Exploration On Cumulative Response Of Hydrodynamics And Water Environment Of Yueqing Bay To Reclamation Works

Yueqing Bay is a rare natural semi-enclosed Bay in southern Zhejiang Province.Historically,it has abundant natural bay resources and superior offshore ecological environment.However,with the development of modernization in Wenzhou and Taizhou,in order to expand urban land area and develop and utilize coastal marine resources,the local government has implemented a series of large-scale beach reclamation projects in Yueqing Bay.Continuous urban development and accumulated reclamation projects have created tremendous social and economic value for the local area,in recent years,the state has vigorously advocated environmental protection,in response to the national policy of building a "beautiful China" and developing a green economy.This paper intends to explore the response relationship between reclamation and Yueqing Bay’s hydrodynamic and water environmental changes,and to provide scientific basis for scientific management,sustainable development and ecological civilization construction of beach resources.In this paper,the cumulative response mechanism of hydrodynamics and water environment in Yueqing Bay to a series of typical beach reclamation projects is studied,and the spatio-temporal influence laws of reclamation projects on hydrodynamics and water environment in the Bay are qualitatively and quantitatively analyzed.This paper collects the resources and environment data of Yueqing Bay in recent 20 years,compares and analyses historical data,and obtains its basic change characteristics.Based on the resources of inner beach in Yueqing Bay,the wet and dry grid treatment for inundated and exposed beach in the Bay is carried out by using MIKE21 software.Two-dimensional hydrodynamic water quality mathematical model of Yueqing Bay in 1997,2007 and 2015 was established and analysis on Rationality of Selection of Reclamation Area by Entropy Method and Correlation Analysis Method.Based on the above calculation and analysis,it is found that(1)The coastline changes of Yueqing Bay are mainly caused by reclamation works.From 1990 to 2000,the coastline at Xuanmen Port changed greatly,mainly due to the implementation of Phase II Reclamation Project of Xuanmen Port.From 2000 to 2007,there was little change in other areas except Puqi Town and Wengyang Town.From 2007 to 2015,the average shoreline extrapolation rate from the inner bay mouth to the interruption surface of Yueqing Bay was 0.1-0.3km/a.Reclamation works from 2007 to 2015 reduced the width of the section from the bay mouth to the bay to a certain extent.(2)Under the continuous implementation of reclamation project in Yueqing Bay in recent 20 years,the current in the Bay has slowed down,The current velocity in Yueqing Bay increased from 1997 to 2007 except points 5 and 6 near the reclamation area of Xuanmen Port,the rest of the region is generally on a downward trend.Among them,the rising current speed at point 1-4 decreases by 12%-17%,the falling current speed decreases by 9%-17%,the average flow speed decreases by 10%-14%,the rising current speed at point 7-9 decreases by 6%-8%,the falling current speed decreases by 5%-7%,and the average flow speed decreases by 1%-2%.During the period 2007-2015,the upstream and downstream velocities at point 1-4 decreased by 2%-15% and 5%-8% respectively,while the upstream and downstream velocities at point 5 and 6 almost did not change,with the maximum variation not exceeding 1%.The downward velocities at point 7-9 decreased by 9%-22%,the downward velocities by 5%-27% and the average velocities by 21%-28%.Among all the points,point 10-13 shows the smallest change in flow rate,ranging from 0% to 5%.However,the current process of the overall current field has little influence.(3)Under the influence of current changes,the diffusivity of pollutants in Yueqing Bay also shows a certain downward trend.(4)Affected by reclamation works,the flow rate of the approach channel of Yueqing Bay has decreased,sediment has silted down and channel resources have been affected to a certain extent.(5)According to the evaluation results of Entropy Method and Correlation Analysis Method,the evaluation value of Gulf estuary development plan is the highest,0.971,which is better than 0.622 of Gulf top development plan.(6)According to the development status and numerical simulation results of the beach from 1997 to 2007 and 2007 to 2015,the implementation of reclamation project in the Bay will affect the hydrodynamic environment,scouring and silting conditions,water quality diffusion capacity of the bay.The implementation of reclamation project at the top of the Bay has a greater impact on the overall Yueqing Bay.Moreover,there are larger wetland parks at the top of the bay with abundant species.Therefore,reclamation and development at the top of the Bay should be avoided as far as possible.With abundant beach resources and superior hydrodynamic conditions,the main current channel is to the east.Therefore,it is recommended that reclamation be carried out on the west side of the bay mouth first.