The effect of long-term sea-level variation on calculating the extreme water levels of multiyear return periods

The effect of long-term variation in mean sea-level on extreme water levels of multiyear return periods was analyzed and discussed on the basis of data of the yearly extreme high(low) water levels and yearly mean sea-levels obtained through observation at Rushankou in a period of 24 a.And also approaches for eliminating the yearly mean sea-level long-term variation were discussed.Through the comparison between the extreme water levels of multiyear return periods in the case of yearly mean sea-level long-term variation being eliminated and those in the case of the long-term variation being retained,one can find that for the extreme high water levels,the results with the longterm variation being retained are higher than those with the long-term variation being eliminated,as for the extreme low water levels,the situation is just the oposite.