To solve the problems that sediment on the bottom of a dam and sediment inside of an intake weir may increase with the lapse of time, energy consumption and a motive force may be required for discharging the sediment to the outside of a weir of the dam and when removing the sediment inside of the intake weir, there is a problem with opening a movable intake weir since, if the movable intake weir is opened, a quantity of soil and sand may flow down in a short time, the quality of water at a downstream side may be changed rapidly such that problems in fishery rights or the like may occur.

Regarding sediment on the bottom of a dam, the sediment is discharged together with discharged water by power of siphon action. In an intake weir, the siphon action is also generated in a flat tunnel shape, and sediment flows down together with discharged water.