Groundwater flows in an urbanised floodplain and implications for environmental management

With population growth, the large lowland floodplains of our major rivers have become increasingly urbanised. Environmental issues have arisen with the juxtaposition of these urban developments and the aquatic and terrestrial ecosystems associated with the rivers and their floodplains. The floodplain sediments are often highly permeable, and hydraulically well-connected to the water courses, and therefore the interaction of the urban environment and groundwater is very important. The overall aim of this PhD is improved understanding of the hydrological regime of urbanised floodplains, in particular groundwater hydrology, leading to better environmental management. The PhD uses as a case study, the floodplain of the River Thames in the city of Oxford. Through surveys, data collection via an extensive monitoring network, and the development of conceptual and numerical models, the floodplain has been characterised and the hydrological processes better understood. Focussed studies, working with key stakeholders, have been undertaken relating to fluxes of pollutants into and through the subsurface, and to the role of groundwater in urban flooding. The research undertaken has resulted in a better understanding of: the impact of river management structures on water and nitrate exchange between rivers and floodplain aquifers; the influence of legacy waste dumps on water quality in floodplain aquifers, and quantification of the fluxes of associated pollutants to rivers via the subsurface; the conditions and mechanisms that control the occurrence of groundwater flooding in urbanised floodplains; and the role groundwater and shallow geology play in controlling the duration of flooding in urbanised floodplains, through the development and application of a model system for simulating flooding that links flood inundation and groundwater flow models. Through these focussed studies a range of generic recommendations are made for environmental managers, as well as recommendations for future work