Fundamental hydraulic flume tests focused on sediment control function using a grid-type high DAM

Abstract

In Japan, the recent check dam (sabo dam) con- struction has been the open-type of the continuity of sediment routing from upstream to downstream a reach in a river basin. Not only in Japan but also in other coun- tries, a lot of experimental and numerical research has been conducted on sediment control using open-type sabo dams. Plans for size and location have been drawn up for grid-type sabo dams with heights of around 20 meters, which is the highest grid-type sabo dam in Ja- pan, in the Amahata river in Yamahashi Pref., where a lot of sediment are yielded and deposited in numerous torrents due to heavy rainfall in 1982. Flume tests are conducted using a straight channel to determine the grid size of a grid-type sabo dam and to confirm its sediment control function. Subsequently, several runs of flume test were conducted supposing several types of debris flow regimes such as steady and uniform debris flows and quasi-steady debris flows, and taking into account sediment transport mode corresponding to bed slope and longitudinal bed profiles in the basin.
In the present study, the sediment control func- tions of the “grid-type high dam (GHD)”, which is de- fined as a grid-type sabo dam with a height over 15 m, were examined using several experimental data sets such as the dimensionless sediment runoff volume which is defined as the ratio of runoff sediment vol- ume to inflow sediment volume, temporal changes of mean diameter, sediment concentration and sediment discharge rate passing through the check dam. Additionally, preliminary flume tests for sediment control using a kind of “steel wire-nets” near the vertically upper parts of the grid were conducted focusing on the simple and the effective countermeasures for the sediment storage in a sabo dam, in order to control the sediment runoff passing through the sabo dam after a lot of sediment is deposited in the sabo dam.