FEDERAL  DEMOCRATIC  REPUBLIC  OF  ETHIOPIA MINISTRY OF WATER RESOURCES
ERER DAM & IRRIGATION DEVELOPMENT PROJECT
INTERIM (PHASE I) REPORT October, 2008
(Final)
CONCERT ENGINEERING AND CONSULTING ENTERPRISE P.LC (CECE) ENGINEERS WATER RESOURCES A AGRICULTURALBM
B/C CCA ET„ EL ENPV EIRR ERA FAO FS
GCA GPS GIS
IS MoFED
MCE MDDL MLPM MOVVR MP MWL Mm3/Ycar NGO
NE-SW PMP PMF RH RQD
acronyms
Bench Mark
: Benefit Cost Ratio
: Culturable Command Area : Evapotranspiratoin
: Elevation
: Economic Net Present Value
; Economic Internal Rate of Return 
: Ethiopian Road Authority 
: Food and Agriculture Organization : Feasibility Study
. Gross Command Area
: Global Positioning System
: Geographical Information System
: Indian Standard
: Ministry of Finance and Economic Development
: Metaferia Consulting Enterprise
: Minimum Draw Down Level Modified Linear Perturbation Model Ministry of Water Resource
: Master Plan of the Wabi Sheble Basin Maximum Water Level
Million Cubic Meter/Year
: Non Governmental Organization North East - South West Probable Maximum Precipitation Probable Maximum Flood 
: Relative HumidityTable of Contents
1. Introduction.......................................................................................................................... 1
1.1 Project Background
»
1.2 Objective and Scope of The Phase I Report................................................................... 1
2. Review of Feasibility Study Report and Findings.............................................................. 3
2.1 Basic Components of the Report.................................................................................   3
2.1.1 Engineering Study................................................................................................. 3
2.1.2 Non-engineering Studies....................................................................................... 3
2.2 Water Resources, Climate and Hydrology.................................................................... 4
2.2.1 General................................................................................................................... 4
2.2.2 Review of Previous Work....................................................................................  4
2.2.3 Conclusion........................................................................................................... 10
2.3 Topographic Surveying............................................................................................... 10
2.3.1 Desk Work and Field Assessment........................................................................11
2.3.2 Gaps Identified..................................................................................................... 13
2.3.3 Measures to Fill Gaps Identified.......................................................................... 16
2.4 Dam Engineering......................................................................................................... 20
2 4.1 Desk Work and Field Assessment............................. ..........................................20
2.4.2 Gaps Identified..................................................................................................... 22
2.4.3 Measures to Fill Gaps Identified.......................................................................... 23
2.5  Dams Appurtenant Structures.................................................................................... 24
2.5.1 Desk Work And Field Assessment...................................................................... 25
2.5.2 Gaps Identified .................................................................................................. 31
2.5.3 Measures to Fill Gaps Identified . ....................................................................... 31
2.6  Geophysical and Geotechnical Investigations.......................................................... 32
2.6.1 Desk Work and Field Assessment....................................................................... 33
2.6.2 Gaps Identified.................................................................................................... 37
2.6.3 Measures to Fill Gaps    Identified......................................................................38
2.7  Road Infrastructure
402.7.1 Desk Work and Field Assessment........................................................................ 40
2.7.2 Gaps Identified..................................................................................................... 44
2.7.3 Measures to Fill Gaps Identified.......................................................................... 45
2.8 Building Infrastructure and Service Centers................................................................ 46
2.8.1 Gaps Identified..................................................................................................... 46
2.8.2 Measures to Fill Gaps Identified.......................................................................... 47
2.9 Irrigation System and Structure....................................................................................47
2.9.1     Desk Work and Field Assessment.................................................................... 47
2.9.3 Measures to Fill Gaps Identified.......................................................................... 53
3.  Out Standing Issues......................................................................................................... 55
3.1 Ground Surveying Task.............................................................................................. 55
3.2 Hydrological Survey................................................................................................... 55
3.3 Re-locating the Harar -Erer Dodota Road.................................................................. 57
Annex I: Estimated inflow into Erer dam (WWDSE & WAPCOS, 2004)........................... 57
Annex II. Field Program of Hydrologic Measurements Erer River at Bridge...................... 58
List of Tabic
Table 2.1 Comparison of climate Data used in FS and the present study
based on Dire Dawa Climate data............................................................................6
Table 2.2 Rainfall Frequency Analysis...................................................................................7
Table 4.1 Measurement Types Equipment and Frequency of Measurements....................... 55
Table 4 .2 Frequency of Measurement..................................................................................56
List of Figure
Figure 2.1 ETo Estimate by FS and Based on DireDawa /Jijiga data...................................6
Figure 3.2 Comparison of flow estimate at Erer Dam Site.....................................................8CECE and CES
1. Introduction
1.1 Project Background
The Erer dam & irrigation project has an overall purpose of developing some 4000 
hectares of land by making use of the storage facility across the Erer River According to 
I
the feasibility  study  prepared  for the project,  it would  have the construction  of an embankment dam of 36.6m high and 1430m crest length to store 50.6 million cubic meter of water The feasibility study was carried out by WWDSE in association with SHIPL in 2007. According to this study the project is expected to contribute to the regional and national economy  by  way  of producing  cash  and  food  crops.  Considering  the existing land  & water resources potential of the project area,  increased  and  sustainable agricultural production is expected once the envisaged irrigation and infrastructure and dam storage facilities are in place.
1.2 Objective and Scope of Phase I Report
This report is prepared to depict the gaps and the measures required to fill these gaps which were identified while going through the feasibility study reports listed below This exercise has basically laid the basis for the subsequent detailed engineering design of the irrigation system and storage dam facility.
Volume 1
Executive Summary
Volume 2
Volume 3
Main Report
Secotral Report 1
Volume 4
Hydrology & Water Resources Planning
Sectoral Report 2
Sectoral Report 3 
Volume 5
Geological & Geotechnical Study Hydrogeology
Sectoral Report 4
Sectoral Report 5
Soil
Land Suitability
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Volume 6
Sectoral Report 6
Dam & Appurtenant Works
Sectoral Repot 7
Construction Materials
Volume 7
Sectoral Report 8
Irrigation & Drainage
Sectoral Report 9
Canal Structures
Volume 8
Sectoral Report 10
Agricultural Planning & Agronomy
Sectoral Report 11
Agricultural Mechanization
Sectoral Report 12
Agricultural Marketing
Volume 9
Sectoral Report 13
Socio-Economic Study
Volume 10
Sectoral Report 17
Settlement Planning
Sectoral Report 18
Environmental Impact Assessment
Volume 11
Sectoral Report 21
Organization & Management
Sectoral Report 22
Cost Estimate
Sectoral Report 23
Financial & Economic Analysis
Volume 12
Drawing Album
In addition to the gap identified and analyzed, this report also presents relevant field assessment & verification made in order to comprehensively address the detailed design task.
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2.  Review of Feasibility Study Report and Findings
2.1 Basic Components of the Report
The pre-feasibility study of the project area was carried out by WWDSE in association with  WAPCOS and  MCE in  year 2005.  The feasibility  level study  was carried  out in 2007 by Water Works Design and Supervision Enterprise (WWDSE) in association with Synergies hydro  (India) Pvt Ltd.  (SHIPL).  The study  involved  a team of multidisciplinary  team of experts drawn  from the two  firms and  local consultancy agencies.  The engineering  and  non-engineering  components of the study  are described briefly below.
2.1.1 Engineering Study
The main engineering components of the project are an earth fill dam, a chute spillway at the left bank, and a canal system located on the right bank of the river. The engineering aspects of the feasibility study report encompass the following main topics:
•    Hydrology,
•    Geological and Geotechnical study,
•    Dam and Appurtenant Work,
•    Irrigation and Drainage, and
•    Canal Structures
2.1.2   Non-engineering Studies
The non engineering aspects of the feasibility study report encompass the following main topics:
•    Socio-Economic study,
•    Livestock of the project area,
•     Fisheries,
•    Public Health,
•    Forestry and
•    Organization and Management.
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Erer / Final Phase 1 Report /2008CECEandCES
There  was  negligible  mention  of  the  Social,  Settlement  and  Environmental  Assessment aspects of this project on the feasibility study
Review  of  the  feasibility  study  report  and  major  findings  of  the  review  are  discussed below.
2.2 Water Resources, Climate and Hydrology
2.2.1 General
Erer River originates from the highland near Kombolcha town and Melak Rafu. The river has total catchment areas of 419 km2 at Erer dam site. The Erer River is located in a semi-arid  area of the north  eastern  Wabi Shebele basin  with  annual rainfall ranging between 650 mm near irrigation area to 800 mm at the upper watershed. Variability of the annual rainfall is moderately high (CV > 0 25).
2.2.2 Review of Previous Work
Two reports have been reviewed. The first one is Hydrology & Water Resources Planning conducted by WWDSE & Synergies Hydro (2007) at feasibility level; the second one is WWDSE & WAPCOS (2003) Erer dam pre-feasibility study. Salient
features of the feasibility study are highlighted below and the pre-feasibility report is also referred to and compared as found to be relevant.
a) Hydronieterological Data Base
WWDSE & Synergies Hydro  (2007) indicated  that the type and  length  of hydro meteorological data available in the Erer irrigation area are limited. There are two rainfall stations (Bisidimo  El.  1340  masl,  and  Harar El 2100  masl) in/nearby  the Erer dam watershed Other climatic data will be available only for relatively near by station (Dire Dawa, El 1260 m asl, Haremaia El 2125 m asl, Babile El 1600 m asl, Jijiga El 1775 m asl).
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Flow data of Ercr River at gauging site (on Harar-Jijiga road) is available only for a period  spanning  1984-1996  with  a number of gaps No  spot measurement data are presented in the report.
Sediment data for 12 spot measurements are available at Erer gauging station.
b)  Estimate of Eto
WWDSE & Synergies Hydro (2007) used Jijiga, Harar and Dire Dawa station climatic data to estimate monthly mean maximum and minimum temperatures (Tmax, Tmin) , humidity RH, Sunshine hours and wind speed of irrigation area. As shown below, ETo estimate given by FS is on the lower side.
Erer irrigation area is located between EL 1280 masl and EL 1365 masl which is close to elevation and climatic condition of Dire Dawa station located at EL 1260 m asl. Dire Dawa mean annual wind speed is unusually high (205 km/day) as compared to Jijiga 123 km/day and Harar 81 km/day Diredwa value could be high due to wind-tunnel effect as it is located in low-lying area compared to the surrounding hills. This phenomenon of wind tunnel has been also observed in Nazeret station. In this review study, the data of Jijiga has  been  applied  The  feasibility  study  used  the  wind  speed  data  of Harar.  Minimum temperature of Dire Dawa reported in Annex 3.1, page 189 of the feasibility study report is incorrect. Wind speed data used in the FS is also underestimated (Figure 1) The mean annual estimate of ETo by the FS is 4.33 mm /day (1581 mm/year) whereas estimate based on Dire Dawa climate data is 4.58 mm/day (1773 mm/year) with a difference of about  192  mm.  Reservoir  evaporation  is  estimated  at  1.15*ETo  =  2039  mm/year Table 3.1 below provides comparison of climate data in the FS and the present study based on climate data of Dire Dawa
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Tabic 2.1: Comparison of Climate Data Used in FS and the Present Study Based on Dire Dawa Climate Data
Temperature (Degree C)
Humidity (%)
Wind speed (m/s)
Sunshine hours
ETo (mm/day)
Dire
Dawa
FS
Dirt
Dawa
FS
JiJin
FS
Dire
Dawa
FS
Erer Irrigation area
FS
Jan
21.4
22.2
60
52.6
1.40
1.61
8.60
8.90
4.14
4.20
Feb
22.7
23.0
56
52.7
1.30
1.62
8.10
8.40
4.45
4.51
Mar
24.6
24.2
55
54.1
1.30
1.28
7.90
7.80
4.90 1
437
Apr
26.3
24.0
54
56.2
1.40
1.11
7.60
7.40
5.15
436
May
27.3
23.1
48
51.0
1.30
0.97
8.30
8.70
5.29
4.51
Jun
28.1
22.4
46
45.8
1.50
0.95
7.70
8.20
5.41
432
Jul
26.3
22.8
52
51.3
1.30
0.98
7.10
7.80
4.84
4.18
Aug
25.7
233
56
54.6
1.50
0.95
7.60
7.80
5.07
4.28
Sep
25.9
23.7
53
54.2
1.30
0.95
7.40
7.70
4.93
4.25
Oct
25.1
22.5
44
45.7
1.10
0.98
8.00
8.60
4.68
434
Nov
22.4
22.2
50
46.3
1.60
1.35
9.00
9.50
4.66
435
Dec
21.3
21 8       52                   51.3       2.09                 1.56      9.30                 9.10       4.72                4.14
Mean
24.7
Mai
28.1
Min         21.3
22.9 52 513 1.42 1.19 8.05 833 4.85 433
24.2 60 56.2 2.09 1.62 9.30 9.50 5.41 4.57
21.8 44 45.7 1.10 0.95 7.10 7.40 4.14 4.14
Figure 2.1: ETo Estimate by FS and Based on Dire Dawa/Jijiga data Erer / Final Phase I Report /2008CECEandCES
c)        Rainfall Analysis
1)   Monthly Rainfall
Monthly rainfall distribution estimated over the irrigation area and Erer dam watershed is in the right order.
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2)  Frequency Analysis of Annual Maximum Rainfall
Frequency analysis of annual maximum rainfall was carried out based on data of Harar, Babile and Bisidimo. Table 2.2 gives comparison of ERA (2002) regional estimate and FS estimate,  which  are quite different.  No  discussion  made whether EVI fits well the annual maximum data of Harar, Babile and Bisidimo. The study might have used Dire Dawa rainfall data with longer series than indicated on page 211 of the report.
Table 2.2: Rainfall Frequency Analysis
Return Period Year
2
5
10
25
50
100
24 hr depth rainfall
(nun)
ERA
(2002)
60
79
93
113
127
142
FS
50
66
76
89
99
X
Hence further work on frequency analysis of annual maximum daily rainfall is required to have reliable estimate IDF curve for the project area
d)  Stream Flow Estimate
FS report estimated a mean annual flow at dam site as 60 Mm . The methods used for estimate is Modified Linear Perturbation Model (MLPM) on monthly time step. Model calibration and verification is not given in the report. No discussion made about the Erer bridge hydrometric data quality,  rating  curve review etc During  Master Plan  pre feasibility study WWDSE (2004) estimated a mean annual flow of 35 Mm . The MLPM model overestimated flows in Jan, Feb, Mar and June as compared to the Master Plan estimate (Figure 3.2) and appendix I.
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3
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Reliable estimate should be made in order to size accurately the dam and irrigation area It is strongly  recommended  that intensive discharge and  sediment measurement be conducted in July, August and September 2008, and April and May 2009. Initial program of the flow measurement at Erer River at bridge is given in Annex II. It is proposed that measurement be conducted  by  the Hydrology  Department of Ministry  of Water Resources and supervised by the Erer dam and irrigation hydrologist.
Figure 2.2: Comparison of Flow Estimate at Erer Dam Site
e)  Design Flood Estimation
The FS adopted standard methods in estimating PMP of 267 mm and PMF peak of 1259 m /s. This PMF peak estimate is close to Creager PMF estimate of C = 30 which is often taken for Ethiopia The adopted design flood of spillway 642 m /s is acceptable, although this design discharge change as dam size change due to new estimate of the Erer River mean annual flow.
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Erer / Final Phase 1 Report /2008CECEandCES
f)   Reservoir Sedimentation
1)  Sediment inflow Estimate
FS estimate is far lower than this 177 ton/km2/year which has not been observed so far except in a very rare case where the river out flow from marshy area. MP study estimated sediment inflow rate of 400  ton/km2/year indicating  that this value is at low side as compared to northern highland Ethiopia sediment rate (often > 1000 ton/km /year) For example,  measured  reservoir sedimentation  rate of reservoir Legedadi catchment area
2
230 km2  (having average annual
3
inflow of 87 Mm and about 50% of its catchment being 
located in relatively plain terrain) shows higher value. Legedadi reservoir volume of 45.9 
Mm3  in 1979 reduced to 43.8 Mm3  in 1998 giving annual
2
sediment yield 762 t/km /year
with sediment composition 67/20/13 : clay/silt/sand (LEK, 2000).
Possible reason for low yield estimate might be suspended sediment measurement is only taken  at low (0.2  m3/s) and  medium flows (5  m3/s) but not at high  flows.  Intensive measurements (one/two rainy season) of suspended sediment at the Erer gauging site is required to arrive at correct value as indicated also for flow measurement.
2)  Sediment Distribution in Reservoir
FS used Empirical Area Reduction methods to estimate sediment distribution at different life time of the reservoir. This method is acceptable but this should be done following revised sedimentation rate into the reservoir.
3)  Reservoir Simulation
Methodology applied following standard procedure. However, as discussed in section 4, the water resources is not sufficient for irrigating 4000 ha 38.84 Mm3 for irrigation + Harar town water supply 7.32 Mm , other demands of 5 Mm ). If new flow measurement indicates that low Erer River flow as compared  to  FS,  the irrigation  area could  be reduced to about 2000 ha. The required dam height could change from what has been proposed.
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Erer / Final Phase 1 Report /2008CECE and CES
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g)   Diversion Flood and Surface Drainage Design
3
Diversion flood of 151 m /s for 50 year return period has been used while estimate was made based on nine year annual maximum data
Surface drainage assessment of the irrigation area is not treated in the report. As the
command area is crossed by a number of creeks, design discharge for culverts is required Moreover flood protection measures of the command area might be required at different location.
2.2.3 Conclusion
In general the Hydrologic Feasibility Study of Erer dam has been carried out following standard procedures. The PMF estimate is in the expected range. However, according to the present assessment,  the estimated  mean  annual flow into  the Erer reservoir is overestimated. The FS study estimate is 60 MmVyear whereas the pre-feasibility estimate is 35 Mm /year which is the order expected. Sediment estimated by the FS is clearly underestimated  177  ton/km2/year,  which  is far below what is seen  in  Ethiopian catchments (> 400 ton/km /year). Reservoir evaporation is also slightly underestimated. The mean annual estimate of ETo by the FS is 4.33 mm /day (1581 mm/year) whereas the present estimate based on Dire Dawa and Jijiga climate data is 4 58 mm/day (1773 mm/ycar) with a difference of about 192 mm.
Such divergence in estimate is due to lack of quality flow data with longer period. It is highly recommended to conduct intensive flow and sediment measurement at the Erer gauging site at the Harar-Jijiga road.
2.3 Topographic Surveying
Topographic surveying  and  mapping  are the first pre-requisites for starting  any programme of development. Maps are basic to all planning and should be prepared before any planning or design may be carried out. A map needs to be sufficiently accurate so that the measurements made from it are accurate for the purpose. The cost of surveying 
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Erer / Final Phase 1 Report /2008
2CECEandCES
and mapping is only a minor fraction of the total cost of the project and when undertaken at initial stage with required accuracy and detail will save a lot of expenditure arising out of incomplete or faulty data.
The topographic survey  undertaken  during  feasibility  study  has many  deficiencies with regards to the benchmarks, leveling survey, feature survey and preparation of drawings. During  this study  additional surveys/resurveys need  to  be undertaken  to  rectify  the deficiencies with the previous topographic surveys as well as to fortify the topographic survey for undertaking detail designs of the project.
2.3.1 Desk Work and Field Assessment
In the first phase of this project a detail desk work and field assessment has been done so as to understand and the status of the works undertaken during feasibility study. Also an assessment is to be made so as to find out how far the data is usable for the detail design.
a) Desk work
Review of the topographical studies has been carried out during the feasibility analysis. 
As indicated in the feasibility reports surveys conducted, maps produced and benchmarks established are outlined below:
1) Topographic Survey of Dam Site
For the dam site and  the areas of appurtenant structures topographic plans/maps at 1:4,000 and 1:2,000 scales with appropriate contour interval are developed. Apart from the topographic maps for the dam site area, the report states that valley cross sections along dam axis and line parallel to the dam axis at 25m interval up to 250m distance on both upstream and downstream of dam axis are developed. Longitudinal profile along the planned center line of the spillway is also generated.
Erer /Final Phase 1 Report /2008
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2)  Topographic Survey of Reservoir Area
The feasibility  study  report indicates that topographic maps of the reservoir area are developed on scales of 1:10,000 and 1:20,000 with contour interval of lm covering an area of 725 ha upstream of proposed dam axis.
3)  Topographic Survey of Command Area
Topographic survey, based command area maps are developed at 1:10,000 and 1: 5,000 scales with contour intervals of 2m and lm respectively. Also 1: 2,000 scale topographic map with contour interval of 0.5m is also developed for a sample block used to undertake detail planning of the distribution system
4)  Control Points / Benchmarks
As indicated in the report a total of 53 permanent benchmarks have been established during  feasibility  stage,  spread  all over the project area.  The UTM coordinates and elevations in meter units of these benchmarks are made listed in the feasibility report.
However the topographic maps made available by the client to the consultant for review and further updating are as given below.
•    1:15,000 scale map hard copy in six sheets for command area (Vol. 12)
•    1:5000 scale map hard copy for dam site (Vol. 12)
•     1:   5000 scale map hard     copy for the sample block (Vol. 12)
•     1 3500 scale map hard copy for spillway channel site (Vol. 12)
•    1:   2000 scale map hard     copy of the diversion channel site (Vol 12)
•    Soft copy drawing of the topography map of the project area in AutoCAD format, which has been used for production of I 15000 scale maps.
b)  Field Assessment
A field visit was undertaken from 4lh
 to 10   May 2008. Following are the observations
th
comprehended during the visit:
Erer/Final Phase I Report /2008
12CECEandCES
•     There  is  quite  a  bit  of  ambiguity  with  respect  to  dam  axis  as  the  axis alignment  is  not  marked  on  the  site  as  well  as  there  is  confusion  with respect to benchmarks representing the dam axis
•     The  benchmark  which  represents  the  Dam  axis  on  right  bank,  BM-16B was not traceable, instead BM-16 was found painted on the rock
•     The benchmark which represent the left dam axis, BM-3, was found to be marked on rock by paint, which was totally worn-out.
•     All the benchmarks which ever found on the ground either has an offset of about 240 to 250m as compared to the coordinate mentioned in the report with  GPS  coordinate  or  do  not  exist  in  the  listed  benchmarks  of  the feasibility report.
•     The benchmarks are either not concreted at all (just painted on rocks) or cemented with two to 4 inch masonry with very poor quality plaster. Most of these cemented benchmarks have been removed by the villagers.
•    The command area benchmarks were not traceable on the ground One benchmark was located as painted on the parapet wall of the confluence of Decho River with Erer River in the command area. This important
benchmark was not listed among the list of benchmark in the feasibility report.
•    The contours of the topography map do not seem to be matching the
ground topography as the map seems to be quite generalized.
•    The elevations also do not seem to be quite accurate, as there seems to be quite a lot of variation from the GPS elevations.
2.3.2 Gaps Identified
The following maps have been reported to be developed during the feasibility study but not yet been supplied to the consultant. We have made request for the same in early and mid May 2008 and kept pursuing for the delivery of the same.
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Erer / Final Phase I Report /2008CECEandCES
a) Topographic Survey of Dam Site
The topographic map of the dam site available with the feasibility report is only 1:5000 scale as against 1: 4,000 and 1: 2000 scale stated in the feasibility report
It has been reported that valley cross sections along dam axis and line parallel to the dam axis at 25m interval up to 250m distance on both upstream and downstream of dam axis are developed. Also longitudinal profile along the planned center line of the spillway is also developed. However these have not been supplied to the consultant
b)  Topographic Survey of Reservoir A rea
The topographic map of the reservoir area is not available with the feasibility report as against the reported 1:10,000 and 1:20,000 with contour interval of lm. for an area of 725 ha.
However softcopy drawing is available which is not geo-referenced, has many problems which are described subsequently
c)   Topographic Survey of Command Area
The topographic map of the command area is available with the feasibility report at 1 : 15,000 scale as against the reported 1:10,000 and 1:5000 scales.
Also it is reported in the topography report that 1: 2,000 scale topographic map with contour interval of 0.5m is also developed for a sample block, but actually sample block available with feasibility report is 1:5000 only.
d)  Control Points / Benchmarks
It is reported in the feasibility study, topography report that 53 permanent benchmarks have been established in the project area and their UTM coordinates and elevations in meter units have been listed
Out of the total 53  benchmarks listed  in  the topography  section  of Main  Feasibility report,  22  benchmarks have duplicate names with  two  benchmark  (BM-2) having duplicate coordinates and  elevations where as two  have same coordinate but different elevation (BM-28B).
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Er er /Final Phase 1 Report /2008CECE and CES
Moreover most of the benchmarks are not available in the field Those benchmarks which are available have their coordinates off by  about 250  meters as compared  to  GPS coordinates.
e)  Drawings
The softcopy of the drawing for the topography survey developed during feasibility study has been studied, the same was found to have following deficiencies.
1)  The drawing is not geo referenced according to the UTM coordinate system, instead has a grid overlaid on the same which is very coarse. This non geo-referencing of the topography drawing is a constraint to integration of further surveys to be undertaken during the detail design phase. That is the old survey data will be of little use as integration with new surveys becomes very difficult Any attempt to geo-reference in this stage risks incorporation of many errors,
2) The drawing lacks the original points (levels) captured during the survey. The non availability  of  the  surveyed  points  restricts  the  further  additional  surveys  such  as densification of the levels in the dam and command areas for detail design
The non availability of the survey points and the clients inability to supply these after long  follow ups gives an  apprehension  that all the drawings might have been prepared by interpolation of the 1:50,000 scale topomap rather than being developed after topographic survey.
In such a case complete survey of the project area has to be carried out from the scratch.
1) The drawing has contours which do not cany any elevation value in their lines. That
the lines are 2d lines and not 3d lines which is essential. The contour carries elevation as written by text.
2)  Drawing does not have important alignments like dam axis, certain canals, command area boundary etc.
3) The drafting standards of the drawing are very poor. Few of the deficiencies in 
drafting standards have been listed below:
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Erer / Final Phase I Report /2008CECE and CES
•     Features are drawn across the drawing layers. For example the layer of quaternary canals  has  features  such  as  main  contours,  secondary  contours,  non  irrigable areas, etc.
•    Similar features are drawn in multiple layers, creating quite a lot of confusion.
•    The features are most of the time broken lines and polygons
•    The drawing does not have scale.
•    The drawing has a very scanty legend and many features stand unexplained.
•    The benchmarks listed are having duplicate names.
It is noted that though the few hard copy maps which have been provided with scales larger than 1: 15000, that is in scales like 1: 2000, 1:3500 and 1: 5000 these are primarily just a blown up outputs of the 1: 15,000 scale map That is, virtually all the maps are of the scale of 1:15,000 in terms of topographic detail and accuracy
As per the standards of mapping, as the mapping scale becomes larger the survey details and accuracy should increase accordingly. In fact there is a serious apprehension within the consultant with regards to topographic out puts like 1: 15,000 scale map (which is the parent map  of all the topographic drawings) that the same has been  prepared  by interpolation  of contours and  other details from the 1: 50,000  scale topographic map published by Ethiopian mapping Authority
2.3.3 Measures to Fill Gaps Identified
There seems to be a need for significant extent of survey to be undertaken (almost amounting to complete resurvey) since the quality of topography outputs produced during feasibility study and the ones delivered to the consultant for the detail design are very poor. It would be quite an uphill task to use the feasibility study topographic data for further densifying the survey
However if the survey levels are made available by the client (for the topographical survey of the feasibility study), for which requisition has been made more than once, then
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Erer / Final Phase I Report /2008CECE and CES
all attempt will be made to  use this data so  as to  reduce the extents of resurveys to  be undertaken  in  the surveyed  areas Yet,  however,  considering  the poor quality  of the survey,  supplementary  and  complementary  survey  is still required  even  if all the survey data are made available.
The complementary and supplementary topographic survey will be undertaken to produce survey data of required accuracy and scale for development of topographical maps to undertake detail design. The topographic maps would be developed at 1: 1,000 with lm contours in steep slope areas and 0.5m contours in gentle slope and plain areas for the locations inclusive of dam, appurtenant structures, irrigation canal system associated structures as well as for the project infrastructure like roads, colonies etc
The following surveys shall be undertaken
•     Establishment of Control Points/Benchmarks
• 
Topographic mapping survey/ Level densification survey
• 
Cross section and longitudinal section survey
a)           Establishment of Control Points/Benchmarks
As the benchmarks established  during  feasibility  study  have quite a lot of problems in terms of coordinates as well as their erection  on  the ground  completely  new set of benchmarks will be established.  The master benchmark  will be called  the Project Benchmark,  whose levels and  coordinates will be transferred  from the GTS benchmark. All the secondary and other benchmarks refer to this project benchmark
A network  of new secondary  benchmarks shall be established,  which  would  be initiated by  erection  of project benchmark  The project benchmark  would  be established  on  one of the existing  benchmarks of the feasibility  study,  so  that the difference in  datum of the topographic survey  of the feasibility  study  and  the new real world  datum defined  could  be accurately  computed  and  corrected  for the levels for design  of different project components.
17
.<     Erer / Final Phase 1 Report /2008 &CECEandCES
b)   Topographic Mapping Survey
Topographic mapping  survey  will be carried  out for densification  of the levels to  fill in the gaps of the survey  undertaken  during  the feasibility  study.  Apart from this survey  an item specific survey  for the important features of the project is also  carried  out.  After the survey  levels will be plotted  on  to  the drawing  and  the datum is rectified  by  the datum correction factor computed from the project benchmark
Level densification survey will be carried out in reference to the nearest secondary 
benchmark in the gap area. The gap area is surveyed to the extent the gaps are removed 
according to the gap criteria described in design criteria.
Item specific survey  would  be carried  out for all important components of the project. The major components of the project are dam site inclusive of spillway  and  outlet, primary  and  secondary  canals and  their structures,  infrastructure like colonies and  roads for construction  and  maintenance of the scheme and  locations of investigation  and  areas of borrows.
1)   Dam Site Survey
Dam site area close interval survey  is conducted  for a length  of about 2km (250m additional length  to  the dam crest length  on  right and  left abutments) and  a width of 500m on either side of the dam axis.
2)   Canal Strip Survey
A canal strip survey is conducted for a tentative length of 14.4 km for the primary canal
and 16.5 km for two secondary canals Strip survey shall be carried for a width of 60m
i.e., 30m on either side of the center line of the canal alignment. Cross sections are taken 
every 100m along the canal alignment.
3)  Structures
Major  structures  along  the  canals  shall  require  special  close  grid  survey.  Major  structures for which structures grid survey will be carried out are the following:
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Erer / Final Phase J Report /2008CECEandCES
•       Escape   -   at   chainage   of   5.5   km   on   the   primary   canal   an   'Escape   Structure’   is proposed
•       Siphon   —   at   the   primary   canal   crossing   the   Harar   —   Jigiga   road   a   siphon   is proposed.
•      Head  regulators  -  the  tail  of  the  primary  canal  i.e.,  at  chainage  14.4km  one  head regulator each for the two offtaking secondary canals are proposed
•      Aqueducts  on  Decho  River  for  secondary  canals  -  at  a  chainage  of  0.91  km  on  the first   Secondary   Canal   and   at   2.45   km   chainage   of   the   second   Secondary   Canal aqueducts are proposed
4)   Colonies Ssurvey
The  survey  conducted  for  the  dam  site  area/  command  area  will  serve  the  requirement  for the colony design.
5)   Road Survey
As existing  roads will be strengthened  the level densified  topographic map  will serve the requirement.  For the canal maintenance roads the canal strip  survey  will serve the requirement
c)  Survey of Investigation and Borrow Locations
During  the level densification  survey  of the project area all the locations of the geological investigations like drilling  and  pitting,  soil investigation  locations and  locations of the borrow areas are recorded.
</) Cross Section and Longitudinal Section Survey
Cross sectional survey  will be carried  for the Erer River for estimation  of the river carrying  capacity  so  as to  design  the flood  protection  works of the Erer River at command area
e) River Cross Section and Longitudinal Profile Survey
Survey  will  be  conducted  for-cross  sections  and  longitudinal  profile  of  the  Erer  River  iu proximity of the command area.
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Erer /Final Phase I Report 72008CECEandCES 
Cross section  survey  shall be conducted  on  Erer River starting  from the upstream of command  area to  the tail reaches of the command  at every  1km interval Longitudinal profile is developed  for the Erer River from the Maximum Water Level in  the reservoir to the tail of the command area by taking levels every 100 m.
2.4 Dam Engineering
2.4.1  Desk Work and Field Assessment
In  the first phase of this assignment a detailed  desk  work  has been  done so  as to understand  the status of the works undertaken  during  the feasibility  study.  Also  an attempt has been  made to  find  out the gaps and  measures require to  be taken.  The field trip  conducted  has also  been  used  to  assess actual field  conditions pertaining  to  dam & appurtenance structures site, construction material etc.
a)   Desk Work
The following have been considered for the design of dam during feasibility study:
1)        Option   -I,   the   U/S   most   site,   is   the   favorable   site   for   the   36.6m   high   proposed zoned  earth  fill  dam  with  concrete  spillway  on  the  left  flank  and  canal  on  the  right bank   of   the   Erer   River.   The   orientation   of   dam   axis   has   been   fixed,   taking   into account the topographical configuration of ridge on left and right abutments.
2)      Dam height has been fixed considering the following
• Functional requirement of adequate storage.
• Dead storage has been arrived at by considering 50 years active life of the reservoir.
• MDDL has been fixed with the consideration of drawl of design discharge into the
canal when the reservoir is at MDDL.
• Maximum Water Level (MWL) corresponds to design spillway flood.
•  Adequate freeboard
• Settlement due to strong ground motion.
3)    The  earth  fill  dam  section  adopted  is  a  zoned  section  consisting  of  impervious  clay core with outer protective casing/shell inclined and horizontal filters and rock toe and
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Erer /Final Phase 1 Report /2008CECEandCES
toe drain on downstream considering the availability of suitable soils close to the
dam.
4)   Foundation Condition :
a)   The  dam  will  rest  on  pervious  foundation  material  in  the  river  section  and  on  both the   flanks   covering   a   length   of   about   1000m   along   dam   axis   and   the   remaining portion  of  400m  length  on  the  left  flank  and  right  abutment  will  rest  on  patchy  / bouldery   rock   outcrops.   The   pervious   material   is   alluvial   in   nature,   unconsolidated, loose,   erodible,   non-cohesive,   and   largely   of   granular   character   composed   of   gravel, pebble,   cobble,   sand   with   subordinate   silt   and   clay.   This   type   of   natural   material covers  the  river  section,  most  of  the  right  flank  and  50%  of  the  left  flank.  It  is  3O-35m deep  along  river  section  and  10-15/20m  deep  on  the  flanks  This  information  is  based on VES surveys, borehole data.
b)   The  earth  dam  is  provided  with  partial  key  trench  in  the  river  section  and  right flank  where  the  depth  of  overburden  is  more  and  positive  cut-off  on  the  left  flank where   the   weather   fresh   rock   is   available   within   10m.   U/s   impervious   blanket   is provided  where  partial  key  I  cut-off  trench  is  proposed  in  the  river  section  and  right flank
5)   Dumped rock rip-rap is provided for upstream slope protection and stone pitching is recommended for downstream protection.
6)   Stability Analysis has been conducted as per the standard practice considering all the conditions
7)   A chute spillway has been provided to ensure the safety against overtopping during occurrence of the inflow design flood The spillway is aligned in NE-SW direction close to dam, say spilling within 500m from the toe of dam.
8)   Dam instrumentation has been proposed to measure
1)   Settlements and movements
2)   Pore pressure
3)   Seismicity
9)   River diversion arrangement during construction period has been provided considering design flood of 50 years return period.
Erer/Final Phase 1 Report /2008CECEandCES
Since the dam length  is considerably  large,  river diversion  arrangement as proposed through  a temporary  channel involving  a gap  through  the body  of the dam while the remainder of the embankment is being  done is found  to  be alright.  But before the stream is diverted,  the foundation  preparation,  foundation  treatment etc need  to  be completed  in the area where the temporary  opening  will be left through  embankment.  The foundation preparation  and  construction  of the embankment on  either side of the diversion  opening may then be completed.
The side slopes of the opening  should  not be steeper than  4  to  1  so  as to  ensure proper bonding  between  the previously  constructed  embankment and  the materials to  be placed for filling  the gap.  Filling  of the gap  should  be undertaken  in  the lean  season  and  to  be completed  as quickly  as possible The average rate of embankment placement must be such  that the gap  can  be filled  faster than  water rises in  the reservoir The capability  of the contractor to  undertake such  job  is very  important.  It is to  be also  seen  that quality  of the work  is not sacrificed  due to  exigency  of the situation.  This is of great importance because the diversion  will be in  the area where the dam will be of maximum height. Extreme care shall have to  be taken  to  obtain  required  densities and  proper bonding  of the newly placed material with the earth fill previously placed.
2.4.2 Gaps Identified
a)   Topographical survey has not been done properly as mentioned by our GIS expert.
b)   Tail water rating curve has not been discussed.
c)   The exact nature, properties and thickness of the pervious material / alluvium below
the dam foundation are yet not proved.
d)   The bed rock profile is also not defined.
e)   The explorations done so far are incomplete and do not precisely present sub
surface geological picture of the site conditions.
f)     Rock  and  soil  properties  require  to  be  tested  as  per  specifications  and  directed  by the  site  conditions  eg.  Depthwise,  spacewise  and  specification  related  in  totality  for earth dam and spillway.
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Ercr / Final Phase 1 Report /2008CECEandCES
g)   Basis of earthquake parameter taken has not been discussed.
h)     The   stability   analysis   conducted   indicated   the   use   of   standard   and   acceptable stability   criteria;   however   it   is   not   clear   if   the   section   considered   for   stability analysis takes into account the alluvium formation of the river under all conditions
i)     The  report  does  not  point  Qut  the  need  for  test  fills  of  shell  material  and  impervious core. This is highly recommended to be done at the start of construction.
j)      The   spillway   is   proposed   as   ogee-shaped   un-gated   structure   with   chute   and   exit structure  at  the  D/S  end  in  the  Homee  stream.  The  alignment  is  approx  500m  long in  NE—SW  direction  and  the  spillway  discharge  will  meet  the  Erer  River  at  right angle  to  its  flow  very  close  to  the  toe  of  dam-say  within  500m.  This  feature  may submerge  the  toe  of  dam  due  to  back  water  flow  and  will  not  allow  inspection  of  the toe    of    dam    for    observing    seepage    flow    conditions    if    any    through    the    dam foundation.  The  unguarded  spill  discharge  may  also  erode  the  river  section  alluvium at d/s of toe of dam thereby endangering the safety of earth dam.
2.4.3 Measures to Fill Gaps Identified
a)   Topographic maps need to be prepared for dam site as indicated below:
1)    Grid  plan  with  contours  of  the  dam  site  covering  the  area  upto  250m  upstream  and 500m   downstream   of   the   dam   axis   extending   upto   an   elevation   of   MWL+5m. Drawing  is  to  be  prepared  in  scale  1:  2500  with  1  contour  interval.  Block  leveling is to be on 10m grid basis
2)    L-section  of  river  is  required  in  suitable  scale  and  levels  are  to  be  taken  at  closer interval.
3)    X-section  of  river  along  the  axis  of  the  structure  with  suitable  scale  and  levels  are to be taken at closer interval highlighting the ground profile.
4)     Some   X-sections   of   river   between   500m   u/s   and   500m   d/s   of   the   structure   in suitable  scale  and  levels  are  to  be  taken  at  closer  interval  highlighting  the  ground profile.
b)   Rating curves (discharge versus depth) are to be developed by project hydrologist.
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Erer /Final Phase I Report /2008CECEandCES
c)    A pattern of exploration is proposed for working out subsurface geology and deciding upon  the  design  parameters.  It  has  been  described  in  Artcle  3.5  -  Geophysical  and geotechnical   investigations.   It   is   required   to   determine   the   characteristics   of   the various strata which comprise the dam foundation and abutment.
Water percolation  tests are to  be carried  out to  find  out the permeability characteristics of the various strata of the foundation which may dictate the type and extent of the foundation treatment.
Standard penetration tests are to be carried out in the holes to determine the relative densities of the strata at various depths and to assess the liquefaction potentials.
d) Construction Material - Samples are to be taken from 2-3 trial Pits to a depth of 3 m each  and  then  extending  to  depth  of  5m  by  auger  holes  lab  testing.  Testing  of engineering properties of soil required are outlined below:
1)  Natural water content
2)  Atterburg limits
3)  Sieve analysis for coarse and fine sediments
4)  Specific gravity
5)  Proctor tests
6)  Triaxial shear test on unconsolidated undrained samples or direct shear test
7)  Dispersive character
8)  Swelling index/ Free swell
9)  Permeability characteristics
10) Density of soil Material
11) Strength test-penetration and shear test
e)           Spillway layout may be carefully examined by project hydraulic engineer from dam safety point of view.
Earthquake parameters need to be finalized for detailed design.
2.5 Dams Appurtenant Structures
The Land and Water Resources Study of the Wabi Shebele Basin identified the present study area as being one of the potential areas for irrigation development. The Ministry of
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Erer I Final Phase 1 Report /2008CECEandCES
Water Resources recently completed the Erer Dam and Irrigation Project Feasibility
Study (September 2007).
The dam appurtenance structures constitute the Erer dam spillway  and  irrigation  outlet Our desk  studies of both  structures have incorporated  an  extensive review of relevant material in 12 volumes (including an album of drawings) on previous studies
As a general observation,  the level of design  detail accorded  during  the feasibility  study to  the dam spillway  is rather sketchy  when  compared  to  the information  provided  on irrigation  outlet works design.  The Feasibility  Study  reports provide valuable background information  on  the dam appurtenance structures.  Certainly,  level of detail required  on account of the objectives of the present study  to  comply  with  the Consultant’s Technical Proposal would  call for more data and  information  to  complete the study  to  an  acceptable standard.  On  the other hand,  existing  MoWR (2007) data would  reduce the level of additional investigation required for completion of the designs.
2.5.1 Desk Work And Field Assessment
a) Desk Work
1) Irrigation Outlet Works
The irrigation outlet is located at the foundation level on the right abutment of the dam
so that it can be more conveniently connected directly to the primary Canal that feeds the
gravity irrigation canal network which is also located entirely on the right bank of the
Erer River.
According   to   the   Feasibility   Study,   the   outlet   work   consists   of   an   intake   device,   a conveyance structure, a control and a terminal device.
A submerged  intake structure with  proper provision  of trash  rack  is to  be provided  at the upstream end  of the conduit.  A bell mouth  entrance at the intake,  which  is designed  as drop  inlet to  the irrigation  outlet conduit,  has been  provided  While the drop  inlet is placed  sufficiently  high  for it ought to  function  free from interference of sediment deposits it is positioned sufficiently below the minimum draw down level of the reservoirCECEandCES
to  prevent  vortex  formation  when  the  water  is  drawn  with  reservoir  at  Minimum  Draw Down Level.
The outlet conduit is a 1.1 m diameter vertical pipe connected by a 900 transition bend to a 120 meters long horizontal reinforced concrete lm by 1 m size conduit. The conduit is provided  with  75  cm high  and  45  cm thick  reinforced  concrete cut-off collars laid  over
15cm thick lean concrete spaced @ 5m c/c and 2 cm thick bituminous joint fillers placed between conduit and cutoff collars in the dam core portion.
A control shaft located at some intermediate point along the conduit is provided to house two control gates, one emergency and one service gate, which are to be operated through an access bridge linking the shaft well with the crest of the dam. Access to the conduit is thus through the gate well to be provided with proper size rungs.
Any expected foundation movements and appropriate provisions to counter its impact on the irrigation  outlet,  and  hydraulic efficiency  and  structural safety  will be given  due consideration during the detail design of the suggested structure described above.
Reservoir simulation  studies undertaken  during  the Feasibility  study  indicated  that apart from the reservoir water lost to evaporation and seepage, the impounded water would be utilized  for meeting  irrigation  demand,  environmental releases,  water supply  to  Harar town, and the livestock and domestic requirement of local villagers. However, the design of the outlet conduit has been governed by meeting peak irrigation water requirement and environmental releases which  in  total amount to  a discharge of 3.05m3/sec.  It is not specifically  mentioned  whether the hydraulic dimensioning  of the conduit takes into account any future expansion of the irrigable area. It is highly unlikely that there will be any future expansion of the irrigable area given the many competing needs for limited water resources. But should there be any possibility for expansion of the planned irrigable area, the project Irrigation Group will reconsider the farm water needs and full supply level of the Primary Canal that feed the gravity irrigation canal network. The irrigation water requirement depends on  the area to  be irrigated,  the consumptive use of water
26
Erer / Final Phase I Report /2008CECEandCES
(duty), types of crops to be grown, cropping pattern, etc. Equally the magnitude of all
other riparian water demands may be quantified separately and aggregated.
In addition to releasing the impounded water to meet demand, as and when needed, the
outlet work shall also be employed to:-
•    pass a part of the design flood to the downstream, as a supplement to the capacity 
of the spillway in case of emergency
•    empty the reservoir up to its sill level to permit inspection, to make needed repairs
or to maintain the upstream face of the dam or the spillway, and
•    control rise of the reservoir during initial filling
The discharge capacity of the outlet works will also be reassessed based on the results of the reservoir operation studies. The most critical period being when the reservoir storage is low but the irrigation water demands are at their peak The discharge capacity of the irrigation  outlet will be decided  considering  the available reservoir storage during  that period.
2) Spillway
Provision of spilling arrangement is an essential part of embankment dam planning and layout since dam overtopping  can  not be allowed.  According  to  the Erer Dam and Irrigation Project Feasibility Study (September 2007), the selected spillway structure is located on the left abutment of Erer dam where the elevation of the natural ground is around 1380 masl and the hydraulic head at the interface between the concrete structures and  embankment is minimal.  It consists of an  approach  channel,  control structure, discharge channel (inclined chute), a stilling basin as an energy dissipator, and an exit channel as its components.
Site conditions generally  influence the location,  type and  components of a spillway Apparently,  the Erer spillway  has been  located  on  the left bank  of the river as the foundation situation are more favorable, the required length of spillway chute is shorter and the spillway works are not intersected by the proposed irrigation outlet works which is located on the right bank of the Erer River. Il should however be noted that the
27
Erer I Final Phase I Report /2008CECE and CES
Feasibility   Study   proposed   curtain   grouting   below   the   foundation   of   the   spillway   along the dam axis in order to reduce the permeability of the foundation
The  spillway  designated  for  discharge  of  floods  is  an  un-gated  (free)  overflow  weir  with ogee  crested  profile.  An  approach  channel  is  provided  to  draw  water  from  the  Erer  dam reservoir  and  convey  it  to  the  ogee  crested  control  structure,  since  the  spillway  which  is located  through  the  left  abutment  could  not  draw  water  directly  from  the  reservoir.  The approach   channel   is   planned   to   have  a   curved   alignment  to   suit   the  topographic  feature that  is  found  to  be  the  foot  of  a  range  of  rising  ground  with  relatively  gentle  slopes  on  its left  side.  Since  a  straight  approach  channel  could  not  be  selected,  the  connection  between the   approach   channel   and   the   ogee   crested   weir   is   made   possible   by   a   single   curve subtending   an   angle   of   60.88   degrees   at   a   radius   of   70   meters.   Finally,   the   approach channel   is   given   a   straight   alignment   as   it   reaches   the   spillway   axis   for   perpendicular connection.   Access   to   the   spillway   crest   for   pedestrians   and   vehicles   alike   is   from   the right bank only, along the dam crest.
At the entrance to  the spillway  the bottom width  of the approach  channel is about 30m and  the channel starts with  relatively  bigger bed  width  at its inlet.  Other dimensions of the channel have been left incomplete during the Feasibility Study.
The height of the weir has not been fixed during the study The coefficient of discharge
for the ogee crested weir for flood routing computations was 2.18. The theoretical value
of the coefficient of discharge disregarding any reduction due to friction etc is 2.96. The
practical limit of coefficient of discharge, without allowing sub-atmospheric pressure is
2.21. Hence the value adopted is within the limits.
Beyond  the weir axis,  the discharge channel continues in  a straight alignment with  a uniform width  of 30  meters The end  of the chute is planned  to  be a stilling  basin  with  its ancillary  devices.  According  to  the Feasibility  Study,  the 335.8m long  inclined  chute terminates in  a 43  m long  stilling  basin.  After the dissipation  of energy  in  the stilling basin  by  a hydraulic jump,  the flows over the spillway  will be conveyed  back  to  the river
28
Erer / Final Phase I Report /2008CECE and CES
through  an  outfall channel joining  the Humee stream,  a left bank  tributary  of the Erer River.  However,  there is limited  information  as to  the size of the spillway  chute,  i.e.  there are no  data on  chute bed  width,  depth  and  freeboard,  and  geological formation  along  the longitudinal profile of the chute.  Subsequent studies will focus on  ensuring  that the design fulfills the essential requirements of a good spillway.
b)  Field Assessment
Preparatory  review of reports and  drawings has been  supplemented  by  a ground reconnaissance of the Erer dam and  irrigation  project area.  The field  trip  was undertaken from 7  to  10  May  2008.  Visits were made to  the proposed  dam site,  appurtenant structure locations,  the irrigable area and  the dam catchment area.  The approach  was essentially  to consider the entire project area section  by  section.  Outline conclusions of the site visit findings relevant to  the appurtenance structures,  namely  the spillway  and  irrigation  outlet works, follow:-
•      The  severity  of  soil  erosion  in  the  Erer  River  catchment  has  been  observed.  In  the context  of  the  development  of  water  resources  for  irrigation,  the  principal  effects are  rapid  sedimentation  in  the  reservoir  and  the  introduction  of  high  silt  loads  into the irrigation area.
•     The field assessment also indicated that given that there are no catchment erosion 
curbing activities insight in the project area, protection measures in the Erer dam
catchment area will be unlikely to effectively mitigate the level of sedimentation 
in the reservoir for years to come.
•       For  this  reason,  the  overview  concluded  that  it  could  be  unrealistic  to  plan  the Erer   dam   irrigation   outlet   on   the   expectation   that   the   erosion   situation   could   be contained    or    improved    in    the    short    term.    Therefore    sufficient    dead    storage capacity    ought    to    be    provided    during    the    detail    design    based    on    reservoir sedimentation estimates.
•        Clearly    there    exists    a    significant    potential    for    improvement    of    the    erosion situation   both   by   engineering   practices   such   as   terracing,   bunding   and,   more importantly,     by     biological    control    methods    such    as    minimum    tillage    and alternative cropping patterns. Although the latter methods are being widely
29
Erer / Final Phase I Report /2008advocated  in  Ethiopia,  such  methods have yet to  be tested  for their appropriateness in  the local context However,  contour ploughing  is being practiced by local farmers in the area.
•      The  importance  of  accurate  topographic  maps  of  interest  areas  at  appropriate  scale need    not    be    overstated    in    gravity    irrigation    systems.    Observed    discrepancy between   plots   of   topographic   survey   coordinates   taken   at   the   location   of   Bench Marks  during  the  Feasibility  Study  of  the  project  and  actual  readings  taken  during the field assessment using a hand head GPS was very significant.
•      Visual  observation  of  the  project  Geologist  out  in  the  field  suggested  that  a  slight shift  of  the  spillway  centerline  towards  the  East  of  the  original  alignment  could ensure  the  downstream  toe  of  the  dam  to  be  open  for  inspection.  The  proposal  was prompted   by   seeming   proximity   of   the   spillway   terminal   structure   under   the existing   alignment   to   the   dam  toe   on   the   one   hand   and   the   need   to   keep   the downstream toe of the dam open for inspection at all times on the other.
•      The  feasibility  of  the  proposal  is  yet  to  be  tested  pending  availability  of  detail topographic  maps  of  the  area  to  learn  more  about  river  slope,  x-section  and  the proximity   of   the   discharge   outfall   to   the   dam   toe   and   the   potential   hazard   it presents   due   to   its   location.   Therefore   at   this   stage   the   proposal   could   not   be confirmed  nor  is  possible  to  quantify  the  risk  of  the  spillway  terminal  discharge backwater  encroachment  on  the  dam  toe  with  any  degree  of  certainty  and  whether it is at all a matter for concern.
•       However,   should   the   new   findings   justify   the   proposed   change   in   spillway alignment;  it  would  not  be  effected  with  out  consequences  The  new  route  would require  a  large  culvert  at  the  crossing  of  the  spillway  chute  and  Humee  stream channel,   spillway   chute   will   not   only   be   longer   but   it   would   entail   additional excavation.  Though,  the  orientation  of  the  spillway  chute  flow  will  be  more  direct to the Erer River downstream water course.
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2.5.2 Gaps Identified
All data and  information  required  to  the design  of the dam appurtenance structures is expected  to  be supplied  by  the relevant subject matter specialists.  Thus the presentation under this section  is not as such  a presentation  of identified  data gaps,  instead  it is essential data that need  to  be acquired  from the respective specialists in  the course of the project design phase.
For the irrigation  outlet,  topographic map  of the area,  dam layout and  sections,  subsurface geology,  reservoir capacity  curves,  results of reservoir sedimentation  studies,  results of reservoir simulations,  downstream water demand  (design  discharge) and  Primary  Canal dimensions and level etc shall be used as input for design
Similarly  for design  of the spillway,  topographic map  of the area,  results of reservoir simulations and  flood  routing,  spillway  crest length  and  design  flood  discharge,  reservoir capacity  curves,  flood  discharge channel capacity,  dam layout and  sections,  subsurface geology,  steepness of terrain  and  stability  of slopes,  etc are important data and information.
2.5.3    Measures to Fill Gaps Identified
The data enumerated above are expected to be furnished by the respective specialists. 
Hence this section does not present specific measures to fill data gaps separate from the
work of other specialists. At same time there is no desired to make changes in the
Consultant’s methodology and approach to the one given in the Technical proposal.
In the meantime it is agreed to proceed with the design based on available data and 
information in the Feasibility Study documents. Should there be any discrepancy between 
the findings of the present investigations and the one during the Feasibility study, the
design shall be accordingly adjusted as required by the new findings.
However,   accurate   representation   of   ground   features   of   a   project   area   can   not   be compromised in the design of gravity irrigation systems. Hence there is urgent need to
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reconcile   and   correct   the   anomalies   related   to   the   available   topographic   maps   once   and for all.
2.6 Geophysical and Geotechnical Investigations
As  per  the  investigation  made  at  the  feasibility  stage,  the  project  details  were  decided  to be as follows:
•      Option  -I,  the  U/S  most  site,  is  the  favorable  site  for  the  36.6m  high  proposed earth  dam  with  spillway  on  the  left  flank  and  canal  on  the  right  bank  of  the  Erer River.
•      The  earth  dam  is  provided  with  partial  key  trench  in  the  river  section  and  right flank,  and  partial  cut-off  on  the  left  flank  and  part  right  flank  where  the  thickness of   overburden   is   limited   to   10m   depth   considering   the   foundation   media   as impervious  to  semi-pervious  in  nature.  The  key  trench  and  cut-off  is  6m  wide  and 3m  deep  An  upstream  blanket  is  to  be  provided  for  a  length  of  160m  reducing  on the right flank.
•    The spillway located on the left abutment, is aligned in NE-SW direction close to
dam,  say  spilling  within  500m from the toe of dam.  It is proposed  to  be located  on rock.  The spillway  crest is at EL 1385  m with  sloping  chute and  an  exit structure at the down stream end in the Homee stream.
•       The  subsurface  geological  interpretations  are  based  on  geophysical  (VES)  surveys and   drilling   by   11   boreholes.   Accordingly,   the   depths   of   key   trench   and   cut-off are  proposed  in  the  river  section  and  on  both  side  of  the  flanks.  Curtain  grouting  is also   proposed   below   the   key   trench   and   cut-off   to   a   depth   of   10m   in   the foundation material, consisting of alluvial sediments.
•      Consolidation  grouting  is  proposed  in  the  foundation  of  spillway  structures  as  the foundation   rock   is   jointed   and   blocky  underneath  the  ungated  ogee  structure  and the chute.
•       Quantities   for   dam   fill   were   estimated   for   impervious   core,   shell,   filter,   rip-rap and rock-toe and their suitability assessed by laboratory' testing.
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The present study  reviews the Pre-Feasibility  Report (2004) and  the Feasibility  Report (2007),  conducts site visit and  summarizes the findings for undertaking  the detailed design  studies.  This study  recommends a pattern  of exploration  to  arrive at the selection of parameters for design  criteria of dam and  component features,  including  the Peak Ground  Acceleration  (PGA) of the project area in  consultation  with  the Earthquake department of Ethiopia.
2.6.1 Desk Work and Field Assessment
a) General
A  review  of  the  Feasibility  Stage  Report  (2007)  reveals  that  the  geological,  engineering geological   and   geotechnical   aspects   of   the   project   features-   mainly   the   site   selection, layout   and   details   of   component   features   are   primarily   based   on   regional   geological assessment  of  the  site  conditions  on  scale  of  1:50,000  and  smaller  scale  maps  generated from  the  satellite  imagery  and  aerial  photo  interpretations  with  limited  field  check.  This  is also   supported   with   minimal   geophysical   surveys   and   drilling   works.   This   study   covers reservoir area, sites for construction material, dam area and component features.
b) Geological and Geotechnical Study
The project area is occupied by old basement rocks comprising variants of granite-
gneisses, foliated mica gneisses, migmatite with granite intrusions and marble bands, in 
an one-end open bowl-shaped basin
The bedrock  is exposed  in  patches and  also  along  isolated  ridges The project area has undulatory  topography  where the Erer River flows in  a narrow section  within  wide valley profile.  Thick  alluvial deposits occupy  the Erer River section  and  the wide flanks.  The project area is in  the vicinity  of upper reaches where the Erer River valley  widens at the dam site with low bank heights.
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The  bedrock  at  this  site  is  dissected  by  major  geological  defects  as  shear  zones,  fracture zones,   faults,   lineaments,   pegmatite   and   quartz   veins   etc..   These   are   disposed   obliquely, across  and  along  the  river  section.  As  a  result,  these  features  cut  across  the  dam  axis  at three   places.   Major   trends   of   the   fracture   systems   are:   NE-SW,   N-S   to   NNW-SSE,ENE- WSW,   WNW-ESE   with   steep   to   near   vertical   dips.   Bedrock   foliation   is   in   NE-SW direction    with    a    general    north-westerly    dip    of    about    30-60    degrees.    Most    of    the geological   features   exist   beneath   a   thick   alluvial   soil   overburden   cover.   Any   geological defect  trending  across  the  river  flow  is  favorable  feature  where  as  those  along  the  flow  of the river is unfavorable feature.
The dam site has three distinct alluvial cover/ overburden deposits
•     A riverine alluvial deposit along Erer River comprising sand, gravel and 
subordinate silty-sand,
•     Flood plain of sand, silt and less of clay and
•     Older terrace of silty-sand.
This alluvial material may  be part of old  shifting  river course with  deeper valley  section along  the present course.  The geophysical survey  and  drilling  also  confirm this nature with  most of the alluvial sediments as dry  sand  within  lenses of silt/clay  on  top  underlain by loose, medium to coarse sand and gravel layers
c)  Dam Site
The 36.6m high  and  1.4km long  earth  dam is aligned  along  E-W direction  across the N-S flow of the Erer River course It will rest on  pervious foundation  material in  the river section  and  on  both  the flanks covering  a length  of about 1000m along  dam axis and  the remaining  portion  of 400m length  on  the left flank  and  right abutment will rest on  patchy / bouldery rock outcrops
The pervious material is alluvial in  nature,  unconsolidated,  loose,  erodible,  non-cohesive, and  largely  of granular character composed  of gravel,  pebble,  cobble,  sand  with subordinate silt and  clay.  These types of natural material cover the river section,  most of the right flank  and  50% of the left flank.  It is 30-35m deep  along  river section  and  10-
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Erer /Final Phase I Report /2008CECE and CES
15/20m deep  on  the flanks.  This information  is based  on  VES surveys,  borehole data and field  assessment..  Permeability  characteristics of the pervious material have to  be assessed  carefully  during  water tests in  the boreholes proposed  now and  in  the trial pits by  Falling  Head  or Rising  Head  method  as this pervious material forms the foundation  of proposed 36.6m high earth dam..
I
Apart from recording  the depth  of water level,  percent core recovery  and  RQD,  special emphasis be given  for recording  the zones of partial or complete loss of return  water.  The site engineer or local geologist or drilling  engineer may  observe these features during drilling  and  water percolation  tests,  and  brief my  colleague- Dr.  Asrat,  Geotechnical Engineer available locally for final confirmation.
The pre-feasibility studies proposed a positive cut-off below the earth dam considering 
the foundation material as pervious. The feasibility studies proposed a 6m wide and 3m
deep partial key trench with 160m length of U/S blanket and curtain grouting below the
key trench in the river section and right flank
In the prevailing site conditions and subject to the availability of additional water
percolation test data, an alternative proposal of a positive cut-off below the dam by 
providing a thin concrete diaphragm is a better solution for safety and stability of the dam
against excess water loss and expected internal erosion of the pervious alluvial material. 
Hence, a thorough review and or reconsideration is required keeping in view the overall
nature and thickness of alluvial sediments in the river section and flanks besides the
aspects of undependable alluvial grouting as proposed, below the key trench.
d)           Spillway
The spillway is located on the left flank near the abutment site. It is underlain by granite-
gneisses which are jointed and blocky. Sound foundation is available at the site below a
shallow depth of soil/weathered rock.
The  spillway  is  proposed  as  ogee-shaped,  un-gated  structure  with  chute  and  exit  structure at the D/S end in the Homee stream. The alignment is approx 500m long in NE—SW
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direction  and  the spillway  discharge will meet the Erer River at right angle to  its flow very  close to  the toe of dam-say  within  500m.  This feature will submerge the toe of Dam due to  back  water flow and  will not allow inspection  of the toe of dam for observing seepage flow conditions if any  through  the dam foundation  The unguarded  spill discharge will also  erode the river section  alluvium D/S of toe of dam thereby endangering the safety of the earth dam.
An  alternative spillway  is proposed  where the spill discharge will meet the Erer River along  its flow direction.  From hydraulic design  angle,  it may  be a better curvature for flow dynamics at the crest location.  The Homee stream if not obliterated,  may  flow underneath  the chute to  meet Erer River.  For verification  of flow dynamics,  a topo  map of the left flank  D/S of existing  spillway  location  may  have to  be extended  for a length  of 500m more i.e. the left flank survey done for a total length of 1000m D/S of dam site.
An  exploratory  pattern  is proposed  for identifying  bed  rock  profile and  for deciding  the slope of the chute and  exit structure for tying  with  rock  and  also  suggesting  the nature of consolidation  grouting,  if any  and  finalizing  the dimensions of the spillway  structures along flow direction.
e) Construction Material
The    feasibility    stage    investigations    have    identified    the    availability    of    construction material for the zoned sections of the proposed earth dam and have given the figure as
below.
• 
Impervious core
• 
Shell (semi- pervious to pervious)
• 
Filter (Med-Coarse sand)
• 
Rip-rap and Rock toe
1180 thousand m3
1950 thousand m3
144 thousand m3
197 thousand m3
For clayey  impervious core,  borrow area-3  is considered  suitable because of its non- dispersive and  lowly  plastic character.  For other types of material,  availability  and suitability are assessed as per required specifications.
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In the present study and site visit, it is noted that various types of required construction material are available in the vicinity of dam site. It is also recorded that the soils are generally admixture of one or two types of material e g. No pure clay is available at or near the dam site. It is admixture of silty-clay or clayey-silt or sandy-clay.
However, it can be used in the core of the proposed earth dam provided the material is non-dispersive,  low plastic,  compactable to  attain  the required  density  and  of low permeability in nature.
Three such types of sites are selected in the vicinity of Clay village in association with my colleague Dr Danel for testing of soil properties for which test pits and auger drilling are required at 2-3 places of each site i.e. trial pits and auger drilling are required to a depth 3-5m. Initially trial pits may be dug and if these do not progress beyond a depth of 3m, then auger drilling be taken up from the bottom of pits to continue up to a depth of 5m.
2.6,2  Gaps Identified
a)      The implications of the major geological defects like shear zones, fracture zones, lineaments, pegmatite, quartz veins etc., on the dam and component features are not known as these are not delineated and assessed at the site.
b)     The exact nature and thickness of the pervious material are yet not proved.
c)      The  bed  rock  profile  is  also  not  delineated  and  defined  Hence  stripping  limit, foundation levels and treatments are not decided.
d)      The  explorations  done  so  far  are  incomplete  and  do  not  precisely  present  sub surface geological picture of the site conditions
e)      Rock and soil properties require to tested as per specifications and directed by the site  conditions  eg.  Depthwise,  spacewise  and  specification  related  in  totality  for earth dam, spillway, construction material and canal structures.
f)      The peak ground acceleration (PGA) is not assessed properly in consultation with Earthquake  Department  of  Ethiopia  to  arrive  at  proper/rationalc  figure  of  PGA instead of range of 0 - 10 % g.
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Erer / Final Phase I Report /2008CECEandCES
2.6.3  Measures to Fill Gaps Identified
The significance of the site study  of the geological features would  be taken  up  after superimposition  of ail the geological features on  the latest topographic maps on  scale 111 000 for the dam area covering an area of 500m U/S and 1000m D/S of dam site and on scale 1:10,000 or 1:20,000 for reservoir area and construction material surveys.
The geological map  of Ethiopia on  scale 1:250,000  and  1:50,000  for the project area would  be required  for support and  cross verification  of the major geological setup. A pattern of exploration is proposed for working out subsurface geology and deciding upon the design parameters. These are outlined below
Exploration  pattern  and  Tests  for  Geotechnical  data  collection  shall  be  carried  out  as follows:
a) Dani
1) In Rock Section
•     One NX size borehole each on the right and left flank near the abutment to a sufficient depth in rock. To record depth of water level, percent core recovery, RQD and zones of partial or complete loss of return water
•    5-NX size bore holes along dam axis to a sufficient depth.
2) In Soil Section
Water percolation tests in alluvial soil be done in the boreholes as the proposed trial pits are shallow depth limited to 2-3m only. Drive NX casing every 5m or 3m section and 
conduct  water  test,  fix  Packer  at  the  bottom of  casing  and  test at  low  pressure  of 1 
A
kg/cm 2. Also use dug wells available in the vicinity of dam site and carry out pump out test to  record  recovery  rate and  then  find  out permeability  characteristics of the soil material. Help of Hydrogeologist may be taken if required.
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b)  Spillway
I) To drill lno NX size boreholes, and pits for foundation investigation along the exit structure.
c)  Construction Material
2-3 trial Pits to a depth of 3m each and then extending to depth of 5m by auger holes and collect samples for lab testing.
d)  Soil properties
To collect samples from trial pits and auger holes for testing of engineering properties as outlined below:
•    Natural water content
•    Atterburg limits
•    Sieve analysis for coarse and fine sediments
•    Specific gravity
•    Proctor tests
•    Triaxial shear test on unconsolidated undrained samples or direct shear test
•    Dispersive character
•    Swelling index/ Free swell
•    Permeability characteristics
•    Density of soil Material
•    Strength test-penetration and shear test
On the bases of results of the proposed subsurface explorations and engineering property tests, foundation grade geological and geotechnical maps and sections will be prepared for providing detailed design criteria
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2.7 Road Infrastructure
2.7.1 Desk Work and Field Assessment
In  regard  to  the  road  infrastructure,  the  current  assessment  considered  road  networks along;
a)  Primary canal length 14.11 km
b)  Two Secondary canals 6.8 Km and 9.53 Km
c)  Tertiary canals not well defined and
d)  In some cases considered quaternary canals not defined in the study clearly
The length of the roads provided for the tertiary and quaternary canals are not defined. However,  the interval between  these canals where road  have to  be provided  for each canal has been illustrated. The existing roads condition and functions were not assessed in terms of their use for the future as related to the project implementation.
One important issue identified on the feasibility study was that the road standards for the different services are not related  with  the existing  road  standard  of the country  In determining the class of the road, its function and volume of traffic expected shall be defined in order to come up with the economical standard of the road it serves. This also could determine the method of construction and maintenance of the road infrastructures in relation to its function.
Apart from the function of each category of road, social and economical importance of the areas under the project influence had to be addressed to meet the required project benefits and social impact due to the project execution.
The design  of road  infrastructure for Erer project will have the production  of specifications and bill of quantities. The road net work is expected to link operation and maintenance locations on the dam and irrigation infrastructure such as spillway, intake, outlet to main canal, etc. The other consideration is the social and economical importance of the project
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Ercr ! Final Phase I Report /2008CECE and CES
The Harar - Gijiga Trunk Road bisects the command area around at 19 to 20 km from Harar Town This road would be crossed by the primary canal at around 6 km from the dam site. From the Harar — Jijiga Road the project could be accessed up to the dam site by dry weather road. This earth road connects another all weather road from Harar to Erer Dodota Worcda At the junction the total length of the road is about 118 km. The Harar — Erer  Dodota  Woreda  is  10.3  km  which  was  constructed  recently  by  local  contractor financed  by  the  Hararei  State.  This  road  is  not  clearly  indicated  on  the  study  map prepared for the feasibility study.
At the beginning of June, field visit was made to assess the existing situation in respect of road  condition  and  accessibility  of the sites and  other facilities.  The team member observed that there is change of centerline of the Harar- Jijigar road at the location of the Erer Bridge. There is minor center line shift (about 10 meter) from the old bridge toward up stream where a new bridge is under construction during the visit. A change is also made on the final elevation of road surface which is lifted by about 2 to 3 meter than the old  one.  These changes in  location  and  elevation  of the road  will also  affect the first preliminary design of the primary canal crossing.
During the site visit the fill for the Erer Bridge is not yet done by the road contractor which may be rationally to locate the crossing of the primary canal and the provision of the opening  prior to  the completion  of the road  construction.  However this will totally depend  on  the final design  of the dam and  the primary  canal where there could  be changes to be incorporated.
The major point is the survey  of the command  area as related  to  the primary  canal location at the road crossing point which might have to be relocated to accomodate the change made by the road realignment. This also would affect the quantities of earthwork for the canal and the road construction for the irrigation scheme.
Erer /Final Phase I Ke port /2008
41CECEandCES
The length of the dry weather road connecting the dam site to the junction of Harar - Erer Dodota is about 11.9  km (as measured  with  car odometer) constructed  using  labour as major input for the construction The road is not surfaced but the alignment is found from fair to poor engineering practice. Some of the curves are unnecessary sharp and gradient are changed  frequently  in  order to  keep  the road  gradient at minimum The route in general follows the contour alignment where by  no  high  grade existed.  The sub  grade material of the road is sandy soil on which it was manageable to drive after few days of rain. The road has not any type of drainage structure. All natural streams and creks flow on top of the surface of the road without any protection.
The segment of the road from the trunk road to the dam site (about 6 km), may serve during  construction  period  to  access the different sites.  Apparently  the pattern  of settlement in the area is scattered and no significant importance of social and economical services centers were observed, other than the health clinic and nursery.
The Road  from the dam site to  the junction  of the Harar-Erer Dodota road  would  be under the reservoir area and it would need relocation.This part of the reservoir is densely populated  and  there exists a school which  would  be under the flooded  area of the reservoir. The road alignment on this part of the road is more curved and with several natural streams crossing the road. Some of the crossings are provided with tail-ford with construction of retaining walls at the down face of the crossings. However due to lack of maintenance some are found in poor condition and some are silted with sand.
The tail of the reservoir at some extent could reach the road from Harar to Erer Dodota Woreda road where the existing crossing of the Erer River might be either shifted to the up-stream or raised the deck elevation in order to be on the safer side. However, this should be determined once the final dam crest elevation is well defined. Since all pan of the road is under the reservoir, it is necessary to change the alignment in order to meet the demand  of the resettlement plan  (the resettlement plan  for the displaced  is not yet defined). The realignment of the road would be on the upper part of the reservoir, that
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Erer / Final Phase J Report /2008CECE and CES
would require side cut of the hills This should be determined with other alternatives once the dam design is completed
The existing access road in the project area at Km 18 from the Harar - Jijiga Trunk Road turns to the right part of the command area. The large portion of the command area is covered in this section of the road. The route of the road passes through flat terrain on sandy soil. This road is kept in well maintained manner and recently was graded that the surface is smooth without failure. Some spots of the road seem like black and this may be problematic during the wet season. However motorized traveling could also be managed easily after few hours of rain stoppage Along this stretch of the road major maintenance activities are taken by the Menschen fur Menschen (an NGO organization) that has been operating in the area for the last several years The NGO has a camp site at Km 11.3 and the road is frequently used by them apart from some commercial pickups
There are several fords (drifts) cross drainage structures provided  along  the road  and most of them are full of silt. During the visit, six of such structures were identified and in the opinion of the road engineer, there still could be some more which are already buried. Few pipe culverts are also installed but they are either fully or partially filled with silt. Two small bridges also give service on the road Due to the nature of the soil along the road high erosion protection measures have to be in place in order to keep the road and the farm from further deterioration
There are two villages served by this road, Beftu and Negeya villages, at Kms 4 1 and 8.3 respectively The existence of these villages has been the main reason for the road to be maintained  for the future use despite additional roads may  be needed  that would  be constructed for the canals operation and maintenance. At km 7.6 another road leads to Bisidimo town which also servers as alternate route connecting the area This road is more durable than that of the previous one and lightly surfaced, but some sections of the road need urgent maintenance due to the rolling nature of the terrain combined with the sandy  soil formation  which  is seriously  affected  by  erosion  on  the side drains that threatened the road formation
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One apparent case along the secondary canals (S2-P) that could be one of the biggest negative environmental impacts of the project is the canal passes through the Bisidimo Hospital. The alignment of the irrigation canal and the road traverse within the compound of the hospital was not addressed properly during the feasibility study.
The approach road to the spillway was not considered during the feasibility study. The structure is located on the other side of the command area and could not be part of the irrigation access road There are two alternatives to approach the spillway, one from the Harar — Jijiga Road crossing the new bridge and the other is around the reservoir on the Harar - Ercr Dodota road which would continue to Combolcha Village. This part of the proposal is not yet studied due to the rainy season which made it difficult to study the approach road.
2.7.2 Gaps Identified
As per the above discussions on the feasibility study and the site visit assessment made, some elements should need further attention and studies. Some may need the decision of the client. So far the followings are identified as gaps in order to proceed with the road design, preparation of specification and bill of quantities.
a)    The  realignment  of  the  Erer  Bridge  along  the  Harar  -  Jijiga  road  affects  the location and elevation of the scheme This should be revised in order to relocate the primary canal crossing the road and the invert elevation including the cross section of the canal. The opening size of the canal could also have impact in this regard.  The  effects  of  the  road  along  the  canal  also  need  junction  design  in connection with the trunk road The junction design could be on both sides of the major road.
b)  The route from the Harar - Jijiga Road to the dam site which is linked to the
Harar — Erer Dodota road serves the area under the command and reservoir areas at present. Due to the construction of the dam this road will no more be able to connect the areas under and near the reservoir areas. Alternate route is required to  connect the two  sites (i.e.  the upper and  lower part of the dam).  But the
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Erer /Final Phase 1 Report /2008
adjacent terrain to the dam site is very hilly and rocky that the construction of the road on this terrain would be very expensive. Hence alternate route should be proposed.
c)   Decision is required for the relocation of existing road (junction to the left from the Harar - Jijiga Road to the dam site) depend on the location of facilities to be provided  for  the operation  and  maintenance of  the irrigation scheme. Here the road serving the primary canal is located on the right side of the canal while the command area is on the left This part of the area could be served by the tertiary canals roads.
d)   Additional route may be needed to connect the spillway to the truck road that should  be  constructed  out  of  the  command  area  or  the  other  side  of  the  Erer River bank There are two alternatives, i.e. one directly from the Harar — Jijiga road  crossing  the  Erer  Bridge  and  the  other  is  through  the  Erer  Dodota  — Combolcha Road. The easiest and more feasible could be the first alternative due to  the  direct  route  for  emergency  cases.  The  feasibility  study  doesn’t  consider the issue.
e)   Conservation of soil as part of soil erosion control which would be caused due to the construction of several roads needs to be taken care of. This is expected at different parts of the command areas particularly where the gradient of the road alignment initiate such occurrence.
f)   Reconsideration on the negative impact of crossing the Bisidimo Hospital by the alignment of the secondary canal (S2-P) has to be judged prior to the final road alignment
g)   No data is available on the existing roads on the traffic volume to be considered for the design of the road alignment.
2.7.3 Measures to Fill Gaps Identified
The identified gaps presented above, require the following actions for the proceeding of the detail design works:
45CECE and CES
a)   Additional survey works required for the above items a, b, d and f to ascertain the conformity of the alternate routes proposed for the irrigation scheme.
b)   If necessary, traffic count shall be made in association with the economist of the team member of the consultant. This might be used to determine the volume and traffic at present and the impact of the development woks that generate additional requirements for each of the road segments.
c)   Measures on the erosion management of the soil due to runoff* water and the introduction of several roads must be made and to be incorporated in the project implementation.
2.8 Building Infrastructure and Service Centers
2.8.1 Gaps Identified
a) Lack of functional structure information on the program
It is very vague what kind of functions wanted by the client for the proper functioning of the project. The client has not provided any particular preferences concerning the project. Hence it is totally up to the designer to decide the kind of functions necessary for such projects
b)  Some of the building infrastructure Site still has to be properly surveyed-
The surveyed site only covers part of the area which was thought for water collection area and irrigation command area. Hence any other parts of the site outside these areas are not surveyed.  It brings us to  the notion  of surveying  a site outside the above mentioned areas which are going to be sites for building structures.
c)   Not clear whether both areas (irrigation and dam) need their own command Centers, or some functions for both.
The organization of the project is a bit vague, it is not very clear whether the whole project area is going to be administered from a single center or there are going to be two centers administrating the two different functions.
46
Erer / Final Phase 1 Report /2008CECEandCES
d)  Size of the administration and staff to be present on the site
It is still unclear how many people are going to be settling on the project site for the smooth  operation  of the project.  In  addition  the type of technical staff,  professional skilled manpower and additional requirements by the client haven’t been provided, which in turn created some vacancy on the program development
2.8.2  Measures to Fill Gaps Identified
Two  options are proposed  with  respect to  administration  of the project area.  The first option is having one major center with smaller center areas The advantage of this option is that the infrastructure intake to the main center would be easier and economical This option, however, entails running the whole project as one bundle, the second option is having  two  separate major centers for both  facilities This option  allows autonomy  for both facilities; however it will be economically unsound.
In addition a relatively flat site for easier construction has been identified as a place for the major center.  With  respect to  functional structure of the project,  the study  and analysis of other similar projects here in our country as well as outside gave us an insight to the idea of the functional structure of a typical dam and irrigation project. Hence a tentative design criteria program has been forwarded. However this design program shall be consulted  with  the client for further enrichment and  input from the client’s preferences.
2.9  Irrigation System and Structure
2.9.1 Desk Work and Field Assessment
Firstly  the Main  Feasibility  Report and  Sectoral Reports particularly  dealing  with Irrigation System, Irrigation Structures, Soils, Land Suitability, Agriculture Planning and Agronomy, Hydrology, Hydrogeology and Environment were gone through. In addition, Master Plan of Wabi-Shebele River Basin- Integrated Development Master Plan Study
Erer / Final Phase I Report /2008CECEandCES 
Project-  Pro-feasibility  Level  Studies  Volume  5-A  Erer  Irrigation  Scheme  has  been studied This was followed by three-day field trip of dam site and command area.
On field visit it was found that the agronomical potentials of the proposed command area are very high and soils are very suitable for irrigated agriculture On account of limitation of water availability the command area is proposed only on right side of Erer River while equally suitable areas are available on the left side. The availability of irrigation water is a limiting  factor otherwise the scope of the project could  have been  increased  by incorporating all the suitable areas situated on both banks of river.
Soils appear suitable for growing  majority  of crops though  most commonly  maize, groundnut and vegetables arc being grown. The land is suitable for orchards as good no. of mango trees exist in and around proposed command area. The depth of soil appears deep to very deep excepting at some local places where it is shallow due to the undulating topography.  The proposed  irrigable area on  the right bank  is surrounded  by  natural vegetation comprising of cacti, thorny bushes, shrubs and acacia trees. There is very little grazing area which is located beneath the natural vegetation and on steep slopes The existing shrubs and trees are used for browsing camels and goats.
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 and local ploughs and hand tools are used in cultivation
About 70.5 % command area is moderately to intensively cultivated and about 27.5 % area is occupied with natural vegetation. The balance about 2 % area is bare having rock out crops.
48
Erer / Final Phase I Report /2008CECEandCES
The land suitability of command area is studied on the basis of criteria prescribed by FAO and accordingly about 50 % area is identified is as highly suitable and about the same area is identified as marginally suitable.
The topography of proposed command area varies from flat to gently slopping. No major efforts will be required for leveling of land 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.
Medium texture soils are found to be situated in higher elevation areas which are either fluvisols or cambisols These are easy to manage and have good permeability and productivity. The soils mainly along riverbed are vertisols which are black to dark brown in colour. These soils have low permeability and expanding and cracking characteristics These types of soils will require special types of management and attention in regard to drainage.
2.9.2   Gaps Identified
The soil parameters have not been measured to analyze the structural safety of bed and banks of canal To fill in this gap following investigations are recommended:
a) Geotechnical Data for main canals
These are carried out with the following objectives:
•     To ascertain the stability of bed and bank material of canal
•     To evaluate water loss and consequent potentials of water logging
•     To select suitable type of lining based on characteristics of bed material, 
permeability, groundwater levels and salinity.
•     To design suitable foundation of canal structures,
•     To choose borrow areas for suitability of material to be used in canal embankments
and deciding suitable compaction procedures.
49
Erer/Final Phase 1 Report /2008CECEandCES 
2
The type and extent of survey should commensurate with the size and importance of project, size of canal and drainage structures. The canals and irrigation structures are of moderate size therefore geotechnical investigation proposed hereunder are of minimum quantity i.e. only necessary and sufficient In this situation small size exploration by trial pits and auger holes would be sufficient with field tests for permeability and penetration.
b) Requirement for Canal Designs
Trial Pits- For collecting soil samples for determining the engineering properties of canal and bank materials
(i)     Primary canals
Total length of Primary Canal is 14.40 km.
6 no. of trial pits @2000m c/c on main canals, pit size 2m  plan and depth 5.0 m.
(ii)   Secondary Canals
Total length of secondary canals is 16 5 km.
8 no of trial pits of 2m deep with minimum plan 1sq.m As per following:
3 no. on Sl-P @ 2000 m c/c
5 no. on S2-P @ 2000 m c/c
Soil samples for laboratory test
(i)     3 no. of 25kg weight carried in strong plastic bags from three trial pits of Primary canals
(ii)    3 no. of 2kg weight carried in strong plastic bags out of remaining three trial pits of Primary canals.
(iii)   4 no. of 2kg weight carried in strong plastic bags from two secondary canals, two from each.
Laboratory Tests
For - Naturai water content - 8 samples
•    Atterberg Limits - 8 samples
•    sieve analysis up to 0.75mm - 8 samples
•    sieve analysis for fines passing through 0.75mm sieve size - 8 samples ___________________________________________________________  50
Erer/ Final Phase I Report /2008
)CECEandCES
Erer / Final Phase I Report /2008
•    Specific gravity - 4 samples
•    Proctor test - 4 samples
•    Triaxial shear tests on unconsolidated undrained- 3 samples
Field Tests
Permeability Tests- For seepage characteristics and uplift pressure
(i)  4 no. of double ring permeability tests to be carried out at suitable uniform intervals if type of soil is the same in entire 14.4 km length of main canal. If the type of soils is different one permeability test may be carried out in each type of soil encountered en route.
(ii) 3 no. of double ring permeability tests in secondary canals
One no on Sl-P secondary canal preferably at mid length.
Two nos. on S2-P secondary canal at RD 3.0 km. and 6.0 km or where two dominant types of soils are encountered.
For Canal Structures
a.  Strength Tests
(i)  Penetration tests- For measuring resistance to penetration under stat and 
dynamic conditions at foundation level
(ii) Shear tests - In situ strength of cohesive soils which are two soft and too 
sensitive to sampling
b.   Density of foundation material - To determine status of compaction
Standard penetration tests and in situ density of foundation materials may be conducted at the following sites:
(i)  RD 14.4 km of Primary canal- proposed site of Head Regulators of off-taking Secondary canals
(ii) RD 5.5 Km of Primary canal between Q9-P and Q10-P Quaternary canals where a drain crosses the Primary canal- proposed site of Escape Structure
(iii) RD 0 91 km of Secondary canal-1- proposed site of Aqueduct where it is
proposed to cross Decho River
51CECEandCES
(iv)       RD 2.045 km of Secondary canal-2-proposed site of Aqueduct where it crosses Decho River
Topographical Data
(a) Strip Surveys
Besides densification  survey  of topographical map  of command  area ( scale 1:10,000),strip  surveys are required  to  be carried  out along  the alignments of Primary 
canal (14.4 km) and both Secondary canals (16.5 km). In the strip surveys cross sections may be observed at every 100 m extending up to 30 m from center line of canal on the both sides. The levels may be recorded at 10 m interval.
( b ) Grid surveys
There are five sites of important structures The location of four sites of structures namely Head  Regulators,  Escape and  Aqueducts are already  given  above The fifth  site is proposed  site of culvert at crossing  of Primary  Canal and  Harar- Jijga road  The grid surveys may  be carried  out in  an  area of 100  m X 100  m at sites of all structures excepting that of Escape with levels recorded at points of grid of 5 m X 5 m size. For Escape, however, 50 m X 50 m area will be sufficient.
(c) River Surveys
To protect the command area from spilling of flood flows in the river the cross sections of river are required at every 1000 m interval in the entire reach of river adjacent to the command area. The X-sections must extend up to 500 m on either side of center line of river and cover elevation up to 5 m plus existing flood marks if available at the site
Agronomical Data
(1) Rice is recommended in 10 % command in Meher seasoned and 12 % command in
Belg season needs to be replaced by other suitable crop/ crops as the cultivators do 
not have experience of growing rice crop.
52
Erer / Final Phase 1 Report /2008CECEandCES
(2) Sugarcane is proposed in 10 % area of command (350 ha) does not look reasonable as there is no sugar mill around the command area.
(3) 5 % area is proposed under haricot beans in Meher season and 3 % during Belg 
season but this crop is not considered in working out total water requirement.
On account of above the above the water requirement computations become subject
to revision by the Project Agronomist
Hydrological Data
On  having  gone through  the Sectoral Report on  Hydrology  it is found  that some hydrology  parameters are not available which  are required  to  be provided  by  Project Hydrologist. These are;
(a) Rainfall IDF Curves
(b) Routed Flood hydrograph for 50-year and 100-year flood for Erer River
(c) Flood hydrograph of lOOyr flood for Decho River at proposed aqueduct site
2.9.3  Measures to Fill Gaps Identified
The gaps identified  in  Topographical data may  be filled  in  by  special topographical surveys to be carried out by Chief Surveyor as per topographical design criteria This will take care of strip surveys, grid surveys and river surveys as mentioned above. Similarly gaps identified in hydrological data may be filled by Project Hydrologist.
In  regard  to  the inconsistencies observed  in  agronomical data the concurrence of the Client may  be obtained.  If the opinion  of the Client matches with  the one expressed above the matter may  be referred  to  Agronomist for affecting  necessary  changes in compulations of water requirement.
The geotechnical surveys mentioned  above are normally  carried  out by  Soil Scientist after the feasibility  stage and  before detailed  designs.  This is an  appropriate time to organize these surveys so that data become available for detail designs
53
Erer /Final Phase I Report /2008CECEandCES
Project Team of Erer Project has  no Agronomist and Soil Scientist in the list of its professionals. Therefore the services of these professionals may be arranged for these specific studies temporarily.
Erer / Final Phase 1 Report /2008CECEandCES
3. Out standing Issues
3.1 Ground Surveying Task
The Erer project do  not have the requisite benchmarks and  ground  survey  data as explained  in  section  3.2  of this report The feasibility  level surveying  task  has several limitations. In line with this, repeated efforts have been to collect the data from the client, to no effect. Thus, overhauling the survey work such as establishing sound benchmarks that are tied up with the national grid system, demands extra input than envisaged in the contract agreement.  Therefore,  unless these data are available,  and  not provided  to  us with in the month of June/2008, the consultants shall be obliged to carry out the ground survey work, which shall demand an extra 2.5 man-months.
3.2  Hydrological Survey
As discussed in section 3.1 of this report, there is a need for updating and getting Erer stream flow data at the Harar Jijiga road bridge The Hydrology Department has a river gauging station on Erer River at the bridge on the Harar-Jijiga road. Thus this facility could be used for collecting stream flow and sediment data as proposed below.
Hydrometric equipment condition:
Staff gauge-Yes, this might be required to reinstall
Bank Operated cable way - No
Automatic Water level record - No
As  there  is  no  bank  operated  cableway,  it  is  proposed  to  conduct  flow  and  sediment measurement using the bridge as platform.
Hydrometric measurement is done by the Hydrology Department staff and supervised by the project hydrologist.  Intensive measurement of flow and  sediment is recommended (Tables 3.1 and 3 2)
55
Erer /Final Phase 1 Report /2008CECE and CES
Table 3.1 Measurement Types Equipment and Frequency of Measurements
Measurement Type
Equipment
Objective
Frequency  of
Measurement
Measurement Taken
By
1
Water Level
Staff gauge
To          Measure River Stage
If there is no AWLR, every two hours
Hydrology Department
2
Discharge
Current meter + Balancing Weight + Bridge
To          Measure Velocity
See Note 1
Hydrology Department
3
Suspended Sediment Concentration Qs
Suspended  Sediment Sampler + Balancing Weight + Cable Way
To Measure Qs
Similar time as Discharge Measurement
Hydrology Department
Table 3.2 Frequency of Measurements
1
July
August
September
October - May 
(the Harar hydrology  branch may  conduct this assignment)
2
Water level
at 6,9,12, 15, 18 hour
at 6,9,12, 15,18 hour
at  6,9,12,  15,  18 hour
at 8 and at 18
3
Discharge
Once per day (possibly after rain)
Once  per  day  (possibly after rain)
Once per day (possibly  after rain)
Once per week
4
Suspended       Sediment Concentration Qs
Once per day (possibly after rain)
Once  per  day  (possibly after ram)
Once per day (possibly  after rain)
Once per week
1
Note 1
Dedicated hydrometric crew (one hydrometrist, one assistant and a driver) with a four wheel vehicle is required for the intensive measurements indicated. The crew will intensively work during rainy season (July/August and September). Camping facility may be required.
Note 2
Suspended sediment concentration from sample bottle is analyzed in the MoWR laboratory
It is preferable to the crew to be stationed near the Erer bridge (possibly at Babile town about 12km passing the station) and conduct measurements shottling from the town.
Erer / Final Phase I Report /2008
56CECEandCES
3.3 Re-locating the Harar -Erer Dodota Road
As was observed during the field trip and verified by the road infrastructure engineer the Harar-Erer dodota road (which is DS 6 standard road) will be submerged under the water of the reservoir for about 8km This road appears to be an important line linking towns such as Woldiaya and Erer dodQta to Ilarrar city, while it also serves as an alternative to the Harar-Babile road. The rc-location of the road is justified from the point of view of its exiting economic use and for its utilization to access the dam site. Thus, if the location is to be studied and designed, additional input of hydrological and road engineering study is required. The total additional input required will be 2.0 man-months.
Appendix I: Estimated inflow into Erer dam (WWDSE & WAPCOS, 2004)
Monthly 
flow MM
C
Table 3:
Ercr-I Da
m inflow
DRAINA
GE ARE
A 419 SQ
.KM
Year
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
1967
0.20
0.14
0.19
3.27
3.28
0.45
3.31
8.44
8.21
4.65
3.12
090
36 17
1968
0.14
0.32
0.49
12.07
10.43
0 95
18 31
23.04
4.85
1.58
1.03
0.68
73.87
1969
0.25
0.45
085
5.10
7.41
1.03
3.81
7.63
5.66
1.52
0.48
0.40
34.59
1970
0.20
0.17
0.46
5.97
5.56
0.54
323
10.13
7.77
2.98
0.72
0.45
38.19
1971
0 18
0.18
0 14
3.00
5 81
0 96
4 11
6.71
3.73
1.60
0 99
0.45
27.87
1972
0.17
0.24
0.37
826
6.45
0.62
3 86
7.19
4.79
1.71
0.70
0.35
34.70
1973
0.17
0.18
0.14
1.41
2.47
0.30
2.44
6.18
5.10
2.41
0.29
0.31
21.43
1974
0.14
0.16
034
5.77
2.38
0.78
3.04
8.03
7.37
0.90
0.32
0.28
29.52
1975
0.10
0 16
0.12
3.25
234
0.58
4.94
13.42
862
1.69
0 49
0.31
36.02
1976
0.14
0.13
0.19
3.26
5.92
0.50
3.30
7.82
4.75
0.71
1.54
0.57
28 84
1977
0.47
0.28
0.25
4.96
5.80
0.95
5.71
13 48
9.49
7.10
2 14
0.67
51.3!
1978
0.17
0.20
0.52
4.24
2.70
0.51
4.31
9.39
5.89
2.18
0.56
0.43
31.09
1979
0.50
0.20
0.41
5.20
6.26
0.82
2.78
4.75
4.12
1 48
0.57
0.38
27 47
1980
0.13
0.15
0.17
3.13
339
0.50
4 60
9.06
4.33
1.30
0 42
0.33
27.50
1981
0.13
0.13
0.35
7.91
3.49
0.40
2.03
10.05
8.98
1.54
0.48
0.36
35.85
1982
0.20
0.23
0.35
439
5.22
0.54
2.61
649
4.90
2.52
0.86
0.67
2899
1983
0.18
0.19
0.24
7.73
18.11
1.01
2.68
13.21
10.95
2.79
1.45
0.57
59.11
1984
0.14
0.13
0.19
291
2.54
0.90
3.55
5.26
475
0.67
0.52
0.40
21.97
1985
0.14
0.14
0.17
4.10
7.50
1.08
4.59
6.86
6.84
1.46
060
0.37
33.83
1986
0 13
0.25
022
4.92
5.70
1.02
3.88
7.19
6 53
2.04
0.55
0.38
32.81
1987
0.15
0.18
0.52
5 85
11.26
1.33
3.50
5.77
5.18
2.75
0.84
0.46
37.77
1988
0.20
0.23
0.21
4.06
3.21
0.74
3.91
10.49
7.77
3.36
0.57
0.37
35.13
1989
0.15
0.18
025
4.19
3.11
045
2.49
5.31
4.91
2.07
0 78
0.77
24.67
1990
0 17
036
0.69
8.40
5.61
0.57
2.69
7.90
4.53
1.10
0.58
0.37
32.99
1991
0.14
0.22
0.42
4.07
4 22
0.41
2.52
11.23
4.83
0.56
0.48
0.38
29.49
1992
0.27
0.26
0.31
684
6.37
0.99
4.30
12.49
7.49
2.97
1.15
0.59
•14.03
1993
0.25
0.27
0.30
4.23
10.47
1.47
5.35
10.70
4.76
3.05
0.83
0.44
42.13
1994
0.16
0.18
0.24
3.51
4.83
1.39
5.66
9.58
4.91
1.22
I 64
0.62
33.93
1995
0.14
0.16
0.33
10.04
5.72
051
2.82
8.67
5.3!
1.10
0.43
0.40
35.63
1996
0.30
0.15
0.40
6.26
8.82
1.79
5.25
7.87
4.91
1.45
0.59
0.38
38.16
1997
0.22
0.13
0.24
4.72
3.88
0.82
3.73
5.76
2.69
329
1.71
0.66
27.87
1998
0.36
0.22
0.36
4.82
16.63
1.19
3 78
7.73
7.15
4.79
092
0 44
48 39
1999
0.17
0.13
0.28
3.50
3.34
0.47
3.00
7.03
4.98
5.85
0.51
0.35
29.60
2000
0.13
0.13
0.17
3.81
4.49
0 43
2.82
7.95
4.08
3.60
1.91
0.86
30.38
mean
0.20         0.20          032           5.15         6.02         0.79         4.09         8.91          5.92          235           6.90         0.48          3533
(MMC)
S(MMC)  0.09        0.07         0.16         2.23         3.72         0.36         2.70         3.44          1.86          1.49          0.62         0.16         10.42 cv             0.46         036          0.50          0.43         0.62         0.45         0.66         0 39         0.32          0.63          0.68         0.34         0.29
57
Erer / Final Phase I Report /2008CECE and CES
Appendix II. Field Program of Hydrologic Measurements
Erer River at Bridge.
The Hydrology Department has a river gauging station on Erer River at the bridge on the Harar-Jijiga road
Hydrometric Equipment condition.
Staff gauge - Yes, this might be required to reinstall
Bank Operated Cable Way - No
Automatic Water level record - No
As there is no bank operated cableway, it is proposed to conduct flow and sediment measurement using the bridge as platform
Hydrometric measurement is done by the Hydrology Department staff and supervised by the project hydrologist Intensive measurement of flow and  sediment is recommended (Tables Al and A2).
It is preferable the crew be stationed near the Erer bridge (possibly at Babile town about 12 km passing the station) and conduct measurements shuttling from the town.
Erer / Final Phase 1 Report /2008
58CECE and CES
REFERENCES
1.   Feasibility Study of Erer Irrigation Project - Reports (Volume 1 to 12) - Errer Irrigation Projects - Scp.’O7 by WWDSE (Ethiopia) in association with Synergies Hydro (India) Pvt. Ltd
2.    LEK  (200)  Lahmeyer  International,  Electrowatt  Engineering,  Knight  Piesold Consulting,  August,  Feasibility  Study  of  Chemoga-Yeda  Stage  I  Hydropower project- Main report.
3.   WWDSE & WAPCOS (2004). Pre-feasibility study of Erer dam and irrigation project (Draft).
4.  “Theory and Design of Irrigation Structure” by Dr R.S Varshney, S.C Gupta and R.L Gupta,
5.   “Earth and Rock fill dams” by Bharat singh and H R Sharma
6.  “Irrigation Theory & Practice” by A M Micheal,
7.  Ethiopia Building Code Standards(EBCS-2) - Structural use of Concrete , 1995.
Erer /Final Phase 1 Report /2008
1KM Uil

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