The sewage coverage rate in Tokyo ward has reached 100%, however, 80% of this coverage is combined sewer systems that were built before 1980. Consequently, large quantities of organic pollutants are discharged from the rainwater outlets into rivers during heavy rainfalls. the organic pollutants accumulate in downstream brackish-water regions, and water quality problems such as floating scum, foul odors, and cloudy water arise as a result of chemical changes associated with bottom water becoming anaerobic. In this study, the suspended solid (ss) runoff characteristics were investigated in the nomi river drainage basin in which a combined sewer system handles 100%. the overflow water depth and ss were measured at the weir in one rainwater outlet during two storm events, and the parameters for miKe urban software that calculates sewer runoff were adjusted in the ranges recommended by the manual so that the observation results could be reproduced well. next, the model was applied to the 38 outlets in the entire catchment of the nomi river, and the estimated discharges were input into a one-dimensional unsteady river flow model. observational results of water level and turbidity measurements within the river channel were satisfactorily reproduced by the calculation
combined sewer system, rainfall runoff, SS discharge, urban catchment
 Bureau of Sewerage Tokyo Metropolitan Government, Sewerage in Tokyo2016, p. 9, 2016.
 Miura, S., Hotta, T., Negishi, H., Tsuruta, Y. & Ishikawa, T., Modelling of colloidal sulfur in salinity-stratified urban streams. Proceedings of the 37th IAHR World Congress August 13–18, 2017, Kuala Lumpur, Malaysia, pp. 3442–3449, 2017.
 Yamazaki, M. & Tsukui, K., Study on the formation of scum in rivers (1) Study on the origin of scum, Annual report of the Tokyo Metropolitan Research Institute for Environmental Protection 1991, pp. 171–179, 1991.
 Yamazaki, M. & Tsukui, K., Study on the formation of scum in rivers (2) Results of Investigation for Sedimental Conditions in Shiratoribashi-Iidabashi Area of Kanda River. Annual report of the Tokyo Metropolitan Research Institute for Environmental Protection 1991–1992, pp. 182–184, 1991.
 Yamazaki, M. & Tsukui, K., Study on the production of scum in river (3) Change in the Sediment Characteristics by a Rainfall. Annual report of the Tokyo Metropolitan Research Institute for Environmental Protection 1992, pp. 167–171, 1992.
 DHI, MIKE URBAN , available at http://mikepoweredbydhi.com/products/mike-urban
 DHI, MIKE 11, available at https://www.mikepoweredbydhi.com/products/mike-11
 Bureau of Construction, Tokyo Metropolitan Government, River improvement plan in the Nomi river basin, 2017.
 Bureau of Sewerage, Tokyo Metropolitan Government, Sewerage Mapping and Information System (SEMIS), available at http://www.gesuijoho.metro.tokyo.jp/semiswebsystem
 Jonathan A.B. & Gerald J.K., Water Resources and Environmental Depth Reference Manual for the Civil PE Exam, 2011.