PURPOSE:To remove soil and sand deposited on the upstream side of a falling dam by a method in which a trench directed in parallel with the falling dam is formed adjacently to the upstream side of the falling dam, and a flexible and expandible bag is set in the trench. CONSTITUTION:When a rubber bag 7 is deflated by discharging air through an air supply and discharge pipe 9, soil and sand 10 deposited in the neighborhood of the bag 7 slide down into a trench 4. When the rubber bag 1 is raised by expansion, soil and sand 10 deposited on the dam 1 are also partly dropped into the trench 4, and thereby the soil and sand 10 to interrupt the rising of the dam 1 are discharged and the dam 1 is completely raised. The need for an operation to remove soil and sand is thus eliminated, the maintenance cost of the rubber dam is saved, and damage of the rubber dam in the soil and sand removal operation is prevented.
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