DESIGN PRINCIPLES OF NATURE-ORIENTED RIVER IMPROVEMENT BASED ON FLUVIAL HYDRAULICS

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This research project has been executed to make clear the design principle of nature oriented improvement works from the view point of the advanced fluvial hydraulics. At first, we discussed the concept of nature concerning to rivers and the fundamental functions of the nature-oriented improvement works based on the field reconnaissance. Then, the key factors for designing the nature-oriented improvement works have been studied by the field investigation, hydraulic experiments and theoretical approaches.The formation of longitudinal bed profiles of alluvial rivers were clarified on the type of river composed of a gravel-bed reach with steep slope and sand-bed reach with mild slpoe. The effect of vegetation on the riverbank formation are also examined by a large-scale experimental flume.On the mechanism of bed-step formation in mountainous streams, the following results have been deduced. The step-pools are generated due to the interaction of antidunes and diagonal cross waves in supercritical flows. When wave lengths of antidunes and water surface waves coincide each other, the antidunes turns out to be diagonal one and then the surface waves begin to be amplified.In order to establish guide lines for designing the bank slope of nature-oriented revetments, the velocity and boundary shear stress distributions in trapezoidal channels with various slopes of side bank were derived by an analytical method. The calculated results were in good agreement with the experimental ones.The multiple step types of revetment were discussed based on physical model tests to clarify the stability of ripraps. The formation process of local flow and scour at flow convergent parts along revetments are discussed from the results of experiments. On the design of riverbed protection works, a series of experimental studies was carried out using several types of protection works. Some methods using riprap works to reduce scour depth were proposed.