超過外力に対する河川堤防の耐水性能評価と流域減災システムへの適用に関する研究

Abstract

近年，都市化の進展と気象水文現象の極値の増大傾向が相乗し，洪水氾濫災害が顕在化している．これらは現行の堤防による治水システムが持つ根本的な課題を浮き彫りにさせており，超過洪水による沿川地域の被災レベルを極力軽減する方策の開発が求められている．本研究では，デジタル写真測量解析により2004年円山川堤防破堤にともなう堤内地の微地形変化の計測および堆積物移動収支の評価を行った．さらに，計測結果をGISデータベース化し，デジタル化した治水地形分類図と結合することにより，デジタル治水地形環境評価の手法を示した．

This study was motivated by the October 2004 levee-breaching case in the Maruyama River that took place under extremely high flood stage. The overflow and outburst brought about a range of sedimentary features to an adjacent paddy field with clayey subsoil. They included a plunge pool and two massive particulate ridges which were formed on either side of the central erosion-dominant zone. The breaching-induced topographical changes were precisely measured using digital photogrammetry and incorporated into a geographical information system (GIS), facilitating an analysis of the sediment budget. The severity of the inundating water was assessed based on a bedload transport theory, with the observation that only the large clay lumps were left on the central erosion-dominant zone. Furthermore, a discussion is made of the usefulness and limitations in a specially designed yet print-based, geomorphological classification map for the flood-prone Maruyama River basin that has witnessed land-use evolution over the past thirty years since its initial publication.