Girmay G/samuel

Lake Water Balance: Water Balance Model on Topographically Closed Highland Lake Girmay G/samuel

This study was initiated to quantify the hydrologic components, assess the water balance and to provide bathymetric information of the lake. Data on change in volume of the lake, precipitation, stream flow and abstraction was recorded while evaporation and runoff were estimated. The net groundwater outflow was then determined from the water balance equation. The major components of inflow during dry season were direct precipitation and stream flow which contribute 66.7% and 33.3% respectively. Most of the outflow is in the form of evaporation constituting the highest portion (83.55%) followed by net groundwater outflow (16.19%). The rest 0.26% is the abstraction. Since the outflow was by far higher than the inflows, the lake level was decreased by 0.32 m over 135 days. The water balance analysis of the observation period revealed an inflow, outflow and decrease in volume of 2.19 million m3, 6.83 million m3 and 4.64 million m3 respectively. The annual water balance assessment also indicated an inflow and outflow of 24.25 million m3 and 21.89 million m3 respectively. The elevation-area-capacity relationship of the lake was developed in monitoring of amount of water and sedimentation.