Hydraulic model tests for evaluating sediment control function with a grid-type Sabo dam in mountainous torrents

There are two kinds of Sabo dams in order to control sediment transport by debris flow and flash floods in mountainous area, which are closed and open-type＇s dams. In Japan, open-type＇s Sabo dams are constructed taking into account the continuity of sediment routing from upstream to downstream reach in a basin. A plan to construct a 20 m high grid-type Sabo dam which can capture a sediment volume of 400,000 m3 is proposed in the Amahata river basin in Japan. Hydraulic model tests are conducted to decide on the section for a dam （Section A, B） and the grid size such as clearance of vertical/horizontal bars for evaluating the plan. Several runs of flume tests are conducted and the sediment control function of the Sabo darn is discussed using several experimental data such as dimensionless sediment runoff rate from Sabo dam, temporal changes of bed profile and mean diameter and so on. It was found that sediment deposition in sediment storage area of Sabo dam was affected by curved channel, and that next the grid size of steel bars and thirdly the section of a dam was able to capture sediment in storage area of Sabo dam. Sediment was controlled well in the section B and in the grid size of 1.0×d95, and the problems related to sediment runoffafter sediment capturing in Sabo dam are pointed out.