DOWNSTREAM EFFECTS OF RESERVOIRS ON FLOOD PULSES IN JAPAN

Flood pulses are indispensable for healthy river ecosystem. Reservoir management gives significant impact onriver flow regime including those pulses. This paper intends to clarify those impacts from statistical point of view. Using daily flow data upstream and downstream of reservoirs, we can find hownatural flood pulses are affected by flow control in reservoirs. 24 dams in Japan are chosen and 11 year recordsare analyzed to find out difference between natural and regulated flood pulses. As a result, pulses greater than 7m3/s/100km2 were less in number for regulated flow, but pulses smaller than the value were often enhanced by reservoirs. Analysis of occurrence frequency and dam impacts suggest that two kinds of pulses can be identified. Daily fluctuations became more symmetric, losing gradually diminishing stage after flood peaks. Change of flushing seasonality has also detected.