FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA
MINISTRY OF WATER RESOURCES
LOWER DIDESSA MEDIUM HYDROPOWER PROJECT
RECONNAISSANCE STUDY
APPENDICES
VOLUME III
(FINAL)
Water Works Design and
Supervision Enterprise
P.O.Box 2561
Addis Ababa
August   2001
Addis AbabaVOLUME I        EXECUTIVE SUMMARY VOLUME II       MAIN REPORT
‘         r;' i-
VOLUME III
VOLUME IV DRAWINGSDiiesm Medium Scale Hydropower Project
Reconnaissance Level study June 2001
TABLE OF CONTENTS
APPENDIX-1
HYDROLOGY............................................................................................ 1
Appendix 1.1
objectives and Terms of reference...........................................................................1
Appendix 1.2
Flood Peak Factors...................................................................................................... 2
appendix 1.3
Summary Statistics of Meteorological variables.................................................. 4
Appendix 1.4
Regulation Curve.......................................................................................................... 5
appendix 1.5
Tail-Water Curve........................................................................................................... 6
Appendix 1.6
Monthly Flow at Dam Site.........................................................................................  8
Appendix 1.7
Assessment of the conditions of the gauging stations...................................... 10
Appendix 1.8
Trap Efficiency Curve................................................................................................ 12
APPENDIX-2
GEOLOGY................................................................................................ 13
Appendix2.1
TOR of Geological Study.......................................................................................... 13
Appendix 2.2
Figures........................................................................................................................... 13
APPENDIX - 3
PROJECT LAYOUT................................................................................. 14
Appendix 3.1
TOR For Engineering Study...................................................................................... 14
Appendix 3.2
Figures........................................................................................................................... 15
APPENDIX-4
ENVIRONMENT & SOCIO-ECONOMIC..................................................18
Appendix 4.1
TOR for Socio-Economics and Environmental Studies....................................... 18
Appendix 4.2
list of consulted Persons.........................................................................................19
appendix 4.3
Checklist for Initial Environmental Assessment of Hydropower projects .20
Appendix 4.4
Checklist applied for Socio-Economic Study........................................................ 22
Appendix 4.5
List of Main Plant Species in the Project Area.................................................... 23
Appendix 4.6
Threatened Endemic Plant Species in Combretum- Terminals Woodland......... 24
appendix 4.7A
leading Causes of morbidity in Kamashi Zone........................................................ 25
Appendix 4.7B
Leading Causes of morbidity in Kamashi Woreda...................................................25
APPENDIX 4.8
POTENTIALLY AFFECTED POPULATION AND LAND AREA BY THE DlDESSA HHP................... 26
Appendix 4.9      Water Quality Assessment........................................................................................ 27
APPENDIX-5      COST ESTIMATE.......................................................................................34
APPENDIX-6 ECONOMIC ANALYSIS................................................................................... 39
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APPENDIX -1            HYDROLOGY
APPENDIX 1.1    OBJECTIVES AND TERMS OF REFERENCE
The specific objectives of this study are:
I)         Assess the records of total flows for as many years as possible,
II)        Estimate average surface-water yields and flows depending on given statistical occurrences, and the low-flow characteristics,
III)       Assess the present water use in the basin both upstream and downstream of the proposed site,
iv)       Estimate flood magnitude and flood frequency for spillway design,
v)        Assess sediment transport, which affects the design of reservoirs, diversion works and supplies system regime.
The following are the TOR for the present study:
•    Review and synthesis existing hydro-meteorological data.
•    Assess requirements of additional weather recording and stream flow measurement stations.
•    Assess sediment load
•    Assessment of the present water use in the basin both upstream and downstream of the proposed sites
•    Estimate ultimate water potential for hydropower.
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APPENDIX 1.2 FLOOD PEAK FACTORS
The design of spillways  is  based on flood peaks  of some magnitude as  measured by the return period. Ideally  both the inflow flood hydrograph and the momentary  flood peak  are needed. However, most of the stream gauging stations  in Ethiopia are not equipped with the necessary  infrastructure to measure the river stage continuously, from which momentary flood peaks could have been estimated. In the absence of such information, a frequently  used practice for the estimation of momentary  flood peaks  is by adopting what is known as flood peak factor, which is nothing but a factor by which the maximum daily  mean flow is  multiplied. The value of this  peak  factor is  influenced essentially  by  the shape of the flood hydrograph, area of basin, frequency  of gauge reading, magnitude of flood, etc. For instance, for a small catchment, it is likely that the flood hydrograph could pass  the gauging station without being sampled at all, if gauge readings are made at an interval of a few hours. As a general rule, the flood peak factor approaches unity as the size of the basin gets larger and larger.
There are records of Momentary Flood Peaks in the Didessa Catchment for about 10 to 12 years  immediately  after the gauging stations  have been established. After this period, the hydrological record obtained from the Ministry  of Water Resources indicates only maximum mean daily flows. Hence, the estimation of the flood peak factor for the subsequent period of time has  relied on the values of the flood peak factor during the first 10 to 12 years since the beginning of gauging in the basins. Graphs of the ratios of MFP and maximum mean daily  discharge have been prepared for both gauging stations as shown in Figure 1.1.
Momentary Flood Peak/Maxlmum Mean DallyFlow (for didessa near Arjo)
Q.
U.
I
U-
o
S
s
■
1.4
1.2
1
08
0.6
0.4
O'    0.2
o--------------------------------- -- ---------------- - ---------------------
300 400 500 600 700 800 900 1000 1100 1200
Max. Mean Daily Discharge (cu.m Ja)
(a)
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Figure 1.1: Ratio of Momentary Flood Peak to Maximum Mean Daily Flow,
a) Didessa Near Arjo, b) Dabana near Abasina
It can be observe from Figurel .1, that the ratio is  clearly  a function of drainage area. The mean ratio for Didessa (Area = 9981 sq. km) is about 1.1 whereas that for Dabana (drainage area = 2881 sq. km) is  about 1.7. Moreover, whereas  the ratio for Dabana exhibited dependence on flow rate (r = -0.78), that for Didessa showed very  poor correlation (-0.15). Hence, an average value of 1.1 (solid line in Figurel.1a) has  been used for Didessa station to augment the momentary  flood peaks  based on the maximum mean daily flow. In the case of Dabana, however, a regression equation has been (solid line in Figure 1.1b) established between the ratio of momentary flood peaks and maximum mean daily flow and the same has been used.
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APPENDIX 1.3 SUMMARY STATISTICS OF METEOROLOGICAL VARIABLES Table 1.1: Summary statistics of relevant meteorological variables for Didessa
Mont
h
Temperature,
°C
Rel. Humidity
%
Mean
Speec
Wind
, m/s
Daily Sunshine Duration, h
Mean
Std.
Dev.
Mea
n
Std.
Dev.
Mea
n
Std.
Dev.
Mean
Std.
Dev.
Jan
22.0
1.43
59
12.51
0.85
0.17
8.6
0.40
Feb
22.8
1.30
59
8.10
0.89
0.19
8.3
0.91
Mar
23.8
0.96
73
15.65
0.86
0.28
7.2
0.61
Apr
23.5
1.08
62
16.19
0.83
0.25
7.7
0.55
May
22.2
0.84
80
11.41
0.88
0.23
6.4
1.04
Jun
20.5
1.18
90
3.19
0.9
0.18
5.2
0.72
Jul
19.6
1.01
91
3.04
0.87
0.16
4.0
1.03
Aug
19.7
0.68
91
4.59
0.87
0.14
4.3
0.77
Sep
19.8
0.51
88
9.03
0.83
0.16
5.5
0.79
Oct
20.6
0.48
80
9.83
0.79
0.21
6.5
0.52
Nov
20.8
0.50
71
10.79
0.72
0.17
8.2
0.51
Dec
20.8
0.68
64
10.90
0.84
0.18
8.1
0.57
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APPENDIX 1.4 REGULATION CURVE
The regulation curve is  a dimension-less  curve presenting the possible water yield, at some level of reliability, that could be obtained from a reservoir of a given storage capacity. The monthly  flow sequences  generated above together with monthly  mean evaporation values have been used to generate the regulation curve, which is shown in
Figure !.
-
2.  The  curve  has  been  generated  by  continuously  simulating  the  operation  of
the  reservoir.  A  simple  operation  rule  has  been  applied,  in  which  the  available  water  is always used for the intended project.
Regulation Curve. D ideas a Dam (MAR - 7290 MCM. MMR - 607 MCM)
Figure 1.2: Regulation Curve for Didessa Dam
In the figure, the horizontal axis refers to the possible yield as a fraction of the mean monthly flow (MMR), whereas the vertical axis represents the storage as a percentage of the mean annual flow (MAR).
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APPENDIX 1.5 TAIL-WATER CURVE
The tail water rating curve shows  the variation of water surface with flow rate in the stream. It has  been derived based on the river cross-section data obtained from the WWDSE. The slope of the river at the location of the proposed dam has  been read from the 1:50 000 scale topographic  map. The area and wetted perimeter have been computed for various  elevations  of assumed water surfaces. Manning's  uniform-flow formula has  been applied to compute the corresponding flow rate in the stream. It has to be emphasised here that the assumption of uniform flow is a very crude one but it is used here to give an approximate picture of the likely  water levels  at different flow rates. The tail-water-curve is presented in Figure 1.3.
Tail-Water Curve (Didessa)
Figure 1.3: Tail-Water-Curve at dam site (Didessa) The ordinates of the Tail-Water-Curve are given in Table 1.2.
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Table 1.2: Ordinates of Tail-Water-Curve
Water  Surface Elevation (m)
y(m)
Area (m )
2
P(m)
R(m)
Q (m’/s)
895.68
0.00
0.00
0.00
0.00
0.00
896.00
0.32
1.03
6.65
0.15
0.31
896.50
0.82
6.78
17.02
0.40
3.87
897.00
1.32
16.75
22.06
0.76
14.69
897.50
1.82
27.59
23.54
1.17
32.33
898.00
2.32
38.91
25.02
1.56
55.05
898.50
2.82
50.73
26.50
1.91
82.44
899.00
3.32
63.05
28.03
2.25
114.10
899.50
3.82
75.87
29.56
2.57
149.91
900.00
4.32
89.16
31.09
2.87
189.71
900.50
4.82
102.96
32.64
3.15
233.43
901.00
5.32
117.25
34.20
3.43
281.01
901.50
5.82
132.04
35.77
3.69
332.44
902.00
6.32
147.32
37.35
3.94
387.66
902.50
6.82
163.10
38.94
4.19
446.72
903.00
7.32
179.37
40.54
4.42
509.57
903.50
7.82
196.13
42.16
4.65
576.13
904.00
8.32
213.39
43.78
4.87
646.62
904.50
8.82
231.15
45.41
5.09
721.00
905.00
9.32
249.40
47.05
5.30
799.22
905.50
9.82
268.14
48.70
5.51
881.31
906.00
10.32
287.38
50.37
5.71
967.22
906.50
10.82
307.11
52.03
5.90
1057.30
907.00
11.32
327.34
53.71
6.09
1151.26
907.50
11.82
348.06
55.40
6.28
1249.19
908.00
12.32
369.27
57.09
6.47
1351.28
908.50
12.82
390.98
58.79
6.65
1457.47
909.00
13.32
413.19
60.50
6.83
1567.80
910.00
14.32
459.08
63.94
7.18
1800.99
911.00
15.32
506.95
67.41
7.52
2051.18
912.00
1632
556.80
70.90
7.85
2318.89
914.00
18.32
662.44
77.95
8.50
2907.90
916.00
20.32
775.98
85.09
9.12
3570.35
920.00
24.32
1026.81
99.54
10.32
5128.97
925.00
29.32
1384.85
117.91
11.74
7542.52
930.00
34.32
1792.34
136.50
13.13
10515.36
935.00
39.32
2249.29
155.25
14.49
14090.73
940.00
44.32
2755.68
174.11
15.83
18310.95
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APPENDIX 1.6 MONTHLY FLOW AT DAM SITE
YEAR
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
TOTAL
1960
217.9
6
115.1
9
93.77
68.30
98.54
225.9
1
1149.6
0
1943.8
8
2106.9
8
962.25
315.5
8
123.0
8
7421.05
1961
68.85
59.18
50.96
128.4
0
88.37
439.6
4
2185.1
7
3256.3
3
2973.4
3
778.66
553.3
4
121 6
4
10703.9
6
1962
109.3
4
58.57
55.88
46.38
90.64
331.8
2
1007.5
2
1553.4
6
2051.1
8
1585.4
7
184.1
5
105.2
5
7179.65
1963
74.20
38.15
34.86
81.18
24081
507.4
3
1097.2
4
2472.3
7
1798.2
2
588.76
293.4
2
276.9
3
7503.55
1964
155.2
9
74.15
48.69
72.97
101.05
359.5
8
1826.8
2
2303.0
5
2076.2
9
2488.0
4
325.8
9
134 8
9
9966.70
1965
104.0
4
49.99
31.92
90.09
53.71
273.2
2
1388.8
7
1803.6
8
1123.0
1
1700.9
9
496.2
3
257.9
8
7373.72
1966
130.7
5
116.6
2
108.28
133.3
9
114.21
234.5
4
1431.6
8
1878.9
4
2203 9
4
668.16
420.7
4
241.8
3
7683.07
1967
248.9
1
17.64
43.49
40.12
174.72
308.7
2
1152.3
0
2245.2
0
2120.8
9
2404.8
7
7396
8
333.5
3
9830.06
1968
169.3
2
99.81
42.14
163.6
2
211.17
467.1
2
899.91
2084.3
1
1305.5
3
535.58
228.6
6
117.9
2
6325.09
1969
97.19
88.79
123.13
75.68
131.52
543.4
5
1616.3
3
2575.8
3
1607.7
2
455.69
156.6
7
88.85
7560.85
1970
67.06
180.7
6
203 84
175.3
3
82 59
455.8
3
1572.9
4
2701.2
3
2348 2
0
1327.4
5
291.0
4
115.6
1
9521.86
1971
72.12
32.14
20.06
23.65
95.55
379.5
9
1386.4
6
2059.2
9
16060
9
1250 4
1
473.9
3
182.6
2
7581.92
1972
99.60
58.81
3847
66.67
105.68
197.5
9
1342.8
7
2185.8
0
1246.3
2
348.66
191.3
8
84.32
5966.19
1973
41.08
17.72
7.57
10.12
179.15
417.8
5
1070.3
4
3154.6
0
2485.6
5
1019.2
8
245.2
2
104.4
7
8753.06
1974
58.24
25.74
22.80
14.42
154.13
438.4
3
1105.0
0
2259.0
8
1958.6
2
401.84
194.8
8
78 34
6711.52
1975
38.81
34.71
18.22
10.54
17.60
82.30
305.90
1382.0
2
1283.7
9
752.14
248.0
7
145.5
0
4319.61
1976
77.48
60.39
39 15
162.6
0
172 64
313.9
9
545.61
1740 3
3
15952
2
731.85
451.1
2
322.4
4
6212.80
1977
107.7
0
41.24
2869
20.20
93.72
372.9
7
856.71
1575.0
6
1140.7
4
637.01
547.5
1
210.9
7
5632.53
1978
90.11
29.44
147.77
18.43
112.14
209.9
1
779.09
1999.8
0
2490.5
0
1675.3
4
577.1
3
394.8
5
6724.68
1979
324.0
8
214.7
7
162.04
42.46
81.24
229.8
3
951.59
1468.2
7
1088.5
3
442.19
154.3
8
70.39
5229.76
1980
28.44
24.22
15.81
110.2
5
316.99
863.9
8
15956
5
2266.7
0
2196.3
3
672.02
168.2
9
150.2
7
8408.94
1981
129.5
4
69.46
69.28
56.41
86.15
85.47
577.28
2047.0
5
1769.2
0
1081.8
6
378.1
9
197.6
2
6547.51
1982
96.28
48.07
45.56
30.61
73.43
416.8
7
1224.4
7
1657.0
7
1198.2
7
1323.2
0
292.6
7
153.8
4
6560.34
1983
69.38
50.47
54.38
37.04
84.71
253.3
0
973.63
2004.2
8
1961.8
8
2206.7
7
443.7
0
198.5
3
8338.07
1984
105.2
0
51.78
40.50
34.01
80.71
442.1
1
1632.1
9
1544.5
4
1211.3
3
318.10
357.4
3
214.3
5
6032.24
1985
40.79
22.56
14.80
40.22
160.40
406.2
8
1068.5
5
2176.9
8
1951.5
3
613.87
199.8
3
120.4
3
6816.23
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All values are in million cubic meters.
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APPENDIX 1.7 ASSESSMENT OF THE CONDITIONS OF THE GAUGING
STATIONS
As  part of the Abay  master plan study, visits  were made to a number of hydrometric stations  in the Blue Nile basin, to which the Didessa sub-basin belongs. Moreover, some of the stations used in the present study have also been visited by the consultant from March 14 to March 16, 2001. Findings  of both visits  to the gauging stations  used in the present study are given below.
Didessa near Arjo: with a catchment area of about 10000 sq. km, this  station is  the most important of all stations  within the Didessa basin. The station is  located just upstream of the Bridge on the road from Nekempte to Bedelle. Measurement of streamflow began at this  station in 1960. However, collection of data was  interrupted in 1987. The collection of data has  been resumed since 1993. The location and condition of this  station has  been found good in the previous  visit. Major recommendations  of earlier visits  in 1995 pertain to the rehabilitation of the staff gauges, and the maintenance of the river bank  so that the bridge and the structure supporting the overhead cable way remain stable.
The station was  visited on March 14, 2001. The staff gauges  are in good condition. An observer takes  measurement in the morning and in the evening. The Automatic  Water level Recorder is  not functional and it is  accessible only  during the dry  season. The Overhead Cable Way  (OCW) is  in good condition. However, the foundation of the right support to the OCW under threat. A small water course just by  the side of the support carrying seasonal runoff has  eroded the overburden soil and exposed one of the footings. It appears  that no rehabilitation work  has  been done since the previous  visits in 1995. This  can easily  be rehabilitated if the seasonal flow is  diverted away  from the support.
Dabana near Abasina: this  station has  been established in 1960. It has  a catchment area of about 2900 sq. km. The measuring equipment consisted of a sectional staff gauge, a water-level recorder, and an overhead cable way. At the time of the field visit conducted in August 1995 as  part of the Abay  Basin Master Plan Study, there was  no observer to record the river stage.
This  station was  visited on March 15, 2001. This  time an observer, who lives  nearby, makes  the reading from the staff gauges  twice daily. The Overhead Cable Way including its  supports  is  in good condition. However, the third element of the sectional staff gauge is  in bad condition. The staff gauge lies  below the surrounding ground level and has  rusted throughout its  height. The observer has  dug a trench so that water can easily  reach the staff gauge when it is  above the highest reading of the 2nd element However, this is not satisfactory and the staff gauge should be relocated.
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Upper Didessa near Dembi: this station is located near Dembi town at the bridge on the road from Jimma to Arjo and Nekemte. The stations measures flow that comes from an area of about 1800 sq. km. It has been found in the previous visits, in August 1995, that the station is  the only  one functioning properly. The location of the gauging station is very  good with stable section and a smooth flow. This  station has  not been visited by the consultant.
Tato near Gude: the gauging station on the Tato river lies just downstream of the bridge on the Addis  to Nekempte road. The station was  visited on March 17, 2001. The measuring system consists  of a staff gauge and a Bank  Operated Cableway  (BOC), which are all in good conditions. Water is  diverted upstream of the bridge for a small scale irrigation. The diverted flow at the time of the visit was estimated to be about 10 to 15 l/s.
Upper Dabana near Bedele: this station is located about 8 km from Bedele town on the road to Metu. It has  been found out that the catchment area draining to the station is not 47 sq. km, as  has  been reported by  the Hydrology  Department of the Ministry  of Water Resources, rather it is 470 sq. km. The channel is straight and fairly stable. High flows, above a river stage of 4 m, cause over flooding of the river banks. In such situations, flow is  measured from the bridge. Moreover, the station is  located at good place in the catchment and hence its  continued operation has  been recommended. This station has not been visited by the consultant.
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APPENDIX 1.8 TRAP EFFICIENCY CURVE
< ><njcii\-inline ratm:(CnpAcity/Vo)ume of annual iuflou)
Fiaure 1.4 : Reservoir Trap Efficiency
Waiter Work Deiijn & Si^crvbkH EHtcijirise
12Dlddessn Medium scale Hydropower Project
Reconnaissance Level Study
June 2001
APPENDIX 2.1 TOR OF GEOLOGICAL STUDY
APPENDIX - 2 GEOLOGY
Geology and Geo-Technique
Make surface reconnaissance to enable inferences  to be made of i.e. depth of alluviums, tectonic  features, availability  of construction materials, previous  formation and slope stability at dam sites and reservoir areas, waterways and powerhouse.
Preliminary  geology  and  geotechnical  investigation  of  the  dam  sites  and  other  major structures.
APPENDIX 2.2 FIGURES
Figure 2.1Geological map of the Didessa area
Figure      2.2Geological      Section      along      the      dam      axis      (Didessa) Figure 2.3.' Seismic map of Ethiopia
water WoHu Design & Supervision Enterprise
13FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA
MINSTRY OF WATER RESOURCE
OEOLOSI CAL CROSS SECTION ALONS
THE QAM AXIS (DEDESSA DAM)
CffM IT
DAT Al TOPOOSAPHIC SURVEY
CHKD. 1 MX
vm 1 WOCMIA.
DATE:-
Auf./2OQt
■MX
DM Na.
WATER WORKS DESIGN AND SUPERVISION ENTERPRISEMAJOR TECTONIC FEATURES
LOCATION OF VOLCANIC CENTRES
<
FIGURE 2.3-6
FIGURE 2.3-7
To*
?5r              “I
FIGURE 2.3-5
1 ACCELERATION CONTOHSC/.9) WITH 100 YEAR RETURN PERM 4.A PRD6A3LITY OF 001 PER OF | BENG EXCEEDED (DATE BA2»75-W7M'
O CAPITAL CITES
-    ACCELERAUOI2   lO’/.g    !
-ACCELERATION 5%a. .
i
KENYA
PREDICTED GROUND ACCELARAT10N
ATTENUATION CURVES
INFORMATION SOURCES
PIERRE GOUIN (1976)
SEISMIC ZONING IN ETHIOPIA
BULLETIN   OF   THE   GEOPHISICAL   OBSERVATORY   OF AAU, ETHIOPIA, N® 17, PP 4 6
-------- (1979)
EARTHQAKE HISTORY OF ETHIOPIA AND THE HORN OF AFRICA
IDRC, OTTAWA, CANADA , PP 250
kbit
DIDESA HYDROPOWER PROJECT
^SEISMICITY OF ETHIOPIA '
DRAWN by
CHECKED BY
DATE
SCALE
approved BY
Fig. 2.3
WATER WORKS DE SING I STFERYTSION EKTRP.Dtddessa Medium scale Hydropower Project
Reconnaissance Level Study June 2001
APPENDIX-3             PROJECT LAYOUT
Appendix 3.1 TOR For Engineering Study
The Objective of the engineering studies in hydropower projects ls:-
•    Identify potential hydropower dam sites for different dam types
•    Make a general investigation of the potential storage reservoirs
•    Give estimates of reservoir characteristics (such as reservoir volume, dam &
other structures)
•    Give estimates of the economic benefits from the reservoir creation (such as,
annual energy production)
•    Propose a site ranking in order to select priority for pre-feasibility studies.
•    To provide preliminary cost figures
Methodology
•    Site visit and collection of existing data
•    Relevant previous study reports on the specific areas
•    Topographical maps (mainly the existing EMA 1:50,000 scale maps)
•    Aerial photographs
•    Access roads maps (in order to study the site accessibility)
•    Contract documents for similar projects
•    site visit to get preliminary knowledge
•    Preliminary analysis and design
•    An initial analysis of the collected documents
•    An initial analysis of the dam site and reservoir area for each site selected on the
maps
•    Analysis of electrical systems studies in the context of interconnected system
•    Power studies and analysis will be co-ordinated with other parts of the
investigation.
Based  on  topographic,  hydrologic,  geologic  and  other  studies,  preliminary  design  of  the following hydraulic structures will be conducted:-
•    Regulation work
•    Dam & intakes
•    Waterway
•    Powerhouse
•    And main part of hydro-mechanical, electromechanical equipment selection
•    Preparation of engineering plans
•    General layout of the sites
•    Dam site cross-section
•    The reservoir area
•    Typical dam cross-section
•    Typical dam cross-section of tribune
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APPENDIX 3.2 Figures
Reservoir Capacity curve
(a)
Reservoir Area curve
(b)
Figure 3.1a & 3.1b Didessa Reservoir Capacity & Area Curve
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Reservoier Optimaztion curve
Marginal cost or benefit MUSD
Figure 3.2 Reservoir Optimization Curve
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Power tunnel Optimization curve
Figure 3.3 Pressure Shaft Optimization Curve
Figure 3.4
Figure 3.3 & 3.4 Power Tunnel/Shaft Optimization curve water Work Desfjn & SiyerMwi Enterprise
17DiSessa Midlnut Scale Hydropower Project
APPENDIX-4 ENVIRONMENT & SOCIO-ECONOMIC
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APPENDIX 4.1    TOR FOR SOCIO-ECONOMICS AND ENVIRONMENTAL STUDIES
The  main  objectives  of  these  studies  are  to  identify  the  main  socio-economic  and environmental impacts of proposed plans and projects thereby:
•    preliminary quantification of agricultural land loss, if any
•    preliminary quantification of the number of families or persons to be resettled, if any and make a general proposal for their integration,
•    evaluation of the inhabitants’ perception towards the project,
•    identifying main environmental issues of importance to all interested parties so that these concerns can be addressed in the assessment,
•    providing qualitative environmental information so that potential impacts can be avoided,
•    identifying management measures to avoid or reduce negative impacts, and
•    identifying the most important environmental components.
•    To achieve these objectives, the Consultant will place emphasis on:
•    reliable field data of the background environment;
•    reliable assessment of environmental and population disturbances likely to result from the proposed projects;
•    relationships between environmental components and resources and the predicted impacts;
•    consideration of impacts on all targets i.e. including plants and animals considered sensitive or critical;
•    reliance on the judgment of local people and knowledgeable officials/professionals.
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18Diddessa Medium Scale Hydropower Project
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APPENDIX 4.2 LIST OF CONSULTED PERSONS
1. Ato Telila Amentie, Vice Chairman, Kamashi Zone Council Office.
2.   " Tagie Dano , Head, economy & social sector, Kamashi Zone Council Office.
3.   “ Gobena Shaka, Chairman, Kamashi Woreda Council Office.
4.   ’ Chaka Buba, Vice Chairman Kamashi Woreda Council Office.
5.   ' Elias Assefa, Development Agent, Kamashi Woreda.
6.   “ Kiltu Ayana , Staff, Kamashi Woreda council Office.
7.   " Girma Tesso, Key Informant, Shimela village, Kamashi Woreda.
8.   " Mendi Gemechu, Vice Chairman, Hena Dugda Gibe PA, Kamashi Woreda.
9." Gelaye Dinega, Head, Economic Dev. & Social Services Office, Kamashi Woreda.
10. "Ahmed Mohamed, Rep., Economic Sector, Economic Dev. & Social Services Office.
11. " Shewel Tessema, Rep., Health Sector, Economic Dev. & Social S. Office, Kamashi W.
12. ” Tegegn Abebe, Rep.,Education Sector, Economic Dev. & Social S. Office, Kamashi W.
13.  “ Woyessa Bagessa, Key Informant, Deguba Badessa PA, Kamashi Woreda.
14.  “ Habib Mohammed, Head, Agriculture Dev't Department, Kamashi Zone.
15.  “ Yemane Dirirsa, Chairman, Bello Jiganfay Woreda Council, Kamashi Zone.
16.  “ Tessema Yenido.Vice Chairman, Bello Jiganfay Woreda Council, Kamashi Zone.
17.  " Abebe Bargo, Member of Executive Comm., Bello Didessa PA, Bello Jiganfay Woreda. 18. “ Abiyu Zegeye, Head, Economic Dev. & Social Services Office, Bello Jiganfay Woreda.
16." Tadelle Demte, Health Coordinator, Economic Dev. & Social S. Office, Bello Jiganfay. 19. “ Mesfin Nigatu, Development Agent, Bello Disessa & Bello Didiga PAs, Bello Jiganfay.
20.   “ Biruk Tamirat, Development Agent, Dimtu PA, Bello Jiganfay Woreda. 21.   “ Solomon Wakijira, Development Agent, Sayi Dalecha PA, Bello Jiganfay 
Woreda.
22 “ Teferi Duhie, Key Inbformant, Kutamuri Village, Dimtu PA, Bello Jiganfay Woreda.
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APPENDIX 4.3 CHECKLIST FOR INITIAL ENVIRONMENTAL ASSESSMENT OF HYDROPOWER PROJECTS
1.        Will the project affect areas important for settlement or utilization of natural resources?
What type of areas (existing land use, types of vegetation etc.) will submerged?
How many people will have to be moved because of inundation or other physical encroachments which destroy settlement areas or areas of importance for
production activities?
Will the establishment of a reservoir create possibilities  for other forms  of utilization of the water resource, e.g. fishing, irrigation, water supply, recreation, tourism, etc?
2.        Will the project affect areas with animal or plant life worthy of protection?
Will inundation, altered water flow level harm important habitats or vital functions 
for conservation - worthy animal or plant life?
Will the dam, roads or power lines create barriers for wildlife?
3.        Will the project affect areas which contain conservation-worthy cultural
relics, landscape etc?
Will  cultural  relics  of  importance  for  the  local  population’s  cultural  activities  be submerged or affected by other construction work?
Will  physical  encroachments  affect  especially  beautiful  or  unique  sections  of  the watercourse or drastically change the water flow?
Will traditional paths or crossings used by the local community submerged?
4.        Will the project change the water flow or other hydrological features?
Will  the  project  increase  or  decrease  the  risk  of  flood  damage  as  compared  to the present situation?
Can one expect a reduction of the total water flow due to increased evaporation?
Is there a risk of a permanent or periodical reduction of the water quality due to reduced water flow and consequently increased concentration of pollution?
Is there a risk of particular pollution problems during the construction period as a consequence of tunneling, digging, etc?
5.        Will the project change the risk of spreading diseases?
Will the establishment of a reservoir or changed water flow in a regulated
watercourse change the conditions of life for disease spreading organisms?
Will the project lead to a population concentration, which increase the risk of
infection?
6.        Will the project increase erosion?
Is  there a risk  that an increased concentration of nutrients  in the watercourse can result in uncontrolled eutrophication and unwanted aqua-vegetation in the reservoir?
7.        Will the project change the nutrient and sediment transport?
Are there valuable species  of fish in the watercourse dependent on migration for nourishment or spawning? To what extent will technical installations  or regulations obstruct migration and/or spawning?
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8.        Will the project change the way of life of the local population?
Will traditional and well-adjusted ways  of life be endangered because of changes in natural environment, changes  in production or influence from new population groups?
Will any potential socio-cultural impacts of the project affecting certain groups?
9.        Will the project influence the utilization of other natural resources?
Will the establishment of a reservoir or connected activities  force other activities (agriculture, animal husbandry  etc) to locate in other areas  that are more ecologically vulnerable?
Is   the   natural   resource   base   sufficiently   suited   and   stable   to   receive   an increased population? WII the ecologically carrying capacity be threatened?
WII  the  construction  work  and  any  new  activities  place  demands  on  water  and fuel wood in areas where these resources are limited?
Will increased accessibility  due to development of infrastructure lead to the establishment of new activities  like agriculture, forestry, industry, etc.? To what extent will these activities affect the environment?
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APPENDIX 4.4 CHECKLIST APPLIED FOR SOCIO-ECONOMIC STUDY
1. Total Population and Households by Sex at PA level Village levels
2.  Major crops, yield/ha by crop type, price/Qt by crop type
3.  Average land holding/HH (at PA level)
4.  Land use Pattern at PA & Village levels
•    cultivated
•    cultivable
•    grazing
•    forest
•    unproductive
•    others
5.  Livestock, size at PA & village levels
6.  Crossing points at villages level
7.  Beehives
8. Fishing
9. Distance of each village from the nearest river
10.  Settlement history and settlement pattern of each village
11. No. of houses and types which would be affected
12. Estimated cost of the thatched and corrugated houses.
13.  No. of families that would be victims
14. Schools, clinics, religious institutions
15. Ethnic/religion
16. Forms of livelihood
17. Major development constraints
18.  Tree species
19. Wildlife
20. Mining sites.
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APPENDIX 4.5 LIST OF MAIN PLANT SPECIES IN THE PROJECT AREA
No.
Scientific Name
Local Name
Type
Gumuzigne
Oromifa
1
Manilkara butugi
Butugi
Tree
Riverine
2
Dijaja
Qaso
It
3
Miwa
Miroro
•1
Dominant
4
Cordia africana
Banja
Wodessa
n
5
Syzygium guineense SSP. guineense
Drwiye
Badessa
N
Riverine
6
Syzygium guineense SSP. ?
Shawaa
Gosu
N
7
Croton macrostachys
Bakanisa
n
8
Entada sp. (E. ?africana)
Bedanjewa
Hambalta
9
Tonkola
Chamo
•a
10
Quni
II
11
Berchemia discolor
Jejjeba
12
Qolati
13
Tamarindus indica
Dogu'a
Roqa
N
14
Aningeria sp.
Ejiwagana
Kararo
15
Celtis sp.
Saga
Moko
*
16
Ficus sp.
Hecha
Harbu
N
17
Dhangala
Dhangala
If
18
Carisa edulis
Suha
Hagamsa
Shrub
19
Hypichariwa
Anduguya
20
Lannea schimperi
Hedanba
Daraku
Tree
Major
21
Andadha
Akuku
22
Albizia sp.
Tihoka
Muke
n
23
Lonchocarpus laxiflofus
Atawiye
Qangasha
ft
Major
24
Kota
Gambelo
•f
25
Tsegede’a
Beqale
Shrub
27
Oxytenanlhera abyssinica
Hinta
Shmela
Bamboo
Dominant
28
Slereospermum Kunthianum
Bewa/Andigila
Botoro
Tree
Major
29
Combretum collin urn
Hafa
Dhadhensa
II
Dominant
30
Combretum sp.
Hata wiya
Atawiya
II
Major
31
C. molle
Rukensa
•1
Dominant
32
Terminalia brownii
Bogawa
Dabaka
Major
33
Terminalia sp.
Bogawa
Warake
Dominant
34
Grewia bicolor
Gadiya
haroressa
Shrub/S.
Tree
Major
35
Piliostigma thonningii
Wag a
Lilu
Tree
Major
36
Piliostigma sp.
Bambuta
Barbute
at
37
Ficus sp.
Echa
Oda/Harbu
M
38
Sigda
Amera
H
39
Qoqora
Qoqora
40
Maytensu sp.
Tesha
Bambda/ Kombolbish
e
S. Tree
41
Pro tea sp.
Hededewa
Yubdo
M
42
Dichrostachys sp.
Jirme
Shrub
43
Ximenia americana
Some
Hud ha
•i
M
44
Bewa
Urgo
45
Hyparrhenta sp.
Tree
Grass
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APPENDIX4.6    THREATENED    ENDEMIC    PLANT    SPECIES    IN    COMBRETUM- TERMINALS WOODLAND
Geographical Areas: BA = Bale; EW = GD = Gonder; GJ = Gojam; GG = Gamo Gofa; IL = llubabor; KF = Keffa; WG = Wollega; WU = Wello Upland; TU = Tigray Upland; HA = Hararge; SD = Sidamo; SU = Shewa Upland.
Status: E = endangered; Ex = extinct; R = rare; V = vulnerable.
No.
Species Nae
Family
Distribution
Status
Type
1
Boswellia pirottae chiov.
Burseraceae
GD   GJ   WU   SU   KF;   1200- 1800m
R
Tree
2
Crotalaria fallax Chiov.
Fabaceae
SD; ca. 1500m
E
Herb
3
Cussonia ostinii Chiov.
Araliaceae
GD GJ WG KF; 1500-2100m
R
Small tree
4
Cuyphostemma              pannosum Vollesen
Vitaceae
WG ILGG; 1500-2000m
R
Pyrophyte
5
Eriosema tuberosum A. Rich.
Fabaceae
TU GD; ca. 1500m
E
Pyrophyte
6
Erythrina burana Chiov.
Fabaceae
HA; 1350-2100m
Tree
7
Euphorbia bittataensis M. Gillbert
Euphorbiaceae
SD; ca. 1600m
E
Succulent shrub
E. furcatifolia M. Gilbert
Euphorbiaceae
SD; ca. 1600m
E
Suffrutescent
9
E. sareciana M Gilbert
Euphorbiaceae
BA; ca. 1500m
E
Herb
10
Ficus ruspolii Warb.
Moraceae
KF SD; ca. 1800m
E
Shrub/small tree
11
Indigofera mooneyi Thulin
Fabaceae
WG SU KF SD; 1000-2000m
R
Herb
12
Pentas tenuis erdc.
Rubiaceae
WG BA KF SD; 1300-2000m
R
Shrub
13
Phyllanthus dewildiorum M. Gilbert
Euphorbiaceae
WG KF; 1400-1800m
V
Suffrutescent
14
Rhynchosia splendens Schweinf.
Fabaceae
GD; ca. 1000m
E or Ex
Sub-shrub
15
R. stipulosa A. Rich
Fabaceae
TU WG GG; 000-1800m
R
Climber
16
Tephrosia fuivinervis Hochst. Ex A. Rich.
Fabaceae
TUGD SU; 1100-1700m
R
Herb
17
Tragia abortiva M. Gilbert
Euphorbiaceae
GG; 1550-1800m
V
Climbing shrub
18
T. crenata M. Gilbert
Euphorbiaceae
BA; ca. 1300m
E
Twining shrub
19
T. triumfettoides M. Gilbert
Euphorbiaceae
SD; 1900-1950m
E
Twining herb
20
T. uncinata M. Gilbert
Euphorbiace
ae
WG; not recorded
E
Woody
climber
Source:       Ensermu K., At Al (1992). Some Threatened Endemic Plants Of Ethiopia.
Botany 2000: East And Central Africa. Napreca Monograph 2:                                      35-52.
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APPENDIX 4.7A LEADING CAUSES OF MORBIDITY IN KAMASHI ZONE
(as recorded by Kamashi Health Center and Clinics in the Zone, in 1992 E.C.)
No.
Diseases
No.    of Cases
%
(of the Nine)
•/•
(of Total Visits)
1
Malaria
2387
41.18
30.08
2
Intestinal Parasites
671
11.58
8.46
3
Diarrheal Diseases
647
11.16
8.15
4
Respiratory T. Infections
594
10.25
7.50
5
Skin Infections
443
7.64
5.58
6
Gastritis
365
6.30
4.60
7
Rheumatism
250
4.31
3.15
8
Duodenitis
249
4.30
3.14
9
Common Cold
190
3.28
2.39
Total of the Nine
5796
100
73.05
Total of all Visits
7934
Source: Kamashi Zone Health Department
APPENDIX 4.7B LEADING CAUSES OF MORBIDITY IN KAMASHI WOREDA
(as recorded by Kamashi H.Center and Clinics in the Woreda, in 1992 E.C.)
No.
Diseases
No.    of Cases
%
(of the Nine)
%
(of Total Visits)
1
Malaria
1989
30.65
20.62
2
Intestinal Parasites
875
13.48
9.08
3
Duodenitis
597
9.20
6.20
4
Diarrhoea
539
8.30
5.60
5
Skin Diseases
534
8.23
5.55
6
Respiratory T. Infections
462
7.12
4.80
7
Gastritis
416
6.41
4.32
8
Rheumatism
371
5.72
3.85
9
Feberile Illness
367
5.65
3.81
10
Other Wounds (other than skin infect.)
340
5.24
3.53
Total of the Ten
6490
100
67.36
| Total of all Visits
7634
Source: Kamashi Woreda Economic Development and Social Services Office
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25Didessa Medium Scale Hydrojwer Project
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Appendix 4.8 Potentially affected Population and Land Area by the Didessa HHP
Woreda
PA
Village
HHs
Pop. including HHs
Affected Area (ha.)
Mo. of Beehiv BS
Mo. of HHs Owning Beehive
s
Houses
Cultivated
Culti
vable
Grazing
Forest
Others
Fotal
Thatched
^orr jg
Total
Hena Dugda Gibie
Hurungu Sayi Jirma
37
156
-
30
60
90
-
-
37
37
Kamashi
Deguba
Bedessa
Godere
28
89
-
20
50
70
■
-
28
28
Soyama
Gawla
Daweta Meti
13
68
*
30
90
120
-
•
17
17
Mukerba
Hunda
Sarnie
29
110
-
15
30
•
45
•
-
30
-
30
Jallo Laika
Shimala
17
128
-
23
65
-
88
-
-
25
-
25
Sub-total
124
557
-
118
295
-
413
-
-
130
-
137
Bello Jiganfoy
Bello Didiga
Senkole Gawo
52
324
35
95
132
50
312
40
12
52
-
52
Bello Didessa
Kersa
37
259
-
22
180
20
222
30
25
37
-
37
Dimtu
Kutamur
45
293
25
50
175
20
270
200
45
45
3
48
Say Dalecha
Arkokassh
Daleacha
190
1350
90
395
495
160
1050
580
190
388
8
396
Sub-total
324
2226
150
-
562
982
250
1944
850
272
522
11
533
Ground
Total
448
2777
150
*
680
1277
250
2357
850
272
936
11
670
Water woris Design & Supervision Enterprise
26DiSessa Medium Scale HyUroyowr Project
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APPENDIX 4.9 WATER QUALITY ASSESSMENT
Introduction
Abbay  basin is  the main basin with high potential of socio-economic  development. In this  report the lower-Didessa river in Abbay  basin is  studied to evaluate this  suitability for hydropower project implementation. This  section tries  to evaluate the water quality and the effects of water quality on the proposed project.
1. Water Quality
In  relation  to  environmental  impact  and  geo-chemistry  on  the  proposed  hydropower project and vise versa.
A. Environmental Impact of Water Quality
When one thinks  about hydropower development the dams  and the reservoirs  as  well as  the rivers  to be diverted are the first things  to bear in mind. Next to them the geologic  formations, topography  and vegetation are very  essential parameters  where one planes  to design dams  and reservoirs. Depending on these the water quality  that has  to be impounded in the reservoir area is  defined based on the type of vegetation and geological formations that covers and forms the reservoir area.
Basically  water quality  is  mostly  refers  the physical, chemical, biological and hydrological nature of water proposed to be used for a specific purpose, in our case for hydropower project.
In proposing hydropower project it is  very  important to have enough knowledge about the existing water quality  of the river as  well as  it’s  future fate once such water is impounded in the reservoir area. Otherwise impacts  on the proposed project, both on flora and fauna as well as on human will be resulted.
In this section the impact on the proposed project is discussed and the later is raised in the subsequent section.
The river water impounded for major reason of power generation is  in countering various  geologic  and organic  materials  of the various  vegetation found in different climatic topographic features and altitudes, for this reason the following change in water quality is expected.
i) Physical Change of Water
The physical nature of water is  associated with color or turbidity, taste, odor etc. such physical change of water is  caused by  the interaction of the river water with the geologic  materials  and organic  materials  decomposed from the vegetation cover of the
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reservoir and water shed area. As  a result color and turbidity  is  observed in the water due to sediment and organic colloidal materials from the clay and silt of the minerals of geologic origin and decomposable vegetation respectively.
Lower Didessa
In the case of lower Didessa the reservoir and dam sites  are proposed to be established on geological rock  formation composed of genesis  and granitic rocks  or the reservoir area is  sited partially  on the old Precambrian basement complex  and partially may be the dominant part of the reservoir and the dam site is, well defined by a local restriction formed by the rige of a massive hard granite like formation included in to the basement genesis of the PULC series.
The sandstone which forms  the partial reservoir area under lain by  Precambrian basement complex  have relatively  higher permeability  though heterogeneity  in permeability of the geological formation is expected.
Therefore, the interaction of the river water with the surfecial material or soil of the reservoir area which is  supported by  the heterogeneous  rock  complexes  like genesis, magnetite, and stone or granitic rock may cause acidity in the reservoir water.
The existence of the reservoir water on sand stone can’t avoid such acidity  problem since there is  vertical and horizontal continuity  between Precambrian basement complex and Adigrat sand stone. Furthermore, there is a higher chance of flow of run off from higher areas  around the reservoir, which can alter the pH of the reservoir water. Such acidic  water will have corrosion effect on the turbines  and other metallic installations. Also such condition has a series effect to the extent of death on the fauna of the reservoir and downstream.
There is  a report made that iron smelting for agricultural instruments  and utensils  from the iron containing ores  found in the geological formation of the Wellega region was exercised by  the inhabitants. Iron is  soluble under reduced condition and low pH therefore such information helps  the environmentalist to be careful in future fate of reservoir water not to be acidic.
Hence a careful geological survey has to be made before one is reaching on decision of the possible reservoir area and dam sites  or a possible solution to resolve such problem in case once such sites  are selected and implemented has  to be suggested before hand.
Four samples are analyzed for Didessa river and the following results are obtained.
Wiiter Works Design & Supervision Enterprise
28Diddessa Medium Scale Hydropower Project
Reconnaissance Level Study
June 2001
Tabic 1. Results of Water Quality Analysis for Selected physical and chemical Parameters
NATURE OF SAMPLE
RIVER
DATE OF COLLECTION
15/03/01
DATE RECEIVED
21/02/01
CLIENT’S ID NO.
Didessa River         at Bridge
Didessa R. at
proposed dam
Sayi R. at proposed dam
Didessa R.          at Bridge  on Nekemti- Gimbi
Road
LAB. ID. NO.
039/93
042/93
043/93
044/93
Color (app.)
Turbidity (NTU)
Total Solids, 105 C (mg/?) ’
u
-
Total Diss. Solids, 105°C (mg/?)
51
74.75
106.6
70.2
Electrical Conductivity (ps/cm)
123
115.0
164.0
108.0
PH
6.93
6.81
6.93
6.95
Ammonia (mg/?NH4+)
Sodium (mg/?Na)
9.0
10.0
8.0
9.0
Potassium (mg/?K)
2.7
2.70
1.30
3.10
Total Hardness (mg/?CaCO3)
44.0
44.0
72.0
40.0
2
Calcium (mg/?Ca )
12.0
12.8
20.8
12.8
2+
Magnesium (mg/?Mg )
3.4
2.91
4.86
1.94
Total Iron (mg/?Fe)
0.09
0.09
0.33
Manganese (mg/?Mn)
0.1
1.10
0.30
0.10
Fluoride (mg/?F‘)
0.36
0.46
Chloride (mg/?Cl")
2.0
1.99
0.99
1.99
Nitrite (mg/?NC>2')
Nitrate (mg/?N03“)
NIL
0.88
NIL
0.88
Alkalinity (mg/?)CaCC>3)
60
60.0
90.0
52.0
2
Carbonate (mg/?CO3 “)
NIL
NIL
NIL
NIL
Bicarbonate (mg/?HCO3“)
73.2
73.20
109.80
63.44
2
Sulphate (mg/?SO] )
1.0
2.0
1.0
3.0
2
Phosphate (mg/?PC>4 “)
0.18
0.21
0.24
0.18
Boron (mg/?B)
SAR
RSC
water Works Destin & Supervision Enterprise
29Diddessa Medium Scale Hydropower Project
Discussion:
Reconnaissance Level Study June 2001
Due to the relatively  clear appearance of those samples  we don’t perform the analysis for total solid. But hopefully  there is  enough data on the sediment load of the river at hydrology department.
The pH is  slightly  below seven, which is  in acidic  range. This  will let some one to be suspicious  on the future fate of the water in relation to geologic  material discussed above.
The iron and manganese concentration amounted to 0.33 and 1.1 milligram per liter respectively  is  measured. These values  are relatively  very  high. Usually  in most other water these elements measured to be below those values.
The dissolution of these elements  is  usually  taking place at low pH and reduced environment. Hence the existence of these elements in the water may use as a clue to confirm the suitability of the water for reservoir or not.
All other parameters are in acceptable range.
As  it was  stated above the samples  from lower Didessa has  a relatively  clear appearance with no appreciable total solid. This  doesn’t mean that the water has  such appearance through out the year.
During dry season where low rain fall is observed at higher altitudes such will be seen but during wet season with high rain fall record run-off full of mineral soils and organic materials  from the catchment area will change the appearance of the color drastically. Therefore seasonal variation of the water's phisico-chemical nature has to be checked.
(ii) Chemical Change of Water
The   colloids   and   decomposed   vegetable   material   have   the   following   Bio-chemical effects.
Oxygen Depletion
Before any  reservoir is  implemented any  woody  biomass  has  to be estimated in the reservoir area and be cleared completely in order to lengthen the lifetime of the project. Otherwise oxygen depletion due to the consumption of oxygen in oxidizing those bio
degradable organic matenal may cause
low pH, CO , H S etc and this inturn will
22
cause
corrosion  effects  on  turbines.  Further  oxidation  is  responsible  for  anaerobic  condition
of the aquatic environment and
formation of CH«, NH , H S, CO
4        2                2  etc. At this stage the
water of the reservoir loses its use for any purpose. Acacia trees, long grass and other
vegetation are typical ones  at the banks  of the lower Didessa river. Those vegetations 
are seasonal type to mean that during dry season fire due to friction burns and destroys 
all while in wet season it recovers. In any case soil of this region is probably composed
Water Worfc Design & Supervision Enterprise
30Diddessa Medium Scale Hydropower Project
Reconnaissance Level Study
June 2001
of large deposit of surfacial organic  materials  which is  capable of causing the above mentioned problem. Therefore a careful soil survey  is  recommended for assurance of a complete clearance of woody  bio-mass  and bio-degradable organic  debris. If such is, impossible I don't think that the project be feasible.
In relation to the above the water retention time of the reservoir which depends  on the rate of flow of the river is  responsible for similar problem of oxygen depletion due to stagnation of water.
Residence time of reservoir of Lower Didessa
The reservoir has a maximum volume of 3531x106m   with mean discharge of
3
169m3/s.
Hence the reservoir retention time is Calculated to be
Volume of reservoir             = 0.66 year
Mean discharge                  = 7.94 months
This  is  to mean that every  7.94 months  the reservoir water is  replenished itself. This period of time is  very  long for the reservoir formed in such geologic  and vegetative region. Therefore a good mixing of the reservoir water is a must.
Variation in dissolved oxygen
Mostly  deep in the reservoir is  well oxygenated where as  on the surface low oxygen level will make the reservoir water unsuitable for power generation due to reasons mentioned above. Therefore, a good mixing is  very  essential during planning and designing a reservoir.
B. Impact of the project on the water quality
Flow fluctuation
Once dam is constructed and water is stored and held back of the dam then the flow of water down stream of the river may  be either reduced or regulated in such a way  of affecting the aquatic  life in the river like fish. The reduction of flow will hinder fish migration and disturb their habitat and reproduction means's. Also depending on the rate of flow there may be stagnation of water in the reservoir so that the down stream aquatic life will be affected seriously due to lack of oxygen. Therefore flow optimization in such a way  of giving attention for the continuity  of life both in the reservoir and downstream is very important in planning and deigning period.
Clearance of Vegetation
The clearing of grasses and the available trees may expose the watershed areas of the reservoir for erosion. As  a result the exposed watershed area is  eroded and runoff
Writer worts Design & Supervision Enterprise
31Diddessa Medium Scale Hydropower Project
Reconnaissance Level Study June 2001
containing clay  and silt will be introduced in the reservoir. This  will change the water quality  of the reservoir and the downstream river by  increasing the sediment load that can cause turbidity  and color as  well as  the change of chemical nature like pH and other nutrients  of NO3‘, PO/, Fe“, Mn~ etc. The turbidity  will hinder the penetration of light (which is  important for aquatic  life movement in water as  well as  breathing. Also the chemical change is  responsible for proliferation of aquatic  weeds  and oxygen depletion in downstream river. The use of the watershed area for recession agriculture and grazing is also responsible for the above problem.
Hence there must be a good soil and water conservation, afforestation and management practice for the sake of project lifetime and avoiding water quality deterioration.
Future Human Activity
The settlement of people following the implementation of the project may arise the introduction of pollutants  and contaminants  from domestic  waste, fertilizer, herbicide and insecticide applications, animal dung, possible industrial effluents etc. such may bring about water quality deterioration. Therefore the natural ecology  of the region will be disturbed. Hence in preliminary study or planning stage the settlement of the project workers and their family and others will have to gate appropriate attention.
Most hydropower projects  exist in the largest basins  of Baro-Akobo and Abbay. Hence those basins  have high potential or agricultural industrial and mining development. Upstream development must be in planed and manageable way  not to affect the downstream development like hydropower reservoir responsible for change in water quality. Such is  observed in Koka hydropower project due to the settlement of large group of people in the different towns  following Awash basin including most industrial zones of Addis Ababa region which are responsible for deterioration of the water quality of the reservoir water and downstream from soil erosion and influx  of noxious  and hazardous  substance not existing at the time the project is  established. Therefore any designer can learn a lot from such project.
Also as  more and more faste rate economic  development is  taking place most of the vegetation especially  in Baro-Akobo basin which is  contributing for the low percentage of forestry of our country will be destroyed. As a result climatic change responsible for low rainfall, high temperature, exposure for soil erosion finally  change in hydrological cycle is  resulted. Such in turn will bring about change in water quality  as  well as quantity. Therefore before development of project like hydropower, the advantage and disadvantage of the development in comparison to the ecological disturbance has to be evaluated.
Instead of destroying the available favorites  environment it is  better to exploit the already  degraded basin like the Abbay  basin and others  for such development simultaneously with upgrading such basins.
Wrttrr work Drsyn & supervision Enterprise
32Diddessa Medium Scale Hydropower Project
Mixing of surface water with groundwater
Reconnaissance Level Study June 2001
The presence of projects  like hydropower which need storage of surface water for power generation may  cause change in water quality  of ground water of the aquifer found around the project area. Because the reservoir water may  be altered quality  with gradually  for the various  reasons  mentioned above as  a result a vertical and horizontal infiltration of such polluted water will spoil the quality  water in the aquifer system. Therefore the avoidance of any  possible cause for change in surface water quality  of the river and the reservoir is  very  important to protect the ground water quality deterioration.
Rift valley  water resources  of springs  and lakes  as  well as  surface water like Awash river can be a good example, in such system of rift valley  the ground water table is below the bed of Awash river. This  ground water is  very  saline while the surface water of the river is  fresh. Such vertical stratification of varies  water type may  cause mix  up and contaminates the available fresh water.
Water works Design & Supervision Enterprise
33Diddcssa Medium scale Hydropower Project
APPENDIX - 5 COST ESTIMATE
Reconnaissance Level Study June loot
The cost estimate for the various civil works components of the project is based on unit costs compiled for the year 2001. Estimates for mechanical parts are based on CIF port Djibouti & inland transport cost levels. For electricaLparts  are-based-on_Aflgust ^9997 priceJevels-&-in USB. Table 5.1 presents  unit rates  for civil works  and Table 5.2 Detail cost estimates.
Table 5.1 Unit Rates for Civil Works.
Item No.             Description
Unit
Unit Rate
(USS)
I
II
III
Excavation:
Soft excavation
Rock excavation
Structural rock excavation
Stabilization of rock slopes
Cavern excavation
Tunnel excavation, 3 m dia.
Tunnel excavation, 5 m dia.
Tunnel excavation, 6 m dia.
Tunnel excavation. 7 m dia.
Tunnel excavation. 8 m dia.
Tunnel excavation, 8.5 m dia.
Tunnel excavation. 13.4 m dia.
Shaft excavation. 3 m dia.
Shaft excavation, 3.5 m dia.
Shaft excavation, 5 m dia.
Shaft excavation. 6 m dia.
Shaft excavation. 7 m dia.
Rock Support
Grouted rockbolts. 2 m long
Grouted rockbolts, 3 m long
Grouted rockbolts. 5 m long
Wire mesh
Plain shotcrete
Fiber-reinforced shotcrete
Concrete:
Mass concrete
Mass concrete to RCC (including f/wk)
Structural concrete
Reinforced concrete to RCC (including f/wk) Concrete lining In tunnel, including f/wk Overbreak concrete in tunnel
Inverted concrete in tunnel
m3
m3
m1
m3
m3
m3
m3
m3
m3
m3
m3
m’
m3
m3
m1
mJ
m3
4.0
7.0
11.0
35.0
75.0
60 0
500
42.0
38.0
38.0
120.0
100.0
95.0
91.0
ea
ea
ea
m1
m3
m3
45.0
65.0
95.0
8.0
240.0
420.0
m3
m3
tn3
m3
m3
m3
m3
85.0
120.0
95.0
2500
85 0
120.0
W/itirr wks Design & Supervision Enterprise
34Dlddessa Medium Scale Hydropower Project
Reconnaissance Level Study June 2001
Item No.
description
Unit
Unit Rate
(USS)
IV
V
VI
VII
Structural concrete, including rebar and formwork Vass concrete in plugs
Concrete in CFRD (including f/wk and rebar)
Concrete in arch dam
Roller-compacted concrete (no cement or flyash) Cement and flyash mixture
Straight formwork, outdoor
Straight formwork, underground
Curved formwork
^ater passage roof
Tunnel lining
Reinforced steel
Embankment Dam:
Overburden excavation in foundation Rock excavation in foundation
Core trench excavation
Foundation preparation for core
Preparation for embankment
Rock fill from excavation
Rock fill from quany
Impervious core material
Transition material
Processed filter material
Rip rap
Grout curtain drilling
Cement grout
Drilling for consolidation grouting
Drainage curtain
Penstock Steel and Steel Linen
Penstock steel
Steel lining In tunnel
Miscellaneous Metalwork
Structural steel
Preparatory Works:
Reservoir clearing, light vegetation Reservoir clearing, medium vegetation Reservoir clearing, heavy vegetation
Access roads:
-flat
- steep side hill in overburden
- steep side hill in rock
m3
m3
m3
ms
m3
tonne
m2
m2
m2
m2
m2
tonne
250.0
145.0
950
28.0
30.0
40.0
60.0
70.0
70.0
980.0
m3
m3
m3
m2
m2
m3
m3
m3
m3
m3
m3
M
Kg
m
m
4.0
11.0
11.0
10.0
2.0
3.0
8.0
5 to 10
10.0
18.0
10.0
550
1.0
50.0
63.0
tonne
tonne
tonne
tonne
3500.0
3700.0
2500.0
3500.0
ha
ha
ha
300.0
925.0
1675.0
km
km
km
50000.0
200000.0
400000.0
water works Design & Supervision Enterprise
35Dtihlessa Medium scale Hydropower Project
Table 5.2 Detail cost estimates
Reconnaissance Level Study June 2001
Description
unit
Quantity
unit rate USD
Local MUSD
Foreign
MUSD
Total
Cost MUSD
1
Main civil work
1.1
Blanket (upstream side)
1.1.1
clay
Mm3
1.86
10
5.58
13.02
18.6
1.1.2
concrete
Mm3
0.14
120
4.902
11.438
16.34
1.2
Diversion work
1.2.1
Downstream cofferdam
Mm3
0.16
3
0 147
0.343
0.49
1.2.2
Diversion tunnels
Mm3
0.065
38
0.741
1.729
2.47
1.2.3
Approach channel excavation
Mm3
0.23
7
0.48
1.12
1.6
1.3
Embankment dam
1.3.1
preparation for embankment
Mm2
0.18
2
0 108
0.252
0.36
1.3.2
rock excavation in foundation
Mm3
0.27
11
0.945
2.205
3.15
1.3.3
core trench excavation
Mm3
0.25
11
0.834
1 946
2.78
1.3 4
foundation preparation for core
Mm2
0.06
10
0.174
0 406
0.58
1.3.5
impervious core material
Mm3
2.6
10
8.4
19.6
28
1.3.6
transition matenal
Mm3
0.13
10
0.39
0.91
1.3
1.37
filter material
Mm3
0.16
18
0.885
2.065
2.95
1.3.8
rockfill from quarry
Mm3
4.52
8
10.839
25.291
36.13
1.3.9
rip rap
Mm3
058
10
1.746
4.074
5.82
1.4
Spillway
1.4.1
structural rock excavation
Mm3
1.4
11
4.62
10.78
15.4
1.4.2
main spillway structure
Mm3
0 002
120
0.072
0.166
0.24
1.4.3
chute channel
Mm3
0.03
120
1.08
2.52
3.6
1.4.4
reinforced steel
ton
2000
980
0.588
1.372
1.96
1.5
Waterway
1.5.1
shaft excavation. 9m dia.
Mm1
0.0032
91
0.087
0.203
0.29
1.5.2
concrete lining in tunnel, (including f/wk)
Mm3
0.006
250
0.447
1.043
1.49
1.5.3
mass concert in plug
Mm3
0.00019
145
0.0084
0.0196
0.028
1.5.4
structural concert for intake structure
Mm3
90.25
95
0.0027
0.0063
0.009
1.6
Surge chamber
1.6.1
cavern excavation
Mm3
0.024
35
0.252
0.583
0.84
1.6.2
mass concrete
Mm3
0.0021
120
0.075
0.175
0.25
1.6.3
reinforced concert
ton
125
980
0.036
0.084
0.12
1.7
Powerhouse*
LPs
0.01005
0.02345
0.0335
1.8
Hydro mechanical works
1.6.1
intake gale Including rack
LPs
0.312
1.768
2.08
1.8.2
penstock steel, structural steel
LPs
2.247
12.733
14.98
1.9
Infrastructure
1.9.1
Access
LPS
0.96
2.24
3.2
1.9.2
site camp
0.027
-
141.2
1.143
2.667
3.81
water Warlu Design & Supervision Enterprise
36Diddessa Medium Scale Hydropower project
Reconnaissance Level Study June 2001
Description
unit
Quantity
unit rate
USD
Local
MUSD
Foreign
MUSD
Total
Cost MUSD
1.9.3
camp facilities
LPs
0.072
0.168
0.24
to fa/ Item 1
48.183
120.957
169.1
2
Electro-mechanical equipment
2.1
Mechanical works
2.1.1
turbine and auxiliary equipment
LPs
1.7445
33.1455
34.89
2.1.2
Governor
LPs
0.139
2.641
2.78
2.1.3
main power house crane
LPs
0 0405
0.7695
0 81
2.1.4
auxiliary crane
LPs
00165
0.3135
0 33
2.1.5
draft tube & its accessories
LPs
0.022
0.418
044
2.1.6
air compressor
LPs
000175
0.03325
0.035
2.2
Electrical works
2.2.1
electrical equipment
LPs
0.814
15.466
16.28
2.2.2
transmission line feeder
LPs
0.64
12.16
12 8
2.2.3
Control & Protection equipment
LPs
0.32
6.08
64
total Item 2
3.7383
71.0268
74.77
3
Environment & socio-economic cost
5.744
1.436
7.18
total Item 3
5.744
1.436
7.18
Sub Total (1+2+3)
57.665
193.42
251.1
4
Physical contingency (25% of 1 ♦ (15% of
2+3)
13.468
41.1088
54.58
5
Total cost
71.134
234.529
305.7
6
Management and supervision 8% of total
5.6907
18.7623
24.45
7
Miscellaneous owner's cost 2% of total
1.4227
4.69053
6.113
Grand total
'8.247
257.982
336.2
’(Source, Tekeze medium HPPpro-feasibility, HOWARD HUMPHREYS etel, 1996)
Water Works Drsyn & Supervision Enterprise
37Diddessa Medium scale Hydropower project
Reconnaissance Level Stii/ty
June 2001
Table 5. 3 Preliminary Mitigation Cost for Didessa HPP (for 160m high dam), in USD
Item
Description
Quantit
y
Unit Cost
Total Capital
Cost
Annual Recurrent
Cost Constructi on Phase
Annual Recurre nt Cost Operatic n Phase
1
Technical Environmental Optimization
Lump sum
100,000
2
Reservoir Area Clearing             (Dense Woodland)
4,000 ha
925/ha
3,700,000
3
Reservoir Area Clearing               (Open Woodland)
2,200 ha
300/ha
660,000
4
Compensation for Cultivated Land
150 ha
600/ha1
90,000
5
Compensation for Grazing Land
700 ha
250/ha
175,000
6
Compensation for Bee Keeping
850
Beehives
15/Beehive
12,750
7
Compensation for Houses (Thatched)
660
Houses
800/House
528,000
9
Compensation  for  Houses  (Corr,  iron sheet)
11
Houses
1200/Hous 
e
13,200
9
Compensation for Churches Relocation
2
Churches
10,000
20,000
10
Compensation for School Relocation
1 School
50,000
50,000
11
Implementation      of       Resettlement Program and Community Gain 2
Lump sum
540,000
23,000
14,000
12
River Crossings Replacement
Lump sum
150,000
10,000
5,000
13
Health Center (for project employees & locals) and Disease Control Program
1 H.C
350.000
350.000
50,000
15,000
14
Fish Hatchery
50,000
50,000
15
Replanting
100 ha
350/ha
35,000
16
Catchment Stabilization Initiatives
125,000
17
Generic BMP for Disturbed Areas
40 ha
500/ha
20,000
18
Monitoring of Construction Work
20,000/yr
20,000
19
Monitoring of Water Quality
4,000
1,500
20
Monitoring of Socio-economic Impacts
5,000/yr
5,000
21
Post Construction Environmental Audit
1,000
Sub-Totals
66.618,950
112,000
36,500
Contingency (at 10%)
661,895
11,200
3,650
Totals
7,280,845^
123,2004
40,1503
34
Total for Construction Phase (assumed at 5 Years) ( +( x5))
7,896.845
5
Total for Operation Phase (assumed at 50 Years)( x50)
2,007.500
TOTAL FOR CONSTRUCTION PHASE AND OPERATION PHASE
9,904.345
LOCAL COMPONENT (ASSUMED TO BE 80% OF THE TOTAL COST)
7.923,476
1,980,869
Foreign Component (assumed to be 20% of the Total Cost)
Three years income from the lost land.
For social & physical infrastructure development, agricultural development package, etc.
BMP Best Management Practices
waiter work D«l^i & Supervision Enterprise
38DiiUesrt Medium Scale Hydropower Project
Reconnaissance Level Study June 2001
APPENDIX-6 ECONOMIC ANALYSIS
Basic assumptions and parameters for analysis work is as follows:-
Project life Discount rate Construction period SCF 
50 years 10%
5 years 0.9
Production to start on year              6.0
Table 6.1 Economic Analysis
Yoar
COST(USD)
Benefit
Investment Cost
1
2
3
♦
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Power    Env &Sco      Subtotal 32.04      0.73                32.77
64.1        1.45               65.55
112.2     2.5                  114.66
80.11      1.81               81.92
32.04     0.73                32.77
discount       discounted 0 & MR Total    factorl 0%     Cost 10%
328    0.909       29.78793
656    0.826       54.1443
115    0.751       86.10966
81.9   0.683       55.95136
6.54         39.3   0.621       24.41151 6.54         6 54   0.564       3.68856 6.54         6.54   0.513       3.35502 6 54         6.54   0.467       3.05418 6.54        6 54   0.424       2.77296 6.54        6.54   0.386       2.52444
6.54         6.54   0.35         2.289
6.54        6.54   0.319       2.08626
6.54        6.54   0.29         1.8966
6.54        6.54   0.263       1.72002
6.54        6.54   0.239       1.56306 6.54        6 54   0.218       1.42572 6.54        6.54   0.198       1.29492
6.54        6.54   0.18         1.1772
6.54        6 54   0.164       1 07256
6.54        6.54   0.149       0.97446
6.54        6.54   0.135       0.8829 6.54        6.54   0.123       0.80442 6.54        6.54   0.112       0.73248 6.54         654    0.102       0.66708 6.54        6.54   0.092       0.60168 6 54         6 54   0.084       0.54936 6.54        6.54   0.076       0.49704 6 54        6.54   0.069       0.45126 6.54        6.54   0.063       0.41202 6.54        6.54   0.057       0.37278
6.54        6.54   0                    0
6.54        6.54   0                    0
6.54        6 54   0                    0
Net             discount    Net cash BP          Benefit      fact1O%    Flow 10%
0                 0.909    0
0                0.826    0
0                 0.751    0
0                0.683    0
0                 0.621    0
168         161.5         0.564    91.0634
168         161.5         0.513    82.829
168         161.5         0.467    754018
168         161.5         0.424    68 459 168         161.5         0.386    62.3236
168         161.5         0.35      56.511
168         161.5         0.319    51.5057
168         161.5         0.29      46.8234
168         161.5         0.263    42.464 168         161.5         0.239    38.5889 168         161.5         0.218    35.1983 168         161.5         0.198    31.9691 168         161.5         0.18      29.0628 168         161.5         0.164    26.4794
168         161.5         0.149    24.0575
168         161.5         0.135    21.7971
168         161.5         0.123    19 8596
168         161.5         0.112    18.0835
168         161.5         0.102     16.4689
168         161.5         0.092    14 8543
168         161.5         0.084    13.5626 168         161.5         0.076    12.271 168         161.5         0.069    11.1407 168         161.5         0.063     10.172 168         161.5         0.057    9.20322
163         161.5         0                 0
168         161.5         0                 0
168         161.5         0                 0
Wrttrr Wjrfe Desijii & Supervision Enterprise
39Dtddessa Medium Scale Hydropower Project
Reconnaissance Level study June 2001
Year
COST(USD)
Benefit
Investment Cost
Power Env ASco Subtotal
34
35
38
37
38
39
40
41
42
43
44
45
46
47
48
49
50
discount     discounted 0 A MR Total      factor10%  Cost10%
6 54         6.54    0                  0
6.54         6.54    0                  0
32.7    0.036           1.1772
6.54         6.54    0                  0
6.54         6.54    0                  0
6.54         6.54    0                  0
6.54         6 54    0                  0
6 54         6.54    0                  0
32.7    0.022           0.7194
6.54         6.54    0                  0
6.54         6.54    0                  0
5.54        6.54    0                  0
6.54         6.54    0                  0
6.54        6.54    0                  0
32.7    0.014           0.4578
6.54        6.54    0                  0
6.54        6.54    0                  0
6.54        6.54    0                  0
6.54        6 54    0                  0
6.54        6.54    0                  0
32.7   0.009           0.2943
289.9194
Net               discount    Net cash BP            Benefit         fact 10%     Flow 10%
168           161.5           0                 0
168           161.5           0                 0
840           807.3           0.036          29.0628
168           161 5           0                 0
168           161.5           0                 0
168           161.5           0                 0
168           161.5           0                 0
168           161.5           0                 0
807.3           0.022          17.7606
168           161.5           0                 0
168           161.5           0                 0
168           161.5           0                 0
168           161.5           0                 0
168           161.5           0                 0
807.3           0.014          11.3022
168           161.5           0                 0
168           161 5           0                 0
168           161.5           0                 0
168           161 5           0                 0
168           161.5           0                 0
807.3           0.009          7.2657
975 541
B/C          at 10%
3.36487
ENVP at 10%
EIRR
685.622 MUSD 27%
W/itfr works Desi/pi & Si^ervlsfun Eiiteyriso
40.1
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TITLE
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CAcc. NO

Summery

Lower Didessa Medium Hydropower Project - Summary

Lower Didessa Medium Hydropower Project - Reconnaissance Study Summary

Project: Lower Didessa Medium Hydropower Project

Location: Ethiopia (Abbay Basin)

Prepared by: Water Works Design and Supervision Enterprise

Date: August 2001

Study Level: Reconnaissance

Project Overview

The reconnaissance study evaluates the feasibility of developing a medium-scale hydropower project on the Didessa River in Ethiopia. The study covers technical, environmental, and socio-economic aspects.

Key Components

Component	Key Findings
Hydrology	Mean annual flow: 7290 MCM Flood peak factors established (1.1 for Didessa station) Reservoir retention time: ~8 months Tail-water curve and regulation curve developed
Geology	Dam site on Precambrian basement complex (genesis and granitic rocks) Potential acidity issues from iron-containing ores Seismic risk assessment included
Project Layout	Reservoir capacity curves developed Optimization curves for power tunnel and pressure shaft Preliminary designs for dam, spillway, waterway, and powerhouse
Environment & Socio-Economic	448 households (2,777 people) potentially affected 150 ha cultivated land and 680 ha grazing land impacted Threatened endemic plant species identified Malaria is leading cause of morbidity in the area Preliminary mitigation cost estimated at $7.28 million
Water Quality	Slightly acidic pH (6.81-6.95) High iron (0.33 mg/L) and manganese (1.1 mg/L) concentrations Potential oxygen depletion and corrosion risks
Cost Estimate	Total project cost: $336.2 million Civil works: $169.1 million Electro-mechanical equipment: $74.77 million Environment & socio-economic: $7.18 million
Economic Analysis	Project life: 50 years Construction period: 5 years Benefit-Cost ratio at 10%: 3.36 Economic Internal Rate of Return (EIRR): 27%

Key Recommendations

Further geological surveys needed to assess acidity risks
Comprehensive vegetation clearing required in reservoir area
Detailed resettlement action plan needed for affected communities
Water quality monitoring program essential
Feasibility study recommended as next step

Conclusion

The reconnaissance study indicates that the Lower Didessa Medium Hydropower Project is technically feasible and economically viable, with an EIRR of 27%. However, environmental and social impacts require careful mitigation measures. The project would contribute significantly to Ethiopia's power generation capacity while requiring substantial investment in infrastructure and community development.