“FLUSHING FLOW” WITH SEDIMENT REPLENISHMENT UNDER THE TRIAL OF FLEXIBLE OPERATION OF MANAGAWA DAM

Abstract

For the purpose of recovering river dynamics to maintain fish habitats by artificially increasing flow discharge from dams, flushing flows have been introduced in downstream rivers under the flexible dam operation. This paper shows results of the field test of the flushing flow from Managawa Dam in November 15, 2004.

Water levels, flow velocities, water quality such as temperature, turbidity, suspended sediment concentration, movement of river bed materials and quantity of detached algae on river bed gravels were measured at several downstream points during the flushing flow. In this field test, sediment replenishment which supply sediment to downstream rivers by damping 220m3 excavated sediment from Managawa reservoir alongside of downstream river. A peak discharge of 50m3/s in three hours has increased flow velocity and tractive force enough to move river bed gravels up to ca.50mm and supplied sediments have increased quantity of detached algae on river bed gravels which will be prefer for maintaining fish habitats.