Watershed Management: An Option to Sustain Dam and Reservoir Function in Ethiopia

Inappropriate use of land for agriculture and poor management of its ecosystem lead to environmental problems such as land degradation through soil erosion. Accelerated soil erosion is a major watershed problem in many developing countries including Ethiopia. Climate change, which apparently causes major climatic events such as flooding or drought, also accelerates soil erosion. Soil erosion in various forms such as sheet, rill, gully bank and bed, river bed and bank and landslides provide sediment to critical water bodies. Nutrients and chemicals from cropland and urban sewage are transported into the water systems. Many reservoirs which have been established for hydroelectric power, urban water supply and irrigation accumulate an alarmingly higher level of sediment than expected. Koka, Angereb, Legedadi, Gilgel Gibe I and other reservoirs are threatened by this accelerated sedimentation. Consequences of reservoir sedimentation include the loss of storage capacity and its subsequent effects. These effects include water supply shortages for human consumption, irrigation and hydropower; increased hydro-equipment maintenance and repair; a decline in water quality; the cost of removing sediment; blockage of navigational waters and loss of recreation opportunities. Aquatic ecosystems are modified by increased deposition of sediments and adsorbed or dissolved nutrients and chemicals, which commonly causes eutrophication which in turn negatively influences habitats of fish and other organisms. Some of the techniques suggested to reduce reservoir sediment concentration are technically less feasible as it requires design considerations during construction (which is difficult to implement for the existing dams). Removal of sediment is also economically demanding. Among the approaches and techniques proposed and implemented, integrated participatory watershed management is strongly recommended to reduce sediment inflow in sustainable pattern.