边界条件对曲流发育影响的过程响应模型实验研究

AN EXPERIMENTAL STUDY OF THE INFLUENCE OF BOUNDARY CONDITIONS ON MEANDERING DEVELOPMENT WITH PROCESS RESPONSE MODEL

基于系统论模型化原理及地貌演化类比性法则的过程响应模型,有利于研究河型演化,河道过程及控制因素的作用。运用该模型所进行的边界条件对曲流发育影响的实验表明,河漫滩物质结构及河床上的抗蚀露头对曲流发育具有控制作用。

The process-response model in fluvial morphology is one of physical models, which is a combination of geomorphic system with cascading system in flume. It is on base of modelling of a system and geomorphic analogism, etc. The calibration and adjustment of process-response model are based upon relationships between control facters in the two systems. This kind of models is available and effective for studies of river processes, controlling facters, geomorphic thresholds, complex response, etc. However, the disadvantages are too much time and physical laboring consumed in it.Boundary conditions influence meadering development to a large extent. The experimental results about it are summarized in Table 1 as follows: meander can not be developed in non cohesive sand, and in very cohesive material,such as clay, a symmetrical meander was found only at ap retty slow rate. A true meander is developed in the floodplain with double-layer structure, which has a top layer,made of clay mixed up with very fine sand, and a bot-tern layer, made of non cohesive sand.Between symmetrical meander and asymmetrical meander there exists a threshold sinuosity of about 1.57. The sinuosity, curvature radius, and asymmetrical index of meander bend are related to the bank height ratio. Furthermore, asymmetrical index is proportional to shear stress difference ratio and sinuosity, too. If there exists none-rodible outcrop on the river bed, the meander above the outcrop will be compressed, while below the outcrop meander will be stretched. The more close to outcrop, the more obvious this tendency is.When considering river harnessing and construction of big hydraulic project in a river, the channels above or below the realignment reaches may be changed a lot, such as increasing or decreasing meander development rate, and accelerating or delaying meander cutoff, etc. The process-response model is very expectable for tentative study on geomorphic thresholds of those changes, including river metamorphosis.