Effect of sea level variation on calculation of design water level

The long-term variation and seasonal variation of sea level have a notable effect on the calculation of engineering water level. Stich an effect is fi rst analyzed in this paper. The maximal amplitude of inter-annual anomaly o f monthly mean sea level along the China coast is larger than 60 cm. Both t he storm surge disaster and cold wave disaster are seasonal disasters in va rious regions, so the water level corresponding to the 1% of the cumulative frequency in the cumulative frequency curve of hourly water level data for different seasons in various sea areas is different from design water leve l., for example, the difference between them reaches maximum in June, July and August for northern sea area, and maximum in September, October and Nov ember for Southern China Sea, The hourly water level data of 19 gauge stati ons along the China coast are analyzed. Firstly, the annual mean sea level for every station is obtained; secondly, linear changing rates of annual me an sea level are obtained with the stochastic dynamic method; thirdly, the astronomical tide and storm surge tide are obtained by subtracting the line ar fitting part from the original hourly data, finally, two distributions c orresponding to the astronomical tide and wind tide are obtain ed according to whether the astronomical tide and storm tide are correlative or not. So the two check water levels are obtained with the joint probability method, The maximal difference between the two water levels of 100 years' recurren ce is more than 30 cm. Both of the two check water levels have disadvantage s in the use of observation data, so the mean value is suggested to be take n as the final check water level. A comparison between the two check-water levels indicates that the effect of sea level variation upon design water l evel and check water level is larger than 80 cm at some stations.