Assessment of sponge facilities by using volumetric method and hydrological model method

In order to improve the scientificity and rationality of the layout for sponge facilities, and fully leverage the efficiency of sponge facilities , a method of sponge facilities assessment based on volume method and hydrological model method was proposed. The pilot area of spongy city in Qian’an City was selected as the study area, the sponge design scheme was quantified by volume method, the optimal path for sponge facilities to control rainwater was proposed by hydrological model. Furthermore, 2 hours design rainfall scenarios with different recurrence periods such as 2-year, 5-year and 10-year were selected to assess the construction efficiency of sponge facilities. The results showed : (1) Compared with the mode of “Outlet Routing” and “Impervious Area Routing”, the runoff discharge mode of “Pervious Area Routing” was more consistent with the concept that rainwater runoff on the site was preferentially absorbed and treated by sponge facilities in the construction of sponge city; (2) Under the 2-year, 5-year and 10-year design rainfall scenarios, compared with the case before the construction of sponge facilities, the total reduction rates of rainwater runoff after the construction were 86.90%, 82.40% and 79.60%, respectively, the average reduction rates of peak runoff were 94.57%, 87.89% and 86.45%, at the same time, the length of the stormwater pipeline with the maximum filling degree exceeding 80% decreased by 86.55%, 85.27% and 64.48%, respectively. (3) Under the recurrence period of the 10 years designed rainfall, the maximum water level in the well of the overflow node at node "J31" decreased by 1.332m after the construction of the sponge facility compared with the case before construction, and the other 9 overflow risk nodes also decreased significantly. Above results showed that under the design rainfall scenario of short duration and low recurrence period, sponge facilities had good reduction effect on the total runoff and peak discharge in the study area, a significant reduction effect on the drainage pressure of rainwater pipelines, and a good control effect on the overflow risk of nodes, which will provide useful reference for the future deployment of source emission reduction facilities in the construction of sponge cities.