Numerical simulation study of urban hydrological effects under low impact development with a physical experimental basis

Global climate change and rapid urbanization led to frequent extreme rainstorms and waterlogging. Low impact development (LID) as an essential measure of urban stormwater control, it is necessary to explore the urban hydrological response under low impact development combined with physical experiment and numerical simulation. This paper takes the Beiyangyuan campus of Tianjin University, where numerous LID practices have been implemented, as the study area. The prototype permeable pavement in the campus was scaled down to a laboratory-scale for infiltration experiments. The results show that the Horton infiltration model could describe the infiltration process of permeable concrete and grass-planting brick. The initial infiltration rate of the permeable concrete is large but decays faster. In contrast, the infiltration process of the grass-planting brick decays slower, and the stable infiltration rate and infiltration capacity are higher than that of the permeable concrete. The mean infiltration rates measured for the permeable concrete and the grass-planting brick were 95 mm/hr and 190 mm/hr, respectively. A SWMM-MIKE21 coupled model was constructed based on the LID experimental results to explore the effects of the removal or density reduction of the LID practices on surface hydrological processes. The results show that permeable pavement performs best in the reduction of runoff volume, inundation area, and inundation depth, while the bio-retention cell takes the second place, and the sunken greenbelt has limited effect. Frequent light rainfall is sensitive to the density of LID practices, and the implementation of even a tiny percentage (4% of the catchment area) of LID practices can be effective in controlling runoff. The removal or density reduction of LID practices has little effect on the inundation region but leads to an increased possibility of flood risk due to increasing inundation depth.