Understanding the effects of composition and configuration of land covers on surface runoff in a highly urbanized area

Abstract

A better understanding of the hydrologic impacts of high-intensity urbanization is necessary for urban planning aimed at mitigating the impact of land development on floods. This study investigated the effects of percent pervious cover (PPC) and associated spatial pattern on surface runoff in a high-density urban area surrounding the North Moat in Beijing, China. We selected 21 rainfall events that occurred in 2011 and 2012. Surface runoff during each rainfall event in the 76 subcatchments with different degrees and patterns of urbanization was simulated with a calibrated Storm Water Management Model. There was high estimation accuracy in both total runoff volumes and variations in runoff volumes per minute for single-event simulations. The modelled results showed that increases in pervious cover were significantly related to reduced runoff regardless of spatial patterns and rainfall levels, but pervious cover was more effective in controlling low amounts of runoff when PPC increased from a low value to 30–40%. Increases in PPC to 30–40% were associated with critical transitions in the spatial configuration of pervious patches, from strong fragmentation to strong connectivity, which greatly reduced runoff. The overland flow routing from impervious area over pervious area to outlet (IMPERV-PERV pattern) could significantly reduce most of the runoff when PPC was below 30%; but only significantly reduced light rain and moderate rain runoff when PPC was 30–60%, especially, the role of flow routing in controlling extreme rainstorm floods was usually not significant. The results demonstrated that the extents and spatial patterns of urban pervious and impervious surfaces have strong influences on runoff.