強い非定常流れにおける飽和浮遊砂濃度を考慮した津波土砂移動モデルの改善  [in Japanese] IMPROVEMENT OF TSUNAMI-INDUCED SEDIMENT TRANSPORT MODEL BY CONSIDERING SATURATED CONCENTRATION IN SUSPENSION WITH STRONG UNSTEADY FLOWS  [in Japanese]

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Abstract

狭窄部を有する宮城県気仙沼湾における東日本大震災の津波・土砂移動を対象として,津波土砂移動モデルによる侵食及び堆積の過小評価の要因を推定し,従来モデルの改善を図った.湾狭窄部では強い非定常流れが生じていたことが数値的に確認された.そのため,従来の飽和浮遊砂濃度モデルでは巻上砂量が過剰に抑制され,地形変化の過小評価の一因になったと推定された.そこで,Log-wake則による実験式とカルマン数の変化を導入した,強い非定常流れに適用可能な飽和浮遊砂濃度式を提案した.岩盤層の取扱いや湾奥での堆積土砂量には依然課題が残ったが,提案した飽和濃度式は期待通り機能し,地形変化の再現性が改善された.強い非定常流れが生じ得る複雑地形の地形変化の再現性のみならず,浸水範囲や被害評価等の精度向上にも繋がると期待される.

 In this study, factors causing the underestimation of morphological changes due to tsunami-induced sediment transport in Kesennuma Bay with narrows during the Great East Japan Earthquake and Tsunami have been numerically investigaed. Based on the estimation, the saturated concentration of suspention model was improved. It was found out that strong unsdeady flows occerred at narrows. The numerical results from conventional saturated concentration model implied that at the narrows, suspension concentration and sediment supply from the bottom to the suspension were limited by high concentration in suspension, leading to underestimation of morphological change, i.e., erosion and deposition. By considering effects of strong unsteady flows on concentration of suspention, a new form of saturated concentration model based on log-wake law and Kármán constant theory has been proposed. Numerical results of the erosion and deposition in Kesennuma Bay were improved. It is expected that accuracy of evaluation about not only morphological changes but also inundation area and damages are improved.

Journal

  • Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)

    Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering) 74(2), I_325-I_330, 2018

    Japan Society of Civil Engineers

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