The Funagira Dam is located in the Tenryuu River in Japan. Within the 1.5 km downstream of the dam the left bank suffers from erosion and further downstream point bars at both banks are growing as shown in Fig. 1.The observed erosion and sedimentation pattern is likely to be caused by a variety of bed shear stress and an eddy formation induced by the gate operation during floods.

In the past, the central gates were opened first and the other gates were opened next, following a pyramid shape operation when the discharge increases. Recently the gate operation has been modified to an equal opening shape operation in which the opening heights are increased equally, following discharge increase.

The dam has nine spillway gates (20m wide and 16 m height) with a crest level of 42.0 m AMSL (Above Mean Sea Level). The dam also has a hydropower plant containing three turbines with minimum and maximum operation water level of 54.8 m and 57.0 m AMSL, respectively.

While releasing the flood peak and flushing the sediment, the dam operator maintains the water level at 50.6 m AMSL in the reservoir, which is below the minimum operational level. During that time sediment is expected to be transported to the river corridor downstream of the dam. The pyramid shape operation is expected to be the reason behind the undesirable morphological changes downstream of the dam.

The focus, mainly, on the period of the flood peak when the turbines are off and the gates are operated. And investigate the performance of both gates operations related to sediment transport.

More information will follow.

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