Driftwood trapping function of a driftwood trap installed upstream of concrete closed dam

Joji SHIMA and Kenichi YASUTOMI


Two methods were proposed for adding a driftwood trapping function to a concrete closed dam, one is to install a driftwood trap directly on the upstream face of the concrete closed dam installed in the bedload section (linear layout), and the other is to install a driftwood trap on the sedimentation face of the concrete closed dam installed in the bedload section (convex layout). In order to understand the effectiveness of the two types of facilities installed upstream of the concrete closed dam, we investigated the status of the driftwood trap in the upstream area of the weir and changes in the water depth upstream of the weir through hydraulic model experiments. As a result, it was confirmed that when driftwood was trapped, the amount of driftwood flowing out of the trap surface decreased at once due to the narrower spacing between the components. To ensure the driftwood trapping function, “the length of the facility > the width of the channel” is required, regardless of the ponding or bedload conditions. If the length of the facility (width of the capture surface) exceeds the width of the channel, the progress of the weir’s depth rise is inhibited. In order to control the progression of weir raising depth, “apparent channel width > 3times the channel width” should be adopted, regardless of ponding or bedload conditions.

Key words

concrete closed dam, woody debris, driftwood trap, bedload section