Evaluation of groundwater recharge dynamics using the WetSpass Model in the Usangu Plains, Tanzania

Abstract

A comprehensive understanding of groundwater recharge dynamics is of great importance in enhancing the sustainable management of the groundwater resources and the sound planning of their utilization. This study aimed at evaluating the groundwater recharge dynamics in the Usangu Plains (20,810 km2) by the help of a hydrological GIS-based model named WetSpass. The Water and Energy Transfer between Soil, Plants, and Atmosphere under quasi-Steady State (WetSpass) model used land use/landcover, soil texture, topography, slope, groundwater table and hydrometeorology data to simulate the temporal (yearly and seasonal) averages and spatial differences of groundwater recharge, surface runoff and actual evapotranspiration. The findings of this study showed that 17.8% of the mean annual rainfall contribute to the groundwater storage while 66.1% and 16.1% are lost through evapotranspiration and surface runoff, respectively. The high rates of evapotranspiration occurred in the wet season and in the seasonal/permanent wetlands and water body. Also, the maximum amount of surface runoff took place during the rainy season and in the built-up and in bare land vegetation types given the impervious state of their ground surfaces. About 25% (1.025km3/year) of the annual recharge was found to be the groundwater that can be safely extracted for domestic and economic purposes. Compared to the water lost through evapotranspiration and surface runoff, the simulated portion of groundwater recharge is noticeably low. Consequently, it could be wise to initiate the rainwater harvesting technologies and artificial groundwater recharge strategies particularly in the zones with moderate and low recharge rates to boost the groundwater storage as its users cannot cease to increase.