DISCUSSION ON PATHWAYS FOR CAPACITY UPGRADING OF STORMWATER DRAINAGE AND FLOODING ALLEVIATION IN DEVELOPED URBAN AREAS BASED ON SWMM

With the high-quality development of urbanization, the standard of urban stormwater drainage and flooding alleviation are gradually increasing, therefore, how to realize the upgrade of stormwater drainage systems in developed areas is one of the important aspects of urban renewal. Taking a post-development area in Beijing as the research object, the pathways for upgrading the capacity of stormwater drainage system and the standard of flooding alleviation according to the revised Standard for the Design of Outdoor Wastewater Engineering(GB 50014—2021) were proposed and evaluated by SWMM. The results showed that, through the sponge city construction, the capacity of the existing stormwater drainage pipe network could be improved to 2-year return periods from 1-year, when the volume capture ratio of annual rainfall was 80%. On basis of sponge city construction, the operation of the stormwater drainage pipe was evaluated under the flooding alleviation standard of 20-year's return periods, then the centralized and decentralized distribution ways of detention tanks were further proposed and compared. The simulation results showed that the centralized distribution of detention tanks, which located nearby the outlet of the stormwater drainage pipe, couldn't alleviate the overflow from the drainage pipes in the upstream area, while the decentralized distribution of detention tanks could effectively eliminate the overflow from the drainage pipes in the upstream area, and upgrading the flooding alleviation capacity to 20-years' s return period. Therefore, according to site conditions, the optimal pathways to upgrading the capacity of stormwater drainage were sponge city construction, and upgrading the standard of flooding defense was the decentralized distribution of detention tanks in urban post-development areas.