PERFORMANCE EVALUATION OF MICRO-EMBANKMENT DAMS IN AMHARA REGION

Abstract

The study area is found in Amhara Region which is bounded by 8°45' to 13° 30' N latitude and 036° 20' to 40° 45 'E longitude. The objective of the research is to evaluate the performance of the Micro-Embankment (M . E.) dams in the region. All dams are constructed for irrigation purpose. The total number of M.E.Dams constructed in the region were14 including those under construction till May 2006. The distributions of these dams in the basins are: 6 in Abay, 3 in Awash and 5 in Tekeze river basins. In this research, the existing status of each dam project was identified with the support of pictures. GIS arcview based database showing all features of the existing ; M.E.Dams ard under construction till 2006-05-07 is prepared. Some of the implemented projects were almost failed and some of them are functioning below 50% of their desiqned capacity. Among them, only one project was I performing a� 100% of its capacity. The major problems and cause of the • reduction of the capacity are drying of the reservoir; shortage of harvesting water; seepage through the dam body, outlet conduit, sedimentation; seepage under spillway bed and foundation of the dam.On the dam body erosion of down stream slope, animal dug holes and trees on upstream and downstream slope were observed.These features may lead to piping failures. Besides scouring the spillway wing wall, poor water management, improper dissipation of the spillway discharge were observed at some of the projects. This work also tried to evaluate the design and construction practices and identified the design problems by analysing reservoir operation, evaporation loss and embankment compaction using case study for three projects selected on the basis of availability of sufficient data . The result of the evaporation loss case study showed that loss by evaporation value was by about 0.58m depths per year. The case of reservoir operation showed that the project is not feasible to irrigate the designed irrigable areas and the dam crest level was not appropriate. The capacity and the reservoir depth reduced by 58*10 4 m 3 and 2.6m, respectively. The analyses of compaction of clay and shell material are only 60%and 70% acceptable out of 294 samples, respectively. The different recommendations are given with regard to reducing the observed problems & improving the current design practices.