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The Climate Controls and Process of Groundwater Recharge in a Semi-Arid Tropical Environment: Evidence from the Makutapora Basin, Tanzania

Seddon, David; (2019) The Climate Controls and Process of Groundwater Recharge in a Semi-Arid Tropical Environment: Evidence from the Makutapora Basin, Tanzania. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Groundwater is a vital source of freshwater in semi-arid sub-Saharan Africa. Climate change, to which this region is particularly vulnerable, and increasing water demand are expected to increase the strategic importance of groundwater. The responses of groundwater systems to these forcings remain unclear. Here, in the intensively monitored and pumped groundwater system in the Makutapora Basin of central Tanzania, an analogue for semi-arid tropical areas underlain by weathered and fractured crystalline rock aquifers, I: (1) assess the relationship between precipitation intensity and groundwater recharge, (2) delineate the predominant recharge processes, and (3) project the impacts of climate change and increasing groundwater abstraction on future groundwater resources. Analysis of one of the longest known groundwater-level records in tropical Africa using a modified water-table fluctuation method, incorporating a numerical flow model to account for transience in response to pumping, shows more intensive precipitation disproportionately generates groundwater recharge. This bias is corroborated by a comparison of the stable-isotope composition of groundwater and precipitation as a function of intensity. Recharge is shown to occur via leakage from ephemeral streambeds through the formation and decay of groundwater ‘mounds’. Stable-isotope tracers and hydrometric evidence of streambed inundation confirm the predominance of focused recharge pathways. Projections of groundwater resources, using a fully integrated MIKE SHE/MIKE 11 model, indicate that changes to recharge due to climate change will be small in the context of likely increases in groundwater abstraction. However, the bias of disproportionate groundwater recharge production from intensive precipitation, together with new insight regarding the processes and controls of recharge in this semi-arid environment, suggest that climate change may not only enhance groundwater recharge but also enable strategies (e.g. Managed Aquifer Recharge) to artificially enhance the sustainability of groundwater withdrawals since these events and processes are predictable.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: The Climate Controls and Process of Groundwater Recharge in a Semi-Arid Tropical Environment: Evidence from the Makutapora Basin, Tanzania
Language: English
Additional information: Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL SLASH
URI: https://discovery.ucl.ac.uk/id/eprint/10078654
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