Zhi-lin Sun*,Sen-jun HungJin-ge JioHui Nie,Mei Lu

aOcean College,Zhejiang University,Hangzhou 310058,China

bScience and Technology Department,Zhejiang University of Water Resources and Electric Power,Hangzhou 310018,China

cZhejiang Province Ocean and Fisheries Bureau,Hangzhou 310007,China

Effects of cluster land reclamation projects on storm surge in Jiaojiang Estuary,China

Zhi-lin Suna,*,Sen-jun Huanga,Jian-ge Jiaoa,Hui Nieb,Mei Luc

aOcean College,Zhejiang University,Hangzhou 310058,China

bScience and Technology Department,Zhejiang University of Water Resources and Electric Power,Hangzhou 310018,China

cZhejiang Province Ocean and Fisheries Bureau,Hangzhou 310007,China

Variations in coastline geometry caused by coastal engineering affect tides,storm surges,and storm tides.Three cluster land reclamation projects have been planned for construction in the Jiaojiang Estuary during the period from 2011 to 2023.They will cause significant changes in coastline geometry.In this study,a surge-tide coupled model was established based on a three-dimensional finite-volume coastal ocean model (FVCOM).A series of numerical experiments were carried out to investigate the effects of variations in coastline geometry on tides,storm surges,and storm tides.This model was calibrated using data observed at the Haimen and Ruian gauge stations and then used to reproduce the tides,storm surges,and storm tides in the Jiaojiang Estuary caused by Typhoon Winnie in 1997.Results show that the high tide level,peak storm surge,and high storm tide level at the Haimen Gauge Station increased along with the completion of reclamation projects,and the maximum increments caused by the third project were 0.13 m,0.50 m,and 0.43 m,respectively.The envelopes with maximum storm tide levels of 7.0 m and 8.0 m inside the river mouth appeared to move seaward,with the latter shifting 1.8 km,3.3 km,and 4.4 km due to the first project,second project,and third project,respectively.The results achieved in this study contribute to reducing the effects of,and preventing storm disasters after the land reclamation in the Jiaojiang Estuary.

Cluster land reclamation;Coastline geometry variation;Storm surge;Jiaojiang Estuary;Typhoon Winnie

1.Introduction

Coastal development coupled with land shortages has recently assumed importance owing to the booming economy in China.Coastline geometry in an estuary is often affected by coastal evolution and development.Coastal development, variations in coastal geometry,and nearshore topography also have an inevitable effect on tides and storm surges(Guo et al., 2009;Tao et al.,2011).Storm surges,characterized as sudden rises or decreases in water level,could be attributed to exceedingly strong winds and dramatically declined pressure. Additionally,in certain locations,apart from factors such as exact position and timing of a landfall,minimal central pressure,and radius to maximal wind,the degree of damage caused by storm surges is also related to coastal geometry and subaqueous topography.Therefore,both storm surges and storm tide levels(the height of the water level)change with geographical position and coastline geometry,which also vary in time and space(Debernard and R?ed,2008;Weisberg and Zheng,2008).As it is dominated by the effects of inverse barometric pressure(Zheng et al.,2013),a storm surge grows severe in coastal communities,coming with strong inshore winds and shoaling effects,and becoming dangerous when itadvances into an estuary owing to the effects of energy convergence(Goudeau and Conner,1968).In view of this, regardless of the effects of alterations to the coastline,a considerable amount of research on storm surge simulation in estuarine zones during typhoons has been conducted,such as the research carried out on the Croatan-Albemarle-Pamlico Estuary System(Peng et al.,2004),the Tuross Estuary (Drewry et al.,2009),and open/closed estuaries in South Africa(Riddin and Adams,2010).Research has also been conducted along the coasts of China,including the Yangtze Estuary(Duan et al.,1998;Hu et al.,2007;Xu et al.,2014), the Yellow River Estuary in Bohai Bay(Li et al.,2011),and Hangzhou Bay(Nie et al.,2012).However,coastal evolution or development has a significant impact on storm surges as well as storm tides(Xie et al.,2007).Thus,the effects of coastline geometry variations on tides,storm surges,and storm tides in estuarine zones are worth studying.

As far as a specific location is concerned,its local coastline geometry plays an important role in the generation of storm surges.Thus,land reclamation projects in estuarine zones make it difficult to study the characteristics of storm surges and storm tides.Bohai Bay,for instance,is located in the northern part of the Yellow River Estuary,and Laizhou Bay lies in the southern part.The growth of the Yellow River Delta due to evolution and reclamation reduces the maximum storm tide level(MSTL)at the top of Bohai Bay with cold-air outbreaks(i.e.,intrusions of an extremely cold polar air mass entering the middle-low latitudes bring strong winds).In contrast,the MSTL appears to be enhanced in Laizhou Bay (Zhao and Jiang,2011).Thus,the effects of coastal geometry variation on the MSTL seem to be diverse even in the same estuary.Even worse,due to land reclamation,variations in coastline geometry can have a negative effect on coastal disaster prevention in terms of flood drainage and storm surge intrusion(Wang and Cheng,2002;Wang et al.,2014).

The central and southern parts of the Zhejiang coast are prone to typhoons and,even worse,the frequency and intensity of these typhoons are causing an increasing probability of landfalls coupled with climate change(Sun et al.,2014a). Significant changes in coastline geometry have also taken place due to land reclamation in the central and southern parts of the Zhejiang coast over recent years.Unfortunately,hardly any research could be found to clarify the effects of the variation of coastline geometry on tides,storm surges,and storm tides in this region.In this study,a series of numerical experiments were carried out in order to investigate the distribution of MSTLs in the vicinity of the reclamation area during different stages of various reclamation projects.This study aimed to provide useful references for disaster management as well as prevention and mitigation of the effects of storms after reclamation during the typhoon period.

2.Basic data

Three cluster land reclamation projects in the Jiaojiang Estuary and its adjacent areas have been planned for the purpose of increasing economic growth.These reclamation projects would lead to significant changes in the estuary's coastline geometry and aggravate the effects of destruction.In this study,the effects of the cluster land reclamation projects on tides,storm surges,and storm tides during Typhoon Winnie were investigated.

2.1.Study area

The Jiaojiang Estuary,the second largest estuary in Zhejiang Province,is located at the end of the Jiaojiang River, which flows through Taizhou City.It is a tidal estuary,which creates an interface between the Jiaojiang River and Taizhou Bay.Taizhou City itself has a thriving economy but suffers from a lack of land resources.The best way of easing this problem is to take advantage of the tideland by engaging in land reclamation projects.Numerous islands and a large area of tideland are located outside the entrance of the Jiaojiang Estuary and in the Puba Harbor Basin,creating favorable conditions for land reclamation projects.

The geometry of the Jiaojiang River is distinctive,opening outwards like the mouth of a horn.Along the Shanjiaopu(SJP, the pink circle in Fig.1)-Sanjiangkou(SJK,the yellow circle in Fig.1)section,the width of the river narrows rapidly upstream towards Niutou Necking(NTN,the red circle in Fig.1).The width is about 5 km at the cross-section of SJP but decreases to 0.85 km at NTN.It then expands to 2 km in the NTN-SJK section.The width of the cross-section at NTN is the smallest at the SJK-SJP section.Undoubtedly,the features of this terrain increase the storm surges and MSTLs and make them more susceptible to variations in coastline geometry,enhancing the destructive potential of typhoons.Examination of the effects of variations of coastline geometry is therefore necessary.

2.2.Cluster land reclamation projects

Three cluster land reclamation projects are planned to be carried out during the period from 2011 to 2023 by combining existing tideland and islands outside the mouth of the Jiaojiang Estuary(Fig.2).The first project includes almost the whole coastal area outside the mouth of the Jiaojiang Estuary and consists of several sub-reclamation regions with a total area of about 130.5 km2.The second project will occur within a total area of 171.4 km2,based on the first project.During a later phase,the third project will be carried out in a small area inside the estuary entrance of about 5.5 km2.In this paper,the original coastline geometry before land reclamation is marked as Old. The coastline geometries ofthe firstproject,second project,and third project are marked as FP,SP,and TP,respectively.

Cluster land reclamation of each project is being carried out in many regions simultaneously.Significant changes in coastline geometry are thus expected to take place,causing corresponding changes in tides,storm surges,and storm tides.

2.3.Topographic data

In this study,the topographic data,which were measured over the period from 2009 to 2012,were provided by theNavigation Guarantee Department of the Chinese Navy Headquarters.The nearshore data were measured over the period from 2011 to 2012.The runoff discharge data during Typhoon Winnie were collected from the Taizhou Water Resources Bureau.The influence of the rise in the sea level on MSTLs has not been considered in this study because the average annual rate of the rise in the sea level was about 2.7 mm per year in coastal areas of Zhejiang Province(Sun et al.,2014a),which can be ignored.

Fig.1.Schematic representation of track of Typhoon Winnie and study area(yellow line in left figure indicates track of typhoon,and orange dots indicate observed typhoon center locations).

2.4.Typhoon Winnie

Typhoon Winnie was chosen in this study to provide a wind and atmospheric pressure gradient field for the whole simulation domain.Typhoon Winnie was a typical tropical cyclone, which made landfall on the central Zhejiang coast.Considered one of the most destructive marine disasters,Typhoon Winnie originated in the Western Pacific on August 10,1997.It subsequently moved northwestward with a growing intensity and caused a tremendous loss of life and property in the Philippines,Japan,and Taiwan during its journey.According to the records of the China Meteorological Administration (CMA),the maximum wind speed of Typhoon Winnie rose to 60 m/s with the minimal central pressure declining to 920 hPa. It made landfall in Shitang Town,Wenling City,in Zhejiang Province,on August 18,1997.The position of the landfall of Typhoon Winnie was about 50 km away from the Haimen Gauge Station.Its maximum wind speed reached 40 m/s and minimum central pressure declined to 944 hPa at the landfall location(Zhong and Zhang,2006).Though Typhoon Winnie was not the strongest typhoon attacking the Zhejiang coast,its effects were catastrophic.It damaged 776 km of seawall along the Zhejiang coast,causing an economic loss of RMB 26.7 billion yuan.In addition,it produced an MSTL with a return period greater than one thousand years at the Haimen Gauge Station(SOA of China,1998).

Fig.2.Locations of three cluster reclamation projects.

3.Methods

3.1.Numerical model

The finite-volume coastal ocean model(FVCOM),widely known as an unstructured-grid,primitive-equation and threedimensional model(Chen et al.,2003),was used to reproduce the storm surge for the tide-surge interaction in this study.Its unstructured grid appears to be beneficial to irregular coastline geometry.FVCOM has been widely used in simulations of coastal ocean circulation(Chen et al.,2007;Xue et al.,2009)and storm surges(Aoki and Isobe,2007; Weisberg and Zheng,2006;Rego and Li,2010;Yoon et al., 2014).With Boussinesq and hydrostatic approximations,the primitive equations governing momentum and mass conservation in the sigma coordinate are as follows:

whereu,v,and u are the velocity components in thex,y,and σ directions,respectively;tis time;fis the Coriolis parameter; ρ0and ρ′are reference and perturbation densities,respectively;Dis the total water depth andD=h+η,where η andhare the surface elevation and reference depth below mean sea level, respectively;ηadenotes the sea level displacement induced by the inverse barometer effect;gdenotes the gravitational acceleration;σ′is the derivative of σ;Kmdenotes the vertical eddy viscosity coefficient,which is calculated using a turbulent closure scheme with a background mixing of 0.0001;FuandFvdenote the horizontal momentum diffusion terms in thexandydirections,respectively;the horizontal diffusion coefficient is set at 0.2;and the number of the vertical levels is 11.

The surface boundary conditions foru,v,and u at σ=0 are written as

where τsxand τsyare the components of surface wind stress in thexandydirections,respectively.

The bottom boundary conditions foru,v,and u at σ=-1 are written as

where τbxand τbyare the components of bottom stress in thexandydirections,respectively.

The initial condition for surface elevation ξ and flow is zero,which can be expressed as

The tidal elevations on the open boundary are calculated through harmonic analysis using the following equation:

wherePbis the atmospheric pressure outside the storm;Pais the atmospheric pressure at the open boundary;Wiis the radian frequency of theith constituent;(U+V)iis the initial phase of theith constituent;fiis the node factor for theith constituent;andhiandGiare the amplitude and phase angle of theith constituent,respectively.

For the upper boundary,the observed time series of runoff during Typhoon Winnie in 1997 is used(Fig.3).Due to the lack of runoff data,the runoff is given just from 20:00 on August 17 and 08:00 on August 20.The moment of the landfall made by Typhoon Winnie shown in Fig.3 is 21:00 on August 18.

3.2.Surface and bottom stress

The surface wind stress is calculated using a surface wind field model,the Fujita and Takahashi model(Sun et al.,2015). This model has been proven to be applicable to the simulation of storm surges along the Zhejiang coast(Sun et al.,2014b, 2015).The surface wind stress is then computed from

wherewxandwyare the velocity components in thexandydirections,respectively,which are derived from the Fujita and Takahashi model;ρa(bǔ)is the air density;andCdsis the surface drag coefficient.

Wind velocity and pressure are calculated as follows:

Fig.3.Time series of runoff discharge given at upper boundary for Typhoon Winnie in 1997.

whereP0is the pressure at the typhoon center;Pris the pressure away from the typhoon center,with a distance ofr;P∞is the pressure far away from the typhoon center,which is considered a constant;Ris the radius to maximal wind (RMW)with a value of 45 km in this study;W is the combined velocity;VxandVyare the components of wind mobile velocity in thexandydirections,respectively;i and j are unit vectors of wind velocity in thexandydirections,respectively;C1andC2are the coefficients with values of 1.0 and 0.6, respectively;and F1and F2are gradient wind fields,which can be calculated as follows:

whereA=（xr-x0）sinθ+（yr-y0）cosθ,andB=（xr-x0）cosθ-（yr-y0）sinθ.x0andy0are the coordinatesofthe typhoon center;xrandyrare the coordinates at therdistance to the typhoon center;and θ is the gradient angle.

The surface drag coefficientCdsis dependent on the wind velocityand is determined by the following equation(Large and Pond,1981):

The bottom stress is determined by flow velocity and can be illustrated as follows:

where the bottom drag coefficientCdbis determined by matching a logarithmic bottom layer to the model at a height of the first σ level above the bottom,as shown in the following equation:

wherekis the Carmen constant andk=0.4;z0is the bottom roughness parameter,which was 0.001 m in this study;BFis the minimum value forCdb,which was 0.0025 in this study; and σkb-1is the vertical level next to the bottom.

3.3.Simulation region and nearshore grid

The vertical datum used in this study was the China 1985 National Altitude Datum,which is defined by the mean sea level at the Dagang Tide Station,Qingdao.

The simulated domain in this study covered the area with longitudes from 120°6'E to 124°12'E and latitudes from 26°24'N to 31°N,as shown in Fig.4,where O1 indicates the Haimen Gauge Station,O2 indicates the observation point outside the Jiaojiang river mouth,and O3 indicates the Ruian Gauge Station.The nearshore water depth of most of the area is less than 10 m along the Zhejiang coast and there are shallow areas in the Jiaojiang Estuary with a depth of less than 2 m.The triangular grid size was set at about 300 m nearshore as plotted in Fig.5(a)and(b),and gradually increased to about 1000 m at the open boundary.The node number in the mesh was 31507 and the element number was 61128.The time step for the simulation was set at 10 s.

3.4.Storm surge calculation

Storm tide level(ζ)is usually defined by the sum of tide level(ζT),pure storm surge(ζS,sea level change caused only by atmospheric forcing),and surge-tide interaction(ζI) (Banks,1974),i.e.,ζ=ζT+ζS+ζI.Thus,a storm surge considering the tide-surge interaction(ζSI)can be derivedfrom ζ and ζTas ζSI=ζS+ζI=ζ-ζT.ζ and ζTcan be obtained through two control simulations.ζ is generated through simulation considering atmospheric forcing and tidal forcing.ζTis generated through simulation under the effect of tidal forcing only.

Fig.4.Simulated domain in this study.

Fig.5.Grid structure of simulated domain.

3.5.Model calibration

Two observation stations were chosen to test the performance of the model:the Haimen Gauge Station(O1 in Fig.4) and the Ruian Gauge Station(O3 in Fig.4).The storm tide elevations,storm surge,and tide level between 20:00 on August 17 and 08:00 on August 20 were modeled to correspond with the time series runoff discharge.For the purpose of calibrating the numerical model,comparisons between the modeled results and observed data at the Haimen and Ruian gauge stations are shown in Figs.6 and 7,respectively.In general,the modeled results agree with the observed data.

Wilmott's goodness of fitR2and skill scoreS(Wilmott, 1981)were introduced to assess the performance of the model.They can be expressed as follows:

Fig.6.Comparison of modeled results and observed data at O1 between 20:00 on August 17 and 08:00 on August 20,in 1997.

whereNis the number of data;is the observed data at time stepis the mean value of the observed data;is the modeled result at time stepi;andis the mean value of the modeled results.The goodness of fit value and skill value of 1 indicate a perfect fit between the modeled results and the observed data.

The skill score has been widely used in model calibration for estuarine and coastal zones(Li et al.,2005;Warner et al.,2005;Vaz et al.,2009).At the Haimen Gauge Station,the goodness of fit of tide levels,storm surges,and storm tide levels were 0.976,0.653,and 0.972 and the skill scores were 0.991,0.911,and 0.992,respectively.At theRuian Gauge Station,the goodness of fit of tide levels,storm surges,and storm tide levels were 0.992,0.677,and 0.985 and the skill scores were 0.994,0.921,and 0.990,respectively.The numerical model applied in this study thus performs reasonably.

Fig.7.Comparison of modeled results and observed data at O3 between 20:00 on August 17 and 08:00 on August 20,in 1997.

4.Results

4.1.Effects of coastline geometry variation on tide and storm surge processes

Two observation stations were chosen to analyze the effects of coastline geometry variations on tides,storm surges,and storm tides inside and outside the estuary.The Haimen Gauge Station(O1)is inside the Jiaojiang river mouth and O2 is outside the river mouth at a depth of 11.5 m(Fig.4).The original tide,storm surge,and storm tide for case Old and their differences before and after each reclamation project at O1 and O2 are plotted in Figs.8 and 9.Tides,storm surges, and storm tide processes on the coastline for case Old correspond to the leftyaxis and time series differences correspond to the rightyaxis.FP-Old,SP-Old,and TP-Old are the differences in tide level,storm surge level,and storm tide level between each reclamation project and Old, respectively;differences greater than zero indicate that the reclamation project has positive effects on tide and storm surge processes while differences lower than zero indicate the negative effects.

Fig.8.Differences in tide level,storm surge level,and storm tide level between each reclamation project and Old at O1 between 20:00 on August 17 and 08:00 on August 20,in 1997.

Through comparison of Figs.8 and 9,it can be seen that variations in the coastline geometry mainly affect the tides, storm surges,and storm tides inside the river mouth rather than outside.Moreover,coastline geometry variation has positive effects on the high tide level,peak surge,and high storm tide,potentially intensifying the disaster caused by storm surges in the estuary.

The tide process at O1(Fig.8(a))shows that the FP and SP had almost the same effect on the tide level,increasing the high tide level by 0.05 m(01:00 on August 19).The TP increased the high tide level by 0.13 m.With regard to the storm surge process at O1,it is clear that variations in coastline geometry affected the peak storm surge at the moment when Typhoon Winnie made landfall(21:00 on August 18),as shown in Fig.8(b).The peak storm surge increased by 0.35 m due to the FP,by 0.44 m on the coastline for the SP,and by 0.50 m on the coastline for the TP.The storm tide,as a combination of a tide and a storm surge,was also affected significantly by variations in coastline geometry,especially between 17:00 on August 18 and 23:00 on August 18 when the increments in storm tide levels were greater than 0.20 m,as shown in Fig.8(c).The FP and SP caused the storm tide level to increase to its maximum by 0.27 m and 0.47 m at 19:00 onAugust 18,respectively.The TP caused a maximum increment of 0.43 m at 22:00 on August 18.Although the maximum increments in the storm tide level did not appear along with the high tide level,it is still notable that the FP,SP,and TP caused increments of 0.08 m,0.14 m,and 0.17 m,respectively, at high tide levels.

Fig.9.Differences in tide level,storm surge level,and storm tide level between each reclamation project and Old at O2 between 20:00 on August 17 and 08:00 on August 20,in 1997.

Variations in coastline geometry had little effect on the tides,storm surges,and storm tide levels outside the river mouth,as shown in Fig.9.With regard to the tides at O2,the changes in tide levels as well as storm tide levels due to the FP, SP,and TP were within 0.03 m.In addition,the changes in storm surge levels were less than 0.04 m.

4.2.Effectsofvariationsin coastlinegeometry on maximum storm tide level envelope

Generally speaking,the MSTL during the typhoon period is a key factor based on which the probability of overtopping of the seawall can be assessed,in order to predict and prevent storm disasters.The MSTL envelopes of the study area corresponding to coastline geometries for Old,FP,SP,and TP are plotted in Fig.10.

As the coastline geometry changed,the envelopes with MSTLs of 7.0 m and 8.0 m moved seaward.That is to say,the MSTLs inside the river mouth increased due to the reclamation projects.Specifically,envelopes with an MSTL of 8.0 m shifted 1.8 km(FP),3.3 km(SP),and 4.4 km(TP)seaward compared with that of Old.The MSTL at the Haimen Gauge Station exceeded 8.0 m due to the TP.Envelopes with an MSTL of7.0 m showed a distinctseaward movementalong the north bank and a slight movement along the south bank,as shown in Fig.10(c) and(d).The envelope with an MSTL of 7.0 m on the coastline forcase Old moved 5.8 kmalong the north bank on the coastline for the SP and 6.0 km on the coastline for the TP.

5.Discussion

The findings presented above are completely new and demonstrate that the effects of the different reclamation projects(i.e.,FP,SP,and TP)on tides,storm surges,and storm tides are diverse in the Jiaojiang Estuary.

Storm tide levels are at water level heights as a result of the nonlinear interaction of tides and storm surges during storms, as has been illustrated in many research papers(Bernier and Thompson,2007;Antony and Unnikrishnan,2013).Because of the tide-surge interactions,storm tide levels are not equal to a simple superposition of astronomical tide and pure storm surge.It is therefore reasonable to consider tide-surge interaction in the simulation of storm tide levels in this study. Although storm tide levels are widely considered to be affected by strong circulatory wind,offshore islands,river discharge,and shallow bathymetry during a typhoon period (Roy,1995,1999),they are also affected by variations in coastline geometry as we can see from the results in this study.

Tides,storm surges,and storm tides inside the river mouth are all affected by variations in coastline geometry,which can mainly be attributed to the changes in the flow field after the implementation of reclamation projects.The average vertical velocity fields of a current for rising tides(22:00 on August 18) corresponding to the Old,FP,SP,and TP coastline geometries are plotted in Fig.11.The landward flow along different coastlines is divided into two parts,one entering the estuary and the other moving southward along the coast.However,the flow fields for different coastline geometries due to land reclamation projects have different characteristics.Seen from the Old coastline geometry,the main flow enters the mouth along the north bank at a maximum velocity of 2.31 m/s(Fig.11(a)). After the FP,the main flow moves along the middle of the river at a maximum velocity of about 2.52 m/s(Fig.11(b)).With regard to the SP,the main flow still moves along the middle of the river mouth,while the velocity has a more uniform distribution than that for Old and FP,with a maximum value of 2.24 m/s.In addition,the construction of Toumen Harbor has an in fluence on the nearshore currentalong the north coast.The TP narrows the mouth width based on the SP,increasing the velocity of flow into the mouth.

If we divide the cross-section of the river mouth along the different coastlines into 50 equal sections with a width of Δl, the flow discharge into the river mouth at 22:00 on August 18 can be estimated as follows:whereQis the total discharge into the river mouth,Qiis the discharge of current at sectioni,Hiis the water depth at sectioni,andViis the vertical average velocity at sectioni.

Fig.10.Maximum storm tide level envelopes with different coastline geometries(units:m).

Along the coastline for case Old,the quantity of flow discharge into the estuary is about 18000 m3·s-1,while,along the coastline for the FP,there is a larger quantity of about 23000 m3·s-1flowing into the river mouth when compared with that of Old.After the SP,although the velocity of flow into the river mouth is reduced due to the construction of Toumen Harbor,which widens the river mouth(Fig.11(c)), the flow discharge still increases to 31000 m3·s-1with a larger depth and width of river mouth.After the completion of the TP,the river mouth narrows,causing an increase in flow velocity.As a result,the discharge increases to about 35000 m3·s-1and the tides,storm surges,and storm tides are all affected by the variations in coastline geometry due to changes in the flow field in different reclamation projects.

It should be noted that the results presented in this study were achieved based on the topographical data measured during the period from 2009 to 2012.That is to say,the bathymetry changes nearshore after land reclamation projects have not been considered in this study due to the lack of bathymetry data.Coastal evolution due to coastal dynamic factors will continue.They may raise the seabed elevation in the vicinity of the reclamation area and thus enhance storm surges as well as storm tide levels(Yin et al.,2004;Nicholls et al.,2007).The storm track and intensity can also affect the results.Further study will be carried out using the latest bathymetry data from another land reclamation project for different typhoons.

6.Conclusions

In order to clarify the influences of cluster land reclamation projects,which are planned for construction in the Jiaojiang Estuary and its adjacent areas,on tides,storm surges,and storm tides,a set of numerical experiments have been carried out to investigate the responses of tides,storm surges,and storm tides to variations in coastline geometry based on FVCOM.The model performs well in terms of reproducing tides,storm surges,and storm tides during the period when Typhoon Winnie affected the Jiaojiang Estuary.The modeled results agree with the observed data at the Haimen and Ruian gauge stations.Inside the estuary,the high tide level,peak storm surge,and high storm tide level at the Haimen GaugeStation increase due to the reclamation projects,where the maximum increments reach 0.13 m,0.50 m,and 0.43 m. However,there is little difference in terms of tides,storm surges,and storm tides at points observed outside the river mouth before and after the reclamation projects.

Fig.11.Average vertical velocity fields of current for different coastline geometries.

MSTLs inside the river mouth increase as a result of the reclamation projects,showing a signi ficant seaward shifting for envelopes with MSTLs of 7.0 m and 8.0 m inside the river mouth.Importantly,the envelope with an MSTL of 8.0 m appears to move 1.8 km,3.3 km,and 4.4 km due to the FP,SP, and TP,respectively.

The reclamation projects have changed the flow field in the estuary,thereby affecting tides,storm surges,and storm tides inside the rivermouth itself.The reclamation projects increase the flow velocity and flow discharge into the rivermouth.As a result, the high tide level and peak storm surge could be enhanced.This study is based on the same bathymetry for different reclamation projects and the typhoon track ofWinnie.Therefore,furtherstudy needs to be conducted when new bathymetry after the reclamation projects is available for different typhoons.

Acknowledgements

The authors wish to thank the Taizhou Water Resources Bureau for providing reclamation data.

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Received 11 April 2016;accepted 22 October 2016

Available online 9 March 2017

This work was supported by the National Nature Science Foundation of China(Grant No.40776007),and Projects Founded by the Science and Technology Department of Zhejiang Province(Grant No.2009C03008-1).

*Corresponding author.

E-mail address:oceansun@zju.edu.cn(Zhi-lin Sun).

Peer review under responsibility of Hohai University.

http://dx.doi.org/10.1016/j.wse.2017.03.003

1674-2370/?2017 Hohai University.Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license(http:// creativecommons.org/licenses/by-nc-nd/4.0/).

?2017 Hohai University.Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license(http:// creativecommons.org/licenses/by-nc-nd/4.0/).