________________________________________________________________ ___ ________________ 119 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd •AArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Sfl. (.......continued) May 2007 EZ 3 11 zzi r«_[ 15 I 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 2 381.5 160.8 73.1 32.4 23 5 23.1 24.7 44 2 130.6 359 7 565 6 4 J 5 elVIZ. 00 00 00 53 00 0 00 00 00 0 00 0 0 0.0 0 00 00 00 0 00 00 00 111 00 82 00 143 46 2 106 00 135 60 0 100 00 146 74 0 108 00 147 85 0 106 00 164 504 11 3 00 146 74 98 00 80 00 54 00 0 00 00 00 0 00 00 00 0 00 00 08 09 10 10 10 10 10 10 10 10 09 08 08 09 10 10 10 00 00 00 00 00 00 46 2 60 0 74 0 85 0 50 4 74 00 00 00 00 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 60 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 1006 3 74 1 1349 9 00 1351 8 0 0 1351 9 401 0 1351 9 667 9 830 4 2087 1351 9 563 2 1351 9 378 3 1351 9 103 0 1351.9 2 1 1351.1 00 1350 1 00 1349 5 00 1349 6 00 1350 2 00 1351 9 8 5 1351 9 358 7 1351 9 564 6 840 3 1978 120 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt LtdArjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Annex C: Standards Cl: Commonly used values of runoff coefficients Class Des cription of catchment iRunoff percen g A Flat, cultivated and blck cotton soils B Flat, partly cultivated stiff soils C Average catchment ^5 D Hills and plains with little cultivation E Very hilly and steep with little or no cultivation C2: Runoff coefficient for pervious surfaces by selected hydrologic soil groupings and slope ranges --------------------- ------------------- ---------------------------------------------- Terrain Tunp Soil 7■ype |A iB c D l Flat, <2% 0.04 - 0.09 0 07 - 0 12 0.11 - 0 16 0 15-0.20 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 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 121 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 C3: SCS Curve Numbers for Various Conditions’ Cover Description Curve numbers for hydrologic soil group r--------------w T Cover type Hydrologi c condition A 1 B c D | Fallow Bare soil 77 86 91 94 Crop residue cover (CR) Pasture grassland, or range- continuous forage for grazing2 Meaoow-contmuous grass, protected from grazing * Brush-weed-grass mixture with Poor 76 85 90 93 Good 74 83 88 90 Poor 68 79 86 89 Fair 49 69 79 84 Good 39 61 74 80 - Poor 35 59 72 79 48 67 77 83 Drush the major element3 | Woods-grass combination5 Woods5 Fair Good Poor Fair Good Poor Fair Good 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 Farms—buildings, lanes, oriveways. — 59 74 82 86 and surrounding lots Arid and semi-arid rangelandse Hyd cond7 ABcD Mixture of grass, weeds, and low- Poor — 80 87 93 growing brusn. with crush the minor Fair — 71 81 89 element Mountain Drush mixture of small trees ano brusn Good — 62 74 85 Poor — 66 74 79 Fair — 48 57 63 Small trees with grass understory Poor — 75 85 89 Good — 30 41 48 Fair — 58 73 80 Brush with grass understory Desert snrub brusn Good — 41 61 71 Poor — 67 80 85 Fair Good — 35 47 55 Poor 63 77 85 88 — 51 63 70 Fair 55 72 Good 81 49 86 68 79 84 J 122 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects C3:(,,, continued) Average runoff condition, and la = 0.2S Poor' < 50% ground cover or heavily grazed witn no mulch Fair 50 to 75% ground cover ana not heavily grazed Good > 75% ground cover and lightly or only occasionally grazed 3 Poor < 50% grojnd cover Fair 50 io 75% ground cover Good > 75% around cover May 2007 uui i iii iy. 4l „ i Fair Woods grazed but not burned, and some forest litter covers the soi Good Wooas protected from grazing, litter and brusn adequately cover soil Poor < 30 % ground cover (litter, grass, and brusn overstory) Fair 30 to 70 % ground cover Good > 70 % ground cover Soil Groups Group A Sand, loamy sand or sanay 10am. Soils having a low runoff potential due to gnrigahveinisfiltration rates These soils primarily consist of deep well-drained sands and Group B Silt loam, or loam. Soils having a moderately low runoff potential due to moderate infiltration rates. These soils primarily consist of moderately deep to deep, moderately well to well drained soils with moderately fine to moderately coarse textures Group 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 near the surface that impedes the downward movement of water or soils with moderately fine to fine texture Group D Clay loam, silty clay loam, sandy ciay, silty clay or ciay Soils having a high runoff potential due to very slow infiltration rates. These soils primarily consist of clays with nigh swelling potential, soils with permanently-high water tables, soils with a clay pan or ciay layer at or near the surface, and snallow soils over nearly impervious parent material 123 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd.n I I N 1 I Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects C4: Reservoir Flood Standards May 2007 ___ i flood inflow Wind speed, Category of reservoir Dam design Initial General condition Spilling long term av Min standard, Rare I Min. wave overtopping J 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 10 000 year extensive drainage Full flood Larger of 0 3 PMF or 1,000 year flood C: Breach witn negligible risk to life and causing limitea damage Full Larger of 0 3 PMF or 1,000 year flood Larger of 0.2 PMF or 150 year flood Average annual max hourly wind Wave surcharge allowance > 0 6 m Av. Annual max hourly wind. Wave surcharge allowance >04 m /Vore For the purpose of PMF the ordinates of the computed PMF hydrograph are multiplied Dy the proportion indicated I I i 124 i Water Works Design & Supervision Enterprise In Association with IntereonUnental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects C5: Ratios of the basic dimensionless hydrograph of theSCS ITTp Qi/Qp Ti/Tp Qi/Qp TiflTp Qi/Qp May 2007 0 0 1.05 0 99 0.05 0 008 1 1 0.98 2.6 0 13 2.7 0.11 0 1 0.015 115 0.95 2.8 0 098 0.15 0 043 1.2 0 92 2.9 0 088 0.2 0 075 1.25 0 88 3 0.075 0 25 0.11 1 3 0.84 3.2 0 056 0.3 0 16 1.35 0.80 3.5 0.036 0 35 0.22 1 4 0 75 0.4 0 28 1 45 0 71 3 7 0 027 4 0.018 0 45 0.36 1.50 0.66 4.2 0.014 0.5 0.43 1.55 0.61 4 5 0.009 0.55 0.52 1 6 0.56 4.7 0 007 0.6 0.6 1 7 0 49 5 0 004 065 0.69 1 8 0 42 07 0 77 1.9 0.37 0 75 0 83 2.0 0.32 0.8 0.89 0 85 0.93 2.1 0 28 2.2 0.24 0.9 0.97 2.3 0.21 0.95 0 99 2.4 0.18 1 1 2.5 0.16 125 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects C6: Guidelines for Interpretations of Water Quality for Irrigation May 2007 Water parameter SALINITY SSyymmbbol ol UUnniitt2- UUss1ua-1?! l rKange in irrigation water Salt Content dS/m 0-3 dS/m Electrical Conduct^ity ECW (or) Total Dissolved Solios TDS mg/l 0 - 2000 mg/l Cations and Anions Calcium Ca” me/l 0-20 me/l Magnesium Mg” me/l 0-5 me/l Sodium Na’ me/l 0-40 me/l Chloride er me/l 0-30 me/l NUTRIENTS- Potassium K’ mg/l 0-2 mg/l MISCELLANEOUS Acid/Basicity pH 1-14 6.0-8.5 Sodium Adsorption Ratio- SAR (me/l) . 22 0-15 Source. FAO. 1994 Water Qualify for Agriculture. Irrigation and Drainage Paper No. Rev 1 Reprinted. 1994 126 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Annex D: Meteorological Data D1: Details of Meteoroioaical Observation Stations May 2007 I--- ------- Latitude Longitude ---------------------. I |! Station Name North East S.No. Deg. Min. Deg ' Min Altitude (m) Class rerioa L---------- - I Pl 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 Deaessa 09 23 36 06 1200 1971-2004 1 5 DemDi 08 04 36 27 1950 1954-2004 3 6 Gimoi 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 10 Nekemte 09 05 36 28 2080 1971-2004 1 11 Wama 08 59 36 40 1450 "'980-1987 3 D2: Types of Climatic Data available at the various Meteorological 9 Meko 08 41 36 02 2000 1980-1989 4 S.No. Station Name Altitude (m) ’Yrs RF TM RH WS SD EP 1 Agaro 2030 25 X X X X X X 2 Arjo 2565 33 X X 3 Bedelle 2030 38 X X X X X 4 Dedessa 1200 34 X X X X 5 DemDi 1950 51 X X 6 GimDi 1970 27 X X X X X X 7 Jimma 1725 53 X X X X X X 8 Kone 2000 26 X 9 Meko 2000 10 X 10 Nexemte 2080 34 X X X X X 11 Wama 1450 8 X X _ __ _ _ ’ Data length refers to Rainfall and Temperature data. Yrs RF Tm RH WS refer to rainfall series monthly rainfall average temperature relative humidity 1 day wind speed_____________ _ ____ Rday number of rain days sunshine duration maximum 1-nour rainfall maximum 1-aay rainfall J 127 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects D3: Mean Monthly Rainfall at Bedele Station May 2007 Annual Year 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1978 1979 1980 1983 1984 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Jan )Feb |l | 00 0 100 67 59 54 50 20 1 0 20 0 19 68 13 44 101 41 29 57 00 00 08 00 2 34 17 2 0 17 48 34 53 2 13 15 28 3 00 0 33 16 4 7 66 63 MarchjApril |May |june jjuly lAugHjeptjQglll 152 33 181 221 212 381 380 167 Nov |Dec 81 198 210 250 275 368 286 98 89 258 258 266 432 280 444 186 41 53 246 334 311 234 455 326 42 178 116 263 337 287 287 110 10 51 337 269 322 403 248 102 1 55 163 0 323 380 324 137 55 37 105 202 215 327 276 245 228 9 497 355 351 292 368 126 156 97 0 267 333 373 472 154 115 179 204 267 370 303 281 204 29 44 169 350 408 276 267 113 0 208 285 174 236 304 363 86 48 62 237 369 499 468 306 197 45 66 291 275 469 211 242 9 80 141 243 222 218 357 200 183 33 106 225 281 250 258 276 21 102 130 257 292 257 318 353 77 208 83 317 232 290 203 128 70 50 142 340 307 221 304 232 309 87 57 203 332 314 327 291 245 13 147 431 441 319 242 324 328 4 123 256 420 *86 273 286 242 87 72 322 390 297 329 370 211 63 38 169 298 296 202 253 63 84 131 37 320 278 258 197 52 46 81 248 447 299 268 273 168 253 0 35 22 70 07 56 25 122 26 21 10 8 29 20 0 62 9 41 72 00 50 0 99 0 25 5 10 17 0 10 24 45 13 38 4 59 1 8 39 29 8 29 14 3 46 13 3 62 15 1980 1539 1897 2322 2101 1788 1790 2171 1796 1993 1926 1655 1706 2293 1637 1680 1484 1837 1670 2001 1942 2321 1827 2155 1450 1446 1917 Average CV Skew Max Min 18 23 1 28 1 28 1 05 1 6 68 101 00 65 705 239 370 303 302 756 0.77 0.58 0.434 291 0.312 0.242 0.21 0.266 0.563 7 09 0 68 0.098 -0.91 0 837 0.56 0 345 0.375 208 258 497 447 499 468 472 328 0 9 0 0 186 202 128 9 41 72 7 256 7 114 2973 1.172 253 46 00 1864 0.14 0.18 2322 1446 ____________________ _______________ _____________________________________ 128 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects 04: Mean Monthly Rainfall at Jimma Station May 2007 pn mr"J Year Jan Feb March Aprril May June July Aug Sept Oct Nov Dec Annual 1953 33 49 88 733 7 72 283 399 211 256 116 1 1954 8 49 88 733 93 210 194 214 152 27 68 JO 1955 33 49 88 135 94 298 235 244 169 103 36 23 1956 91 25 100 109 96 183 288 254 215 50 16 96 1957 29 4 83 290 142 226 169 195 249 118 3 3 1958 1 0 52 117 215 225 278 185 189 82 68 25 11 1959 43 86 53 138 141 292 203 215 288 87 16 42 1960 81 140 86 138 103 170 272 138 151 130 68 32 1961 11 39 104 145 284 279 135 210 212 38 68 28 1963 0 86 98 225 197 237 272 262 243 97 221 73 3 nr 1964 40 57 131 116 106 206 221 206 225 164 24 109 1606 1965 43 4 39 203 102 249 205 191 58 107 116 25 1966 21 73 100 153 122 161 307 172 139 56 17 13 1967 4 15 198 82 157 273 207 283 250 132 215 2 1968 3 74 63 105 154 233 173 248 210 31 59 55 1969 55 61 199 91 109 165 189 185 104 85 35 5 1970 78 135 91 188 103 288 197 263 148 149 68 36 1971 18 3 58 81 267 153 205 204 201 124 107 44 1972 12 74 127 115 101 161 159 193 167 58 183 0 1973 28 11 7 149 148 180 297 160 181 57 10 10 1974 5 56 76 103 320 165 221 265 240 25 1 1 1975 4 65 100 171 12C 198 252 194 151 98 7 55 1976 36 85 107 112 189 324 211 233 190 93 118 25 1977 73 56 54 16 130 197 203 268 191 229 61 15 1978 5 71 42 138 204 222 184 215 203 64 57 38 1979 32 118 111 23 116 232 153 164 115 75 9 22 1980 23 42 100 301 108 189 96 164 141 109 27 28 1981 1 7 136 62 252 114 193 250 164 31 127 1 1982 105 43 61 136 211 223 141 192 157 94 212 37 1983 20 40 97 161 228 166 174 229 299 141 54 7 1984 24 11 32 83 191 183 211 166 187 12 138 50 1985 25 20 77 147 203 136 268 168 128 63 50 12 1986 0 48 82 115 151 256 233 134 163 89 14 47 1987 26 89 158 60 188 204 186 180 136 116 46 52 1988 81 59 31 87 182 165 185 294 220 172 2 0 1990 25 46 133 56 194 320 280 280 245 23 93 19 1991 79 81 62 169 110 223 200 246 140 51 8 78 1992 28 56 56 162 144 287 212 344 175 180 70 36 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd. 1989 28 47 138 179 102 179 232 213 204 107 28 170 1627 1743 1270 1507 1523 1508 1446 1604 1509 1494 2012 1341 1333 1819 1408 1283 1743 1465 1350 1237 1479 1414 1723 1491 1442 1169 1328 1337 1611 1614 1288 1297 1331 1440 1477 1712 1445 1749 129*1 Aijo Dedessa Irrigation Project Meteorological and Hydrological Aspects May 2007 (... LUI ------- I -------- Year Jan [Feb March Aoril May June July 'Aug U.-------- Sept Oct Nov Dec Annual a M a a a ri 1 1 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 1415 1298 1476 2034 1713 1546 1622 1772 1330 1285 1482 Avg CV Skew Max Min 33 49 88 133 172 279 208 210 182 103 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 ri 130 Water Works Design & Supervision Enterprise I In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects D5: Mean Monthly Rainfall at Dedessa Station May 2007 131 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects D6: Mean Temperature at Bedele Station ______JinoC)____________ _____ __ - May 2007 — rear_ Jan Feb Mar t n £ Apr Ma> — - - -- 1971 1972 199 21 2 20 8 21 5 20.4 182 19 5 20 9 18.4 17 9 19.8 18 3 16 7 16 6 Dec 172 15 5 11554.8 159 1973 179 187 21 5 21.5 194 179 14 3 16 4 18 0 17 3 174 24.9 1974 17 7 19 8 19.3 20 2 18 7 18 2 16 9 157 17.2 17 1 17 9 17.0 1975 17.3 193 197 198 194 17 7 16.7 16.2 17 7 18 1 17.2 17 8 17 6 17 2 17 1 17 7 170 167 1976 179 18 1 19 1 18 8 1977 182 19.0 1978 173 18.4 19 3 18.9 18 5 17 5 16 8 16 0 16 1 19 7 21.0 20 5 197 19 5 79 192 19 1 176 173 169 16 0 16 5 17 3 17 5 1979 1980 166 17.2 174 17 0 176 174 1981 17 3 17 5 17 1 1982 170 1983 1984 7.5 19 1 20 1 176 174 178 19 4 20 8 21 4 21.2 22 0 197 18.0 169 18.3 187 17.3 174 190 18 6 18 9 196 1985 20.5 20 5 21 4 20 5 18 6 18 0 17.2 17 1 17 3 177 18 8 18 9 1986 19.9 20 6 20 8 20.9 21 4 18 1 174 17 8 17 7 18 2 18 7 184 1987 194 20 8 20 4 1988 197 20 3 20.8 21 6 19.6 18 1 170 17 3 18 1 18 2 18.3 190 17 5 18 3 18 2 179 1989 17.8 187 19 1 19 3 190 178 1990 18 1 18.7 19.5 20 2 19 3 18 5 15.0 174 17.3 17 7 17.5 18.0 17 8 174 178 18 2 18 9 19 1 1991 19 3 20.6 20 7 21.0 20 4 18.3 174 18.2 18 4 18 7 20 0 1992 19 1 20 1 21 3 20 6 20 7 19 5 18 4 18 0 19 6 19 1 18 8 20 6 1993 1994 1995 1996 1997 1998 1999 2000 20 9 20 9 22.0 21.3 19 5 17.8 17.7 18 2 19 0 19 6 19 5 205 20 8 21 3 21 4 19 9 194 17.6 18.1 18 5 18 8 18 9 19.5 192 21 0 20 6 20 7 19.1 184 178 18 0 18 3 18.3 18 5 18 7 192 199 21.5 19 9 19 3 18.6 17.8 18.0 18 8 13 9 21.2 21 2 23.2 21.0 19.3 18 1 18.3 18.9 192 18.6 19.2 19 6 21 7 21 7 21 8 19.1 187 17 3 17 7 186 17 9 184 19.2 17 7 17.9 18 5 18 9 18 6 189 2001 19 1 20 9 20 7 21.2 199 18 0 17.5 17 7 18 6 19 4 18 7 192 2002 19.2 21 1 21 6 21.8 21 2 18 5 18 3 17.5 18 1 18.1 186 18 9 2003 20.0 21.5 21.1 21 2 21 9 187 17.6 18 1 186 190 196 19.6 2004 20 8 21 0 22 1 21.5 20 8 18 3 17.8 18 1 18 6 18 7 19 1 19.6 Average 187 79.7 20.6 20.6 796 78.0 17.3 17 4 77 9 78.0 78.3 78.9 cv 0 08 0.13 0 05 0.05 0.06 0.72 0.05 0.04 0 05 0.05 0.06 0.09 Skew -1 21 -3 96 -7 79 -0.08 0.00 -4.24 -2 06 -0 86 -0.58 -0.94 -7 35 1 44 Min 13.9 75 17 1 18.4 17 0 79 14.3 15.7 16.0 15.5 15.4 15 9 Max I 20.9 21 7 22.1 23.2 21.9 20 4 18.4 18.3 19.6 19.4 19 7 24 9 132 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°/o Vear Jan Feo Mar Apr May ’ Jun May 2007 1991 55 46 56 67 78 8C 82 84 77 71 65 65 1987 1988 63 80 58 52 70 78 1989 51 53 67 62 68 80 1990 59 62 56 60 70 79 1992 68 65 58 62 66 75 1993 1994 53 48 48 57 78 83 1995 46 50 51 59 72 75 1996 59 54 63 62 75 82 1997 63 Aug Sep | Oct Nov Dec 80 80 69 58 89 84 83 76 63 50 83 85 84 72 64 75 82 80 80 70 69 60 77 81 74 72 69 64 85 72 81 61 66 61 85 83 78 69 69 67 83 84 80 72 68 64 84 84 80 78 64 63 82 84 82 80 74 70 84 84 83 80 74 67 85 86 83 88 86 84 73 69 61 85 84 82 74 70 69 I 1998 65 55 64 1999 59 50 49 55 76 76 2000 58 2001 62 62 65 65 73 83 2002 69 60 66 65 67 81 2003 62 55 63 60 57 81 2004 61 54 56 62 66 81 I Average 60 57 58 61 70 78 84 83 81 69 63 60 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects D8: Wind Speed at Jimma Station (in m/s) May 2007 Vear Jan Feb March April May June July Aug. 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 200C 2001 2002 2003 2004 0.8 08 09 0.9 0 8 09 1 1 1 2 09 1 1 09 0 9 08 09 1 1 0 9 0 9 1 2 08 1.3 1 4 C 9 0.8 08 0.9 0 8 0.8 08 0 7 1 0 1 0 09 09 08 0.9 0.9 0.9 0.8 07 0 8 09 09 10 0 8 08 0 9 0 9 0 8 0 7 07 08 12 1 1 09 09 0 7 0 8 0 8 0 8 1 0 0.9 08 08 0.9 0.6 09 0 7 08 0 8 0 7 0 6 07 08 0.9 0.9 08 07 0 7 0 7 0 7 0.6 0 6 07 08 09 07 08 08 0.6 0 7 0 6 0 6 0 5 07 08 0 8 08 0 8 0 7 0 6 0 6 0 7 06 0 6 0.6 06 08 07 0 7 0 7 0 6 0 6 0.6 0 6 0 6 0.6 • r 0.6 0.6 0.5 0 6 0 6 06 0.5 0.6 0 5 0.8 07 0.6 06 0.5 0.5 0.5 0 5 04 0.3 0 3 05 0.5 06 0.6 0 5 0.5 0 5 0 4 0.4 0 3 02 0 1 0 1 02 0.2 02 0 1 0 1 0 1 0 1 0 1 0 1 0.3 01 0.1 0 1 0 1 0 1 0 1 0.1 0 1 0 1 0.1 0 1 0 1 0 1 05 06 06 06 06 0.6 0.5 06 0 6 0 6 06 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 06 06 0 7 07 07 06 05 0 5 0 6 0.5 0.5 0 5 0.5 0.5 0.6 06 0.5 0 5 0.5 0.5 05 0 5 0.6 05 0 1 0 1 04 0.2 0.3 0.1 0 1 0.1 0.2 0.1 0 1 0 1 04 06 0.6 0.5 0.5 04 0.4 04 04 0 4 04 0 5 04 0.5 06 0 5 0.4 04 04 04 0 4 C 4 04 04 04 0 5 0 5 0.5 0 5 0 4 0.4 04 04 04 0.3 04 04 04 0 5 0 5 04 0 5 03 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 0.3 0.3 03 0.3 0.3 0.2 0 3 0 3 0.2 0.2 02 0.3 0.3 0 3 0.3 0.3 0.2 0.2 0 3 0.2 0.2 0.2 0.2 0.2 Average CV Skew Max Min 0 1 0.2 02 02 0.3 0.2 0 1 0.2 0.2 0 1 0.1 0 1 0 1 0.1 02 0.2 0 1 0.3 0 10 0 11 0 09 0 18 0 19 0 18 0 52 0 62 0 72 0 73 0 75 0 74 0 71 0 76 0 82 0 82 0 83 0 89 0 52 0 5 0 44 0 44 0 42 0 36 0 36 0.35 0.33 0 34 0.32 0 29 -0 04 0 16 0 1 0.29 0 63 -0 ■0.1 -0 0 02 0.3 0 31 09 1 2 1.2 1 3 1 4 0.9 0.9 0.9 09 1.1 1 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0.1 0.1 0 1 0 08 09 01 Water Works Design & Supervision Enterprise 134 In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects 09' Sunshine Duration at Bedele Station (i n hrs/day) Year Jan Feo Mar Apr May 1987 79 72 69 8 5 5.6 1988 9 3 7 1 65 8 2 79 1989 8 5 82 79 7.9 7 4 1990 8.9 56 7 7 64 8 2 1991 79 8 1 68 6 3 7 1 Mav 2007 — Jun Jul Aug Sep Oct J Nov 6 6.3 57 84 8 8 3 6 4 2 6 4 2 5.1 97 1992 57 7 7 7 1 8 3 6 1 34 2 2 6 7 6 2 6 2 6 3.8 5 1 6.5 7 9 8 8 6 4 3 8 4 8 6 9.6 8 7 4 5 2 7 3 4 5.9 8 8 4 1993 7.6 66 75 55 1994 7 7 7 5 7 7 76 • • 2 4 3 4 58 9•5 84 • Dec —i 83 95 6.4 9I 7 83 9.3 • 1995 88 66 77 66 1996 • • 7.9 • • • 37 43 67 9 79 7.8 1997 7.2 92 7.5 68 7 61 41 46 84 76 67 83 1998 7.5 77 64 87 64 67 2.9 33 47 54 84 92 1999 81 91 88 76 7.6 66 35 46 6.6 58 98 88 • 2000 9 88 9 61 78 8 • • 55 64 2001 2002 • 82 75 91 84 61 56 31 69 88 83 76 2003 7.9 86 7.3 88 96 57 29 36 61 9.5 87 86 2004 75 79 6 5.7 74 43 4.2 45 35 8.2 83 77 Average 82 76 75 73 76 6 1 37 4 1 6.2 79 8.3 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Annex E. Hydrological Data E1 List of Selected Hydrological Observation Stations—r---------------------- -—_—— May 2007 s. No Latitude, N Longnuae, r- Station No. Station Name Deg Min. | Deg. I Min. Catch. Area (km2) -t—--------- I I 1 114001 Dedessa near Arjo 08 1 41 I 36 25 9981 Period 1960-2004 2 114002 Angar near Nekemt r 09 I 30 I 36 r 35 I 3742 1994-2004 3 114005 Dabana near Abasina 1 09 r 02 | 36 03 2881 1962-1984 4 114007 Angar near Gutin ____ 5 114008 Yebu at Yebu 07 48 * 36 — J---- ™----- 29 1999-2003 ____ 42 47 1979-2004 He 114013 Dabana near Bunno Bedelle 08 24 36 17 47 114009 Urgessa near Gembe 07 50 36 39 19 1979-2004 1984-2003 08 03 36 27 1806 1985-2003 I------------------- 8 114014 Dedessa near Dembi (ToDa) 9 114016 Loko near Nekemt 09 22 36 36 375 1997-2004 10 114019 Temssa near Agarc 11 113004 Melke near Guaer 51 36 35 47 5 1989-2004 07 1 I 08 51 44 38 1998-2004 37 12 113038 indris near Guder 08 56 37 45 111 1986-2004 13 101006 Uka at Uka 08 10 I 35 22 52.5 I 1980-2004 14 091008 Gilgeignibe near Asendabc 07 45 i 37 11 2966 1967-2004 15 091012 Gojeb near Shebe 07 1 25 36 23 3577 1970-2004 JL Water Works Design & Supervision Enterprise 13b In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa irrigation Project Meteorological and Hydrological Aspects Annex E2: Mean Monthly Streamflow at Dedessan near Arjo Station May 2007 137 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arj° Dedessa Irrigation Project Meteorological and Hydrological Aspects —.------------- -----------—r------------------I E2‘ Continued) Year Jan Feb Mar Aprr----- Mav Uun jjul [Aug j r~ Sep Oct Nov Dec 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 20 4 122 148 194 38 3 83 225 569 486 156 60 - - - 30 4 141 8 373 723 854 598 87 2 41 4 19.0 - - - - - - - - • - - - - - - - - - - 242 135 7 851 595 66 1 57.2 128 3 401 740 1045 1005 674 215 111 7 99 0 572 55 3 634 46 2 175 457 591 578 211 115 839 56 4 36 2 56 2 74.3 48 0 120- 652 - • -- 52 3 40.2 30 3 287 65 2 202 526 639 643 538 140 - Avg cv Skew Max Min 46.2 287 26.0 33.2 66.5 223 654 1007 889 581 177 90 9 0.47 0.52 0.66 0.71 0.59 046 0.34 0.30 0.32 0 68 0.51 0.50 0.66 0.65 114 0.94 1.54 0 74 0.22 -0.16 0 43 0.73 1.26 1.00 99.0 634 67.1 94.9 190.9 503.5 1176 1 1612.8 1502.5 1337 4 459.2 210.4 120 5.4 2.6 6.3 12.8 53.2 225 0 491 1 485.9 130.8 59.9 369 Mean annual flow = 3821 Mm3) Water Works Design & Supervision Enterprise 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 Million mli Jan I Year Feb Mar ApJr Ma y I 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 8 5 5 5 9 7 8 4 94 58 262 208 299 67 22 9 115 59 4 5 9 7 9.2 18 6 105 243 342 218 104 -4 4 1 27 1 17.9 157 12 5 64 23 9 153 217 392 489 142 52 0 18 8 11 0 76 4 5 11 5 82 31 167 253 272 142 24 8 13 8 18 3 58 56 22.7 99 52 252 564 362 126 20 9 9 4 72 6 3 66 12 5 29 5 76 305 522 263 140 13 4 8 9 78 15 3 12 9 8 8 36 6 78 138 269 183 218 45 2 17 1 11 2 172 16 6 37 6 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 7 129 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 1 130 6 5 8 3 9 5 54 9 148 242 245 214 302 48 4 18.3 102 56 4.5 97 41.2 119 290 309 242 209 82 0 21 9 12.7 96 112 14 5 55 5 226 330 322 296 212 59 6 22.5 6.5 69 66 9.0 65 63 192 255 195 68 27 7 14 9 74 4 0 92 24 0 6 7 59 241 223 324 82 20 3 100 13.0 130 13 7 33 0 98 5 198 208 208 145 39 18 8 18 8 __~ 64 3 7 4.2 78 26.8 92 83 165 302 272 70 2 21 9 Average CV Skew Max Min 12.2 9 47 77.5 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 7 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.Arjo Dedessa Irrigation Project Meteorological and Hydrological Aspects Annual Maximum Floods May 2007 (1 Year n m3/s) Dedessa Upper Dedessa Dabana near Abasina Angar near Angar near Gilgel Ghibe near Asenoabo Gojeb nearSbebe neqem tc 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 HO 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 55 124 107 134 105 125 142 136 142 149 178 172 109 106 79 181 128 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.t Concentiation at Gumara Gauging Station I Field II sample I ab No River / Stream Station Date & Time Time | _ No Sediment F G/height Flow Depth Width Concen Remarks No * 1 of Sampling (Sec) (m) (m’/s) 'm' (mg/l) i AV 484 1 485 2 486 3 664 1 Dedessa Toba 15-Mar-90 Dedessa Toba 15-Mar 90 _ Dedessa Toba 15 Mat-90 _ 0 43 0 43 0 43 Dedessa 1 oba 21 Mar-90 0 50 665 2 Dedessa Toba 21 Mar-90 0 50 666 3 1057 1 Dedessa "loba 21 Mar-90 0 50 Dedessa Toba 2-Jul-90 1 81 _. 1058 2 Dedessa Toba 2-Jul-90 1 81 1059 3 Dedessa Toba 2-Jul-90 1 81 1190 1 Dedessa Toba 22 Dec 90 50 0 40 1191 2 Dedessa Toba 22-Dec-90 50 0 40 1192 3 1223 1 Dedessa Toba 22-Dec-90 50 0 40 I I2 2 2 2 2 | 27 Dedessa Toba 16 Sep-90 1224 2 Dedessa Toba 18-Sep 90 1225 3 Dedessa Toba 18-Sep-90 698 1 Dedessa Toba 16-May-93 45 699 2 Dedessa Toba 16-May-93 45 700 3 Dedessa Toba 16 May-93 40 704 1 Dedessa Toba 12-Apr-93 705 2 06 3 Dedessa Toba 12-Apr-93 Dedessa Toba 12-Apr-93 2 46 2 46 2 46 0 46 0 46 0 46 0 64 0 64 0 64 4 16 0 26 6 9 4 16 0.70 13 8 4 16 0 36 20 7 5 41 0 54 7 0 5 41 0 80 14.0 5 41 0 39 6 1 9 14 8 40 6 6 9 14 8 00 13 3 9 14 7.00 19 9 4 37 0 43 7 0 4 37 0 74 14 0 4 37 0 46 21 0 98 50 98 50 98 50 2 89 0 66 19.5 2 89 0 61 6 5 2 89 0 71 13 0 8 01 8 01 8 01 51 56 40 00 42 81 59 69 173 13 90.63 215 31 135 62 190 00 90 94 99 37 63.13 141 56 187 82 124.69 87.90 108 63 81 40 73 05 64 61 61 59 59 20 Water Works Design & Supervision Enterprise 141 In Association with Intercontinental Consultants and Technocrats Pvt LtdMeteorological and Hydrological Aspects may ^uu/ E5: (... continued) Field No sample No Lab.No River / Stream Station Date & Time of Sampling Time (Sec) G/height Flow jm’/sL Depth Width (m) L L ) m Sediment Concen (mg/l) Remarks AV 541 1 179/04 Dedessa Arjo 10 Aug-04 30 2 45 542 2 Dedessa Arjo 10-Aug-04 26 245 543 3 Dedessa Arjo 10 Aug 04 28 245 544 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 29 361 560 2 Dedessa Arjo 1-Sep-04 28 3 61 561 3 Dedessa Arjo 1-Sep-04 29 3 61 143 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 9 6ft 54 0 611 23 137ft 180 611 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 STUDIESArjo Dedessa Irrigation Project Hydrogeological investigations May 2007 TABLE OF CONTENTS ___________ _____ I table of contents list of tables LIST OF FIGURES 1. INTRODUCTION 1 1 General 1.2 Location I .... 2 1.3 Physiography ......................................................................................................... 1.4 Methodology and approaches 2. PHYSICAL HYDROGEOLOGY 2.1 Hydrogeological setup 2.2 hydrogeologic units 2.2 1 Fractured and/or weathered volcanic rocks --................................................................... 6 2 2.2 Alluvial sediments - —............................................................................................................ 2.2.3 Delluvial sediments 2.3 INVENTORY AND WELu DATA 2.4 Hydrodynamic parameters of aquifers 3. GROUND WATER POTENTlAi.................................. .......................................... —--- 3.1 Groundwater recharge estimation -- 3.1.1 Base flow analysis 3.1.2 Water balance method -....................................................................................................- 4. A TER U A LITY 4.1 Water samples-.................................................................................................................. 42 Sampling techniques and analysis 4.3 Pictorial representations of water quality analysis IS 4 3 1 Piper diagram -................................................. ... 18 4 3 2 Schoeller diagrams.............................................................................................................................W 4.3.3 Stiff diagram ...................................................................................................................................... J9 4.4 agricultural/irrigation water quality23 5. PIEZOMETERS OBSERVATION WELLS AND WELL FILED... 5.1 Distribution of Piezometers/Observation Wells -27 5.2 Future well field ............................................................................................................................. 28 6. waterlogging and drainage 6.1 Topographic features and soil characteristics ....................................... ....................................... 62 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.................................................... ~................................................. 4 8.2 Future groundwater prospect Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd. C « Qo Oc Qo '4 O'Arjo Dedessa Irrigation Project Hydrogeological investigations May 2007 LIST OF TABLES 9 Table 2.1 Details of boreholes in the study area.................................................. Table 3.1 Monthly total flow and Minimum flow of Dedessa river near Arjo12 Table 4 1 SAR and EC values in terms of irngation water suitability Table 4.2 SAR and EC values for surface and groundwater in Arjo-Dedessa area Table 5.1 Locations of the Proposed Piezometers................................................................. Table 6 1 Annual gross crop water requirement at primary canal head Table 6.2 Estimation of wetted area for Arjo- Dedessa irrigation canal 27 Table 6.3 Seepage loss from unlined Arjo- Dedessa irrigation canal....................................... 33 LIST OF FIGURES Figure 1 1 Location map of Arjo- Dedessa irrigation project3 Figure 1.2 A map showing 3- D view of Deoessa river Catcnment5 Figure 2.1 A map showing hyarogeoiogic units of Deaessa river cathment10 Figure 4 1 Location of water sample points17 Figure 4.2 Piper Trilinear Diagram for Water Samples20 Figure 4.3 Scnoeller diagram for water samples......................................................................21 Figure 4 4 Stiff diagram for water samples22 Figure 4 5 Electrical conauctivity (EC) in ps/cm and Total Dissolved Solids (TDSj in mg/L for24 Figure 4-6a Map Showing Contour for TDS 26 Figure 5.1 Proposed Piezometers/Observation wells ->9 Figure 6 1 Profiles along different lines in the command area37 Figure 6.2 A map snowing lines of profiles in the command area 38 Figure 8.1 A map showing groundwater potential areas 42 Water Works Design & Supervision Enterprise 11 In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Hydrogeological investigations 1. INTRODUCTION 1.1 General May 2007 Hydrogeoiogy refers to the occurrence, movement, chemistry (quality), etc of g o in general. It nas a diversified application in developing, utilizing and m g g groundwater Furthermore, different aspects of groundwater such as recharge d s g condition, aquifer type and set up, its interaction with surface water, etc are trea e this discipline. The nature of groundwater and how it behaves, when subjected to nature man-made activities is studied for different purposes sucn as for water supply (domestic, agriculture and industry) and construction of surface and sub surface engineenng structures (e g., dam, tunnels, drainages, etc). In order to develop and manage groundwater, one has to know its potential, quality and movement. Ethiopia nas diversified hydrogeological features tnat are attributed to its geology, structure, hydrometeorology, topography, etc The hydrogeology of the country has not been studied thorougnly so far With the exception of few areas such as Rift valley that has Deen mapped at scale of 1.250.000, the country has only small scale (1.2,000,000) hydrogeological map Hydrogeoiogy is usually applied for locating borehole sites in light of water supply Groundwater has Deen 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 nas 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 nas 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 Aoay River Basin Master Plan study Hydrogeological investigation and study that mainly focuses on g roundwater occurrence, movement, chemistry, etc nas been included as one of the components of the feasibility study and des.gn of the project. Accordingly, this study at Feasibility Study level has been undertaken. Association with Intercontinental Consultants and Technocrats Pvt. LinArjo 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 River basin. It is within the Western Oromia National Regional State, particua y junction of East Wollega, llubabor and Jima zones. The sub basin of the imgat o p j bordered by O mo-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 5,63 project location is shown in Fig. 1.1. The project area can be reached from Addis Ababa through two alternative high ways 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 Aadis Aoaba through Jima and Bedele 2Fig. 1-1 Location map of Arjo-Dadessa Irrigation project ¥ P’cpmad w R*arStf»«m 1 2 o f o^vni-d ■>»« WVo-Ma BcunOar,Arjo-Dedessa Irrigation Project Hydrogeological investigations 1.3 Physiography May 2007 The basin drams a part of Jim. high lands Including Goma (Agaro). Setema. Sig.mo, . Sana, and pad of llubabo, Indudlng Boreeha. Dedessa. Gachl and Bedelle Woredas above the proposed dam. Arp. Nunu Kumba. Sibu Sire and Wama Bonaya woredas are also within the catchment. The command area is drained by river Dedessa and othe such as Wama River. The general slope of the basm/or catchment is toward NE, E and directions The area has generally a rugged topography with the highest 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 Dedessa river catchment is shown in Fig 1 2. 1.4 Methodology and approaches In order to undertake the hydrogeolgoicai 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, ana 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 GlS and remote sensing software to identify and delineate lithology and geological structures, and finally to analyze, ano compile the spatial data, and to incorporate them as maps for various themes. • in-situ measurement of pnysical parameters of water quality indicators by using field water quality test kits (Ph, EC. TDS and Temperature meterj. . Finally, preparations of hydrogeolog al IC maps with different thematic layers such as hyarogeoiogic units, depth to groundwater table, water quality, groundwater yeld based on all the collected and analyzed data. 4Fig. 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 t»s,n comprises rofcan.c lava flows ma.niy Basalts and igmmBrte as well as pyroclastic Ians on j,ma side, where as nn llobabor and Wollega sides, me outcrop is manly basalfc lava flows except within the Dedessa River Valley, where the outcrop is crysta basement of venous granHes. gneisses and pegmafte The voidable rocks on Jim. Side are referred fo as Lower pan of Jim. volcnlc. composing flood Basalt with minor salics on the western, southwestern, eastern and southeastern part of the river catchment, e p y on the nigh land. However, at the lowtand pad 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 voicamcs are of Late Eocene- Late Oligocene age. where as the gneisses are of Arcnean age. The volcanic rocks (basaltic lava flow) in Bedele area is referred to as Makonnen oasalt comprising flood basalts It directly overlies the crystalline casement that shows the unconformable relation for the two outcrops. It is Oligocene-Miocene age Similarly, Arjo area is comprised by such flood oasalts of the so-called Makonnen basalt. Based on tne investigations made in the area, various aquifer set up exist. The main aquifers are weatnered and /or fractured basaltic lava flows and other acidic volcanic rocks such as rhyolite and ignimbrite The aquifers of volcanic origin have both confined and jnconfinea cnaracter; 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 as revealed from existing well drilling data. There are aquifers that are attributed to sediments especially alluvial sediments along river valley and streams, and colluvial sediments near mountains and escarpment. In addition to these, there are also minor aquifers attributed to weathered Dasement rocks (granites and granitic pegmatatites). This last aquifer types nave little significance in the area aue to their limited areal extent and limited aqu.fer productivity The presence of therma! springs, cold groundwater and saline springs in the area shows the diversification of the hydrogeologicai set up of the nver catchment. The aquifers of sediment and weatherea basement rocks origin are un confined. In addition to the lithological Water Works Design & Supervision Enterprise 6 In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Hydrogeological investigations diversification, geological structures dynamics and quality of the area Ma) 3DCT ™„,y tou-B s,n. .can, roH on ( Within Dedessa River valley, deep penetration of groundwater may be hindered y underlying massive basement crystalline rocks except where they geological structures as revealed by the presence of thermal springs in the The . olcamc esn a nd day < o-m , he c onf.n.ng I aye- to- w ale- oea-.ng I onnalton , aqude- Aquifer in Agaro area can be mentioned as an example The volcanic lava flows ar high y weathered (fractured) enhancing the infiltration of precipitation (mawMy a groundwater recharge Groundwater recharge in the area is very maximal due to d reasons, among them are the high precipitation dense vegetation cover, and highly weathered and/or fractured volcanic lava flows The mam groundwater recharge of the area istheSE. SW and the NE par of the nver 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 charactenstics of the therma' springs higniy vary from upstream to down stream along Dedessa River within the protect area Althougn 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 favors the existence of well demarcated groundwater recharge and discharge area 2.2 Hydrogeologic units Groundwater occurrence, movement and quality are mainly governed by the existing hydrogeologic units The phrase hydrogeolog.c unit refers to the rocks (consobdated <x unconsolidated; form.ng the frame work for groundwater occurrence, movement and qua|,t> Water Works Design & Supervision Enterprise in Association with Intercontinental Consultants and Technocrats Pvt LtdArjo Dedessa Irrigation Project Hydrogeological investigations The hydrogeologic units in Dedessa nver catchment have Deen categorized following units. They have Deen shown on map available at Fig 2.1 discussed nere under in brief. 2.2 .1 Fractured and/or weathered volcanic rocks May 2007 2 This comprises basaltic lava Hows, acidic lava flows and falls such as ignmbrites and pyroclastic falls In this category of hydrogeologic unit, secondary porosities fractures produceo due to weathering and geological structures play immeasurab e compared to the primary porosity/permeability The areal coverage of this hydrogeo g unit in Dedessa river catchment is 8,189.35 Km (79 56%). 2.2.2 Alluvial sediments As t ne n ame implies i 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 ooulders The areal coverage of this hydrogeologic unit in Dedessa river catchment is 1651 05 Km (16. 04%). 2.2.3 Delluvial sediments These sediments exist at t ne t ransition 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 hydrogeologic unit has been described separately Delluvial sediments with in the project area have coverage of 452.91 Km (4 40 %). 2.3 inventory and well data in order to undertake detailed investigation of the groundwater of the area, water supply schemes nave been inventoned and their geographical locations have been identified using GPS Borehole data have Deen 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 phys.cal parameters ot water quality by using fieid test kits such as TDS. PH and temperature meter 2 Water Works Design & Supervision Enterprise 8 In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Hydrogeological investigations May 2007 In addition to these pnmary data, secondary data have also been collected ,Q quality a nd other Well d ata. S atellite images a nd a erial p hotos h ave b ee identify geological structures and other lithological boundary demarcation that verified by field work. 2.4 Hydrodynamic parameters of aquifers As it nas Deen 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 borenoles drilled previously in the study area and their depths. Taoie 2. i Details ot boreholes in the study area Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt Ltd. 9Fig- 2-1 A map showing hydrogeologic units of Arjo-Dedess* rtver o WELEGA T7"; If ★ A\a Jima Arjo ILLU-ABA-BORRA JJMMA icuxxi 1WOL AXKli ◄ c “— 1Arjo Dedessa Irrigation Project Hydrogeological investigations 3. GROUNDWATER POTENTIAL 3.1 Groundwater recharge estimation May 2007 in order de.eiop groundwater of an area, ds potenua! Induding its annual replenishment, which is usually referred to as groundwater recharge, has to be known. Grpu recharge of an area can be estimated based on different approaches. One of the best approaches ,s through water balance method In order to employ this method ol groundwater potential estimation, the necessary data have been acquired for a y suppementary io th.s method, base flow analysis tor Rwenslream flow (Dedessa River) nave been jndertaKen 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 Dase 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 aata 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 Deoessa 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 m as shown in the Table 3.1 The basic assumption in deriving groundwater recharge from Dase flow analysis is that the monthly minimum stream discharge is equal to the case flow This approacn has been mentioned by Wundt (1978) that the monthly minimum stream discharge best approximates the base flow, especially for humid climate Therefore t ne b ase f low t hat i s supposed t o c orrespond t o t ne groundwater recnarge i s round to De 196.6mm. This value is obtained by dividing 1,962,092,938m3 by the area of the gaugea catchments, which is 9,981 km . This amount of ground water recharge is very 2 Water Works Design & Supervision Enterprise in Association with Intercontinental Consultants and TecLcrats Pvt Ltd. ' IlArjo Dedessa Irrigation Project Hydrogeological investigations minimal as it amounts to only aoout 13.53% of the total annual precipitat which is 1452.9mm. May 2007 Furthermore. Oeser, on the same method, the surface rundff of the Rrver catchment has been estimated as the difference Deiween the total river flow of Dedessa and I flow on annua, base and works out to 2.105.796.874 m’ that is attributed to surface runo This value IS used to denve the run off coefficient of (he river catchment to asses the surfacerun offfor the e ntire D edessa c atchmenl t hat will be used in the waterbalance approach of the groundwater recharge estimation in the next section. Table 3.1 Monthly total flow ana Minimum flow of Dedessa river near Arjo Parameters _ ______________________- Qtot Qantn Months IVp/se c M3/month M'/sec M /month M/se c Difference M/montn L- J 1764 47238048 4 473 11980483 13 16 35257565 ,j 1■ F --------------, 124 29994209 2.25 544320C 10 15 24551009 M 10 44 27973924 0 966 2587334 9 48 25386589 A ■5 54 40527302 4 557 11811744 11.08 28715558 M 29 14 78052326 10 364 27758938 18 78 50293388 J 98 47 255236832 45.433 117762336 53 04 137474496 J 263 37 705408958 137.365 367918416 126 337490542 A 423 39 1134009026 220.652 590994317 202 74 543014709 S 343 82 891191981 217 777 564477984 126.05 326713997 0 218.67 585697513 58.377 156356957 160.3 429340556 N 68.32 177074554 26 258 68060736 42 06 109013818 D 3565 95485139 13 792 36940493 21 86 58544646 Qtot 3 (m ) 4,067,889,811 1.962,092,938 2.105,796,874 Q,o(= total monthly discharge (m ). Min Q = Minimum monthly discharge (M’/S) Diff. = difference between J 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 hydrogeolog.c system, over a given duration for a g.ven area Hence it ts a d ynamic system, ( Detay 1997). The hydrogeolog.c s ystem can be a dramage basin/or catchment, groundwater basin, soil layer, or any surface water reservo.r (natural or artificial). Water oaiance is a valuao.e tool in the analysis of water availability i--------------- can be employed for different purposes, computation of groundwater . . Wafer Works Design & Supervision Enterprise in a region. The method -----recharge, evapo- 12 In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Arjo Dedessa Irrigation Project Hydrogeological investigations transpiration, continuous record of soil moisture, and stream flow from a May 2007 recoro and a few observations on the soil and vegetation, seasonal and geograp P of .rogation oemand. the flux ot water to takes, prediction ot human e dec. o n h ydroiogrc cycle, 'Leopold and Dunne. 1978). in this study the water balance method is aimed at estimation ot groundwater recharge T e basic assumption that is considered in this case is mat the surface water divide coincides with me subsurface drainage basin Accordingly, otner than the water that is percolated within the limit ot the surface water divide, there ,s no Inter-aquifer flow (inflow or out flow) of groundwater The basic equation of water balance is. inflow = outflow *AS Where AS is cnange in storage For the study area, the main inflow component is precipitation, out the outflow components are evapotranspiration and surface runoff assuming all other components such as water abstraction oy human for other purposes to be negligible. Besides this, the change in storage, can be considered to oe zero if the water balance is made Dy taking water year /or nydrologic year Hence, the value of AS will be negligible/or zero since the calculation is to be made or annual basis Since rainfall record can be obtained from meteorological stations in the area, the main task left is to estimate /or calculate the potential evapo-transpiration from which the Actual Evapotranspiration (AET) can be derived for the catcnment. In addition to this, the surface runoff has also to De estimated/or calculated since there is no actual measurement of this component in the study area. The surface runoff for Ago- Dedessa river catcnment has Deen derived (estimated) as follows 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 iand flow from which the runoff coefficient. Rc, ,s caiculateo Water Works Design & Supervision Enterpris?---------------------- 13 In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo Dedessa Irrigation Project Hydrogeological Investigations Rc = D/PA Where Rc= Runoff coefficient D = overland flow = 2,105,796,874 m P = annual precipitation =1452.9 mm = 1 452m May 2007 2 A = drainage area = 9.981.000.000 m (dramage area at the over gauging station But this does not mean that the total drainage area of the stud Hence. Rc = 2.105,796.874 m3/1 4529 m x 9.981,000.000 m2 = 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 prec.p.tation 1452 9mm has been used Hence, the sunace runoff for the entire Dedessa River catcnment becomes 0 1452 X 1 452m X 10.293.303.358 08 m2 = 2,170.141.264.31 m3 Thus the surface runoff works out to 210.83mm This value is only aoout 14.51% of the total annual precipitation, in the area Note that the total area of the studied nver catchment at the out let of the command area is 10.293.303.358.08 m2 By assuming, the coincidence of groundwater oasin with that of surface water divide and also by assuming that there is no artificial or natural intra-basin suDsurface or surface flow, the groundwater recharge of Dedessa river catcnment can oe estimated as follows GWr = P - (Sr * AET) Where GWr = Groundwater recnarge P = Annual precipitations 1452.9mm AET = Actual Evapo-transpiration Sr = Surface runoff = 210.83mm The Actual Evapotranspiration. (AET) can be estimated based on different methods one of them is tne empirical Tore method Turc method is represented by the following formula: Water Works Design & Supervision Enterprise 14 In Association with Intercontinental Consultants and Technocrats Pvt Ltd.Arjo 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 recnarge in the Dedessa river catchment oecomes 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 recnarge 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 metnod (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 15Arjo 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 p o 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 ano 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 nave been taken for physicochemical and microbiological analysis cased on the actual/existmg geology hydrogeology and geomoronology of the area. Accordingly, a total of thirteen samples have been taken from springs and Wells. Fig 4 1 snows 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 oy different institutions nave been jsed for hydrogeological interpretation of the area. Among the collected water samples, four samples were taken from spnngs and nine were trom ooreholes The numbers of samples have Deen aetermined based on various conditions such as geological ana hydrogeological setup of the area and availability of previously analyzed pnysico-chemical and microbiological data in the area Water Works Design & Supervision Enterprise Id Association with Intercontinental Consultants and Technocrats Pvt Ltd. 16Fig 4.1 A map showing water sample points in Arjo - Dedessa project area 400000Arjo-Dedessa Irrigation Project Hydrogeological Investigations 4.2 Sampling techniques and analysis A total of thirteen samples have been collected from i eren May 2007 cniirces One duplicate (t sample ,s coUecled from spring in order <0 see the reproduce of the iaborb.ory Natura, waler ,s samp.ed .n wew o< carrying out various anaiyses on ,t in order to undertake water quality analysis water samples have been collected tor physicochemica y collected water samp.es were from ground wa.er (spnngs and Welts) sources. The samples nave been taken with one liter capacity plastic Dotties. In order to compare physicochemical parameters, some physical parameters such as ( Solids), Temperature and PH have been measured at field in order to compare with that of Laboratory 4.3 Pictorial representations of water quality analysis 4.3.1 Piper diagram Dissolved the result 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 sample points indicate samples that are selected in the database and are also highlighted on all other open grapmcal displays. According to the water samples plotted in Piper trilinear diagram lor Arjo-Deoessa area, samples can be categonzed based on their clastering as Ad-01. AD-10. AD-12 and AD-13 as one category. AD-02. AD-03. AD-04. AD-05 AD-09 and AD-11 as second category; AD-07 and AD-08 as third category and finally AD-08 as loodh category However. If we refine further the water type based on the chem.cat composition, they can be categonzed in to five categones. i . Works DeslgI14 s .ss.et.tl.. fcrcd..^ “P«>nslon Enterprise---------------------------------------------- C „„1U11B ud T b 18Arjo Dedessa Irrigation Project Hydrogeological investigations • Na-HCO3 type (Sample AD-01. AD-07, AD-08, AD-10. AD-12 and A • 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) May 2007 The cation to amon ratio atso vanes for the different samples md.cat.ng various conditions of rock-water interaction. 4.3.2 Schoeller diagrams These semi-logarithmic diagrams were developed to represent major ion analyses q ana io aemonstrate different hyarochemical water types on the same diagram. This type of graphical representation nas the advantage that unlike the trilinear diagrams, actual sample concentrations are displayed and compared The Scnoeller 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 De included along the x-axis and the symbols representing the sample points can De customized according to snape and color The highlighted lines indicate sDecific 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 snow differently snaped curves Accordingly two major types of water can De 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 >s shown for some of the analyzed samples in Fig 4 4. According to this figure water samples of the project area can be categonzed in to three major groups Na HCO3 type (samples AD-01. AD-07. AD-08 AD-10. AD-12 and AD-13) Ca-HCO3 type (samples AD-02. AD-03. AD-09 ano AO-ff); ano Ca- a-HCO3 .ype (samples aD-04 AD N Water Works Design & Supervision Enterprise " 19 In Association with Intercontinental Consultants and Technocrats Pvt Ltd.ao 80 00 eo 40 40 20 20 SO4 * 80 ..................' ueg&na: O AD-01 □ AD-02 ♦ AD-03 — AD-04 X AD-CS ♦ AD-06 o AC-0" A AD-Od V AD-09 -r AD-10 X AD-71 ♦ AD-12 AD-13 ♦AD-06 oo .................... 30 - 8C <0 . ................. r................................. A X _________ •- £ x S7 , . , 80 80 40 20 20 Na-KHCO3 Cl Fig. 4-2 A map showing Piper trilinear diagram for water samples in Arjo- Dedessa CaI Concentration (meq/l) Legend —•— AD-01 - 4i — AD-02 .. -e ... AD-03 ---------- AC-34 —X— AD-05 ---- •---- AD-06 - -e — AD-07 - -A • AC-06 - e - AD-09 - ■- AD-10 ■ AD-11 — AD-12 Mg Ca Na-K Cl SO4 HC03 Fig. 4-3 A map snowing Scnoeller diagram for water samples in Arjo-Dedessa areaNa —k Cl Ca - HC03 Mg Ti SO4 K CO3 10 50 3 AD-07 3 50 Cl MCO3 SO C03 10 5 AD- C2 ' Na Ca Mg K I £ c: HCC3 SO4 CO3 15 AD-03 ~ 5 5 Na Ca Mg K Cl rlC03 S04 C03 Na Ca Mg K 5 ’ AD- 05 ’ Fig. 4-4 A map shwing Stiff diagram tor water samp.es ,n Arjo- Deoessa Project area (Concent meq/L,Cl Na Ha t x i HCO3 Ca > HCO3 Ca X X S04 Mg ir S04 Mg T C03 K □03 K — iO 5 5 10 X 15 X AD- 09 ” AD- 08 • • AO-12 I iArjo Dedessa Irrigation Project Hydrogeological investigations 4.4 Agriculturai/irrigation water quality Agricultural suitability of water depends on crop type, climate, soil type, and amount o irrigation water use. (Davis 1966) The mam parameters to be analyzed to evaluate irrigation water quality are Boron. Sodium h azard. and Salinity These paramete plants either directly (e.g by causing an adverse physiological effects) or indirectly (eg y May 2007 limiting plant root nutrient or moisture uptake). Salinity is best estimated based on Elect ica Conductivity (EC) value Other direct indicator of salinity is Total Dissolved Solids (TDS) Tne two parameters. TDS & EC are related by the following equation TDS (mg/L) = 640 x EC (dS/m). wnere 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 nazard 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 ana magnesium Water is said to De sodic if its SAR is greater than 12 SAR is calculated as follows SAR= [Na*]N0.5[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 ana references there in), the water quality evaluation for irrigation basea on SAR ana EC are as shown in Table 4 1. Taoie 4.1 SAR ana EC values in terms ot imgation water suitability 22 Water class Excellent Good Fair Poor SAP < 10 — 10- 18 18-26 >26 Water ciass Excellent EC (ps/cm/ <250 Good 250- 750 Permissible Doubtful Unsuitable 750- 2000 2000- 3000 lO&'rr = w ns/cm ——---------------------------- — ------------------------- ! >3000 —1 order ,o evaluate waler quality for imqation from Salinity anq Sodium nazard pom. of ..r. tor Arjo-Deoessa area. th. parameters have Peen measured and catenated and they are shown in Table 4-2. Water Works Design & Supervision Enternrise ------------ ? i io Association with Intercootlnenui Consults and Te^nocrats Pvt Ltd.Arjo Dedessa Irrigation Project Hydrogeological investigations Table 4.2 SAR and EC values for surface and groundwater in Arjo-Dedess^ _____ ___ ____ — TrCTn . AadD--i'oI M May 2007 1 ‘ad-a AD-*1 .pie aO-7 1 <310 OU* 2560 2370 S*e 3160 _2_1_6 , 38 4 0 7 04 05H According to SAR values obtained for the water samples, AD-01. AD-07. AD-10. AD-13 are all sodic water and AD-08 is slightly sodic, where as. the remaining wa samples are all non sodic. From .mgation water qualrty 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 ps/cm to 4450 ps/cm. In other words, it can be sa.d the salinrty ranges from medium salinity to very h.gh salinity F.g 4.5 shows values of TDS and EC for different water samples in the project area Figure 4-5 Electncal conductivity (EC) in ^s/cm and Total Dissolved Solids (TDS) in mg/L for water samples in Aqo-Dedessa area This graph oeatty .nd.ea.es me extern of selmtty for aj(feren, water samp|es or tot the EC ano me TDS Contour map of the TDS is eveilaote al Fig 4 6 tor the pro,ear area For oescnpt.on one the water sarnp.es may he categonzed tmo three cetegones based on tner, Eieemc eonductwity and TDS vetoes. According,y. seven sempies (7D O2 .. 24Arjo Dedessa Irrigation Project Hydrogeological investigations AD-03 AD-04. AD-05 and AD-06) have low salinity, four samples (AD . and AD-13; have high salinity . and two samples (AD-01 and AD-10) are extreme y This qualitative description doesn't follow the standard procedure of classification based on TDS and/or EC. but it is simpty for the sake of descnpt.cn Wa samples codec as AD-01. AD-10. AD-12 and AD-13 are al! from springs; all other water samples are from Dorenoles (drilled shallow Wells). Hence, it is possible to co even if they are all from groundwater, they are from different aquifers. The mo water (having high TDS values) are mainly from weathered basement rocks (granite and granitic pegmatite), and deep-seated volcanic aquifers especially along fault lines ( 9 thermal springs). May 2007 fr Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd. 25002 Fi 9 *4 4 map 5how>ng the contour for Total Dissolved Solids (TDS - mg/L) for Arjo - Dedessa Project area Rivef/Stream 60F,ff 4-6 4 map showing tha contour for Total Dissolved Solids (TDS - mg/L) for Arjo-Dedessa Project area o 60Arjo Dedessa Irrigation Project Hydrogeological Investigations 5. PIEZOMETERS OBSERVATION WELLS AND WELL FILED 5.1 Distribution of Piezometers/Observation Wells In order to monitor groundwater quality and quantity of the area both befo construction of the dam under investigation, a total of fourteen Piezometers/O wells have Deen proposed and their sues have Deen located. The geographic configuration/distribution of the piezometers/Observation wells is selected geoiogy hydrogeology, topography groundwater flow direction, etc of the area depth of the piezometers to be constructed rarely exceeds 100 meters, PVC cas g recommendable In some cases the existing well depth at the immediate down stream o the proposed oam 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 May 2007 ------------- I Geographical coordinates (UTM) “■I Ser No Piezometer Easting Northing code Altitude (m) Pad-1 241283 | 945079 1332 PZ 2 P.o-2 239578 942443 1348 3 P.o-3 239229 948568 1354 4 P*d-4 232368 945622 1345 5 P.o-5 L. 237407 951746 _______ 6 P*o-6 I —----------------- 1391 228492 944575 1374 7 Pad-7 230198 952870 1386 8 Pad-8 225779 947133 1324 9 Pad-9 220119 954111 1341 to Pad-10 217677 951707 1319 11 Pad-1 1 217135 961437 1332 Pad-12 12 1354 13 Pad-1 3 212716 4------------- 214654 95244a 956087 1323 | 14 Pad-1 213336 961320 1320 The construction of these p.ezometers shall follow the standard procedures althougn some sHe-specific condit.ons such as hydrogeoiog.cal set up will also matter The location of the proposed Piezometers is available on the map shown in Fig. 5-1 Water Works Design & Supervision Enurnrise--------------- in Association with Intercontinental Consultants and TechnocL Pvt Ltd. 27Arjo Dedessa Irrigation Project Hydrogeological investigations rXXZ Io..o^ale. s.o.a e ,n .He a.ea a.e oasaH.c -a " May 2007 g sa.es rhyolite ano ^e. ano a,^a. -a , This can De verified by existing boreholes data in the area Agarc area snow this situation. Well field sites on which detail geophysical investigation shall be undertaken have identified based on geological, hydrogeological and geomorphologicai setting approacnes Test wells drilling and construction shall follow the detail geophysical investigation Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd. 285-1 a map showing proposed piezometers, water points and water sampling points -, 70000 Merors Sibu Sire iuto Wayu Wama Boneya Ljmu SexaArjo Dedessa Irrigation Project Hydrogeological investigations 6. WATER LOGGING AND DRAINAGE 6.1 Topographic features and soil characteristics The undulating and rolling topography in upper part of the project area grad y gentle slope of flat land in the bottom valley of Dedessa. especially the lower part command area becomes almost flat. This flat land is covered with sediments colluvial/delluvial and alluvial origin. This sediment is underlain mainly by base May 2007 y The topography and land characteristics of the command area can be said to a level (0- 1%). nearly level (1- 2% slope), very gentle (2- 4% slope), and gentle (4- 6 x 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 nas a rolling topograpny and there are several small hills dispersed in the command There are rising hills also on the outer boundanes of the command area on ootn 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% ana 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 nelps 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 tc flow out easily. 6.2 Existing groundwater table Groundwater level in the project area vanes from 2 to 20m b g I In 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 deeper than 5 meters below natural ground surface The nse of the groundwater table can happen due to different natural conditions and man made activities. The application of irrigation practice is the major human interferences for rise of groundwater table The method of irrigatton (drip furrow, etc) that is practiced and the crops proposed to be grown will determine the extent to which it may affect the rise in groundwater level of the area Water Works Design & Supervision Enterprise U o. ..u, ,„„.011Ull BUI . ------- '<> uaArjo Dedessa Irrigation Project Hydrogeological investigations May 2 007 6.3 Future groundwater table and recharge from irrigation Whenever there is a major irrigation project with continued and intensive irng there . always an app.ehens.on of rise of groundwater table If (be nse of the grounowa er lapie is significant, and it continues unabated, it may cause serious adverse p fertility of the land. Some of the factors that affect the nse of groundwater a • Topographic features • Land characteristics • Natural drainage system • intensity and amount of rainfall • Existing grounowater taole • Soil cnaracteristics • Crops and its water requirement • Seepage ana other losses from canal system • Sunace drainage system implemented and its effectiveness The estimated annual crop water requirement at primary canai nead, for various crops to be cultivated in the command area of the proposea Arjo- Deaessa project comprises four set of values categorized under two pnases each phase having two rotations. This has De en snown in TaDie 6.1 Taole 6.1 Annual gross crop water requirement at primary canal head Ser No Phase Rotation GCWR (mm) 1I 1 987 40 21 II 1086 14 3 II 1 1311 47 4 II II 1423.234 In order to assess groundwater recharge from irrigation water, the maximum value of the Gross Crop Water Requirement (GCWRj in the second phase of second rotation that is 1423.234 mm/yr has been used Therefore, the groundwater recharge from the application of irrigation nas oeen estimated under two main situations as follows Water Works Design & Supervision Enterprise-------------- In Association with Intercontinental Consultants and Technocrats Pvt Ltd. 31Arjo Dedessa Irrigation Project Hydrogeological investigations M ay 2007 1 According to groundwater recharge estimation made in this report. annual precipitation in the area, only 17% is going for recharging the g o If the same scenario is considered, the annual groundwater recharge Trom the application of irrigation in the command area becomes 241.95 mm. This crude estimation since various factors among which the irrigation method ca the groundwater recharge 2 Along with other crops, cultivation of paddy has been proposed i n the co mma nd area Paddy is the only crop that requires constant standing water in the fi eld 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 cnance 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 reacning groundwater wnich 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 pnase- II. Considenng the entire command on average, the annual contributions of irrigation water tc the groundwater would be 99mm in tne Phase- I, which will increase to 148.5 mm under phase- II. Regarding other crops, they are all dry imgated i.e., no standing water is required The irngation water applied tc 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 wmcn will be taken care Dy sunace drainage system. As such the addition to groundwater □ue to irrigation of all other crops except paddy may be cons.dered very negligible and therefore, may be neglected. Seepage loss <o the groundwater from the cana.s (mam canals, secondary cana.s and canals) has also oeen esl.ma.ed According United Sfa>es Bureau of Reclamation (U S B R.,. seepage loss from unlined .mgarion cana. is 15 m’lsec per one million souare meter or wedeo area lot da, and da, .earn soiis. Based on this approaches, seepage loss from Arjo-Dedessa irngation canal is shown in Table 6.2 and 6 3 32Arjo Dedessa Irrigation Project Hydrogeological investigations Table 6.2 Estimation of wetted area for Arjo- Dedessa irrigation canal Average May 2007 I Ser. No Canai category wetted perimeter (m /m) Total length (m) Area (m ) 2 Total Area (m ) 2 Rignt L.eft ------------ i Rignt Lett Rignt ------------ ~i Len 2 I 1 Main canal ------------ 87115 10 211 4-- —— — 740.512.00 42.800 00 ----- i 60 180 00 279.639.00 "460 873.00 131.896.05 2 Secondary canal 3 Tertiary canal Total 2 795 2.795 49.370.00 47.190 00 137,989.00 ___ — 1.02 1.02 199,464 00 239.100.00 203.453.00 — --------------------' 243.882 00 269.885.05 447.335.00 1,457,732.05 621.081.00 836,651.05 I Table 6.3 Seepage loss from unlined Arjo- Dedessa irrigation canal NO Command area (wing) ------------------------------------------------------------------------- Wetted area of Canai (m2) Main canal Secondary Tertiary canal canal 1 Total wetted area (m ) 2 Total seepage loss (mm) r Right Bank 279.639 00 137 989 00 203,453.00 L— 621,081.00 ' 2 Lett Bank 460 873.00 131,896 05 243,882 00 836,651 05 3 Total area (m‘) I 740,512.00 269,885.05 447.335.00 1 457,732.05 hr 3 ToUl Seepage (m ) 23,320,796.31 6,400,809.75 10,609,354.73 40,330,960.80 226.26 In the 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 - May) ano twenty four hours a day for the main canal; where as for six months of twenty four hours for secondary and tertiary canal. The command area on which the seepage loss has Deen averaged out is tne gross command area, i.e., 17,825 hectares (178 250. 000 m 2) i.e.. the total seepage loss of 40,330,960.80 m3 is spread in the gross command area which gave an average seepage loss of 226.26mm from the irrigation canal Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd. 33Arjo Dedessa Irrigation Project Hydrogeological investigations Hence, if we reduce this amount from the recharge due to the applies mentioned above (241 95mm). the net recharge that contributes to the grou nse becomes only 49 4mm Therefore, under this scenario the groundwater le the application of irrigation will be May 2007 _ z * Groundwater I evel r ise due to application of i rrigation. 0.141m. r = G R/ru = 49 4 mm/0 35 - Scenano III According to the paddy cultivation and seepage loss from canals, the annua groundwater recnarge from the application of irrigation is 3 4 76 mm as mentioned 7 if this is the case, the groundwater level nse due to the application of irrigation under stagnant groundwater condition becomes Groundwater level rise due to application of irngation. 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 catcnment. Hence, only 20 42% (76 53 mm) of the groundwater recnarge from irngation water will contribute to tne groundwater level nse Therefore, the groundwater level rise under this Scenario becomes, GWLr = GR/n = t 76 53 mm/0 35 = 218.66mm = 0.219m. In conclusion, the assumption of stagnant groundwater condition Scenarios (scenario I ana III), over estimates the groundwater level rise due to the application of irngation Because it assumes static)or stagnant groundwater condition that is not the case in reality since groundwater is usually in a dynamic condition The second Scenario (Scenano II) relies on groundwater recharge estimation from irngation water application equals that from precipitation However groundwater recharge from irngation water application, particularly from paddy irngation and canal loss should be higher than from precipitation Hence, this scenano underestimates the groundwater recharge. Therefore, according to this mvest.gat.on, the Scenano that works best is Scenario IV. Hence, the annual groundwater level nse due to the application of irngation water will be 0.219 m However, it has to be noted that the existing soil in the 10am soils as reveaiea from soil survey (sampling and command area is mainly clay and analysis) under the same project Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvx Ltd. 35Arjo-Dedessa Irrigation Project The soil has an average hydraulic conductivity of 0 0000056 m/s, i.e. 0.482 m/day value is very small inhibiting the infiltration of any water (precipitation or irrigation) to Groundwater Hence, the contribution of groundwater recharge from the application imgation should be less than the amount stated here. Therefore, the groundwater level rise Que to the application of imgation cannot exceed 0.219m/year Another factor that can reduce the contribution of irrigation application to groundwater recnarge is the presence ot number of creexs that are transversal to the trend of the command area and Dedessa River. Some infiltrated water from the imgation application will come out as regeneration through the creeks before reaching the groundwater table. Profile across some creeks and Dedessa nver in the command area is available in Fig 6.1 (a, b c, d and e). The lines along which the profiles nave been taken are also shown in the map Fig. 6.2. Although there is no well documented well completion aata in the command area, the depth to groundwater in the area is beiow 5 meters during dry seasons except in some creeks such as Chuli area (eastern pan of command area) wnere the water table is about 2 meters beiow 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 ot contour map depicting depth to groundwater is hardly possible under such data limitation since tney are entirely constructed for emergency purposes. 36!i h H ■I ■i * * * * 0 0 0 II’From Pot: 232335.077, 944187 179 lo Pot; 213587.927. 956965.006 fig 6! t)Wkfa<r*r^tofiwnstrMm "MM ^DMnnMr 1300 m 1370 m 1360 m 1350 m 1340 m 1330 m 1320 m 1310 m 1300 m — 2.5 km 5.0 km 7.5 km 10.0 km 12.5 km ■W 15.0 km 17.5 km 20 0 km 22 72 kmFtorn Po» 219184 091, 943954 006 lo Pos: 226412.470, 954446.014IFrom Poo 210709.844, 952208 348 HOU m To Pos: 210531.205, 957198.261 t) Mb khk$ Mb$9 river ivm W M to rigti M 1375 m 1350 m *> . * . » • — 2.0 km 3.0 km 4 fl km 5.0 km 6.0 km 7.0 km 0 0 km 9.2? km10000 0 10000 MatarsArjo Dedessa Irrigation Project Hydrogeological investigations 7. SALINITY AND SODICITY May 2007 Salinity of soils/water can be defined in terms of electncal conductivity. Particularly it is the electrical conductivity of the saturation extract. However, sodicity is defined of e xchangeaDle sodium percentage. Salinity may be categorized into two based o sources, primary (innerent) salinity and secondary salinity Primary (inherent) salinity derived from the weathering/degradation of pnmary 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 ana soil salinity occur aue to different reasons. Among them are over irrigation that causes groundwater level rise due to in appropnate provision of drainage and/or crop water requirement calculation, poor method of irrigation, capillary rise of ground water due to naturally high grounawater level below surface, etc When such raised grounowater level is suojectea to evaporation loss, the chemical constituents of the water will be left over and becomes concentrated on the sunace leading to soil and/or water salinity. The leaching of some existing nutnents in soil is also the potential source of salinity of water and soil in irrigation. In oraer to assess the possibility of salinity for the project area in the future, data have oeen collected and have been evaluated. Among them are the existing ground water quality (physicochemical characteristics of groundwater), ana 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 chionaes, sulphates and carbonate salts The distribution of relatively saline water is SDoradic in thP ar =. Q i« Total Dissolved Solids of the project area is available at Fig 4 5 Water Works Design & Supervision Enterprise 1. M. with co.suiu.ts TX,crats lM 39Arjo Dedessa Irrigation Project Hydrogeological investigations Hence, the hazard soil/water salinity during the design period of t P rtf all controlled naturally (through high precipitation and topography of the a through appropriate irrigation water management. May 2007 Water Works Design & Supervision Enterprise In Association with Intercontinental Consultants and Technocrats Pvt. Ltd. 40Arjo Dedessa Irrigation Project Hydrogeological investigations 8. EXSITING AND FUTURE PROSPECT OF GROUNDWATER 8.1 Existing groundwater development May 2007 Presently, the majority of the Woredas' capital town and the rural community in the rive 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 througn the treatment of raw water The yieid 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 wnere 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 grounawater 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 borenoies. in addition to this, the Quaternary sediments in the nver 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 geological, meteorological, hydrogeological and geomorphoiogical conditions in the river catchment indicate there are areas that can be developed in light of groundwater for various water supply purposes. Accordingly, potential well field sites have been identified in order to develop groundwater These identified well field sites nave to be verified based on geophysical investigations and test well drilling before being entirely developed. The likely limitation in the future groundwater development in the area is not the quantity but the quality (relatively high iron concentration). The map of potential groundwater areas for future development is available at Fig. 8.1 Water Works Design & Supervision Enterprise 41 In Association with Intercontinental Consultants and Technocrats Pvt. Ltd.Fig 8-1 A map showing Groundwater potential areas for future development 0 £3000 Verws ’TWO iscccr TXjOUQ » I10COCT fOEZCOC iqduooc escort. «11OL I I I •6CtU KKK00 I l I I ■OOr 750000
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