NUMERICAL STUDY ON ORGANIC SEDIMENT DEPOSITION IN NOMI RIVER ESTUARY, TOKYO

In the brackish water reach of Nomi River in southern Tokyo, anaerobic reduction of organic sediments discharged from combined sewer system causes water quality problems such as floating scum, foul odors and cloudy water after rain storms. In this study, a numerical model was developed for the sedimentation process from sediment generation by rain runoff, through discharge from sewer system outlets to deposition in the downstream brackish water reach by combining a MIKE URBAN-based sewer runoff model with a two dimensional hydrodynamic model including sediment deposition and resuspension. Numerical simulation was conducted for the storm events during one-month of summer in 2017 by adopting the sediment settling velocity which was obtained by laboratory test, and the characteristics of deposition and resuspension in the river was discussed. The model performance was verified fairly well using the results of sediment trap experiments carried out in the simulation period.