A Dissertation Submitted in Partial Fulfilment of the Requirements for the Degree of Doctor of Philosophy in Water Resources Engineering of the Nelson Mandela African Institution of Science and TechnologyConjunctive use of surface water and groundwater is rapidly growing in many developing
countries as an adaptation strategy to climate variability and change. However, the interactions
between the groundwater and the surface water systems are not adequately understood, especially
among the East African rift valley lakes, where data paucity has limited studies and reporting on
the spatial influence of catchment heterogeneity. In its humble contribution to sustainable water
development, this study aimed to present a platform for understanding the influence of climatic
variation and anthropogenic activities on surface water–groundwater interactions. To be relevant
locally, Lake Babati, a freshwater lake in Northern Tanzania that provides the community with
fish, freshwater, and a habit for hippopotamus, was studied. The study applied hydrological
simulation, grey relational analysis, and stepwise regression analysis to model the hydrological
behaviour of the lake. Further, it used hydrogeochemistry and environmental isotopes to identify
groundwater fluxes and draw the conceptual understanding of surface water – groundwater
interaction and applied topography-based indices to spatially map groundwater potentials within
the catchment. The results showed that Lake Babati level is significantly declining (p-value < 0.01)
at a rate of 25 mm per annum. The lake level decline could not be explained by climatic variability
since the decline occurred when both evaporation and rainfall showed no significant changes either
seasonally or annually. Instead, the consistent decline of the lake level in all seasons could be due
to the expansion of the spillway, which effectively lowered the lake reservoir level and increased
the lake outflow in rainy seasons. The hydro-geochemistry and isotopes data showed that the lake
water and groundwater interact and are in hydraulic connections. Further, using Height Above
Nearest Drainage based and Topography Wetness Index based methods, the study developed two
groundwater potential maps to predict groundwater spatial variability and guide groundwater
prospecting efforts and subsequent development. Given that Lake Babati is in a hydraulic
connection with the groundwater, its consistent decline will likely impact the groundwater system.
Similarly, abstracting groundwater at unsustainable rates could lower the lake levels further.
Therefore, integrated water resources management is required for sustainable water resources
development and management in the catchment. Mandatory and continuous monitoring of the
water resources (groundwater levels, river flows, and lake levels) is recommended to generate
quality in situ data for future studies
