Groundwater Models to Support Rural Water Development in Tanzania's Internal Drainage Basin (Kiteto and Simanjiro Districts)

The Internal Drainage Basin (Tanzania) is a semi-arid, enclosed basin with limited surface water resources. Groundwater has the potential to sustain communities through annual dry seasons, but groundwater development has been hindered by unpredictable well yields and water quality in the fractured bedrock aquifer, particularly in rural areas such as the districts of Kiteto and Simanjiro (Manyara Region). Computer models are one tool for understanding such fractured bedrock aquifer systems. In this study, I develop a groundwater flow model using the finite difference code MODFLOW for subbasins spanning Kiteto and Simanjiro Districts and validate the model with water level measurements from 69 wells. Data for the regional geology, well, and aquifer properties were gathered from the Istituto Oikos Onlus, the Ministry of Water, and the Japan International Cooperation Agency. In the best-fit model, median groundwater residence time from particle-tracking was 4,470 years, suggesting very slow renewal of groundwater. Of all water recharging into the subbasin, 83% evaporated or discharged internally to wetlands, and 17% was lost to interbasin flow. Near the Ndedo Fault and east of the Kimotorok Fault are favorable areas for groundwater development because the groundwater level is near the surface, but salinities are not extreme. To understand the role of major fault structures and changes in climate on the groundwater budget and residence times, I also performed a sensitivity analysis where I varied the hydraulic conductivity of faults and rate of recharge. Varying the recharge by a factor of 500% increased the proportion of recharge that discharges internally by 13% and caused characteristic groundwater residence time to increase by three percent. Decreasing recharge to 20% decreased the proportion of recharge that discharges internally by 48% and decreased the characteristic groundwater residence time by 8%. Changing the fault properties had a strong effect on compartmentalization and average depth-to-water, but little effect on residence time and internal discharge. Given the aquifer's sensitivity to recharge and uncertainties in future recharge rates under a changing climate, more recharge investigations are needed to improve groundwater models and management within the study area. Also, given the influence of fault zone hydrologic properties on average depth-to-water, field investigations of fault zone properties are recommended.College of Arts and Sciences Undergraduate Research ScholarshipCollege of Arts and Sciences International Research GrantNo embargoAcademic Major: Earth Science