| The return values of positive and negative storm surges are important parameters to design disaster-prevention structures in coastal engineering. This paper examines the errors in estimating the return values, which result from the assumption that the whole individual data must have a common parent distribution. Twenty-seven years of storm surge data measured from Rizhao Hydrologic Station are selected to set up different statistical samples according to time division, such as year, season or month. Owing to different reasons of storm surge, the Combined Distribution Method is presented based on one-dimensional compound extreme distribution. Comparison shows that the traditional method under-estimates the return values. The return values of storm surge in Rizhao area are given with Combined Distribution Method under the consideration of seasonal variation. Extreme high tide level is also calculated for coastal engineering design. The main content of this study is as follows:(1) To collect the observed positive and negative storm surge at Rizhao Hydrologic Station from 1970 to 1996 and analysis the meteoric causes of storm disasters.(2) Two-step least square method is proposed to estimate the three unknown parameters of Pearson HI type distribution for statistics of storm surge. Fitting results show that the presented method is simple and stable. It also leads to less labor of calculation.(3) To summarize the univariate extreme value distribution and put forward a Combined Distribution Method, which is suitable in statistical analysis of storm surge in typhoon-influence area.(4) Data samples are selected from 27-year observed storm surge series. Considering the occurrence of typhoon frequency, this thesis calculates the return values of storm surge.(5) The design tide level and extreme tide level are computed with different approaches. Calculation results are given as decision-making references for departments of government, planning, and design.
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