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

本研究旨在从先进的河流水力学观点，阐明以自然为导向的整治工程设计原则。首先，在实地考察的基础上，探讨了河流自然的概念和自然导向型治理工程的基本功能。然后，通过野外调查、水力学试验和理论分析，研究了面向自然的整治工程设计的关键因素，阐明了由陡坡砾石河床和缓坡砂河床组成的冲积河流纵断面的形成规律。本文还利用大型水槽试验研究了植被对河岸形成的影响，并对山区河流床阶形成的机理进行了初步探讨。台阶池是在超临界流中由反沙丘与斜交波相互作用而形成的。当岸滩与水面波波长重合时，岸滩变为斜岸滩，水面波开始被放大，为指导天然护岸边坡的设计，采用解析方法推导了不同边坡坡度的梯形渠道中流速和边界剪应力的分布规律。在物理模型试验的基础上，探讨了多台阶式抛石护岸的结构型式，阐明了抛石的稳定性。根据试验结果，讨论了局部水流的形成过程和沿着护岸汇流处的冲刷。在河床防护工程设计方面，采用几种防护工程形式进行了一系列的试验研究。提出了利用抛石工程减小冲刷深度的方法。

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.