Author(s): Norio Tanaka; Junji Yagisawa
Linked Author(s): Norio Tanaka
Keywords: Moment by drag force; Shear stress; Rehabilitation of gravel-bed river
Abstract: As to the prediction on the possibility of forestation on a gravel bar in rivers, previous studies mainly discussed the wash-out condition of trees. However, the degree of damage should be elucidated, because trees of which trunk are broken or bent down due to floods regenerate after the floods. Tree breaking and wash-out situation after a flood event were investigated with different locations on a gravel bar in the Arakawa River, Japan. Two dimensional unsteady depth-averaged flow model was applied for the analysis. Indices for evaluating trunk breakage, BOI and for washing out trees, WOI were defined. The BOI and WOI express well the tree breaking situation due to 2007 flood within the reasonable limit. At the investigated gravel bar, even if 40-years? return period flood occurs, WOI shows that trees vegetated at highest relative height cannot be washed out, even though they can be evaluated as? broken? from BOI. Trees can easily regenerate at the habitat and sometimes accelerate the forestation. These results indicate that indices for evaluating trunk breakage (BOI) and wash out of trees (WOI) are useful for analyzing the possibility of the continuity of the forestation and discussing the necessity of the management.