EXPERIMENTAL STUDY ON MITIGATION EFFECT OF SLIT DAM TO DEBRIS FLOW WITH DRIFTWOOD

Mountain torrents and debris flows carrying with driftwood are common in nowadays. The damage caused by driftwood has increased in recent years. However, there are few researches about the effect of driftwood in present prevention works for debris flow. Therefore, it is necessary to study the mitigation effect of debris flow check dams with driftwood. Taking the slit dam as an example, we carried out a series of physical model tests. The results show that the driftwood always moves on the surface of the fluid and arrives at the dam before sediment. Whether driftwood accumulates at the openings of the slit dam, it has a significant influence on the sediment deposition in front of the dam, the sediment outflow rates, and the retention rates of driftwood. Without driftwood accumulation, obvious erosion takes place on the sediment deposition before the dam by subsequent flow. Sediment outflow rates are slightly lower than that without driftwood. Once a driftwood accumulation is formed, the sediment deposition in front of the dam has no obvious erosion. The sediment outflow rates obviously decrease, while the total retention rates of driftwood increase remarkably. The retention rates of different driftwood components are various with the difference of driftwood length. The larger the length-width ratio L/b(L:the driftwood length, b: the opening width of slit dam) is, the easier the retention of driftwood is. The total retention rates of driftwood increase along with the increase of the amount of the driftwood with L/b>1. In addition, the existence of the driftwood with L/b>1 is a key condition for the formation of driftwood accumulation.