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1999年12月14-16日にかけて南米ベネズエラで900mmを超える記録的な豪雨が発生し, カリブ海に面したバルガス州の多くの河川流域で土砂災害が発生した。本研究では, その中でカムリグランデ川流域を対象として, 流量ハイドログラフの見積もり, 土砂氾濫・堆積過程の再現計算, および砂防ダムと流路工による砂防施設配置効果を検討している。従来, 砂防ダムや流路工といった砂防施設の機能や効果を評価する場合, 水理模型実験を行うことが多かった。これは, 数値計算精度や基礎方程式の不確かさとともに, 複雑な構造物に対しては数値計算の境界条件が与えにくいといったことも原因していると思われる。しかしながら, 比較的単純な構造の施設であれば, 数値シミュレーションによる施設の評価はある程度可能であり, 経費的にも節約が図れるなど有効な手段と考えられる。, A disastrous debris flow occurred in the Camuri Grande River basin due to a heavy rainfall on December 16, 1999 in Venezuela. This paper shows the estimated debris flow hydrographs of the Camuri Grande River and its tributary by using one-dimensional simulation model, in which the grain size distribution of the riverbed materials is taken into account. Moreover, flooding and deposition processes on the fan of the river are reproduced using two-dimensional model, where calculated results obtained by one-dimensional model such as flow discharge, sediment discharge, and sediment diameters are used as inflow boundary conditions on to the fan area. In this model, the unstructured meshes are adopted to express the shape of the rivers, buildings, roads, and etc. in accurate on the fan. Calculated sediment deposited area and thickness of deposits correspond fairly well with the actual ones. The effects of countermeasures by Sabo dams and channel works against debris flow disasters are investigated by using one- and two-dimensional numerical model. The numerical simulation method is found to be very useful to evaluate the effectiveness of countermeasures such as Sabo dams and channel works.

A disastrous debris flow occurred in the Camuri Grande River basin due to a heavy rainfall on December 16, 1999 in Venezuela. This paper shows the estimated debris flow hydrographs of the Camuri Grande River and its tributary by using one-dimensional simulation model, in which the grain size distribution of the riverbed materials is taken into account. Moreover, flooding and deposition processes on the fan of the river are reproduced using two-dimensional model, where calculated results obtained by one-dimensional model such as flow discharge, sediment discharge, and sediment diameters are used as inflow boundary conditions on to the fan area. In this model, the unstructured meshes are adopted to express the shape of the rivers, buildings, roads, and etc. in accurate on the fan. Calculated sediment deposited area and thickness of deposits correspond fairly well with the actual ones. The effects of countermeasures by Sabo dams and channel works against debris flow disasters are investigated by using one- and two-dimensional numerical model. The numerical simulation method is found to be very useful to evaluate the effectiveness of countermeasures such as Sabo dams and channel works.