By taking the Yong River for example in this paper,based on the multiple measured data during 1957 to 2009,the change process of runoff,tide feature,tidal wave,tidal influx and sediment transport are analyzed.Then a mathematical model is used to reveal the influence mechanism on hydrodynamic characteristics and sediment transport of the wading engineering groups such as a tide gate,a breakwater,reservoirs,bridges and wharves,which were built in different periods.The results showed the hydrodynamic characteristics and sediment transport of the Yong River changed obviously due to the wading engineering groups.The tide gate induced deformation of the tidal wave,obvious reduction of the tidal influx and weakness of the tidal dynamic,decrease of the sediment yield of flood and ebb tide and channel deposition.The breakwater blocked estuarine entrances,resulting in the change of the tidal current and the reduction of the tidal influx in the estuarine area.The large-scale reservoirs gradually made the decrease of the Yong River runoff.The bridge and wharf groups took up cross-section areas,the cumulative affection of which caused the increase of tidal level in the tidal river.
When subway tunnels are routed underneath rivers,riverbed scour may expose the structure,with potentially severe consequences.Thus,it is important to identify the maximum scour depth to ensure that the designed buried depth is adequate.There are a range of methods that may be applied to this problem,including the fluvial process analysis method,geological structure analysis method,scour formula method,scour model experiment method,and numerical simulation method.However,the application ranges and forecasting precision of these methods vary considerably.In order to quantitatively analyze the characteristics of the different methods,a subway tunnel passing underneath a river was selected,and the aforementioned five methods were used to forecast the maximum scour depth.The fluvial process analysis method was used to characterize the river regime and evolution trend,which were the baseline for examination of the scour depth of the riverbed.The results obtained from the scour model experiment and the numerical simulation methods are reliable;these two methods are suitable for application to tunnel projects passing underneath rivers.The scour formula method was less accurate than the scour model experiment method;it is suitable for application to lower risk projects such as pipelines.The results of the geological structure analysis had low precision;the method is suitable for use as a secondary method to assist other research methods.To forecast the maximum scour depth of the riverbed above the subway tunnel,a combination of methods is suggested,and the appropriate analysis method should be chosen with respect to the local conditions.
