Control of flow volume and contamination of surface runoff by Low Impact Development infrastructures in Shenzhen, China

Low Impact Development (LID) is aimed to construct green infrastructures which are able to make flexible responses to environmental extremes, specially to cope with natural disasters. With rapid development of urbanization, LID plays an increasingly important role in the Shenzhen city, located in southern China adjacent to Hong Kong, since it is characterized by high population density, high construction density of new buildings as well as frequent tropical storms. However, the current LID infrastructures in many areas in Shenzhen does not have desired functions: for instance, the pollutants in the storm water is not properly managed, the geology underneath the permeable installations is not considered so that optimal drainage effect can be obtained. Such impropriate design has resulted in serious issues of both flow volume and contamination in the surface runoff. In the present study, we use the campus area of the Southern University of Science and Technology (SUSTech) as the site for our case study. There are three types of LID infrastructure that have already been installed on SUSTech, namely the green roof, the permeable pavement and the grass ditch. We monitor the rainfall intensity and the surface runoff for 10 storms at the LID installations, and the change of composition of the typical containments in the storm runoff with time, at 1, 2, 5, 10, and 20 min. Sediment, nutrients (N and P), industrial organic chemicals, heavy metals and BOD are analyzed for both the inlet and outlet of the LID installations, so we have an overview of their current capacity for pollutant reduction. A coupled SWMM model and groundwater model (setup in MODFLOW) is developed, and the infiltration in the study area is simulated by giving different geological structures underneath the LID installations. This way, the location and type of the LID installations can be optimized to achieve maximum drainage effect. Our study can provide valuable insights into the future LID designs both in Shenzhen and elsewhere in the world.