Planning for Environmental Water Allocations: Hydrology - Based Assessment in the Awash River Basin, Ethiopia

Abstract

The research is financed by the Egyptian Government through the Nile Sector bilateral cooperation project

Abstract

With expanding water demand due to rapid socio-economic growth and shrinking supplies due to pollution and climate change impact, there is an increasing strain on the water resources of the Awash river basin. Furthermore, flow alterations due to the existing and the ongoing water resources infrastructure projects may adversely impact the natural life cycle of aquatic ecosystems in the river basin. In order to manage these consequences, compensation releases or allocation of environmental flows may be mandatory and calls for the establishment of environmental flows framework in Ethiopia. In this study, the environmental flows at selected five existing and proposed dam sites in the Awash river basin were investigated using six worldwide used hydrology-based methods, viz.: Desktop Reserve Model (DRM), Global Environmental Flow Calculator (GEFC), Tennant, Tessman, 7Q₁₀ and Q₉₅. The environmental flow volumes from the six methods were compared on mean annual, monthly average and monthly basis and it is found that the predictions from the DRM and GEFC are more reliable than the others. Comparative results indicate that minimum annual average flow rates of 4.4 m³/s (15 % of Mean Annual Flow (MAF)), 10.5 m³/s (19 % of MAF), 16.4 m³/s (22 % of MAF), 2.5 m³/s (17 % of MAF) and 24.2 m³/s (26 % of MAF) are required at the immediate downstream reaches of Melka kuntre, Koka, Awash Compensation, Kesem and Tendaho dams respectively. Accordingly, the annual average environmental flow throughout the basin varies from 15-26 % of the natural MAF. Although preliminary, being the first attempt in the Awash river basin, this study is expected to stimulate dialogue among experts and decision makers in Ethiopia.

Keywords: EFR, EFA, Tennant, Tessman, Q₉₅, 7Q₁₀, DRM, GEFC Software, Awash

DOI: 10.7176/JEES/9-11-08

Publication date: November 30^th 2019