堆積土砂の再移動を考慮した切り下げ直後の砂礫州の再樹林化評価に関する研究

抄録

For clarifying the possibility of forestation in gravel bed bars or islands, sediment load change index (SLI) has been proposed considering deposition and washout of fine sand during flood discharge is declined. The applicability of this index was validated in the middle stream reach of the Oppe River and the Arakawa River. Before and after typhoons in 2007, 2011 and 2012, field investigations were conducted on five gravel bars in two rivers. River flow was also analyzed by two-dimensional depth-averaged Reynolds equations, and SLI was calculated. In comparison with SLI and sand deposition situation on observed gravel bars, SLI has been found to express well the sand deposition situation on most of observed gravel bars. However, when this method is applied to the gravel bar which has small relative height from low channel or long distance along the flow direction, SLI could not express well the actual deposition situation. The effect of the excavation of gravel bar was investigated at Honda location in the Arakawa River through SLI. The re-colonization of the grass-type vegetation can be confirmed at the location where SLI becomes higher due to the excavation. This result indicates SLI is suitable parameter for evaluating the effectiveness of the excavation of the gravel bar.