黄河下游游荡性河段浮桥建设对河势及防洪的影响分析.ppt

EFFECT ANALYSIS OF FLOAT BRIDGE ON RIVER REGIME CHANGE AND FLOOD CONTROL ON WANDERING REACHES OF THE YELLOW RIVER 黄河下游游荡性河段浮桥建设对河势及防洪的影响分析,李永强 刘筠 张靖 Li Yongqiang Liu Yun Zhang Jing Reconnaissance Design and Research Institute of Yellow River Henan Administration Bureau,Back ground of the study 项目研究背景 2.Brief Introduction of Fenkai float Bridge 封开浮桥简介 3. Analysis of Effect of Float Bridge Construction on Flow Condition 浮桥建设对水流条件影响的分析 4. Analysis of Possible Effect of Float Bridge on River Regime Changes 浮桥建设对河势的可能影响分析 5. Conclusions and Suggestions 结论和建议,Outline of the Presentation,More and more float bridges having been built on the lower Yellow River due to Economic development So far, 53 bridges in Shandong Province,Since 2000, float bridge has gradually moved to the upper wandering reaches of the Lower Yellow River.,1. Background of the study,Ceaseless going on of abnormal river regime near some float bridges make people pay more attention to the effect of float bridge on the river regimes Studying the change in water flow and river regime, and the possible effect on flood control can provide positive and scientific basis for the future float bridge construction,River regime evolution of Dagong to wangan reach from 2004 to 2006,Abnormal river regime,1. Background of the study,2. Brief Introduction of the Feng-Kai Yellow River Float Bridge,Feb. 2003 began to be built Mar. 2004 open to traffic. The channel of the reach where the bridge is located is 690 m wide, and the main flow is 4 m deep in average The float bridge is 880 m long in total and runs over the new floodplain and the main channel, and is composed of 44 sections The body of the bearing boat of the bridge is 21.38 m long, and single boat length is 4.3 m,Route of Fengkai Float bridge,Fengqiu county of Xinxiang city,Kaifeng county of Kaifeng city,3. Analysis of Effect of Float Bridge Construction on Flow Condition,The flow condition changes will be analyzed for four flow rate magnitudes (500 m3/s, 1000 m3/s, 2000 m3/s and 4000 m3/s).,Flow Condition Prior to Float Bridge Construction,3. Analysis of Effect of Float Bridge Construction on Flow Condition,Items to be analyzed,Back water calculation Change of average flow velocity Silt carrying Capacity River bed longitudinal deformation,8,3. Analysis of Effect of Float Bridge Construction on Flow Condition,Back water calculation,壅水高度,承压舟 bearing boat,9,3. Analysis of Effect of Float Bridge Construction on Flow Condition,Back water calculation result,10,Flow Velocity Change,Due to effect of backwater near the bridge, at the same flow the water depth increases and the average section flow velocity decreases.,3. Analysis of Effect of Float Bridge Construction on Flow Condition,flow velocity slows down by about 6.1% 10.6%.,11,Silt carrying Capacity,3. Analysis of Effect of Float Bridge Construction on Flow Condition,Silt carrying capacity of the flow can be expressed as:,Silt unit discharge,Coefficient,3.6,Flow velocity,At small flow, the silt carrying capacity decreased by one-third, which will greatly affect the sediment discharge rate of the flow, for small flow process occupies most times in the lower Yellow River.,12,Lanes Balance Equation is used to analyze the bed deformation that float bridge building may cause. Lanes Balance Equation can be expressed as:,Change of Bed Longitudinal Deformation,3. Analysis of Effect of Float Bridge Construction on Flow Condition,Values of Bed Deformation after Bridge Construction,13,4. Analysis of Possible Effect of Float Bridge on River Regime Changes,Effect of Float Bridge Section Fixing on River Regime Changes Analysis of Effect on Works and Floodplain Safety,14,4. Analysis of Possible Effect of Float Bridge on River Regime Changes,Effect of Float Bridge Section Fixing on River Regime Changes,In the wandering reaches of the lower reaches of the yellow river, the “slight bend“ scheme is adopted. Now the river regime of the reach differs much from the planned route and with the improvement of the river training works, the river regime will be restrained to the planned flow route .,15,Effect of Float Bridge Section Fixing on River Regime Changes For the safety of the Feng-Kai Float Bridge, the banks at both ends of the bridge were reinforced. The reinforced ends are similar to heads of opposite groins, which will restrain the lateral bed deformation in small flow condition. river regime evolution under the river training works will be broken.,4. Analysis of Possible Effect of Float Bridge on River Regime Changes,Dock is constructed,Stones were thrown to protect river bank,16,Effect on floodplain safety Because of backwater Backwater height caused by the bridge is around 2.0cm, and the backwater scope is relatively short, about 220 m 250 m. Therefore, the bridge will not cause great adverse effect on the upstream floodplain on both banks with backwater.,4. Analysis of Possible Effect of Float Bridge on River Regime Changes,17,On the point view of fixed nodes The reinforced banks at both ends of the bridge are like heads of opposite groin, on the one hand, the existing flow route tends to cause the main flow to break away from the control of river training works on the other hand, due to water check of the bridge, the flow losses some of its energy, so that the main flow does not have sufficient power to run to the downstream works; moreover, the main flow is scattered, thus easy to form abnormal river regime downstream of the bridge. Due to the bad effect of this situation, whether the flow is large or small, the main flow may rush directly to the floodplain downstream of the float bridge, endangering the production and life in the floodplain,4. Analysis of Possible Effect of Float Bridge on River Regime Changes,18,Conclusions,Under the condition of small flow, the backwater caused by float bridge building does not extends far, nor is it quite high, therefore, it will not produce large effect on flood control. The silt carrying capacity of the channel upstream of the float bridge will decrease, which will probably make the upstream channel more gentle, therefore, river regime regulation will slow down. The location of the float bridge is directly related with the degree that it affects river regime changes. The fixed nodes at both ends of the float bridge formed during small flow period should be consistent with the planned regulation line.,5. Conclusions and Recommendations,19,Recommendations,The analysis and calculation were all done supposing that the float bridges have been removed completely before flood occurs, while the possible adverse effect caused by the situation where float bridges have not been removed in