Author(s): Shin Miura, Tetsuo Hatta, Hitoshi Negishi, Yasushi Tsuruta, Tadaharu Ishikawa
Linked Author(s): Shin MIURA
Keywords: Tide-affected reach of urban stream, milky water, behavior of sulfur, field measurement, numerical model
Abstract: The generation of sulfide and colloidal sulfur was modelled for the tide-affected reach of urban streams. Field measurements conducted in the Meguro River, which flows through a highly urbanized area of the Tokyo Metropolis, suggested a change in the chemical form of sulfur in the river: In the saline underwater, anoxic conditions developed due to oxygen consumption by organic substances discharged from the outfall of a sewer system, and sulfide was generated by the action of sulfur-reducing bacteria. The deep water was transported to the shallow upstream reach by adverse tide flow, where the sulfide was oxidized rapidly, resulting in colloidal sulfur. A series of laboratory experiments were done to quantify the sulfide generation rate in a still-water column containing samples of bed sediment and saline water collected in the river. Experimental results were used to formulate empirical relations for the dependence of sulfide generation rate on the ignition loss of bed sediment and the COD of river water. A numerical model was developed for the variation in concentration of sulfide and colloidal sulfur in river water based on the experimental results and previously reported values. A practical model for numerical simulation of sulfur behavior in the tide-affected river reach was constructed by combining this model for the water with a two-dimensional (longitudinal /vertical) unsteady flow model. A numerical simulation was performed for the hydraulic conditions of the Meguro River during two weeks in the summer of 2008, when the sulfide concentration became very high due to a high level of organic sediment deposition from an intense rain runoff. The calculation results showed good agreement with the longitudinal distribution of sulfide concentration obtained from field measurements, two weeks after the rain runoff
Year: 2017