Links between environmental change and its impacts on river flow regime and quality in urbanising catchments

This study was undertaken to investigate the effects of urbanisation on the river flow regime and water quality. The links between environmental changes represented by rainfall and Urban Extent (URBEXT) with the changes in the river flow, river temperature and dissolved oxygen were explored. This thesis focuses on the following question “does urbanisation has an effect on the river water quantity and quality changes?”. Two urbanising catchments in the United Kingdom, the river Ray at Water Eaton and the river Cut at Binfield were selected for this study. As a comparison, nearby similar sized rural catchments, the river Enborne at Brimpton and the river Winterbourne at Bagnor were also selected. There was no significant time-trend of rainfall found in all urban and rural catchments in all aggregations (annual, summer and winter). For river flow, positive time-trends were found in the two urban catchments in all aggregations with the exception of no significant trend was found in the winter in the river Cut at Binfield. The log-log regression analysis found that in the two urban catchments, URBEXT alone had a strong positive relationship with the changes in mean annual flow. When climate variability is included, the URBEXT signal was amplified. Contrasting results were found in all rural catchments where there was no significant evidence of time-trend in the river flow. Increasing temperature and dissolved oxygen values were found in all aggregations in the river Ray, while in the river Cut these values increasing only in the winter. URBEXT had a significant positive relationship with temperature and dissolved oxygen in the river Ray. When rainfall and river flow are included, the URBEXT signal was reduced. This study also found a strong positive relationship between river flow and the increase of dissolved oxygen value in the river Ray. On the contrary, there was no significant time-trend in temperature and dissolved oxygen was found in all rural catchments. Urbanisation was found to be a potential driver of the increase in river flow, which might lead to detrimental rather than beneficial effects. Nevertheless, the effect on water quality was somewhat spurious and showed mixed results. Despite not showing any significant trend, the present temperature and dissolved oxygen values in the more natural environment of rural catchments still showing a better state.