Hydrodynamics of Selected Ethiopian Rift Lakes

Abstract

The Main Ethiopian Rift Valley Lakes suffer from water level fluctuations due to several natural and anthropogenic factors. Lakes located at terminal positions (no surface water outflow) are highly affected by the fluctuations. These fluctuations are disturbing the stability of the ecosystems, putting very serious impacts on the lives of many animals and plants around the lakes. Hence, studying the hydrodynamics of the lakes was found to be very essential. The main purpose of this study is to find the most significant factors that contribute to the water level fluctuations and also to quantify the fluctuations so as to identify the lakes that need special attention. The research methodology includes correlation and least squares regression of lake levels on rainfall, discharge and evaporation, multi-temporal satellite image analysis and land use change assessment. The results of the study revealed that much of the fluctuations in the lake water levels are caused by human activities especially for the lakes in the Central Ethiopian Rift. Lakes Abiyata, Chamo, Ziway and Langano are declining while Abaya and Hawassa are rising. Among the studied lakes, Abiyata is drastically reduced in size (about 28% of its area in 1986) due to both human activities (most dominant ones) and natural factors.  The other seriously affected lake is Chamo with about 11% reduction in its area between 1986 and 2010. Lake Abaya was found to be relatively stable during this period (showed only a 0.8% increase in its area).

KEYWORDS: Correlation, Fluctuation, Lake Level, Landsat Satellite Images, Land Use Change, Least Squares Regression.