| The Qiantang river estuary located right in the heart of Shanghai metropolis circle,there are close economic and trade exchanges between the cities.As the offershore area of the Qiantang estuary,the Hangzhou bay has vast water area,which provided convenient waterway transportation,meanwhile,caused the natural obstacles on landway transportation.The construction of sea-crossing bridge is an effective method to solve this problem.At present,the total number of constructed or in the planning in total length more than 10 km of cross-sea bridges has been more than 6.The large-scale bridge construction in the estuary is bound to have an impact on the factors of tidal dynamics,while the tide level,tide current and other tidal dynamics factors are also related to the coastal water conservancy facilities construction standards.At present,the domestic and foreign research mostly concentrated on the analysis of the influence of the single bridge and paying less attention to the situation of two or more cross-sea bridge construction.Therefore,this article adopts to carry on preliminary discussion with the method of numerical simulation,to deal with the problem of the influence on the tidal dynamic to many bridges in the same estuary.Firstly,build a wide range of numerical model contains the Qiantang and Changjiang estuary,after comparing with the measured data and being verified,analyzed tidal dynamic characteristics of the Hangzhou bay area,got the results of water level from the wide range of models,to provide accurate small area model of the Qiantang estuary a coast open boundary condition.Secondly,remain the prototype of piers of the main bridge,and only generalize small and numerous approach span piers among the cross-sea bridge to add to the accurate small area model of the Qiantang estuary.Finally,in view of the conditions of independent influence and superposition effect of the two bridges,discussed the response of tide level,tide current and tidal volume of Qiantang estuary.The main results are as follows:(1)Water flow of Hangzhou bay has obivous characteristics of reciprocating flow,the flood tidal duration is shorter than the ebb tidal one,while the flood current velocity is larger than ebb current.Tide movement of the Hangzhou bay mainly divides into five,due to the obstruction of Zhoushan islands in the bay mouth.Among them,the largest tide flux is from Zhenhai-Dinghai channel,the smallest is from Qushan-Yangshan Channel.(2)The impact from bridge construction on tidal power is reflected in weaken of tidal energy totally,including the reduction of the tidal range,tidal current velocity decrease and tidal volume cut.The results of response on tidal range and tidal prism can be mutually confirmed.In addition,due to trumpet coastline features of Hangzhou Bay,the value of the tidal range affected by the construction of the bridge is increasing upwards until it is 60km away from the Wenyan.For the situation of two bridges constructed together,the value of the reduction on tidal range is up to 4.6cm.(3)The Hangzhou bay bridge plays a key role in the cumulated impact of two cross-sea bridges of tidal power factor along the estuary and on the whole,while the Jiashao Bridge only has a more prominent effect near the bridge site.For example,from the variations of tide level and tidal prism along the coastline of the estuary,we can find that the overall trend is still deteimined by impact of the Hangzhou Bay Bridge,but the Jiashao Bridge has a dramatic impact on the area near the bridge. |
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