FLOOD SIMULATION MODEL COUPLED WITH VEGETATION WASH-OUT CONSIDERING HORIZONTAL DISTRIBUTION OF VEGETATION HEIGHT AND NON-DIMENSIONAL CRITICAL TRACTIVE FORCE

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  • 植生高分布と限界掃流力を考慮した植生流出を伴う洪水流解析モデルの検討

Abstract

<p> Flooding with a discharge of approximately 4500 m3/s occurred in the lower Asahi River in 2018 because of the Heavy Rain Event of July 2018. This flooding engendered wash-out situation of vegetation such as woody and herbaceous species and lodging situation of bamboo forest. Earlier works on the critical wash-out condition commonly assumed that the related properties of flow resistance due to vegetation and non-dimensional tractive force can be estimated by flood simulations without considering the wash-out situation of vegetation. However, such treatment cannot be applied reasonably to the case in the lower Asahi River flood in July 2018.</p><p> In order to examine numerically the wash-out situation of vegetation during the flood, this study proposed a flood simulation model coupling two processes: (1) vegetation wash-out attributable to local vegetation height and non-dimensional tractive force under local flood flow, and (2) change of flood flows attributable to decreased drag force induced by vegetation wash-out. We analyzed data of topo-bathymetry, land-use type, and vegetation attributes, using ALB data. Results show that our model improves reproducibility of the wash-out situation after the flood, compared with earlier models that incorporated uniformly the critical non-dimensional tractive force, not considering the vegetation height distribution.</p>

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