arjo didessa

8/22/2019 ARJO DIDESSA

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1.1 ARJO-DIDESSAIRRIGATIONPROJECT1.1.1 GENERALArjo Didessa Project is located along Didessa River, which is said to be the largest tributary of

the Blue Nile River. It drains to the Abbay River contributing roughly a quarter of the total flowof Blue Nile. The catchment area from where the river drains is estimated to be 34,000 km 2originating from the Mt. Venino and Mt. Wache ranges. It flows in an easterly direction for about75 km, then after, turning rather sharply to the north until it reaches the Blue Nile River. Themajor tributaries of to Didessa River among others include Rivers of Wama from the east,Dabana from the west and Angar from the east (see Map 03 for location of Project).

The catchment area at the proposed Dam site is 5,280 km2, and it extends to area 8 districts of

the two zones (Jima-Arjo and Illubabor) of the National Regional State of Oromia. The districtsto which the catchment and command area of the project extends include among others, LimuSeka, Limu Kassa, Manna, Goma, Setema, Sigmo, Gera and Seka Chekorsa of West Welega

zone, and Gechi, Boracha and Didessa of Illuababora zone.

As per the feasibility study of the project (WWD&SE, May 2007), the project is intended todevelop the area for irrigated agriculture by impounding the river flows, through the provision

and construction of an 40.6 m high earth and rock-fill dam for which a feasibility design isavailable. The dam would be located in the Jima zone, on the river Didessa at about 1.5 kmupstream of its confluence with Wama river. Two main canal systems would run along the rightand left side of the river in order to irrigate the potential arable land (17, 825 ha) located onboth sides of the river. Watershed management is also proposed as the major component andpart of the development activities to be undertaken.

1.1.2 REVIEW OF AND ANALYSIS OF PREVIOUS STUDIESThe following studies pertaining to the Arjo-Didessa Irrigation project are available for reviewand analysis of the project:

Study made by USBR (1964): The United States Bureau of Reclamation (USBR) was thefirst to undertake the studies for the investigation of Land and Water ResourcesDevelopment in the Blue Nile River Basin in General and the Arjo-Didessa River Sub-basinin Particular. The study was at reconnaissance level. The study identified several Large-scale irrigation and multi-purpose projects including the Arjo-Didessa project.

Study by TAMS (1975): Following the study of the area by USBR, a consulting firm namedTAMS based in USA made a study of the Didessa upper Valley. The purpose of the study

was focused on the agricultural potential of the valley.

Study by WAPCOS (1990): This study made by the Water and Power Consultancy Service,India, was also a reconnaissance level that extended to all river basins of Ethiopia for thestudy and update of the Ethiopian Basins. The study proposed two dam sites on RiverDidessa for the purpose of irrigation and hydropower development.

The ARBID/MPS of 1999: this study covered the Arjo-Didessa Project by a reconnaissancelevel study. The project was not covered by a PFS at the time as it was not ranking high

enough.

However, WWD&SE in association with ICT studied the project at feasibility level in 2006/2007.

The following reports had been produced and all details given hereunder are based oninformation/data extracted from these study reports:

Main Report

Sectoral Studies in 5 Volumes:


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o Volume I (a): Surveying and Investigation,o Volume I (b): Appendices,o Volume II: Water Resources (4 Annexes),o Volume III: Natural Resources (3 Annexes), and

Volume IV: Environmental and Socio-economic Aspects(7 Annexes)


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Map 03: Irrigation projects in Anger, Didessa and fincha sub-basins


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1.1.3 PROJECT OUTLINEThe Didessa Irrigation Project is located in Jima (East Welega) and Illuababora zones of OromiaNational Regional state within the Blue Nile River Basin of Didessa Sub-basin. It is a tributary of Abbay

River. The following are the main features of the project as outlined by the recent feasibility study andpresented in the Main Report

The project comprises a rock-fill earth dam of 40.6 meter height, The dam is to be built on the main stream of the river Didessa upstream of the confluence of

Wama River;

Two canal systems are proposed to offtake water to both flanks, right and left banks, to supplywater to a gross command area of 17,825 ha;

The project area comprises 4 major components:o The reservoir area covers 8,785 ha and extends to 15 kebeles;o The catchment area is 34,000 km

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o The dam site is located within two kebeles /localities/: right bank located in Wamaand the left bank located in Chitu Bosona Kebeles;

o The command area is located along both banks of the river, covering 3 and 8 kebelesat the right and left sides respectively. The gross command area is estimated to beabout 17,825 ha with net cultivable area assumed to be 13,665 ha 7,450 ha on theleft and 6,225 ha on the right banks.

The average elevation of the project area is 1,340 masl receiving a mean annual precipitation of1,600 to 1,800 mm;

The soils of the project area vary from sandy loam to clay for reddish brown soils and clay to heavyclay for vertisols that vary with depth indicating the existence of moderately deep-to-deep soils;

The area is sparsely populated with very low cropping intensity of about 15-20%; The average temperature of the project area ranges from 20 0C to 25.4 0C with a maximum

temperature reaching 27.7 0C and a minimum temperature declining to 16.3 0C;

Teff is the main subsistence crop followed by maize and sorghum, and a high maize productionwas registered compared to other crops;

The farming system in the project area is, as many of other areas in the country, a mixed farmingsystem. That is, the rainfed crop cultivation integrated with livestock rearing is the mainagricultural system in the area.

1.1.4 PRESENT SITUATIONThe feasibility study reports for the irrigation developments have been completed and submitted tothe Ministry of Water Resources. The Ministry had reviewed the reports a long time ago. The detaileddesign of the irrigation component is presently in progress by the consultant.


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As the main objective of the project was to optimise the benefits from the available water resources atthe proposed dam sites, a pre-feasibility study is now being undertaken by the same consultant inorder to harness the available potential for the generation of hydropower along with the developmentof the proposed irrigation schemes. If this proposal were found attractive, the immediate objective

would be to go ahead with the preparation of a feasibility study and detail design for the hydropowercomponent as well. It has been confirmed that a firm power generation of 20 MW could be achieved.Adopting a load factor of 60% the installed capacity could be kept as 33 MW but this has resulted in

raising the dam height by 20 meters in order to harness the potential hydropower generation availableat the site. Simulation studies had been conducted for power generation by increasing dam heightsprior to arriving at the final decisions.

The Project area covers 2 zones of Oromia National Regional State in 8 and 3 districts of the twozones respectively. Geographically it is bounded between latitudes 8 30 and 8 40 N, and longitudesbetween 36 22 and 36 43 E. The project is within the Didessa River sub -basin, and the river flowsinto Nile River. Many rivers like Wama, Angar, Kolati and Sope Rivers are the main tributaries ofDidessa River, which in return is the main tributary of the Abbay River.

The Project area is accessible via two highways and from two directions. The AA Nekemte main roadand the road from AA to Bedele are the main highways joining the project area with other areas viaArjo-Bedele or Nekemte-Arjo-Bedele. It is approximately 30 km north of Bedele town. Thus Bedele-Arjo or Nekemte-Arjo-Bedele tracks links the project site with the main roads to AA. Infrastructuresare poorly developed and needs serious attention and consideration. The occurrence of Malaria andTsetse flies are the major constraint to voluntary and spontaneous settlement in the valleys, which isarable but idle land.

1.1.5 PHYSICAL ENVIRONMENTThe project site lands form a complicated system of hills, bordered and interrupted by, savannahplains sloping gently towards the river, while the nature of topography negates consideration foreconomic gravity flow irrigation at the extreme end of the river. The catchment area consists ofundulating topographies with different ridges, valleys and steep slopes. There are many permanentand seasonal streams of water found between the ridges. The soil is very much degraded due to highpopulation and overgrazing. The climate of the area is mild. The average temperature ranges from

20 0C to 25 0C, whereas the maximum temperature reaches 27.4 0C. The heavy annual precipitation isindicative of rainfed agricultural development potentials. The area forms part of the tertiary TrappeanLava composed of largely basalts and basaltic tuffs.

1.1.6 SURFACE AND GROUNDWATER RESOURCESThe Arjo-Didessa flows within three zones of Oromia Regional National State. The general slope of thesub-basin or catchment is toward NE, E & NW directions. The area has generally a rugged topographywith the highest and lowest elevations of about 2,890 masl & 1,030 masl located at Sigmo-Gera andDidessa River Valley respectively. The presence of thermal springs, cold groundwater and salinesprings in the area shows the diversification of the hydrogeological set up of the river catchment. Themain groundwater recharge of the area is the SE, SW& the NE part of the river catchment. The

intercalations of the volcanic ash with fractured and /or weathered volcanic lava flows cause theemergence of many springs within the Didessa River Valley. The surface runoff of the Didessa rivercatchment at the gauged station was recorded to be 2.11 BCM, whereas the total minimum monthly

flow of the river (base flow) which was the best estimate that would potentially recharge the groundwater was found to be 199 m3/s.


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1.1.7 SOILS, LAND SUITABILITY, AND PRESENT LAND USEGenerally, the parent soil material of the project area is the result of colluvial & alluvial deposition.The soil types of the project are different. Soils like vertisols; weakly developed with dark grey toblack & very greyish to dark brown colour covering an area of 13%, cambisols; weakly developed soilswith area coverage of 15.2%, Luvisols; deep to very deep, dark reddish brown soils covering 8% of

the area, Nitosols; having B horizon with shiny pedfaces and covering 6% of the area.

Land suitability of the project command area was assessed versus the proposed and potential cropscomposing of rice, wheat, maize, vegetables, and sugarcane and forage under the conditions ofdifferent soil suitability classes. The present land use pattern was also studied for four districts wherethe command area of the project falls in. As per this study, the cultivable area accounted at 36.8% ofthe districts total area followed by 21.4% of uncultivated land. The grassland covered 14.2 %, whilecultivated land accounted 17.7%. The other land uses were forest and woodland land (8.6%),buildings and settlement (1.0%) and swampy or water logged areas (0.5%). In general, the projectcommand area was sparsely populated with very low cropping intensity of about 15-20%.

1.1.8 AGRICULTURE, LIVESTOCK AND FISHERIESThe main crops grown in the project area included among others maize (7,119 ha), sorghum (3,328ha), Teff (8,827 ha), barely (706 ha), wheat (383 ha), and f. millet, horse bean etc are also croppedwith less intensity in the order of the area coverage and productivity. The rainfed crop cultivationintegrated with livestock rearing is the principal farming system in most parts of the project area. Thearea is sparsely populated with a few small holders; hence major part of the area was undevelopedeven under rainfed agriculture.

The grazing areas account 14% of the overall area; nevertheless the grasses are low nutritional valuein the absence of any legume. The cattle are being reared mainly for sale and draught power for landpreparation and threshing. Bullock local plough (Maresha), and manual operated tools are used for theland preparation. Generally, crops were cultivated only during the wet seasons through rain fedagriculture; hence the mono cropping was a dominating factor in the project area. Despite the higheconomic contribution of the livestock population in the project areas households, no significant

changes had occurred in adopting a better management practices for increased animal productivity.The main problems discouraging this are animal diseases prevailing in the project area and shortage

and unavailability of animal feeds.

Didessa River is one of the main tributaries of Abbay River, which has fish resources at differentsegments of the river channel. The studies conducted in this respect indicated that fishery resourcescould be exclusively utilized for subsistence where the intensity varies along the different segments ofthe river Didessa and its tributaries.

It is, however, concluded that in the project impact area, which was proved to be a virgin land, non-interaction of human activities with fish resources had existed. And thus no subsistence or commercialfisheries were experienced and practised in order to exploit these readily available resources.

1.1.9 ENVIRONMENTAL ASPECTSThe Environmental Impact Assessment (EIA) of the proposed project area was conducted at feasibilitylevel by WWD&SE in association with ITC along with an integration of mitigating measures required inthe design of the project, implementation and operation activities.


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The study had indicated and proved that most part of the Didessa valley including the project area hadbeen left undeveloped due to the influence of human and animal diseases particularly malaria andTrypanosomiasis respectively. The trend, however, has recently changed with the settlement of largenumber of people and expansion of cultivation by clearing vegetation covers. The settlement policy

made by the government increased the movement of human interventions in the area. Settlers fromthe highlands had moved their animals to the low lands mainly looking for livestock grazing, but alsofor some cultivation and settlement. These phenomena had, therefore, triggered and resulted in the

shortage of land and degradation due to population pressure in the uplands.

The natural vegetation dominating in the project area was dominantly woodland Savannah, but withvariation in density of woody vegetation, type of vegetation, drainage and slope.

Wilde life of the Didessa valley including the project area has not been well studied. As mentioned

earlier, as of the year 2003/04, due to the governments settlement policy programme, many peopleare settled in the project area as a result; big wild animals like lion and Gazel have migrated probablyto downstream areas where there was room for these creatures. On the other hand, some species ofwild animals such as primate species (eg Anubis baboon, Grivet monkey and colobus monkey), smallantelopes, Warthog, wild pig, etc are still available in the area. With regards to aquatic fauna,Hippopotamus & Nile crocodile commonly occur in the Didessa River.

On the other hand, the Environmental Management Plan of the Project encompassed in the studydocument has recommended the provision of monitoring modality mechanism so as to deal with abovematters.

1.1.10 SOCIO-ECONOMIC AND INSTITUTIONAL ASPECTSAs is the case for most of other rural parts of Ethiopia, the majority of the inhabitants of the projectimpact area are driving their means of livelihood from mixed farming, involving crop production andlivestock rearing. The need, however, was not promisingly satisfactory, by any yardstick, apart fromperpetuating the prolonged peasant life that had involved a lot of toiling.

As per the current study made by WWD&SE, on house hold socio-economic status of the project area,out of the total surveyed household 96% are earning their major source of income from crop

production. This indicated that the farming system was dominated by crop farming.

The number, type and distribution of social services like schools, health centres, water supply points,road networks & other infrastructures vary from district to district of the project area. In all cases ofthe districts, the provisions of socio-economic infrastructures are not sufficient and in some places itcould be said as non-existent.

The socio-economic impacts to be attributed from the project are identified as those of food securitythat would be attained sustainably, promotion of family welfare, creation of job opportunities,implementation of infrastructure that would probably be evenly distributed, promotion of incomegenerating activities, and establishment of agro-industries.

Similarly, the project would adversely impact the socio-economic conditions by threat of malaria,

displacement of dwellers, loss of social services etc unless proper mitigation measures are to be takenprior to and after the implementation of the project is realised.

Resettlement planning for the project was envisaged is envisaged in the current feasibility level ofstudy of the project. As the proposed dam would submerge 8500 ha of land and the development areawill cover 13665 net irrigable areas this situation on the ground would result in displacement of thehabitants and damage of private and public properties. The major findings of the project revealed thatthere were also various communal properties that would be affected and damaged as a result of theimplementation of the project. Further, the report details out the possible displacements that couldoccur and property damages due to the realization of the project.


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Similar to the resettlement aspect of the project, the institutional set up of the envisaged project wasalso well addressed in the feasibility study (WWD&SE, 2007) of the project. In the report it wasproposed that the institutional structure of the project to be effected in two phases:

Phase I: Planning, Design and Implementation (the responsibility is fully entrusted to MoWR), and Phase II: Operation and Maintenance (the responsibility bestowed to Oromia Irrigation Authority).

1.1.11 ECONOMIC ASPECTSFinancial and economic analyses of the project have been conducted at feasibility study level.Accordingly, the Net Present Value (NPV) incremental of the project at 10% discount factor isestimated to be ETB 607.5 million with the same discounting factor, the BCR is found to be 1.87. TheIRR for the financial cost flow is found to be 15.4%. Thus, the analysis indicated that the project wasviable at 2006 constant prices prevailed in the country, Ethiopia.

The economic analysis, on the other hand, had indicated that the incremental benefits of the project at19% discount factor to be at ETB 1312 million Birr. With the same discounting factor the economicB/C ratio was to be found 3.2. The EIRR for the financial cost flow was found to be 22.06% indicating

that the project is economically most viable and robust.

The updated project investment and recurrent costs are shown in the Chapter on Cost Estimates.

1.1.12 CONCLUSIONS AND RECOMMENDATIONSIt was proper and high time to recommend the project for further detail design and implementation,as it is vivid from the study output of the project that prevailed in all terms of the project. It waseconomically viable and environmentally friendly and sustainable with insignificant limitations, whichwere not indicative to careful scrutiny in order to come up with serious mitigation measures.

The Arjo-Didessa Irrigation Project, which would be a large-scale irrigated agriculture development

project, would no doubt contribute to improving the socio-economic situation in the region inparticular and in the country in general.

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