Quantitative calculation of stormwater regulation capacity and collaborative configuration of sponge facilities in urban high-density built-up areas.

Implemented in the frequent extreme rainstorms, aggravation of non-point source pollution, and complex drainage system of urban built-up area, sponge facility practices often intertwine with a very large number of hydro-environmental and socio-economic considerations and constraints. Due to the lack of basic and measured data, fragmented engineering design, more systematic and strategic approaches to address this multi-scale, and multi-parameter problem of practice allocation should be planned and optimized. In this study, a practical quantitative calculation method of stormwater regulation capacity in urban built-up areas is proposed. The details are as follows: the sub-catchment areas are divided by using the drainage pipe section editing function of Auto CAD and the regional analysis function of ArcGIS, and the stormwater regulation capacity in study area to be reconstructed is divided into four grades to define the water-sensitive areas according to the comprehensive runoff coefficient (α), which were excellent (α < 0.6), good (0.6 ≤ α < 0.7), medium (0.7 ≤ α < 0.8), and poor (α ≥ 0.8). The stormwater regulation capacity of green spaces is determined by empirical model calculation and soil moisture hydrograph field measurement. The measured soil saturated hydraulic conductivity in the study area was about 110 mm/h. The drainage capacity of the pipe networks was determined by the length of the overloaded pipe section. Under the conditions of 10a and 50a rainfall return period and 3-h rainfall duration simulated by SWMM, the length of the overloaded pipe section accounts for 33.0% and 40.8% of the total, respectively. Based on the identification of water-sensitive areas in urban high-density built-up areas, the quantitative calculation method of stormwater runoff regulation capacity was constructed through the calculation of the coupling coordination degree of "source-midway-terminal" infrastructures and the layout of storage tanks in the overloaded pipe section. These can estimate the current situation of stormwater regulation capacity of different sizes in urban built-up areas and formulate the optimized planning scheme of sponge reconstruction projects.