Effect of improper water and land resource utilization on the central Main Ethiopian Rift lakes

Abstract

The Ethiopian Rift is characterized by a chain of lakes varying in size, hydrological and hydrogeological setting. Some of the lakes and tributary rivers are used for irrigation, soda abstraction, commercial fish farming and recreation; and they support a wide variety of endemic birds and wild animals. Few lakes shrunk due to excessive abstraction of water; others expanded due to increase in surface runoff and groundwater flux from percolated irrigation water. Excessive land degradation, deforestation and over-irrigation resulted in sedimentation in lakes and increase in soil salinity. The chemistry of some of the lakes has also been changed dramatically. This paper addresses the major environmental changes in the last few decades in the central Main Ethiopian Rift lakes that resulted mainly from anthropogenic factors. The methods employed include field hydrogeological mapping supported by aerial photograph and satellite imagery interpretations, hydro-meteorological data analysis, water balance estimation, catchment hydrological and groundwater flow modelling and hydrochemical analysis. A converging evidence or integrated approach has been adapted to reconstruct the temporal and spatial variations of lake levels and hydrochemistry. The result revealed that the major changes in the rift valley are related mainly to recent improper utilization of water and land resources in the lakes catchment and direct lake water abstraction aggravated intermittently by climatic changes. The terminal lakes show dramatic reduction in level and increase in salinity. These changes appear to have grave environmental consequences on the fragile rift ecosystem, which demands extremely urgent integrated basin-wide water management practice.