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Ethiopia is planning to expand irrigated agriculture to help support its rapidly growing population and reduce its dependency on the import of sugar. The World Bank financed the Ethiopian Nile irrigation and drainage feasibility studies. The largest of the areas studied was in the Upper Beles river basin where water availability was substantially augmented by the completion, in May 2010, of the Tana Beles hydroelectric tunnel scheme which diverts water from the Tana basin. This paper focuses on the Upper Beles scheme and describes the creation of a digital elevation model from stereoscopic satellite imagery, the planning process used to delineate irrigation command areas (including irrigation and drainage layouts) and detailed engineering studies, including an assessment of the operating environment and challenges facing scheme operators. Social and environmental considerations were integrated in the proposed development, both in the planning process and in the identification of mitigation measures. The project team looked at irrigation schemes in Ethiopia and tried to build on successes to ensure informed recommendations were given in the feasibility study.
1. Introduction
The Upper Beles scheme, with a net irrigation area of 63 000 ha, located in the Amhara and Benishangul-Gumuz region of Ethiopia about 30 km south west of Lake Tana (Figure 1), was by far the largest of the proposed irrigation projects studied under the World Bank financed Ethiopian Nile irrigation and drainage project (MoWE, 2011). With little natural dry-season flow, the irrigation scheme only became viable with the completion in, May 2010, of a hydropower tunnel that releases up to 160 m3/s of water from Lake Tana into the upper reaches of the Beles River. Extensive water balance modelling was carried out, which created operating rules for releases through the hydropower tunnel that considered water levels in Lake Tana while maximising both power and irrigation potential. The modelling found that up to 75 000 ha of net irrigation, comprising commercial sugarcane and a range of small smallholder crops, could be developed in the Upper Beles catchment without providing additional storage, with dry-season flows through the tunnel averaging 77 m3/s. Given the broken terrain of much of the Upper Beles valley, a large project area of 138 145 ha was identified, extending along 60 km of the river valley and...