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流域と海岸域を繋ぐ流砂系の本質を理解するには、流体―堆積物系のダイナミクスに関する健全な知識が不可欠である。本報文では、流域スケールの流出解析と飽和/不飽和浸透解析を結合した豪雨時の斜面崩壊発達過程の解析をはじめ、表面侵食による山腹斜面からの土砂生産実態の観測、河道安定に深く関わる水制周りの三次元的な流況と河床変動の解析及び室内水路実験による検証、超過洪水による堤防破堤とそれにともなう三次元重力流の解析、そして台風来襲にともなう後浜への大規模な砂の打上げ現象等に関する研究成果を論述している。, This paper focuses on complex fluid-sediment interactions that may characterize the dynamical nature of sediment routing systems. Particular attention goes to storm-scale phenomena, and trends of mesoscale modelling are briefly reviewed first. Discussions are then directed on specific topics, which include: long-term observations of surface erosion on a hillslope; basin-scale analysis for predicting the development of shallow landslides in a heavy rainfall event; Numerical and physical modelling of the three-dimensional flow field and bed deformation around spur dykes, with implications in river stabilization; flow-out modelling for assessing the impact of levee breaching; and remarkable onshore transport of beach sand in a typhoon event. Collectively, the coverage emphasizes the importance of integrated analysis procedure for treating the three-dimensional nature of fluid-sediment interactions.