Effects of Flush Discharge Hydrographs on the Removal of Attached Algae

A flush discharge is a small scale flood induced by artificial water release from a reservoir. Flush discharges have been widely executed to improve river environments downstream of dams. The impacts of flush discharges on river environments vary widely, and the impacts are not quantitatively understood. The optimal design for flush discharges has not been established, and methods to estimate impacts in advance of implementation are needed. This study quantifies the effects of a flush discharge hydrograph on the environment of the Johge River located in downstream of the Haizuka dam, Japan. Detailed field observations and a two-dimensional numerical simulation have been performed to reveal the detachment of attached algae from the bed. The 2010 flush discharge hydrograph had a sharper increase in the rising stage and maintained a maximum peak value longer than the 2009 hydrograph. Amounts of detached algae were shown to be strongly influenced by the discharge hydrograph.