The role of superficial geology in controlling groundwater recharge in drylands

Zarate, Emanuel 2023. The role of superficial geology in controlling groundwater recharge in drylands. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Groundwater is often the principal and most reliable source of water in drylands. Improved understanding and quantification of groundwater recharge is critical to water security in these regions. The structure and hydraulic properties of superficial geology likely plays an important role in governing the spatiotemporal complexity of groundwater recharge in drylands. However, these hydraulic processes are poorly understood and/or quantified. To elucidate the role superficial geology plays in controlling groundwater recharge, a combination of analyses and interpretation of field data, synthesis of literature and numerical simulations were performed. Conceptual models of groundwater recharge were developed from the results of geophysical surveys conducted in semi-arid Tanzania and combined hydrometric and geophysical investigations from an ephemeral stream in semi-arid Australia. The field investigations show that (1) ‘windows’ of superficial sand deposits occurring within layers of clay underlying intermittent rivers and ephemeral streams (IRES) provide pathways for potential focused recharge (2) these deposits act as collectors and stores that redistribute infiltrated water to zones of active faulting and/or similar permeable pathways, enabling recharge to the regional water-table and (3) a combination of the permeability contrast between these deposits and surrounding geology, and their volume controls this redistribution. The findings from the two field sites were combined with literature on drylands to propose a new framework for understanding recharge in drylands. The new framework groups recharge controls into a hierarchy of processes that encapsulate their role in converting rainfall to recharge. A series of numerical simulations were conducted using a distributed model representing an idealised IRES system with heterogeneous geology. The results quantify the sensitivity of geological and climatic controls on IRES systems predominant in the framework. This framework provides a ‘springboard’ for more accurately mapping, quantifying, and forecasting groundwater recharge in drylands with variable geology.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Earth and Environmental Sciences
Funders:	NERC GW4+ DTP
Date of First Compliant Deposit:	19 October 2023
Last Modified:	19 Oct 2023 10:32
URI:	https://orca.cardiff.ac.uk/id/eprint/163297

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