Numerical Study Of Wave Characteristics In Typical Mangroves Bays Of Guangdong Province

Mangroves are the saline plant communities growing on the salt marshes in the estuaries of tropical and subtropical bays,which play important roles in wave attenuation and coastal protection.It is conducive to deepening people's awareness of protecting mangroves to research their wave dissipation effects.However,most of the current researches focus on the attenuation of short-term wave by mangroves,and few focus on the attenuation of wave in years.Guangdong Province has the largest distribution areas of mangroves and the longest continental coastline of China,which is an ideal zone to study the wave dissipation effects of mangroves.This paper is based on the SWAN wave model,firstly,the wave properties during typhoon "Muifa" passing through Jiangsu Province were simulated,and by comparing the result with the measured data of wave station,the accuracy of the simulation of propagation of wind generated wave was verified.Then the physical model experimental carried out by Ozeren et al was simulated,the results verified the accuracy of the simulation of wave propagation in vegetated zones.Finally,the wind velocity of the ECMWF driving wind field was verified by the measured wind velocity of the ground exchange station.With the numerical model and the driving data verified,four typical mangrove-growing bays in Guangdong Province were chosen;they were Leizhou Bay,Hailing Bay,Zhenhai Bay and Honghai Bay.Firstly,the 30-year(1989~2018)wave data without considering mangroves of the four sites were calculated.The statistical analysis of the results revealed that the prevailing wave directions of the four sites are E,ESE,SE,SSE and S.Then the P-? distribution?s moment-seeking and curve-fitting method was used to do the frequency analysis by writing MATLAB script and the final curve parameters were determined according to the absolute value criterion.After that,the significant wave heights of different directions and return periods were calculated according to the final P-? curves.The results showed that the largest significant wave height in 100 years of the four sites was 2.22 m,which occurred in the Leizhou Bay with the deepest water.For Hailing Bay with smallest water depth,the difference between the significant wave height in 2 years and the significant wave height in 100 years was not significant,both of which were about 0.4 m.By counting the average community characteristics of trees and shrubs in the mangroves of 15 coastal creeks in the Baguang zone of Shenzhen,the characteristics of mangroves of the four research sites were determined,and the distribution areas of mangroves were determined according to the survey results in the year of 2018.With those,the numerical model of wave propagation in the mangroves zone of typical bays in Guangdong was set up.Then the 30-year wave data considering the effects of mangroves were calculated,and based on the data,the corresponding significant wave heights in years were calculated and compared with the results without considering the effects of mangroves.At last,the attenuation effects of the significant wave heights in different directions and return periods were analyzed.The results showed that the average attenuation rates of significant wave heights of different directions and return periods were all above 20%,and the maximum was 66.86%.