Abstract
Tidal urban rivers have severe environmental problems like massive fish death which was mainly caused by formation of hypoxic water mass. However there was little information on DO environments in large tidal rivers. To investigate DO environments in tidal rivers and its relation to floodings which are closely related to CSO(Combined sewer overflow) impacts, we conducted field measurements on water-quality environments in the Sumidagawa and Kandagawa Rivers, Japan. The result indicates that massive fish death in tidal reach of small urban rivers appeared frequently just after flooding events in summer seasons. The measured results reveal that DO on Sep. 9, 2010 were lower than 2 mg/ L in overall region of Sumidagawa River due to the flooding event. These facts indicate that inflows of CSO due to flooding events have an important influence on reduction of DO concentration in the Sumidagawa River.
