Development of Decision Support Tools for Sustainable Water Development and Management in Urban Areas: Case Study of Asmara Water Supply System, Eritrea

Abstract

The scarcity of water for urban use is the major problem in many developing countries. With increasing pressures due to urbanisation, population growth, aging infrastructure, climate change, coupled with an unsustainable and ineffective urban water management, cities and urban areas in developing countries are facing enormous difficulties. This study sought to develop decision support tools for sustainable and efficient management of the water supply resources for Asmara city and surrounding areas. The study aims on the process of building systems for performance measurement, monitoring and analysis, and setting benchmarking targets to improve the efficiency of the water supply system and the operational and management practice of Asmara Water Supply Department (AWSD). The level and quality of water supply services provided by AWSD was evaluated using standard performance indicators and with information gathered from customers. The technical, financial and management efficiencies of AWSD were found to be very low, which were reflected through poor score on several standard performance indicators and low level of customers’ satisfaction. To assess the water resources potential of the existing surface water sources and new catchments, hydrologic simulation model, SWAT (Soil and Water Assessment Tool) was utilized. The model was calibrated and validated using Mai-Nefhi reservoir water balance. The annual average streamflow volumes of the current catchments utilized as sources of water supply and the future catchments were estimated to be 21 MCM (21 x106 m3) and 27 MCM respectively. The hydrological model was also applied to establish the impact of climate change to the water resources of the region. The streamflow in the Mai-Nefhi watershed was analysed with projected rainfall and temperature changes for the periods 2011-2100 under A1B, A2 and B1 greenhouse gas emission scenarios using five Global-Circulation-Models (GCMs). While the models predicted an increase in monthly precipitation, the results of the hydrological analysis show that changes on annual streamflow were less significant because of the corresponding increase in evapotranspiration due to increasing temperature. As a decision making tool and for effective operation and management of the Asmara water the supply system, it is important to develop water balance of the reservoirs and estimate their safe yield at a certain level of reliability. In this study a deterministic water balance model was developed to estimate the safe yield and corresponding reliability of the existing water supply reservoirs. The analysis results and projected water demand were used for assessment of the current situation and expected critical water shortage problems in future. The assessment indicated that the gap between demand and supply at high population growth rate scenario is wide and very critical. One of the most important decision making tools for a well-managed and efficient water supply system is knowledge of hydraulic performance of the water distribution network. In this study, analysis of the water distribution network was performed with a hydraulic simulation model, EPANET-2.0. Extended period simulation, based on patterns of hourly water demand and operational parameters, were conducted. The existing pipe network system in Asmara has a fair distribution covering most of the demand zones within the city. The analysis showed that the demand zones in the North East of Asmara are experiencing very low nodal pressures and low velocities. The water supply system in Asmara is in critical situation and the challenges for the future could be enormous. The current problems provided strong impetus to evaluate the management capacity and performance of the water utility. It was found that the level of water production and water consumption are low, and AWSD was found to be less effective and less efficient. The performance and benchmarking outcomes of this study are expected to provide mangers of AWSD with information or tools for decision making aimed at improving water service coverage through appropriate management, technical and financial interventions in the short term, and to achieve sustainable water resources utilization and development, higher management efficiency, and equitable water distribution system in the long term.