Groundwater-surface water connectivity of heavily modified rivers, County Durham, UK

Abstract

Groundwater and surface-water systems have long been considered fragmentally, lacking a holistic integrated understanding that is considered essential for sustainable catchment management. The high heterogeneity of local systems and the influence on water quality is typically unaccounted due to limited monitoring of hydrologic and hydraulic variables, particularly of minor aquifers. Often there is a dearth in understandings of the system characteristics, consequently impacting on wider catchment management. This thesis focuses specifically on water bodies in County Durham that are heavy modified attributing to their industrial past, with the current water quality being compromised by a multitude of historic and contemporary pressures. The research employs a combination of desk- and field-based approaches to investigate flow and solute patterns and processes operating at the groundwater-surface water interface.

The research demonstrates that through the collation of spatial data it is possible to assess the stream-aquifer connectivity by evaluating simple patterns in the landscape characteristics. In-turn challenging the local-scale connections and leading to subsequent investigations of the groundwater-surface water controls on water quality. Field-based investigations of the local systems highlight the integral role of near-stream sediments on the fate of flow and solutes from the surface and subsurface. Through the application of numerical modelling, flow pathways have been further interpreted, assessing the spatial and temporal interactions at the stream-aquifer interface in response to changing hydrological conditions. Findings indicate the likely role of the shallow groundwater having a detrimental effect on the cycling of flow, with dynamic responses reflecting variations in stream levels, thus highlighting the need to consider processes at the stream-aquifer interface that are typically overlooked. The findings of this research challenge the predominant targeted reductionist approaches to water management in systems of this sort, where the influence of the multitude of pressures pathways and their relation to the contemporary water quality has been overlooked. There is a need for practitioners to consider the freshwater systems over multiple dimensions and time to achieve sustainable water management.