Hydrology of the Lake Tana Basin, Ethiopia: Implication to Groundwater-Surface Waters Interaction

Abstract

Hydrological studies have been done in the Lake Tana basin to determine the groundwater recharge rate based on different methods, groundwater inflow to and outflow from the Tana Lake, and to understand the groundwater and surface waters interaction. Recharge rates of 195.6, 284.0 and 285.4 mm/year have been estimated based on base flow analysis, chloride mass balance (CMB) and soil water balance (SWB) methods, respectively. Base flow separation method shows mean shallow aquifer recharge that feeds the streams. The recharge estimates from CMB and SWB are nearly similar and the average of the two (284.7 mm/year) can be taken as the mean basin recharge rate. The difference between the basin recharge and the base flow (89.1 mm/year or 31.3% of the recharge) contributes to deep aquifers recharge.Tana Lake balance study has also showed leakage underflow of 954.8 hm³/year, which mixes with groundwater mainly in the Beles basin and to some extent in Tis Abay area. Groundwater inflow directly to the lake is found to be negligible.

Keywords: groundwater recharge, water balance, base flow, groundwater and surface waters interaction, Lake Tana, Blue Nile River, Ethiopia