The Research Of Backwater Height And Flood Control Countermeasure For Urban River With High Pier Density

As riverside lighting road spreading, piers dispose along river flow direction isbeing built at more and more city watercourse which shrink flood discharge section ofwatercourse in a great degree and that will cause heterogenize of backwater andvelocity distribution which will threat flood carrying capacity and river bankprotection.Many domestic and international scholars have thoroughly and deeply studied on flow structures around single pier or double cylinders and phenomenon of flowaround a circular cylinder. In backwater of piers, mostly former researches focus onorthogonal piers and skew bridge piers. However, there is no calculation formula andscientific reasonable evaluation method for wake flow of piers in tandem arrangementand backwater it causing, especially for the calculation of velocity loss and backwaterheight which caused by piers in tandem arrangement of city watercourse, neithercorresponding technical control standard.In this paper the problem of wake flow and backwater of piers in tandemarrangement are studied systematically in aspects of theoretical analyses, physicalmodel experiment and numerical simulation.In the aspect of theoretical analyses, the biggest loss velocity formula andcross-sectional velocity loss formula of piers in tandem arrangement based on trailingvortex superposition principle of wake flow are derived. And this paper establishes ahalf experience and half theory formula of backwater height with engineeredcalculation precision. In the aspect of physical model experiment, using ADV currentmeters and water level point gauge, wake flow velocity distribution of piers in tandemarrangement in different working conditions and the height of backwater are measured.In the aspect of numerical simulation, a three–dimensional hydrodynamics model is built by using FLOW-3D in CFD, the regularity changing of flow regime aroundpiers in tandem arrangement is discussed, the distribution of wake flow field and theheight of backwater was analyzed, and the result of study is well fitted to the modelexperiment.Based on the above results, this paper proposed some flood controlcountermeasures for urban river with high pier density: pier spacing should be shrankas short as possible, and keeping the amount of piers as less as possible and thediameter of piers as small as possible. For impact height increasing which caused bycurrent speed increasing in flood period, the effect of impact height to piers should befully considered, and the intensity of piers and protection for bridge bracing should beenhanced.