A Study Of Delayed Response Of Water & Sediment Load Variation Impact On The Cross Section Of The Channels In Mid-Yangtze River

This paper studies the delayed response rules of the river bed evolution in the alluvial reaches in mid-Yangtze River on the variation of the incoming flow and sediment conditions, focusing on mid-Yangtze River and adopting combined study methodstheoretical studies and measured data analysis. It widens the research scope of the delayed response for alluvial rivers. And it has a great significance for illustrating the rules of the river bed evolution in the alluvial reaches in mid-Yangtze River, for it provides theoretical reference for harnessing the Yangtze River.Based on the analysis of the variation of incoming flow and sediment conditions in the following 6 stations in mid-Yangtze River, namely, Yichang station, Shashi station, Jianli station and so on,and especially of the features of the flow and sediment changes before and after the impoundment of Gezhouban Water Control Project and Three Gorge Project. This paper hold the opinion that Gezhouba water Control Project and Three Gorge Project helps significantly weakening the sediment discharge in the stations in midYangtze River and the peak discharge as well. And it also plays an important role in increasing water runoff during non-flood season and thus the annual distribution of water runoff is greater similar.After analyzing the adjustment of the cross section of the channels in the following 4 stations in mid-Yangtze River, namely, Shashi station, Jianli station, Hankou station and Qilishan station in Chenglingji, This paper believe that the bank revetment in mid-Yangtze River binds the cross section of the channels so heavily that the bottomland and the main flume has an unobvious transition. So there are some troubles in determining such variables as bankfull area and bankfull discharge with strict physical concepts. And this paper the paper select the “cross section area A” calculated from the average water level in flood period of hydrological stations as the characteristic variable to reflect the adjustment of the cross section in the typical alluvial reaches in mid-Yangtze River.This paper justifies the phenomenon that the cross section A in alluvial reaches in mid –Yangtze River has delayed response on the incoming flow and sediment conditions. Based on the delayed response model for fluvial process of alluvial rivers put forward by Wu Baosheng and Li Lingyun’s basic equation of the delayed response model, This paper propose to improve the delayed response model in three ways:(1) Change the characteristic variable of the delayed response model from the previous one to cross section A.(2) Introduce ”annual combined flow “ so as to evaluate the bed-forming role of the flow in dry season.(3)Utilize piece wise function in iterative formula in order to embody the impact of Gezhouba Water Control Project and Three Gorge Project on water and sediment conditions.The improved delayed response model has achieved good application effect in Shashi station, Jianli station and Hankou station in mid-Yangtze River. According to the calculations, the correlation between calculated value and measured value is in a range from 0.7~0.9.So It can safely draw the conclusion that the improved delayed response model is able to better describe the adjustment features of the cross section in the midYangtze River. And with the help of the flow and sediment data in the 1990 s, the improved delayed response mode can also predict the changing trend of the cross section A in mid –Yangtze River.