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

本课题旨在从先进河流水力学的角度，明确面向自然的整治工程的设计原则。首先，在实地勘察的基础上，论述了河流的自然概念和自然整治工程的基本功能。然后，通过实地调查、水力试验和理论分析等方法，研究了设计面向自然的整治工程的关键因素。阐明了冲积河流纵向河床剖面的形成，并将其划分为陡坡砾石河床段和缓坡沙河床段。通过大型试验水槽考察了植被对河岸形成的影响。关于山溪层阶的形成机理，我们推导出以下结果：台阶池是超临界流中反沙丘与斜叉波相互作用的结果。当反沙丘与水面波的波长重合时，反沙丘变成对角波，水面波开始被放大。为了建立自然护岸岸坡设计的指导方针，采用解析法推导了不同岸坡坡度的梯形河道的流速和边界剪应力分布。计算结果与实验结果吻合较好。在物理模型试验的基础上，讨论了多阶护岸类型，以阐明抛石的稳定性。从试验结果出发，讨论了护岸局部水流的形成过程和沿护岸水流汇聚处的冲刷。在河床防护工程设计上，采用几种类型的防护工程进行了一系列的试验研究。提出了利用抛石工程减少冲刷深度的几种方法。

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.