Research On Influence Of The Bridge Engineering On Tidal Bore In Qiantang Estuary

The tidal bore is the front of flood tide as the water lever rises suddenly, it is the result of nonlinear-formed tidal wave under some conditions. Generally, tidal bore is wave alignment moving upstream estuary, and its surface will break when the wave alignment is strong, which leads to water roll tracing the source. The velocity, which is between small-disturbed wave velocities before tidal bore happens and the one after tidal bore happens, increases with the ratio of tidal bore height to the water depth in wave front. There are tidal bores in many estuaries over the world, but it is Qiantang bore that is the most typical. Its roaring, fantastic and amazing spectacle has attracted countless visitors long before.As the natural marvelous spectacle in the world, the Qiantang bore has been increasingly focused on. So the impact that paddle structure has on tidal bore is regard as the key point in the feasibility of engineering approved. Beginning with the cause of tidal bore, then making use of measure data and combining with scale physical modeling, this paper does the research about the impact that bridge engineering has on the Qiantang bore, such as Hangzhou Bay bridge, Guzhu Bridge, Xiaoshan Bridge etc. It provides the scientific evidence for approving those engineering above. In addition, with the physical modeling it does research in the impact the united bridges have on the tidal bore.Now tidal bore is one of hotspots and difficulty in scientific research. With advanced tide-controlling technology and high accurate equipment, this paper does the research successfully on the formation and changes of tidal bore under natural condition and after the bridge being built. And those processes are observed effectively. The research result shows that the basic conditions for tidal bore formation are the funnel-shaped Hangzhou Bay and sand bar rising. The local current disturbance after bridge being built in Qiantang Estuary leads to correspond changes of riverbed near bridge. But there is not any impact on astronomical tide, runoff large-scaled river shape and riverbed after bridge being built. So it doesn't change the formation of tidal bore at all after bridge being built, but there is some impact on the shape and intensity of tidal bore because of pier resistance. It is local impact that bridge being built has on the shape of tidal bore, and this local impact can be recovered in the place which is 300-500 long upstream bridge. The impact that bridge being built has on the intensity of tidal bore depends on the water-resisting area of bridge. Generally the more water-resisting area is and the nearer the place is away from the bridge site, the more impact is on the intensity of tidal bore. According to the result of physical modeling, the regression equation about the decrement of tidal bore height, the percentage of water-resisting area and the distance away from the upstream bridge site is constructed in this paper, the regression equation can be applied in the impact which bridge has on the tidal bore height in Qiangtang esturary.