Seasonal groundwater recharge in Arusha town basin, Tanzania (finite difference method).

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University of Dar es Salaam
Arusha Town has in the recent years experienced rapid growth in its commercial, industrial and agricultural sectors. Its present water demand stands at 40,000 M3/day. The water sources are mainly springs and bore holes. The aim of this study is to estimate the groundwater recharge into the Arusha Town aquifer by mathematical modelling techniques. The area of the aquifer is 36 square kilometers covering Arusha Town and its well field. The period considered was from January 1992 to April 1993. The year 1992 was used for model calibration while the first four months of 1993 used for verification. The aquifer was divided into a grid system of 26 by 26 nodes for the application of a mathematical model. With Dupuit assumptions, a finite difference equation describing groundwater flow for transient state was derived and a Fortran computer model to simulate the flow over the entire grid system developed. Due to lack of data on the boundary conditions, surface interpolation of the observed water levels from the observation wells was done to provide the water surface for the initial conditions in January 1992. Hydraulic conductivity of 3.9 M/day and specific yield of 0.15 for the aquifer were obtained from pumping tests analysis. The model estimates recharge by an optimization procedure (simple search technique). It tries different values of recharge to generate a series of computed head values at grid points of the domain area. The value of recharge, whose computed head values compares most closely to the observed values at given observation wells, is taken as the recharge at that time step or month. The study revealed that 13.7% of annual rainfall ended up as recharge and on average the recharge rate was 14,000 M3/day. Results from calibration showed that the optimum value of hydraulic conductivity of the aquifer is 11.5 M/month. The response of the water table to rainfall is about two months. In conclusion the aquifer cannot provide the expected 25,000 M3 of water per day to satisfy the Town's demand. This therefore calls for development of alternative water sources and a strict management strategy, which may be based on this study.
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Groundwater flow, Hydrologic models, Arusha region, Tanzania
Odero, O. M. (1998). Seasonal groundwater recharge in Arusha town basin, Tanzania (finite difference method). Masters dissertation, University of Dar es Salaam. Available at (