Understanding the impact of the built environment mosaic on rainfall-runoff behaviour

Despite the importance of urban flooding, there are surprisingly few experimental studies of observed flood events from high-resolution hydrological data in urban systems to inform model development and parameterisation. The aim of this study was to understand how the interaction between rainfall and the layout of the built environment influences rainfall-runoff behaviour. A 2-year field campaign was undertaken to monitor rainfall runoff behaviour of two small (<1 ha) catchments representing different types of residential developments in southern England. Statistical analysis of 34 events captured in both catchments was undertaken to investigate the link between key event characteristics (peak flow and percentage runoff) and event drivers (event causing rainfall and antecedent soil moisture). The results show that peak flow is most sensitive to 10 min rainfall intensity while antecedent soil moisture is less important. The sensitivity to rainfall is strongest on the most densely urban catchment. In contrast, no relationship between percentage runoff and neither rainfall nor antecedent soil moisture could be detected in the densely urban catchment, while both factors were found to be significant in the less urbanised catchment. These results reported here demonstrate that the layout of the build environment exerts a strong influence on the hydrological characteristics at the local scale of relevance in urban hydrology and further model development of important when planning flood mitigation measures in urban areas.