Groundwater hydrodynamics and sustainability of Addis Ababa city aquifer

Abstract

In the past two decades, Addis Ababa city has been under continuous demand of additional water supply improvement due to critical shortage of supply became particularly a serious problem at the outskirts of topographically high places. In order to overcome the existing problem, groundwater development optioned as emergency water supply project. However, the development continued without giving attention to its sustainability and now takes about 63% of the share. Over the last decade, many well-fields have been drilled; Akaki, Legedadi-Legetafo-Ayat, South-Ayat-North-Fanta, and Addis Ababa pocket areas in the same watershed that have an area about 1490 km2. The main objective of this study was to assess the groundwater hydrodynamics and sustainable utilization of the sources. For the study, 166 deep borehole completion and pumping test well fields within and around Addis Ababa were used. From the analysis it was found that hydraulic conductivity and transmissivity in the watershed vary from 0.02 to 256 m/day and 5.4 × 101 to 2.16 × 104 m2/day respectively. The major aquifers are fractured & scoriaceous basalt, scoria, fractured ignimbrite or a combination of these rocks. Analysis of water level contour map for Akaki well-field indicated that 84.50% of the current pumping water levels were below the dynamic water level. In particular, old Akaki well-field has been severely depleted. Out of 24 drilled wells, 13 of them are abandoned as water level and discharge have significantly declined. Despite huge importance of groundwater, it has been understood poorly and undervalued. It is a finite resource and the aquifers can become depleted as this extraction rates which exceed recharge rates. Therefore, groundwater management should be practiced through reliable aquifer characterization, sustainable development, planning of conjunctive use of surface water and artificial recharge.