0<W' FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA MINISTRY OF WATER RESOURCES ERER DAM & IRRIGATION DEVELOPMENT PROJECT Executive Summary (Final) Detailed Design Report May, 2009 CONCER 1 ENGINEERING A NP CONSUL UNG ENTERPRISE P. LC. (CECE) ENGINEERS WA7ER RESOURCES A AGRICULTURAL PEVELOPMENT PLANNERS P.O BOX 6064 1H. 251-11-4659744 FAX 251 -11 -6659245 ADUIS ABABA E-fo4ilconcng4« dhkjnet.rf ETHIOPIA WWW ConccrtengnerTirKj com , ht QSiociQtion with Cot nulling Engineering Service (LTP)Executive Summary Volume 1 : Dam & Appurtenant Structure Annex A: Dam Design Annex B: Dani Appurtenant Structures Annex C: Geotechnical Study Annex D: Hydrology Volume II: Irrigation & Drainage Annex E: Irrigation & Drainage Design Annex F: Road Infrastructure Annex G: Project Control Centers Annex H: Operation & Maintenance Manual Volume 111: Project Worth AnalysisTable Contents 1.0 INTRODUCTION 1.1 General.................................................................................................................................. 1 Table 1.1 Salient Features of The Project1 1.2 Location of Project 1 4 Access to the Project Area 1.5 Source of Irrigation Water 2.0 DAM DESIGN •«•••••••••■•••••••«••••••••••••••••••••••7 2.1 Dam site-............................................................................................................................... 7 2.2 Hydrological Aspect7 2.2.1 Drainage Flow estimation7 2.2.1 Peak Flood estimation8 2.2.1.1 SCS Method8 2.2.1.2 Floodway Determination8 2.2.1.3 Equations for basic profile calculations9 2.2 1 4 Cross Section Subdivision for Conveyance Calculations10 2.2.1.5 Comparison of total measured surface Runoff Potential of Erer River with feasibility study10 2.4 Dam Design aspect12 2.4.1 Material Properties Considered for Analysis12 2.4.2 Loading Conditions14 2.4.3 Minimum Factor of Safety14 2.4 4 Seismic Design15 2.4.5 Stability Analysis16 2.5 Dam Appurtenant Structures17 2.5.1 Intake17 2.5.1.1 Irrigation Demand18 2.5.1.2 Supply for Downstream Users18 2.5.1.3 Design Discharge19 2.5.2 Spillway Structure19 2.5.2.1 Location and Suitability19 2.5.2.2 Design Criteria20 2.5.2.3 Selection of type of Spillway20 2.5.2.4 Spillway Chute Structure20 2.5.2.6 Spillway Energy Dissipation Structure21 3.0 IRRIGATION SYSTEM DESIGN22 3.1 Topography and Land Use of Command Area22 3.2 Soil Suitability..22 3.3 Irrigation Scheduling23 3.4 Depth of Watering23 3.5 Field Size and Channel Discharge24 3.6 Irrigation System 25 3.7 Gross Command Area27 3.8 Irrigation overall Efficiency27 3.9 Irrigation Structures28 3.10 Field Drainage System28 3.11. Land Grading29 cm xr4.0 INFRASTRUCTURAL DEVELOPMENT........................................................................ 30 4.1 Road Network.................................................................................................................... 30 4.1.2 Road Classification.................................................................................................... 30 4.1.3 Geometric Design...................................................................................................... 31 4.2 Project Control Centres...................................................................................................... 32 4.2.1 Selections ofPCC sites............................................................................................... 33 4.2.2 Types of Building Infrastructure and Services...........................................................34 5.0 FINANCIAL AND ECONOMIC ANALYSIS....................................................................37 5.1 General............................................................................................................................... 37 5.2 Financial Analysis.............................................................................................................. 37 5.3 Economic Analysis.............................................................................................................38 6.0 Construction Schedule............................................................................................................. 39Errer Dam & Irrigation Project ZCECE &CES 1.0 Introduction 1.1 General The project was identified and conceptualized during the course of Integrated Development Master Plans Studies of the Wabi Shebele river basin and the work in phase-1 (reconnaissance survey) commenced in 2001-2002 Subsequently, considering the importance of irrigated agriculture in all round development, the Govt of Ethiopia had initiated action to bring more and more area under irrigated agriculture To identify potential sources of water resources Preliminary Water Resources Master Plan for Ethiopia was got prepared by WAPCOS in 1990, and also the Pre-feasibility master plan of the country. Later on in 1998, Wabe Shebelle River Integrated Master Plan was drawn up and Erer irrigation project was identified as one of the potential scheme for development of irrigated agriculture. Consequently Pre- Feasibility and Feasibility studies were carried out by Water Works Design and Supervision Enterprise ( WWDSE ) in association with WAPCOS and Synergies India Pvt,Ltd. respectively in 2002-05 and 2006-07 This project was found technically feasible, economically viable, environmentally sound and socially equitable and therefore recommended for implementation. The detailed designs are now being prepared to enable the government to implement the project with promptitude. The salient features of the project are shown in table 1.1 Table 1.1 Salient Features of The Project Description • Figures Latitude and Longitude (Command area) UTM 1009300 N to 1028300 N (9°07 17 N to 9°17 40 N) and UTM 193375 E to 199650 E (42°12' 24" E to 42°16 03" E) Catchment area 419.00 Sq Kni Annual rainfall 650 mm to 800 mm Net CCA 3722 Ha River Bed (deepest) 1348 00 m Dead Storage Level / New Zero Elevation (50 years) 1369.85 m Executive Summary/ Final Detail Design Report/2009 1Errer Dam & Irrigation Project ZCECE &CES *• MDDL : 1371.OOM FRL : 1379.00 M MWL : 1382.60 M Dam Type : Zoned Earth fill Top of Dam 1384.60 m Maximum height of dam : 36.60 m Gross storage : 5067.50 Ha-m Live storage : 2303.40 Ha-m Spillway Type : Ogee weir with inclined chute Waterway of spillway : 30 m Inflow design flood (greater of 0 5 PMF and 10,000 year return period) 641.90 Cumec Spillway routed flood 440.50 Cumec Area to be irrigated (CCA) 3370 hectares FIRR 11.16 (%) EIRR 14.56 (%) B/C ratio 1.50 NPU (financial) 204»10<bii7 NPU (economical) 122*106birr Financial and economic viability Verified 1.2 Location of Project The Erer Irrigation Project proposes to draw irrigation supplies from Erer River which is a tributary of Wabe Shebelle River. The project is located at about 530 km from Addis Ababa and 19 km from Harar town (figure 1.1) Executive Summary/ Final Detail Design ReporL/2009 2Errer Dam & Irrigation Project ZCECE &CES Figure 1.1 Location Map The command area is situated on both sides of Harar-Jijiga road which is 11 km from Babile town towards Harar. The proposed dam site i\situated about 6 km on left side of Harar-Jijiga road. Erer Irrigation Project is located in two Regional States, namely Regional State of Harari and Regional State of Oromia. In Oromia, project area is situated in Babile of the East Hararge Zone In Harari it is situated in Erer and Soft Woredas. The command area is situated in 2 Kebeles ( Kile and Erer Dodota) of the Harari Region and in about 7 Kebeles ( Erer Ibada, Ifadin, Gamachu, Erer Guda, Tula, Berkele and Tofiq ) of Oromia region. Major part of command lies in Erer Ibada and Efadin Kebeles. Executive Summary/ Final Detail Design Report/2009 3Errer Dam & Irrigation Project ZCECE &CES The command area starts from some distance downstream of the dam and extends only on right bank of Erer river. The command area is narrower and smaller near the dam site and becomes wider in the downstream side. The irrigable area is mainly situated below the bridge on Harar Jijiga road and extends beyond confluence of Erer River and Bidisimo stream covering only the right bank of the river. Although suitable areas are available on left side of the river also, due to limitation of water availability for irrigation only the command on the right bank of Erer River is chosen for this project. The command area is located between UTM 1009300 N to 1028300 N ( 9° 07’ 17” to 9° 17’ 40”Latitude ) and UTM 193375 E to !99650 E (42°12’24”to 42° 16’ 03’’Longitude) (figure 1.2) 1.4 Access to the Project Area The project area can be accessed by an asphalt road (511 km) from Addis Ababa to Harar town and further 19 km by all weather gravel road which connects Harar with Jijiga town Harar town can also be accessed partly by air up to Dire Dawa and remaining about54 km. by road from Dire Dawa to Harar.Babile is the nearest town which is 11 km from project area. The proposed dam site which is about 6 km from Harar- Jijiga road, is connected by fair weather road. The entire proposed command area from head to tail is connected by fair weather road and therefore, the area can be accessed for carrying construction materials and equipment without making special arrangement of approach roads 1.5 Source of Irrigation Water The source of irrigation water for the proposed command area is the flows of Erer River. Errer is a tributary of Wabe Shebelle River which is situated in the semi arid area of Wabe Shebelle basin Wabe Shebelle river basin is located between 0°N to 9° 30’ latitude and 38° 30’ E to 46° E longitude. It originates from the Bale mountains at an approximate elevation of 4000 m above mean sea level and drains in to Indian Ocean, after crossing Somalia The total basin of Wabe Shabelle is approximately 280,000 km2, of which 72 % lies in Ethiopia. Large part of Somalia, part of Oromia, Executive Summary/ Final Detail Design Report/2009 4ERRER DAM IRRIGATION PROJECT ROAD NETWORK DAM AXIS. PRIMARY CANAL SECONDARY CANAL INDEX CONTOUR 2^55 o INTERVAL CONTOUR RIVER NATURAL DRAIN UN SUITABLE LAND T1TL«> UY UY; TOMASO UYMItAII.E nv:AMF.Naisni T«IIErrer Dam & Irrigation Project ZCECE &CES part of Southern Nations, Nationalities and People (SNNP), part of Dire Dawa and the entire Harari, are located in Wabe Shebelle Basin. Ercr River and its tributaries originate from the highlands close to kombolcha town where general elevation is about 2500 m above mean sea level. The Ercr catchment up to the proposed dam site is about 419 km2 The water shed has dense network of tributaries. The major tributaries are samte, Gadi, Ulan-ula, kombolcha, Bosensa, Hida and Daka. The topography of the catchment is dominantly mountainous and hilly with relatively flat and rolling land along Erer River Owing to intensive deforestation, cultivation and overgrazing the land degradation is serious problem in the Erer River catchment The catchment area of Erer River at bridge on Harar —Jijiga road is 469 km2 where discharge data are available for shorter length of time. The discharge of Errer is mainly dependent on rainfall which is highly variable in time and space. The water demand for irrigation does not match with the water availability in the river, therefore storage dam is proposed to store the flood discharge and utilise in the times for irrigation and other uses 1.6 Scope of the Report The current study for which this and other reports mentioned below are presented Constitutes the detailed design of the Errer dam and irrigation development project. Volume I: Dam & Appurtenant Structure Annex A Dam Design Annex B. Dam Appurtenant Structures Annex C: Geotechnical Study Annex D: Hydrology Volume II: Irrigation & Drainage Annex E: Irrigation & Drainage Design Annex F: Road Infrastructure Executive Summary/ Final Detail Design Report/2009Errer Dam & Irrigation Project /CECE &CES • Annex G: « Project Control Centers Annex H: Operation & Maintenance Manual Volume III: Project Worth Analysis Volume IV: Tender Document Volume IV 1: General Condition Condition of Particular Application Volume IV2 : Bill of Quantities Specification Volume IV 3 : Drawing Album The detailed deign is basically focused to prepare the engineering design that will enable the client to implement the project. In course of this process several works have to be re-worked, adjusted or analyzed at great depth and practicality. The topographic map preparation for the whole command area at a scale of 1:2000, main and secondary canal strip survey at l:1000scale, cross sectional survey of the Errer river at scale of 1:500, the entire topographic map survey of the dam site at 1500 scale, etc are some of the re-worked activities.Estabilishing temporary hydrometric stations for conducting the measurement of river flow and sediment sampling in the months of June-August was also among the tasks handled as new Further more geotechnical investigation has been conducted at greater depth in order to verify the feasibility conclusions and also to enhance the dam and main canal detailed design. Apart from such intensive investigation, the detailed design was conducted to the extent that would make the implementation with efficiency and cost effectiveness by providing the necessary and important details. Executive Summary/ Final Detail Design Report/2009 6Errer Dam & Irrigation Project ZCECE &CES 2.0 Dam Design 2.1 Dam site Erer Dam is one of the major components of Erer Irrigation Development project. This is basically a storage dam across river Erer to utilize the annual flows of the river for the purpose of irrigation development in its command area Three alternative dam sites (dam axes), including the one selected during pre-feasibility study, were studied in detail to decide most suitable site from techno-economic considerations. Option III has unfavorable geological set-up and has a longer length. Option II has comparatively weaker foundation for locating spillway and spill channel and without any specific attractive features. Thus option I was found to be best suited for locating the dam and chute spillway structure. The orientation of dam axis has been fixed taking into account the topographical configuration of ridge on left and right abutments. The selected axis is aligned exactly in East-West direction, the coordinates of reference point are lying on the dam axis are 1028361.961 North, 195963.404 east. The total length of dam is about 1460m, excluding 30m crest length of spillway. The maximum height of dam above deepest river bed level is 36 6m. 2.2 Hydrological Aspect 2.2.1 Drainage Flow estimation The Drainage pattern in the Erer Irrigation project defines runoff routes and according to the existing flood routes the plain area is divided into 3 parts for determination of peak floods. The main canal starting from the dam outlet runs at the right bank of the Erer river and crosses about 18 creeks or drainage gullies on the elevation contour of 1360m amsl. The catchment areas of the creeks range between 0.15km to 6.5km . 2 2 Executive Summary/ Final Detail Design Reporl/2009 7Errer Dam & Irrigation Project ZCECE &CES The flood used for design against failure can usually be determined by estimating the run off that result from an occurrence of a design storm based on meteorological factors. This hydro meteorological approach is necessary because stream records often are not available. In the design of hydraulic and irrigation structures, the peak flow that can be expected with in assigned frequency is of primary importance. Under estimation of peak flow would result inadequate capacity of structures and its consequence will be failure. 2.2.1 Peak Flood estimation 2.2.1.1 SCS Method All methods if flood estimation are ultimately dependent upon recorded measurement of rainfall in the actual catchment (watershed). Rainfall records are often available at locations close to the proposed project sites, which could be utilized for frequency analysis and computation of flood flows For our proposed project area the available data of Harar station which is of 10 years data is used, for frequency analysis and computation of flood flows. We used the rainfall data of Harar station with its elevation of 2060m above sea level. So it is assumed that the climatic condition of the above mentioned station is also representative for the project area. Here SCS Dimensionless Hydrograph method is considered for catchment areas greater than 0.5 km2. The peak flood expected to occur in 100 years return period at out let of all the drainage channels have been computed. 2.2.1.2 Floodway Determination The flood way determination requires reservoir routing which was carried out and as it is seen from figure 2.1 below, the maximum discharge of the reservoir after routing is 250.5 cumec at 10.5 hour. Executive Summary/ Final Detail Design Report/2009 8Errer Dam & Irrigation Project ZCECE &CES Time (hrs) Fig- 2.1 Reservoir Routing (L=30m) Inflow (m3/se) ----------Outflow (m3/sec) For Floodway determination the basic hydraulic system of computation has been used and here the model called HEC-RAS model has been adopted. HEC-RAS is currently capable of performing one dimensional water profile calculations for steady gradually varied flow and unsteady flow in natural and constructed channels. 2.2.1.3 Equations for basic profile calculations. Water surface profiles are computed from one cross section to the next by solving the energy equation with an iterative procedure called the standard step method. The energy equation is written as follows: K + Z2+^- = Ki + Z, + 2 2 2g ' 1 29 + Where, Yj, Y2 =depth of waler at cross sections Z|, Z2 - elevations of main channel inverts Vi, V2 = Average velocities (total discharge/Total flow area) a ,a - velocity weighting coefficients }2 , , g = gravitational acceleration Hc = energy head loss Executive Summary/ Final Detail Design Report/2009 9Errer Dam & Irrigation Project ZCECE &CES 2.2.1.4 Cross Section Subdivision for Conveyance Calculations The determination of total conveyance and velocity coefficients for a cross section requires that flow be subdivided in to units for which the velocity is uniformly distributed. The approach used in HEC-RAS is to subdivide flow in the overbank areas using the input cross section n-value break points (locations where n-values change). Conveyance is calculated within each subdivision from the following form of Manning’s equations. It is seen in the analysis that, that the maximum floodway level attained after reservoir routing is 1353 8m at about 1.4km downstream of the dam axis for 100 year return period flood. But for the 100 year return period flood before routing, the floodway level was about 1354 9m However, the main canal is running at an elevation of 1360m a.m.s.l. Based on the above results, the main canal can not be affected by flood of 100 years after routed. At this level there is an elevation difference of about 7.0m between the floodway and main canal levels. 2.2.1.5 Comparison of total measured surface Runoff Potential of Erer River with feasibility study In order to get more confirmation and to assert the analysis made during the feasibility study, the adopted approach is to evaluate the catchment yield of Erer Dam based on the direct measurement of flow data collected at the Dam site by Concert Engineering Laboratory Department The method employed to calculate the annual yield of the catchment was by averaging the observed data as daily mean stream flow and convert it to monthly mean flow of the stream. The mean annual flow of the river is calculated considering the main four rainy seasons of the area excluding base flow of the stream. From these data series, the mean annual yield of the catchment was estimated. Executive Summary/ Final Detail Design Report/2009 10Errer Dam & Irrigation Project ZCECE &CES Based on this approach for assessing catchment yield, it was estimated that the runoff yield of the catchment entering the Erer reservoir will be in the order of 80.2 MCM for the main four rainy seasons only On the other hand, the total mean annual net flow, which can be impounded in the reservoir from Erer catchment is estimated at the dam site based on the 39 years (1967-2005) of data and was about 60.4 MCM ( WWDSE) . But the gross capacity of the reservoir serving at 100% of the total irrigation command of 3963ha area of the project is about 50.11 MCM. Therefore, the estimated yield of the catchmnet based on the observed data even for only four months without considering the base flow and other months of the year will be enough to ascert the dependable flow. 2.3 Dam Type Based on the bore holes drilled at the dam site, the thickness of the overburden at the river bed portion is found to be around 19m followed by crystalline gneissic rock. The overburden is mainly characterized by about 7m deep silty clay, sand mixed with gravel spreading all along the axis of the dam But in the river bed portion it is underlain by about 1 lm deep coarse gravel and cobble mixed with sand. The length of the crest of the dam is about 1.46 km and the site falls in high seismic prone area. In high seismic prone area, the earthfill dam or earth and rockfill dam is always preferred due its flexibility than to have a rigid structure like concrete dam. Now considering huge overburden, large length of the dam and seismicity of the area, the site is found not fit for construction of concrete dam. The site appears ideal for construction of either Earth dam or Earth and Rockfill dam. Since adequate quantity of suitable earthfill materials are available from different borrow areas at site, it is decided to go for a zoned Earth dam. Executive Summary/ Final Detail Design Report/2009 11J ] 1 J II Errer Dam & Irrigation Project ZCECE &CES 2.4 Dam Design aspect 2.4.1 Material Properties Considered for Analysis a) Clay Material The material in impervious core shall be clayey sand/sandy clay. Samples of such soils collected from identified borrow areas have been tested at WWDSE laboratory. The test results are indicated in the Table 2.1 Table .2.1: Properties of Clay Borrow Areas: CLAY BORROW AREAS Laboratory Tests EB-1 EB-2 EIP- 11/06 EIP- 12/06 EIP- 13/06 EIP-14- 16/06 Grain size analysis Clay % 5.00-35.00 17.00-29.90 16.50 27.00 25.00 9.00-41.00 Silt % 13.63-71.29 16.41-24.30 27.44 40.36 32.20 7.5-41.48 l! i! Sand % 7.71-81.37 40.10-63.59 56.06 32.64 42.80 17.52-83.5 Atterberq limit LL 24.27-50.80 33.00-48.90 39.37 47.69 49.67 24.26-46.35 PL 13.37-26.26 14.19-24.29 16.19 26.59 26.27 12.63-23.77 PI 15.29-28.79 14.28-29.18 23.18 21.10 23.40 11.63-22.58 r Procter test MDD (gm/cc) 1.567-1.89 1.768-1.823 OMC % 12.20-23.70 14.80-16.80 Shrinkage limit 1.00-14.00 11.00-16.00 9.79 14.20 14.98 4.91-14.95 Free swell 35-75 40.00-60.00 13.50 14.00 13.00 11.00-14.90 Specific gravity 2.52-2.70 2.61-2.65 Consolidation 0.083-0.134 Direct shear C (Kpa) 43.67-92.67 48.67-83.30 20.56-34.22 27.47-28.81 Permeability (cm/sec) 0.749- 3.97*10'7 ( i Triaxial test (UU) - CJK^a) 16.01-26.67 14.79-32.42 I 0> (□) 6.00-16.00 7.00-13.00 b) Material in Shell tones The important engineering properties ( table 2.2)relevant to the stability of dam slope are specific gravity, dry density of compacted soil, permeability and effective shear parameters Executive Summary/ Final Detail Design Report/2009 12Errer Dam & Irrigation Project ZCECE &CES Table 2.2: Properties of Shell Material Tests Conducted ESHQ1 (%) ESHQ2 (%) Gravel (%) 58.91 -64.28 42.67-47.12 Sieve Analysis Sand(%) 32.62-39.3 50.16-54.24 fines (%) 1.75-3.25 2.72-3.01 Direct Shear Test Cohesion (kpa) N.A 9-23.33 4>(degree) NA 37.05-37.25 Permeability K (cm/s) NA 0.16-2.35* 10'3 Since the sandy gravel soil placed in shell zone is cohesionless, it is very important that the material is compacted to fairly high relative density The soil in the shell zones is to be compacted to achieve an average relative density(RD) of 75%. For the purpose of stability analysis the compacted unit weight of the soil has been taken corresponding to 70% relative density. The values of dry unit weight in densest state (yamix) and dry unit weight in loosest state (ydmin) have been considered as 16.4 and 20.2 kN/m3 respectively. The corresponding value of dry weight for 70% relative density works out to 18.9 kN/m3. The dry unit weight of 18 kN/m has been considered for the purpose of stability analysis. The value of shear parameters adopted for sandy gravel material in shell zones are guided by the laboratory tests on material in selected borrow areas which are yet awaited The assumed value of O’ is taken as 35° for stability analysis. Value of <t>' for down stream shell zone material is assumed lower than the corresponding value for u/s shell zone 2 material. Thus, for the purpose of stability analysis following two sets of values of <!>’ have been considered: 3 Set Zone 2 Zone 2A 1 35° 32° 2 33° 30° The permeability of shell material is generally found to vary from 10"" to IO’2 cm/s. Accordingly the following of permeability have been assumed for stability analysis Zone 2 = 5 x 10 cm/s Zone2A= 10“* cm/s Executive Summary/ Final Detail Design Report/2009 13Errer Dam & Irrigation Project /CECE &CES Based on above considerations, the material characteristics as per table 2.3 have been considered for stability analysis. Table .2.3: Material Characteristics Zone Sp. Gravity Unit Weight (kN/m ) 3 Permeability (cm/s) C’ (kpa) 4’ Degree 1 Core 2.64 17.9 3 9 x 10^ 20 29 2 Casing 2.64 18.5 5x1 O'3 0 35/32 2a Casing 2.64 18.5 2.5x10-4 0 33/30 4 Filter 2.64 18.0 io2- 0 28 5foundation 2.65 1.6 10s 25 20 2.4.2 Loading Conditions IS: 7894 states that stability of upstream & downstream slopes be checked for following conditions which are usually found to be critical for the stability of an earth dam. 1) Construction condition with or without partial pool (for U/s and D/s slopes) 2) Sudden drawn down (for U/S slope) 3) Steady seepage (for D/S slope) 4) Earthquake condition (for U/S and D/S slopes). 2.4.3 Minimum Factor of Safety Minimum desired values of factor of safety under various loading conditions, specified by Indian Standard are as per Table 2.4 Executive Summary/ Final Detail Design Report/2009 14Errer Dani & Irrigation Project ZCECE &CES Table 2.4 Minimum Desired Values Of Factors Of Safety For Various Loading Conditions Case No. Loading condition Critical Slope Minimum Factor of Safety 1 Construction condition with or without partial pool U/S & D/S 1.0 II Sudden draw downs with tail water at maximum U/S 1.3 III Steady seepage of Dam with reservoir full D/S 1.3 IV Steady seepage with seismic loading D/S U/S 1.0 2.4.4 Seismic Design The dam site is considered to be falling in zone IV of seismic zoning map of Ethiopia It’s the zone of major damage in which seismic ground shaking is said to be producing intensities VIII and above. For not having any site specific information, seismic co-efficient of the area is compared with the zone IV of seismic map of India, for which the basic horizontal seismic coefficient (ao) is 0.05 In seismic coefficient method as per Indian standard the design value of horizontal seismic coefficient Oh = p I ao Where P = a coefficient depending upon the soil foundation system. The value of p for all types of dam is taken as 1.0. I = a factor depending upon the importance of the structure. For all types of dam, the value of I is taken as 3.0 ao = basic horizontal seismic coefficient The horizontal seismic coefficient (ah) thus comes to 0.15 and vertical seismic coefficient (a ) v = l/2dh i.e. 0.075. These coefficients are adopted for dynamic analysis of slope stability. Executive Summary/ Final Detail Design Report/2009 15Errer Dam & Irrigation Project ZCECE &CES As regards using of seismic co-efficient value of zone IV of seismic zoning map of India, it may be mentioned that for some other similar projects, almost same seismic co-efficient value has been adopted In the light of the fact stated above, it appears to be quite justified to use seismic co efficient value as per zone IV of seismic map of Ethiopia. 2.4.5 Stability Analysis Stability analysis and analysis for seepage through the dam body was said to be carried out at the feasibility stage by using soft ware SLOPE/W and SEEP/W developed by Geoslope, Canada The software uses the general limit equilibrium (GLE) formulation for estimating the factor of safety in stability of upstream and downstream slopes for various loading conditions. The GLE formulation is based on two factors of safety equations and allows for a range of inter slice shear normal force assumptions. One equation gives the factor of safety with respect to moment equilibrium (F ), while m the other equation gives the factor of safety with respect to horizontal force equilibrium (Ff) The GLE method satisfies both moment and force equilibrium by finding the cross-over point of the Fm and Ff. The software analyses large number of slip circles based on Bishop, Janbu, Morgenstem-Price & Spencer methods and exhibits the minimum factor of safety for the critical failure surface. Stability analysis of Erer dam for steady seepage state was carried out by considering head pond level at FRL and no water at tail of the dam The stability of downstream slope under steady state was checked with and without consideration of seismic loading. The stability of upstream slope, under steady seepage state, was checked only with seismic force acting from right to left. For the stability of upstream slope under sudden draw down condition the derived factor of safety is dependent upon the rate of reservoir draw down and the rate of dissipation of pore water pressures. In case of Erer Dam, the draw down was Executive Summary/ Final Detail Design Rcport/2009 16Errer Dam & Irrigation Project ZCECE &CES considered to be taking place from FRL to MDDL, by flow passing through irrigation outlet. The discharging capacity of irrigation outlet being limited, the draw down below spillway crest level of 1379m to MDDL of 1371m will be slow. The construction condition represents a situation when the dam is just constructed and the pore pressures developed as a result of dam material compression are only partly dissipated. The residual pore water pressures depend on the moisture content and the compaction efforts deployed during construction as well as on the rate of rise of the dam. The residual pore water pressures under this condition are considered as based on the pore water pressure ratio R«, a coefficient that relates the pore water pressure to the overburden stress. The pore water pressure u is given by: u = K Yi H s Where, = total unit weight H$ = the height of the soil column The value of the Ru considered in the analysis is 0 35. The stability analysis carried out on adopted section was found to be safe since the factor of safety values under all loading conditions were found to be within the permissible limit. The stability analysis of the dam section as adopted at feasibility stage is also carried out with the help of‘SLIDE’, a software meant for slope stability analysis of soil and rock developed by Rock science Inc., Canada. The section is found to be safe. The section of the dam finally arrived at is enclosed vide Fig. 2.1 2.5 Dam Appurtenant Structures 2.5.1 Intake The Erer dam outlet works pass through the embankment at foundation level. Il is provided in order to regulate and release waler impounded by the Erer dam al rates dictated by downstream needs and less by evacuation considerations. For this the outlet work is designed to satisfy certain performance and capacity requirements. Executive Summary/ Final Detail Design Report/2009 17Errer Dam & Irrigation Project ZCECE &CES For Erer dam, the minimum irrigation outlet size is determined at the most critical draft from the reservoir that is when the reservoir storage is at its Minimum Drawdown Level (MDL) and daily irrigation demands are at their peak. In other words the capacity of the outlet must be sufficient to release downstream water needs, both irrigation and environmental, with the available reservoir storage at its MDL. 2.5.1.1 Irrigation Demand The Erer dam outlet works are provided for the sole purpose of releasing irrigation water demand and environmental flows. Concurrently the water impounded in the dam, less evaporation and seepage losses, is intended for meeting water supply demand of Harar town, and the livestock and domestic requirements of local villagers. But other than a single irrigation outlet, there is no separate outlet provided for abstraction of all other needs mentioned earlier. Water demand for 4000 hectares irrigation development in the Erer project area is estimated at 3m3/sec. Owing to the many competing needs pointed out above, future expansion of the irrigation area would obviously be constrained by limited availability of water resources in the project area. Yet concerted effort in managing irrigation water demand might create scope for some degree of expansion of the irrigation area. In this regard, selection of crop varieties and optimization of cropping patterns to help achieve as much as possible reduced peak irrigation demands should be seriously considered. 2.5.1.2 Supply for Downstream Users Mandatory river releases arc earmarked for ecological requirements as well as to meet water demand of wildlife habitat downstream, of Erer dam. A continuous flow of 0 05m3/scc is earmarked for such releases. Executive Summary/ Final Detail Design Report/2009 183 Errer Dam & Irrigation Project ZCECE &CES Arrangements for continuous releases to meet the downstream requirements are proposed by providing a 10 cm diameter steel pipe in the sidewall of the irrigation outlet. The inlet of the pipe will open up upstream of the service gate in the intake tower and end up at the glacis at the exit end of the outlet conduit. 2.5.1.3 Design Discharge Selection of the size of the irrigation outlet has been governed by meeting the peak irrigation water requirements which are estimated at 3m3/sec at the most critical period The most critical period for irrigation development being when the available reservoir storage is low but daily irrigation demands are at their peak Combining irrigation and environmental demands, the outlet has been designed for a discharge of 3.05m /sec at the minimum operating head of 1.0 meters In other words the outlet discharge capacity would guarantee release of adequate water to meet water requirements downstream, both irrigation and environmental, under varying upstream head and even if the available reservoir storage is at its Minimum Drawdown Level (MDL set at El. 137 Im). 2.5.2 Spillway Structure 2.5.2.1 Location and Suitability Site conditions generally influence the location, type and components of a spillway. The Erer spillway is located on the left abutment of the dam where elevation of the natural ground is around 1380 masl and hydraulic head at the interface between the concrete structures and the embankment is rather minimal. Apparently, the Erer spillway has been located on the left bank of the river as the foundation situation are more favorable owing to the information available from the Feasibility Study documents, and the spillway works are not intersected by the proposed irrigation outlet works which is located on the right bank of the Erer river. It should however be pointed out that the Feasibility Study had proposed curtain Executive Summary/ Final Detail Design Rcport/2009 19Errer Dam & Irrigation Project /CECE &CES * * grouting below the foundation of the spillway along the dam axis in order to reduce the permeability of the foundation. However, that proposal has not been found relevant as per the core drilling investigation made.. 2.S.2.2 Design Criteria Spillway selection criteria fall into functional considerations and safety considerations Generally the spillway is designed to fulfill the following criteria.- • Adequate capacity to prevent dam overtopping which is detrimental to an embankment dam • Adequate overflow capacity to limit infringement on dam freeboard during emergency • Appropriate hydraulic setting to permit excess energy dissipation • Minimize hydraulic head losses using proper transitions • Hydraulic and structural safety • Erosion resistant construction • Avoid erosion or undermining of the downstream toe of the dam • Ensure safe discharge capacity of the downstream river channel to avoid over bank flooding 2.5.2.3 Selection of type of Spillway Both functional and safety considerations justified selection of an un-gated free overflow spillway crest. Unlike gated spillways, the selected type gives reliability due to its simplicity, freedom from operating mechanisms, and not requiring operating personnel especially in remote locations like the Erer project area where flash floods must be released before endangering dam safety. 2.5.2.4 Spillway Chute Structure Beyond the weir axis, a rectangular chute connects the spillway crest curve with the terminal structure. Initially the chute continues in a straight alignment with 30 meters width for a distance of about 57 meters before it gradually converges to 20 meters and maintains the same width as a curve subtending an angle of 56 degrees at a radius of Executive Summary/ Final Detail Design Report/2009 20Errer Dam & Irrigation Project /CECE &CES 178.50 meters initially, followed by a straight alignment for the rest of its length. Smooth transitions are provided between straight and curved reaches. Water surface profile along the 590 m long inclined chute terminating in a stilling basin is computed and sidewall freeboard is added above the profile. Velocity in the chute is maintained to be supercritical; thus throughout the chute the Froude number is greater than one The chute floor bed slope is also steeper than the critical slope The height of the chute sidewalls is designed to contain the spillway design discharge. 2.5.2.6 Spillway Energy Dissipation Structure USBR stilling basin Type III is employed for dissipation of energy by a hydraulic jump at the end of the spillway chute. The 21m long stilling basin with its apron elevation set at El 1340.7m is fitted with ancillary devices. Installation of ancillary devices such as chute blocks, baffle blocks and end sill is expected to produce a stabilizing effect on the jump, thereby permit shortening the basin length and guard against sweep out caused by inadequate tail water depth. Executive Summary/ Final Detail Design Report/2009 21Errer Dam & Irrigation Project ZCECE &CES 3.0 Irrigation system Design 3.1 Topography and Land Use of Command Area. The topography of proposed command area varies from flat to gently slopping. The altitude of command area varies from 1280 to 1365 m above mean sea level. The surrounding cultivated areas of Harar and Babile Woreda are situated on higher elevation. No major effort would be required for levelling of land if irrigated agriculture is to be practised. Also, natural vegetation is sparsely located and shallow rooted excepting some patches where acacia trees exist. Only moderate expenditure will be involved in removing the natural vegetation and preparation of land for irrigation. The designated area of Erer irrigation project is surrounded by extensive coverage of natural vegetation comprising of cactus, thorny bushes, shrubs and acacia trees with very little grazing land which is located beneath the natural vegetation and on steep sloping lands. As observed, the cultivation is mainly rain fed in majority of areas situated in the proposed command area of the project excepting in riverbed where some irrigated agriculture is being practised There are three small irrigation schemes already operative in the command area. These arc said to have been constructed and operated by Munchen fur Munchen, a NGO. The total irrigated area from these schemes is of the order of 20 ha. The agriculture practices are traditional oxen-cultivation based and local ploughs and hand tools arc used in cultivation. Amongst the crops, most commonly cultivated crops observed are maize, groundnut, vegetable crops (of onion, tomato, pepper) and fruit trees of mango. To some extent sorghum, sweet potato, haricot beans, banana, papaya and citrus are grown in and around command area. Chat, a stimulant is also grown extensively. The local crop varieties are used. No fertilizers and insecticide/pesticides are being used in rain fed agriculture 3.2 Soil Suitability Soils influence crop suitability, choice of land utilization, types, drainability etc. Therefore extensive soil surveys and investigations are carried out in fairly large area encompassing the whole of the proposed command of Erer irrigation project. The soil Executive Summary/ Final Detail Design Report/2009 22Errer Dam & Irrigation Project ZCECE &CES surveys and investigations have provided detailed information on the soils and land of command area for selection of crops and irrigation designs. 3.3 Irrigation Scheduling • Irrigation schedule is designed to start irrigation from the first planting date of the crops when all of the readily available soil moisture has been used. The irrigation amount will be equal to soil moisture deficit. The soil moisture deficit will return to zero after the irrigation. • The water application time is planned when all (100%) of the readily available moisture has been used up In this situation the crop will not become moisture stressed. • The water application depth is calculated to refill the soil moisture storage so that the soil may return to its field capacity. (100% of the readily available moisture is replenished) • Monthly ETo and monthly rain fall are distributed using polynomial curve fitting. To generate rainfall events, each 5 days of distributed rainfall is accumulated as one storm. • For total and readily available soil moisture the calculation procedure is indicated below. TAM = Total Available Moisture = (FC% - WP %)♦ Root Depth [mm]. RAM = Readily Available Moisture = TAM * P [mm] Where: FC = Field Capacity WP = Wilting Point P = Depletion Percentage 3.4 Depth of Watering The plant uses the soil moisture available between field capacity (at 0.1 or 0.33 bar pressure) and permanent wilting point (at 15 bar pressure) which commonly called as » Available Water holding Capacity usually denoted by AWC. In practice the soil Executive Summary/ Final Detail Design Report/2009 23Errer Dam & Irrigation Project /CECE &CES moisture is not allowed to go up to permanent wilting point and next water is applied when available soil moisture is depleted by about 75% or so. This is known as Readily Available Water holding Capacity( RAWC ) However some agronomists use a rule of thumb and assume two third of the total available moisture between field capacity and permanent wilting point as available soil moisture for plant. In case of Erer project this figure is taken as 70 % 3.5 Field Size and Channel Discharge The field channel discharge must be limited 80 lit/sec ( average about 60 It/s ), which can be conveniently managed by the individual farmer. Under no situation it may be allowed to exceed 80 lt/s. Therefore, it is recommended that the design capacity of the field channels may be adopted equal to or less than 80 lit/sec. preferably 60.0 lt/s. Normally a discharge of 201t/s is considered as minimum flow rate to irrigate a field. The field size can be determined as below: Unit watering depth =90.0mm Field efficiency =70% Gross unit watering depth =128.6mm(90/0.7) Irrigation interval =20 days Field channel discharge(max) =60 lit/sec Field size (ha) max 4 =(60*20*24*3600)/(1000*0.1286* 10 ) = 80.5 Say 80ha 80 ha max field size is adopted for the design of quaternary canal. This is the size of command of quaternary canal carrying discharge of 60 lt/s. The field is divided into 3 to* 5 sub fields depending upon topography. Each sub field of 20 to 40 ha will be served by a field channel taking water from quaternary canal. A small masonry Executive Summary/ Final Detail Design Report/2009 24Errer Dam & Irrigation Project ZCECE &CES structure termed as turn-out is provided as per requirement for delivery of water in to field channels at suitable places Considering loamy soils and 0 1- 0.2% slope of land the furrow length of 250m is adopted Most of the crops are sown on furrows having 0.9m spacing. The same spacing is adopted in this project. 3.6 Irrigation System The Canal system (figure 3.1) comprises of primary canal which off takes from Irrigation Outlet located on the right bank of river downstream of dam structure The layout of the primary canal is guided by minimum drawdown level in the reservoir and topography of the command area. The full supply level (FSL) of the primary canal is fixed in such a way that it is able to provide flow irrigation under gravity to its entire command. In design of the dam sufficient working head has been provided between proposed FSL of the primary canal and maximum drawdown level in the reservoir. The full supply level of the primary canal at its head is kept at EL.1365.0 m above msl. The primary canal is aligned as a contour canal providing sufficient slope ensuring adequate velocity As per nomenclature followed in Ethiopia the primary canal is termed as “P”. Tertiary canals off taking from primary canal are designated as Tl-P, T2-P etc. The quaternary canals off taking from primary canal are designated as Ql-P, Q2-P and so on Two secondary canals off take from primary canal at change km 14.67 and are designated as SI and S2. Both these canals have head regulators which act as cross regulators for other secondary canal. First secondary canal (SI) travels across the contour and negotiates a fall of 40 Ow s'- K through small vertical falls of 0 5m drop. The depth of drop is taken Executive Summary/ Final Detail Design Rcport/2009Errer Dam & Irrigation Project ZCECE &CES is planned as a contour canal to irrigate an area situated on its left side at a level lower than FSL Second secondary canal (S2) off takes from the tail of primary canal and passes through the rugged mountains comprising of ridges and valleys. The canal is planned as a contour canal on the hill slopes and has a very tortuous alignment till it crosses river Dencho. The alignment of this canal, as proposed in feasibility report is not considered appropriate around the site it crosses Dencho river because the required height of aqueduct will be very high. Therefore the alignment is amended considerably around its crossing with Dencho river and the height of aqueduct has been reduced. After crossing Dencho river the canal is planned as contour canal to extend irrigation to about 1031 ha CCA. The selected system provides for total no of five tertiary canals, one off taking from primary canal, two off-taking from each of secondary canals Quaternary canals are the smallest canals which off take from primary secondary and tertiary canals. The quaternary canals carry the full supply discharge for the area it is serving All the water is diverted in to field channel of one field to irrigate the same. The layout of the quaternary canal is planned in such a way that it provides proper orientation of fields in proper direction of irrigation. There are 51 no of quarterly cannels off taking from primary, secondary & tertiary canals. Executive Summary/ Final Detail Design Report/2009 26Errer Dam & Irrigation Project ZCECE &CES 3.7 Gross Command Area The Gross Commanded Area of 3963 ha has been delineated on the basis of following considerations and indicated on the map appended with the report 1. Topography - favourable for extending gravity flow. Lands situated on the periphery having slopes more than 5% are excluded. 2. Agronomical potentials - good soils having adequate depths, suitable physical and chemical characteristics, water holding capacity, infiltration rates, permeability and free from erosion and salinity hazards 3. Location - Accessible and closest to source of irrigation water. The command area is divided in two parts; first part lying in the head reach proposed to be served by primary canal. The command area in this part is a narrow belt, nearly 12.0 km long having 0.5 to 2.0 km. width. After deleting unsuitable areas, the net culturable command area(CCA) of this part works out to about 1022 ha. The command area beyond Dencho River is served by two secondary canals. This area comprise of bit wider belt of about 8 km length and 4 to 5 km width The net CCA of this command works out to about 2700 ha. 3.8 Irrigation overall Efficiency The field efficiency is the ratio of the volume of water used by plant by evapo transpiration and volume of water reaching the field. Water used in transpiration includes the effective rainfall also. This efficiency is assumed as 70 % considering 30 % loss. Total Efficiency of Water Use for Irrigation is multiplication of above three 4 efficiencies. The overall efficiency of system is assumed as 50 % (0.8*0 9*0.7=50 5 say 50 %) Executive Summary/ Final Detail Design Report/2009 27Errer Dam & Irrigation Project ZCECE &CES 3.9 Irrigation Structures « The detailed design of irrigation and drainage structures are carried out in two phases. In first phase hydraulic designs are carried out which are intended to determine the optimal location, configuration of components of hydraulic structures, waterway requirement, protection against sour, seepage and uplift pressures, energy dissipation arrangements etc. In second phase Structural designs are carried out which aims at evaluating the forces/ stresses on each component of structures on account of dead loads, dynamic loads, seismic loads and earth pressures and each component is designed to resist the forces and bending moments caused by all these loads The canal structures are hydraulically designed as per aforesaid design criteria set out for Erer project. The detailed structural designs are carried out as per detailed procedures in vogue internationally 3.10 Field Drainage System In general the drainage system comprises of field drains, tertiary drains, secondary drains and main drains The excess water from the land is gathered by a network of field drains. The excess water which ponds on the surface, flows laterally in the form of overland flow and enters the field drains. The field drains discharge into tertiary drains which finally carry water to secondary or main drain. The field drains are aligned along the field boundaries. The surface drainage system is most effective in case of soils which are impermeable (vertisols or black cotton soils) or in special situation when vertical flow of infiltrated water is impeded by presence of impermeable layer. There is total 40 number of field drains planned in entire command area. These comprise of 13 field drains. The list is given in three tables as given below. These drains are aligned along the depression lines so that the fields may directly discharge in them under gravity. The lengths of majority of these drains are within the range of 1000 to 1500 m. However there are few drains which are above 2000m long. These drains directly drain into existing drainage system in the area. This has happened J Executive Summary/ Final Detail Design Report/2009 28Errer Dam & Irrigation Project ZCECE &CES ♦ • because the canals are proposed to irrigate their commands comprising of strips of lands situated on their left sides in widths varying from 500 m to 2000 m. On account of this special layout the need for tertiary drains has minimised. There are only two tertiary drains proposed in the whole of command area The field drains are designed to evacuate superfluous rain and irrigation water from the command area in 24 hours as the dominant crops are maize and cotton which can stand flooding of 24 hours. In a situation when any field is being irrigated and heavy rain occurs, the field drainage system should be capable of removing excess rain and irrigation water effectively during stipulated time otherwise it will result in impairment of crop growth and farm operations. 3.11. Land Grading Land grading is the reshaping of the surface to ensure even application of irrigation water and quick disposal of the excess surface water for proper growth of the crops. Plane method type of land leveling has been used for this project for its simplicity. The area of the sample block for which land leveling has conducted is 98 ha that has been divided in to four blocks. The first block is divided into 200m wide & 150m wide sub-blocks. The 2nd block is divided into two 200m wide sub-blocks Each sub block is divided into units having 50m length and either 200m or 150m width Grid points of the blocks and their units are based on letters and numbers on Y axis & X axis respectively. Considering a total cultiurable command area(CCA) of 3370 ha, we need to move an earth volume of the following magnitude if a complete land levelling is requird It is worth noting that gradual levelling by the farmers themselves could be practiced instead of putting it out to contract construction Culturable Command Area is 3370 ha 3 3 Total cut needed = 34.38 * 146,550 m = 5,039,526 m 3 3 Total fill needed = 34 38 ♦ 128,025 m = 4,402,492 m Executive Summary/ Final Detail Design Report/2009 29Errer Dam & Irrigation Project /CECE &CES 4.0 Infrastructural Development 4.1 Road Network The classification of the road ( figure 4.1) that had been designed to facilitate the purposes of the dam and irrigation scheme was discussed in detail in the design phase report. To summarize and high light the important parameters under consideration are, • The Ethiopian Roads Authority’s Standard Specification 2000 would be the bases for the design. • This however may alter the roads for lower design cases where the beneficiary themselves may undertake the construction and maintenance works of such structures as may be appropriate to be outside the scope of the contractor. • Factor influencing the road design standards, and in particular the design speed, is the volume and composition of traffic. The design of a road should be based in part on factual traffic volumes. • The geometric standards for low volume roads, for the case of the project, have less importance than whether a road exists and whether it is passable at all times In such circumstances, it is appropriate to adopt inexpensive standards that enable the further development of a system of such feeder roads at minimal cost. • The basic road infrastructure network would generally follow the irrigation scheme. • Social and economical centres in the Weredas under the influence area would be considered in order to meet the requirements of the beneficiaries. 4.1.2 Road Classification Three categories of road types are identified in the irrigation scheme to serve different purposes with different standards. The very basic, as put in the inception report, is to follow the country’s established standards so. as to ease the road construction and maintenance economics. The first and the highest road in the project is adopted from the DS-6 standard while roads which are already serving the community will be in the standard for the DS-7. The lowest hierarchy road standard under the project is for those roads out of the scope of the contractor and would be implemented for their construction and maintenance by the beneficiaries will be DS-9 or DS-10. Executive Summary/ Final Detail Design Report/2009 30Errer Dam & Irrigation Project ZCECE &CES • The DS-6 road standard is following the primary and the two secondary canals that are designed as per the specification. The DS-7 is a rehabilitation of existing roads within the irrigation scheme without alignment change. These roads are connected villages in the areas and to the main highway road and will also serve during the project implementation and in the irrigation development. 4.1.3 Geometric Design Using road functional classification selection and design traffic flow, in the Erer Irrigation project, the feeder road standards was selected as per the design report made for the client. As per the report and to review in this report, Table 4-1 below w'as reviewed to highlight the class of road under discussion. The feeder road with the design standards and expected AADT has five road design standards. Table 4-1 Design Standards vs. Road Classification and AADT Road Functional Classification Design Standard No. Design Traffic Flow (AADT) Design Speed (km/hr) Flat Rolling Mountainous Escarpment DS6 50 - 100 60 50 40 30 F E w" E D E R DS7 30-75 60 50 40 30 DS8 25-50 60 50 40 30 DS9 0-25 60 40 30 20 DS10 0-15 60 40 30 20 The geometric design of the road project has been carried out as per ERA Geometric Design Manual - 2002-class DS6 as recommended on the design standard report. During the selection of horizontal and vertical alignment the design criteria and Executive Summary/ Final Detail Design Report/2009 31Errer Dam & Irrigation Project ZCECE &CES controls, which have been agreed between the client and the consultants, have been utilized in conjunction to safety requirements. The design has been conducted by the use of computer-aided design using soft desk and Eagle Point software. The software generates every detail with regard to horizontal alignment, vertical alignment, superelevations, etc. The higher hierarchy road network would be road provided for the primary and secondary canals and other social and economical centers under the scheme. Since all roads of the DS-10 will be connected to these roads and more intensive canal maintenance required and the operation of the irrigation system performed at these levels, furthermore farm in and out puts would be transported through these routes prior to before and after every farming and harvest periods respectively, there would be a need for higher and more durable roads standard section required. The higher level of the road network under the Erer irrigation project is the connection of the above roads to the higher standard of roads or to the nearest town where the Ethiopian road network existed. This level of the road network could be design to the DS-6 standard. This standard connects all the lower roads of the scheme to the outside world by which more trucks are expected during the operation of the farm. 4.2 Project Control Centres Conventionally dam and irrigation operation needs a center for controlling its day to day activities. This helps for effective and efficient output of the project. Like any dam and irrigation project, this particular project also needs independent centers with sufficient infrastructure and facility for controlling the smooth operation of the dam as well as the irrigation task. Hence the relevance of providing working, living, and leisure and storage spaces for workers and visiting guests which are going to be using/working in the centers comes in to picture Thus such a facility is provable for the Erer dam and irrigation project. Executive Summary/ Final Detail Design Rcport/2009 32Errer Dam & Irrigation Project ZCECE &CES The orientation of the water storage (dam) area, and the command areas run a north to south direction where as there are hills and mountains running on either side of the above mentioned areas on the eastern and western side. In order to operate the dam and the irrigation areas efficiently after they are constructed, a proper building infrastructure and facility should be in place for proper functioning of the entrire project. The location of building infrastructure and service centers considered necessary for the smooth operation of the dam and irrigation project more of less depends on the easy access to the basic infrastructural needs. These are mainly electric power, telephone connection, availability of domestic water supply and access to circulation (roads). 4.2.1 Selections of PCC sites The dam and the irrigation Areas need their separate service centers with their respective working structure. However as a mandatory basic outline the two areas has been identified as follows- The dam area shall comprise space provisions for technical staff offices, maintenance areas, stores, generator, transformer and pump houses, and other ancillary functions which are the basic necessities of any dam. The availability of a feeding road, electric power, telephone line and water is mandatory to the dam operation center. The center will be continently connected to the dam and its appurtenant structures site for ease of regular operation and during emergency. Hence for the above main reasons the compound for the dam command center has been identified adjacent to the dam location, hence proximity being the major critarea. This site will be with minimum site works, i.e. more flatter site and less expensive interms of sanitary works and domestic water supply aspects. Executive Summary/ Final Detail Design Report/2009 33Errer Dam & Irrigation Proje'ctVCECE &CES Similarly for smooth operation of the irrigation area there shall be buildings and structures which shall house offices, nursery sheds (optional in this case), and tractor sheds, administration offices, stores, garages, pump houses and the like. It should be noted that such functions of the center could be used by the organization that will run the irrigation farm and also by the beneficiary farmers. The maintenance of the above buildings should not be difficult as the construction is envisaged using standard building materials available in the market. It is very essential: to have a road for smoother transportation of inputs and products of the farm in. and out of the area. However the availability of electric power infrastructures is also crucial for the smooth operation of the center. The other main character of this area is that storages of raw materials and agricultural products should be provided with ample spaces. Hence the above reasons impose a significant requirement in selecting a more flat surface adjacent to-the proposed road and infrastructure for both centers. The centers will have their own independent plots, for operational reasons both sites should be linked with communication of telephone lines and road connection. 4.2.2 Types of Building Infrastructure and Services The type of various building infrastructures which are properly planned considering Architectural, Structural, Sanitary and Electrical detailed design are shown below. The buildings are to be located at the dam and irrigation project control centers, (table 4.1) Executive Summary/ Final Detail Design Report/2009 34Errer Dam & Irrigation Project ZCECE &CES Table 4.1 Dam & Irrigation PCC Infrastructure Dam Project Control Center No. Description 2 Area(m ) 1. Office • 132.5 2. Cafeteria 55.1 3. Laboratory 71.1 4. 3 bed room house 76.7 5. 2 bed room house 45.6 6. Transformer house 12.5 7. Generator house 12.5 8 Garage 11.6 9 Small toilet 1.8 10. Service quarter 11.3 11. 2 Bed room without toilet 26.1 12. General store 392 13. Guard house 6.8 Total 856.1 Irrigation Projcct Control Center No. Building Purpose Area(sq.metre) 1. office 132.8 2. Cafeteria 55.8 3. Three bed room house 74.4 4. Guard house 6.8 5. One bed room house 29.8 6. Toilet 59.4 7. Service quarter 11.8 8. Type C house 51.2 9 Store 16.10 10. Toilet block 1.8 11. Muliti purpose hall 91.3 Executive Summary/ Final Detail Design Report/2009Errer Dam & Irrigation Project ZCECE &CES No. Building Purpose Area(sq.metre) 12. Guest house 16.6 13. Transformer room 12.5 14. Two bed room with out toilet 26.10 15. Garage 72.8 16. Generator house 12.5 17. General store 392 18. Clinic 38 Total 1106 I Executive Summary/ Final Detail Design Report/2009 36ErrerDam & Irrigation Project ZCECE &CES__________________________________________ 5.0 Financial and Economic Analysis 5.1 General The benefits of the project are estimated by evaluating the benefits “without the project and “with the project”. The net area of land that could be developed through irrigation has been considered as 4000 ha. Quite a large part of the area (about 70% of the land) has natural vegetation comprising mostly dense cactus, thorny bushes, shrubs and occasional trees (mostly of Acacia spp) with little grazing land that, that is unfit for cultivation. But all this land can be properly developed through irrigated farming with the implementation of the project. In evaluating the present benefits without the project condition, the remaining 30% of the area or 1,200 ha is considered as rain fed irrigation. A350-370 ha land that submerges under water will loose its production after the impoundment of the reservoir. An area of 350 ha at thereservoir site has been considered along with the area of 1,200 ha in the command area making a total 1,500 ha of land for estimating the without the project benefits. Out of the total area of 1,500 ha of land included for the analysis of the without the project case, 23.4% or 362.9 ha is occupied by maize and sweet potato ,45.4% or 703.3 ha by sorghum and groundnut and 31.2% or 483.8ha by maize and haricot bean. 5.2 Financial Analysis In order to determine the extent of viability of the project from financial point of view, the Financial Internal Rate of Return (FIRR), the Financial Net Present Value (FNPV) and B/C ratio have been calculated. As it has been tried to verify in the methodology, these values have been calculated by discounting from the incremental cash flow. The incremental cash flow over the years is estimated by deducting the net return of the “without” the project and all the cost of the project like investment, operation and maintenance costs from the net returns of the “with project” condition. The Financial Internal Rate of Return of the project, the Financial Net Present Value and the B/C ratio results show that the values are above the threshold values. The Executive Summary/Final Detail Design Report/2009 37Errer Dam & Irrigation Project ZCECE &CES project is, therefore, feasible from the financial point of view. The table presented below shows the FIRR, the FNPV and the FC/B results of the project. Table : Summary of Financial Sensitivity Test Financial No Sensitivity Test B/C Ratio NPV (MBirr) IRR 1 Base Case 1.43 210.72 10.74% 2 Increment of cost by 10% 1.31 164.29 9.87% 3 Reduction of Crop Prices by 10% 1.25 121.74 9.45% 4 Yield Reduction by 10% with symelteneous 10% Cost Increment 1.16 82.20 8.73% 5.3 Economic Analysis In order to determine the extent of the viability of the project from national point of view, the Economic Internal Rate of Return (EIRR), Economic Net Present Value (ENPV) and EB/C ratio have been calculated. As it has been tried to verify in the methodology, these values are calculated by discounting from the incremental cash flow. The incremental cash flow over the years is estimated by deducting the net return of the “without” the project and all the cost of the project like investment, operation and maintenance costs from the net returns of the “with project” condition. Table: Summary of Economic Sensitivity Results Economic Result No Sensitivity Test B/C Ratio NPV (MBirr) IRR 1 Base Case 1.43 125.17 14.02% 2 Increment of cost by 10% 1.31 98.72 13.03% 3 Reduction of Crop Prices by 10% 1.26 75.21 12.61% 4 Yield Reduction by 10% with symelteneous 10% Cost Increment 1.31 98.72 13.03% Executive Summary/ Final Detail Design Report/2009 38Errer Dam & Irrigation Project ZCECE &CES 5.4 Conclusion The results of the financial and economic analyses carried out for the base condition as well as for other conditions to test the sensitivity clearly show that the project is viable from financial point of view Therefore, implementing the proposed irrigation development project as early as possible is worthy so that the community could benefit and improve its livelihood. As discussed in the different sectoral reports of the Feasibility study, the project is technically feasible, socially acceptable by both the beneficiaries and stakeholders. It is also financially and economically attractive, institutionally possible to organize and manage. The National policy again favours the establishment of such projects in food insecure and poverty ridden areas. Therefore it is highly recommended that the project be implemented as early as possible Executive Summary/ Final Detail Design Report/2009 39Errer Dam & Irrigation Project ZCECE &CES 6.0 Construction Schedule The total construction period of the project is expected to be a total of 36 calendar months as shown in figure 6.1 40 Executive Summary/ Final Detail Design Report/2009FIGURE 5 1 ERRER DAM AND IRRIGATION DEVELOPMENT PROJECT SUMMARIZED SCHEDULE ID Task Name 1 MOBILIZATION Quarter 1 l Quaker 2 [Quarters | Quarter 4 [Quarters [Quarter6 Quarter 7 [ Quarter 8 i Quarter 9 i Quarter 10 I Quarter 11 I Quarter 12 2 DAM EZ • 3 DAM APPURTENANT 4 IRRIGATION SYSTEM ......................... :......... • 5 PROJECT CONTROL CENTER L-------- ................ '.. ' MW 6 ROAD INFRASTRUCTURE . ' • ■ 7 MISCELLANEOUS pl ■ 'J'• /'> • ERRER PROJECT OBSTRUCTION SCHEDULE FIGURE 5.1 Page 1 H
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