Estimation of groundwater recharge in the Mzinga watershed, a sub-catchment of the Ruvu river basin: a case of Dar es Salaam

This study has attempted to estimate natural groundwater recharge in the River Mzinga watershed, a sub - catchment of the Ruvu River basin. Groundwater recharge was estimated using three methods including chloride profile, water balance and Hydraulic method. Estimates of groundwater recharge of 64.9mm/year, 70.12mm/year and 37.5mm/year were obtained using the methods, respectively; resulting in mean groundwater recharge value of 57.5mm/year to the watershed. This mean groundwater recharge value account to about 5% of the long-term mean annual rainfall of about 1200mm. The average aquifer parameters were evaluated to be 4.07E-04 m2/s and 1.75E-05m/s for Transmissivity (T) and Hydraulic conductivity (K), respectively. Flow net analysis shows that groundwater is recharged at the Pugu and Manerumango hills and flows towards the East. Chemical analysis reveals that about 60% of the boreholes are intruded by salt water. It has been recommended that hydro - meteorological data and groundwater levels monitoring be conducted within the watershed for future refinement of the groundwater recharge estimates.