Role of Low-Impact Development in Generation and Control of Urban Diffuse Pollution in a Pilot Sponge City: A Paired-Catchment Study

Low-impact development (LID) is increasingly recognized as one of the most important stormwater source controls on a small scale. However, few studies have reported how LID practices affect the generation and control of urban diffuse pollution at the scale of urban drainage units. In this study, paired conventional and LID drainage units (CDU and LDU) were used to distinguish the role of LID practices in urban sediment accumulation and release at a residential drainage units scale (about 1-2 ha). The urban sediment dynamic build-up process, amounts per unit to equilibrium, amount and percentage of urban sediment washed-off by rainfall, pollutant concentrations during rainfall-runoff processes, and discharge water volume and pollution load from drainage units were all notably different between the paired drainage units. These results indicated that (1) LID practices have a combined effect on urban sediments accumulation and release on a drainage unit scale via reduction of the source area, changes in microtopography and formation of a greater sink area; (2) landscape alterations with LID practices within a small catchment reduced and disconnected areas with impervious surfaces, subsequently reducing the kinetic energy of wash-off and transport for urban sediment; (3) LID practices exerted notable hydrological responses and water quality responses at a micro urban catchment scale by reducing the first flush load and entire process discharge load. The results presented herein will facilitate optimal design for reliable treatment performance and assessment of the effectiveness of LID practices on an urban drainage units scale.