Research And Application Of Hydraulic Geometry To Reach Of The Yangtze River

Hydraulic geometry is one of main ways to research riverbed evolution,the hydraulic geometry and its application study in tidal reach of the Yangtze River could not only make predictions about the evolution and developing trend of the reach,but also provide a reference basis for systematic management and development in Yangtze River estuary. However,at present the river phase formula which was suitable for tidal estuary is too old and can be improved,and there are some existing problems such as plausible method for determining main parameters、low prediction accuracy in practical applications, which justify further research on the application method.In this article, our purpose is for the prediction of riverbed evolution,in view of the problems hydraulic geometry encountered in the process of application to the Yangtze river tidal reach, we make some necessary improvements about hydraulic geometry formula presented by GuoRen Dou, and make analysis of measured data of topography, hydrology, sediment of the Yangtze river tidal reach, comparison of methods used to calculate main parameters in the Yangtze river tidal hydraulic geometry,hydraulic geometry formula of the river section was built based on the typical cases of Cheng-Tong river reach,then the derived hydraulic geometry formula was used to predict the related cross section shape (river water depth, width and area) and its response mechanism to changes of coming water and sediment in the upstream, relatively complete hydraulic geometry application methods and processes were developed. The main results of the thesis are as follows:(1) Improvement of hydraulic geometry formula:From the viewpoint of the combined effects that runoff and tide exert on reach of the Yangtze River,we improved hydraulic geometry formula given by GuoRenDou through the principle of minimum activity combined with new sediment-carrying capacity formula and established a new hydraulic geometry formula which be suitable in tidal estuary.(2) Determination of method in calculation of main parameters in hydraulic geometry:Relevant application results of hydraulic geometry were used for reference and combined with the specific river discharge and sediment in the Yangtze river tidal reach,the comparison results showed that it helps to draw more realistic hydraulic geometry formula by proper adjustment of riverbed stability and overall roughness coefficients according to the actual situation of cross-section. Furthermore, a feasible method was put forward to determine the main parameters in Yangtze river tidal hydraulic geometry.(3) Application of hydraulic geometry:The Cheng-tong reach was taken as the sample area,we use the improved formula of hydraulic geometry and sort out the measured data according to the calculation method for main parameters in hydraulic geometry, then the river section hydraulic geometry formula is established; based on this, we predict the trend of river bed adjustment under the condition of a variety of water and sediment changes-This study result shows that the sediment discharge to the sea is decreasing sharply although the water runoff was controlled effectively after the three gorges project. Channel was flushed deep in Cheng-tong reach when sediment content dropped to0.05kg/m3more or less at Datong Station. The river width would be narrowed and cross-section is greatly increased, which may lead to an unstable riverbed.