PURPOSE: To discharge soil and sand precipitated in a reservoir in a low investment and running cost.

CONSTITUTION: A stream way 3 is made to pierce a dam from the reservoir side 4 to the downstream side. An upper end opening 6 opened to the stream way 3 and a lower end opening 7 opened to the lower end of the reservoir 4 side of a dam 1 are connected to each other through a sand suction way 5. When water flows in the stream way 3, the pressure in the stream way 3 gets low in accordance with the flowing speed and the soil and sand in the sand suction way 5 are sucked into the stream way 3 to discharge it to the downstream side. The soil and sand is sucked into the sand suction way 5 through the lower end opening 7 from the reservoir 4 side in accordance with the above volume. the same motion is repeated to remove soil and sand.