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Study region\ud Little Kinyasungwe River Catchment, central semi-arid Tanzania.\ud \ud Study focus\ud The structure and hydraulic properties of superficial geology can play a crucial role in controlling groundwater recharge in drylands. However, the pathways by which groundwater recharge occurs and their sensitivity to environmental change remain poorly resolved. Geophysical surveys using Electrical Resistivity Tomography (ERT) were conducted in the study region and used to delineate shallow subsurface stratigraphy in conjunction with borehole logs. Based on these results, a series of local-scale conceptual hydrogeological models was produced and collated to generate a 3D conceptual model of groundwater recharge to the wellfield.\ud \ud New hydrological insights for the region\ud We propose that configurations of superficial geology control groundwater recharge in dryland settings as follows: 1) superficial sand deposits act as collectors and stores that slowly feed recharge into zones of active faulting; 2) these fault zones provide permeable pathways enabling greater recharge to occur; 3) ‘windows’ within layers of smectitic clay that underlie ephemeral streams may provide pathways for focused recharge via transmission losses; and 4) overbank flooding during high intensity precipitation events increases the probability of activating such permeable pathways. These conceptual models provide a physical basis to improve numerical models of groundwater recharge in drylands, and a conceptual framework to evaluate strategies (e.g., Managed Aquifer Recharge) to artificially enhance the availability of groundwater resources in these regions.

The geological map shows a wide range of geoscientific information, primarily Bedrock Geology, Superficial Geology, Mass Movement Geology and Artificial Ground. The emphasis has traditionally been on “bedrock geology” and “superficial geology”, but an improved understanding of the nature and distribution of Artificial Ground is becoming increasingly relevant to development and regeneration in the urban environment (Rosenbaum et al., 2003). Information about previously developed ground is especially important, as it is often associated with potentially contaminated material, unpredictable engineering conditions and unstable ground. The mapping and classification of Artificial Ground using borehole information, historical maps and field visits provides valuable information to a variety of BGS and external users.