M. Umeda - JapanWater Resources Environment Technology Center, Tokyo, Japan
M. Okano - JapanWater Resources Environment Technology Center, Tokyo, Japan
G.Yokomori - Ministry of Land, Infrastructure and Transport of Japan, Nagano, Japan

Sediment bypass systems have recently been planned and constructed in several reservoirs as effective countermeasures against sedimentation. Nowadays howto control the behaviors of fine sediment has made an important issue on reservoir sedimentation management systems. In this study, field measurements and numerical analyses were conducted on behavior of fine sediment in Miwa Dam, Japan, where a redevelopment project is just being carried out. First, typical time variation was confirmed on fine suspended solid concentration by means of field measurements during flood events since 1988. Then behavior of fine suspended load in the reservoir was analyzed by using a vertical 2-dimensional reservoir hydraulic simulation model.We also observed movement of fine sediment mass on reservoir bed caused by lowering reservoir water level. Consequently we are going to propose practical methods to prevent inflow of fine suspended load and to reduce sedimentation in the reservoir.