Investigation on the water balance pattern of Lake Ziway
Lake, with one of the largest freshwater lakes in the rift valley of Ethiopia is very essential for agricultural, industrial and domestic water supply as well as stabilizing of ecosystem in the region. However, the total amount of water available in the lake has been diminished which resulted from the rapid increasing of population and hence expansion of industrial activities and irrigated agricultural around the lake. The objective of this study was estimating the hydrological fluxes and
... al fluxes and amount of water flowing to and from the lake. The conceptual rainfall-runoff model, HBV was used to model the hydrological components and over all water balance of the lake. Runoff from both gauged and un-gauged sub-basins of the basins were estimated using this model. Flows from un-gauged sub-basins were estimated by using spatial proximity method. Runoff was simulated for the period of 1993-2012. The HBV model was calibrated with the datasets from 1993-2005 and validation using an independent data from 2006-2012. The performance of the model was evaluated by comparing observed and simulated runoff and found to be acceptable with NSE value of 0.81 and 0.80 during the calibration and 0.75 and 0.73 during validation period for Meki and Katarr sub-basins, respectively. Results indicate that total areas of 1212 km2 un-gauged sub-basins are estimated 8.3% the total inflow to the Lake. This study indicates that annual inflow components of lake water budget showed declined trend whereas outflow components (evaporation and abstraction) showed increasing trend. Water abstraction had a significant role in temporal variation on lake level during average to low rainfall years. The declining of outflow of Bulbula River from this lake and rising in annual evaporation rate from the lake water surface certainly will be responsible for changing of this Lake to Endorheic Lake in near future. Therefore, it is recommended to look a solution for minimization of outflow components by considering future sustainability of the lake.