Effects of sediment deposit on the hydraulic performance of the urban stormwater drainage system

Abstract

Sediment deposit is a critical factor strongly affecting the drainage capacity of the conduits due to its cross-section area narrowing and roughness increasing. In this study, a numerical model was applied to investigate the influences of sediment deposit on the hydraulic performance of the drainage conduits. The Nhieu Loc - Thi Nghe (NL-TN) basin, located in Ho Chi Minh City, Vietnam, was selected as a case study. The drainage network of the NL-TN basin was simulated by using the EPA-SWMM model. The effects of sediment deposit were assessed by a non-dimensional comparison of the simulated peak flows of the sediment-deposited conduits and the clean ones. The results indicated that the sediment deposit significantly affects the flow capacity of the conduits and could cause severe inundation. Narrowing of the cross-section area has more impact on the hydraulic performance of the conduit than the increase in the roughness. A 40% increase in the Manning coefficient could decline the peak flow to approximately 80-90%, while a 40% increase in sediment thickness depth could degrade the peak flow by about 60-70% to compare with the peak flow of the clean conduit. The findings could support decision makings on the operation and maintenance of the sewer system and adaptation to extreme rainfall events.