Numerical Study Of The Impact Of Oujiang Estuary Reclamation On Sediment Transport Under The Action Of Storm Surge And Typhoon

Oujiang Estuary is located in the southern part of Zhejiang Province,with a superior geographical location.There are many excellent ports and wharves near the estuary and the shipping industry is developed.In addition,seafood farming,shark product processing,shipbuilding and tourism are booming.With economic development,land resources are becoming in short supply.The reclamation project of Oujiang Estuary Shoal is carried out around Wenzhou Shoal,which is expected to increase the total land area by 88km~2.The implementation of the project will change the original hydrodynamic environment,thereby affecting the salinity distribution and sediment transport.How to ensure that the water environment is not destroyed while the project is being constructed is an important topic in the current coastal engineering research.Due to the special geographical location of Oujiang Estuary,the region is vulnerable to extreme weather such as typhoon.Typhoon results in dramatic changes in the dynamic environment of the estuary,and then destroys the original state of sediment transport,resulting in local deposition or erosion.Therefore,it is very important to explore the influence of the reclamation project on the hydrodynamic characteristics,salinity distribution and sediment transport under different weather conditions.Due to the large scale of calculation area and the high cost of establishing physical model,this paper uses numerical simulation to analyze the engineering impact in detail.In this paper,a numerical model of Oujiang Estuary is established based on FVCOM,and the model is verified by the measured tidal level,tidal current,salinity,storm surge tidal level and sediment data.On the premise of ensuring the accuracy of the model,the tidal current field,salinity field and sediment field before and after the shoal reclamation project are analyzed.Finally,the typhoon wind field is added to explore the storm surge water increase,flow field distribution and sediment transport changes in Oujiang Estuary under the coupling effect of typhoon and engineering,and comprehensively analyze the engineering impact.Summarizing the results of the study:Under no wind conditions,the north streamway of the Oujiang River is the main channel for tidal movement.After the project is implemented,the proportion of diversion continues to increase;the salinity distribution gradually increases from the estuary to the sea,and the salinity of the north streamway is higher than that of the south.The salinity distribution gradually increases from the estuary to the open sea,and the salinity in the north streamway is higher than that in the south streamway.The results of sediment distribution show that the sediment concentration in the north streamway is slightly higher than that in the south,and there is no concentrated suspended sediment accumulation area in the whole sea area after the first stage of the project.However,after the second stage of the project,there is a high sediment concentration area near the Shatou waterway,Damen island and Xiaomen island,with the highest sediment concentration of 1g/L,which has the risk of deposition and should be paid attention to.Under the action of typhoon,the maximum storm surge increase near the estuary is2.10m in the south and 2.28m in the north.In Yueqing Bay,storm surge is mainly reduced.The implementation of the project has a certain inhibitory effect on the storm surge increase in the south river course and a promoting effect on the north.There is little difference in the water increase process between the first and second stages of the project;the overall flow velocity of the sea area under the action of the typhoon is greater than that in the calm state,and the Lingni North Dike blocked the water flow channel between the north and south,resulting in an overall decrease in the flow velocity of the southern sea area after the project.After the project,the velocity of Shatou channel and Huangdaxia channel decreases to a certain extent,and the flow field of the open sea and Yueqing Bay changes little.Analyzing the sediment field under various working conditions under the influence of typhoon:the typhoon caused an overall increase in the sand content of the sea,and high sand content areas appeared in the Oufei Shoal and the southern boundary;the sand in the Yueqing Bay was distributed in a tongue shape,and the inside of the bay was smaller than the outside of the bay.The first stage of the project blocked the north-south sediment transport channel,resulting in the decrease of the area of high sand content area in the south.The sediment distribution after the second stage of the project is similar to that after the first stage of the project.The above research results can provide suggestions for channel planning,disaster prevention prediction and sediment dredging of Oujiang Estuary shoal reclamation project.