Application of isotope and water balance approaches for the study of the hydrogeological regime of the Bishoftu crater lakes, Ethiopia

Abstract

The major Ethiopian rift lakes have been studied for various purposes in the last few decades. However, crater lakes situated elsewhere in the country are some of the poorly understood hydrologic systems. This study focuses on quantifying the groundwater fluxes and assessment of the hydrogeological regime of the Bishoftu Crater Lakes using conventional water balance and stable environmental isotope (2h and 18o) techniques. The convenient geological setting of these lakes has provided a suitable base for determining groundwater exchange rates using stable isotopes coupled with hydrologic balance. The result indicates that these lakes have highly variable groundwater fluxes. Evaporation and groundwater fluxes are the major components of the hydrologic balance. Unlike the other lakes, lake Hora appears to have extremely low groundwater outflow. The lakes are highly evaporated with respect to the present day precipitation. Other groundwater and surface water sources are relatively depleted in the heavy isotopes. The isotope and hydrochemical signature indicates that the circulation of groundwater and recharge is fast and the regional groundwater flow direction is from north to south. SINET: Ethiopian Journal of Science Volume 24, No. 2 (December 2001), pp. 151-166 Key words/phrases: Crater lakes, Ethiopian rift, groundwater, isotopes, water balance