抄録
Flood mitigation dam (FMD) is a gateless outlet dam designed only for the purpose of flood control which provides long-term and efficient protection against floods. FMD is expected as environmentally friendly, since almost all incoming sediment during flood periods can pass through bottom outlets that designed at the original river bed level and there will be fewer impacts to downstream river environment. However, during the flood discharge retardation, the characteristics of sediment (sand and gravel) outflow rate are changeable and unknown compared with the normal stage. Especially, coarse gravels and stones may be difficult to be transported through bottom outlets because of a gap of tractive forces between upstream and downstream of dams.This paper tried to find these gaps at Masudagawa dam which is the typical FMD in Japan. RFID technology has been used to monitor movement of placed gravels in the reservoir area and clear correlation has been obtained between transported length of each grain sizes and estimated tractive forces.
