Assessment of Water Resources and Analysis of Safe Yield and Reliability of Surface Water Reservoirs of Asmara Water Supply System

Abstract

In a water supply system safe yield is the average annual volume that can be supplied to the system subject to an adopted set of operational rules and a typical demand pattern without violating a given level of service standard. It is dependent upon storage and hydrologic (rainfall/runoff/evaporation) characteristics of the sources, the source facilities, upstream and downstream permitted withdrawals and minimum in-stream flow requirements.For effective operation and management of a water supply system, it is important to have knowledge of water balance of the reservoirs and estimate their safe yield at a certain level of reliability. In this study, to assess water resources potential of existing surface water sources and new catchments and estimate the water balance of the water supply system, the hydrologic simulation model, SWAT (Soil and Water Assessment Tool) was utilized. The model was calibrated and validated successfully. The safe yield and corresponding reliability of reservoirs were estimated using a deterministic water balance model. The results of the water balance analysis and projected water demand were used to assess existing water supply situation and challenges in future. The assessment indicated that the gap between demand and supply at high population growth rate scenario is wide and very critical.To close the gap between the available water supply and the increasing water demand in the study area, utmost attention is needed by the decision making authorities and the management of the water utility to improve performance efficiency of the water supply system by instituting effective water governance and reducing leakage losses.