Assessing sponge facilities by volumetric and hydrological model methods

To improve the scientific framework and rationality of sponge facilities, and fully leverage their efficiency, assessment based on volume and hydrological models was proposed． This was first applied to pilot area of spongy city in Qian’an, to be quantified by volume method, with optimal path for rainwater control． Short-term (2h) design rainfall scenarios with different recurrence periods (2-, 5- and 10-year) were used to assess construction efficiency. Compared with “Outlet Routing” and “Impervious Area Routing”, “Pervious Area Routing” was more consistent with the construction concept of sponge city. Under 2-, 5- and 10-year design rainfall scenarios, total reduction rates of rainwater runoff after construction of sponge facilities were 86.9%, 82.4% and 79.6%, respectively, average reduction rates of peak runoff were 94.57%, 87.89% and 86.45%, the length of stormwater pipeline with maximum filling degree exceeding 80% decreased by 86.55%, 85.27% and 64.48%, respectively． Under the recurrence period of 10 years designed rainfall, the maximum water level in the well of the overflow node at node “J31” decreased by 1.332 m after construction of sponge facility compared with before, and other 9 overflow risk nodes also decreased significantly． These data suggest that under the design rainfall scenario of short-term and low recurrence period, sponge facilities showed good reduction on total runoff and peak discharge, significant reduction on drainage pressure of rainwater pipelines, and efficient control on overflow risk of nodes． These data will be useful for future deployment of source emission reduction facilities in the construction of sponge cities．