Research On Sea Dike Disign High Water Level Under Environmental Change

Under the conditions of environmental change,how to calculate the sea dike disign high water level is worth to do reseaching.Taking the coastal area of Guangxi as an example,this paper firstly studies the changes of typhoon and sea level which are tidal major environmental factors,Secondly Builds a model to analyze the change of tide level under the condition of major environmental factors change.And then uses the method of wavelet analysis and univariate linear regression to analyze the tidal trend under the condition of all environmental factors change.Finally,the tide sequence is decomposed and calculated basing on the nonuniform hydrological frequency calculation of time series decomposition,and the method of calculating the sea dike design high water level under the environmental change condition will be determined.Using the method of sliding average method,spearman analysis and r/s scale method to analyze the typhoon affecting the coastal area of Guangxi,we can get the following conclusions:The frequency of typhoon affecting the coastal area of Guangxi decreased from 1949 to 2015 with the intensity and annual intensity increased,and impact of the region's typhoon frequency,intensity,the annual strength of extreme increases in the future.To sum up the law of coastal sea level changes in Guangxi,we can get the following conclusions:After 2000,the sea level along the coast of Guangxi has been on the rise.It is expected that in the next 30 years,the coastal sea level in Guangxi will continue to rise,the annual rate of increase of 2mm/a?4mm/a.Using MIKE21 software to establish the northern bay mathematical model,we can get conclusions by analyzing the trend of tide change under the condition of major environmental factors change:Typhoon intensity increasing will increase the difference between the tide level,sea level rising will rise in the overall tide level;with the common of both typhoon and sea level changing,the tide will increase when the storm surge maximum water level occurs.Further analysis of the storm surge water level fluctuation and wave height change,we can find that storm surge water level fluctuation and the wave are greater affected by typhoon changing while less affected by sea level changing.By means of wavelet analysis and univariate linear regression,it is found that the highest tide level is significantly increased at the rate of 4.9mm per year under the condition of major environmental factors change.This will lead to the problem that sea dike design high water level does not meet the tide changing while using existing norms to calculate,it increase the sea dike embankment or dike risk.Based on the principle of time series decomposition and synthesis,using bne-dimensional linear regression,Fourier series,Pearson three-type curve to calculate the trend item,period item and random item,On this basis,we use the four methods to calculate the design high water level and get the following conclusions:The distribution synthesis method works best and the trend item +ARIMA model prediction synthesis method is the second,The numerical synthesis method is not ideal while the trend term + cycle term forecast synthesis method is the worst.For the calculation of the sea dike design high water level under the condition of environmental change,it is suggested to use the distribution synthesis method or trend item + ARIMA model prediction synthesis method to carry on the correlation calculation.