Thermal and hydraulic regime interactions in urban groundwater systems

Patton, Ashley 2026. Thermal and hydraulic regime interactions in urban groundwater systems. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Understanding subsurface thermal and hydraulic regime interactions has great potential to support hydrogeological characterisation. The Cardiff Geo-observatory, a rare dataset in terms of the spatio-temporal richness of groundwater levels and temperatures, was used to interrogate these relationships. The research aimed to develop understanding of these relationships in urban aquifers to ascertain how changes to urban landscapes are reflected in the subsurface by using groundwater level and temperature time-series data and repeat temperature-depth profiles (RTDPs) to derive subsurface properties and processes. Underutilised time and frequency domain methods were applied for the first time to boreholes across an aquifer to enable spatial hydro-geomechanical characterisation from tidal and barometric responses in groundwater heads. This identified changes in tidal signals following the construction of a barrage and, significantly, the technique allowed hydro-geomechanical properties to be mapped across the city, revealing the aquifer to be broadly confined. A new method of classifying seasonal groundwater temperature time-series curves into characteristic shapes was derived. It was demonstrated how this technique can be used to categorise the heat transport mechanisms at boreholes as either conduction-dominant or as also affected by recharge-driven advection. Neutral curves denote conduction-dominance, right-leaning curves occur with recharge, and ‘mixed’ curves identify the combined groundwater response to recharge and river influence. An existing method of interpreting RTDP shapes was refined using data available from Cardiff. Three profile shapes have been established and a conceptual model proposed to explain the behaviour. Type A profiles indicate conduction-dominant heat transport. Type B may represent a more thermally evolved profile of either Type A or C associated with earlier development of the city. Type C highlight historic changes in recharge patterns. The changes in heat propagation impact the subsurface temperature development associated with the subsurface Urban Heat Island effect and altered recharge conditions induced by the city’s development. This variation includes differences in the Zone of Seasonal Fluctuation and has implications for the siting of geothermal systems.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Earth and Environmental Sciences
Date of First Compliant Deposit:	26 June 2026
Last Modified:	26 Jun 2026 13:13
URI:	https://orca.cardiff.ac.uk/id/eprint/187758

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