Study On Transport Law Of Discontinuous Wide-graduation Sediment

Discontinuous wide-graduation sediment widely exist in natural river as the specific type of non-uniform. It has different characteristics while comparing with traditional non-uniform sediment. There are only a few researches on the discontinuous wide-graduation sediment. Exploring the movement law of discontinuous wide-graduation sediment can broaden the study scope of non-uniform sediment, enrich non-uniform sediment theory and provide theoretical and technical support for the water conservancy construction and channel evolution trend forecasts.In this paper, firstly, the threshold motion and transport laws of non-uniform sediment law at home and aboard are analyzed. With the date about Ganlanba reach of Lancangjiang River, Baihetan reach of Jingshangjiang River and the reach from Yichang to Zhicheng of Yanzgtze River, the characteristics of river bed which have the discontinuous wide-graduation shape and discontinuous wide-graduation sediment the are analyzed, finally, the formation condition of discontinuous wide-graduation are summarized.According to the present study on discontinuous wide-graduation sediment, three groups of discontinuous wide-graduation bed material and one group of continuous wide-graduation bed material were designed for the scour flume experiments。The flow velocity structures and turbulent characteristics of rough bed were analyzed based on the flume results; the vertical flow velocity distribution formula for rough bed with S-type velocity structures is proposed. Based on the non-uniformity of discontinuous wide-graduation sediment, bimodality parameter is used to define the non-uniformity. The resistance characteristics of river bed with non-uniformity of discontinuous wide-graduation sediment are analyzed according to flow condition, bed form and grain size. A technique for calculating the resistance coefficient of rough bed is proposed based on the test data with high accuracy.Thirdly, Based on sediment transportation of the flume experiments containing the incipient motion and transporting , the author studied the size distribution of bed load and decay form of transport rate, the coarsening sediment transport rate formula are put forward for the discontinuous wide-graduation bed material. Thirdly, Based on sediment transportation of the flume experiments containing the incipient motion and transporting, the author studied the size distribution of bedload sediment and coarse bed, the coarsening sediment transport rate formula are put forward for the discontinuous wide-graduation bed material. The analysis results show that the silver sand content has a very important influence on the transport law of bedload material, the flow structure and sediment transport laws of discontinuous and continuous wide-graduation bed are close while the discontinuous wide-graduation bed material contains high silver sand content.