基于逐时潮位推求设计水位的统计分布选型研究

Study of Theoretical Curve Type for Design Water Level Estimation Based on Hourly Tide Elevation

基于沿海长期观测的历时潮位资料,提出了推求设计高(低)水位的传统最大熵分布模型。该分布能够拟合逐时潮位具有双峰的概率密度曲线,计算所得设计高(低)水位,与修改的最大熵分布高潮10%和低潮90%的水位值相比,误差较小。选型的历时潮位曲线分布为港口工程设计水位推算提供了更多的选择,计算精度高,克服了手工方法推算历时潮位设计值的不足,有理论和工程意义。

With given data of long-term measured tide elevations,there exist two methods to determine design high water（DHW）or design low water（HLW）.One is to determine design water（DW）with tide duration curve.The other is to calculate DW with high and low tide elevation data.According to the Code of Hydrology for Sea Harbor,for harbors at sea coast and river estuary with obvious tidal actions,the DHW shall be the water level with 10% of high water accumulation frequency（HW10%）and the HLW shall be the water level with 90% of low water accumulation frequency（LW90%）.For coast harbors and estuary harbors with obvious tidal actions,if statistical data of accumulated frequencyies of water level duartion are available,the water levels with 1%and 98% of accumulated frequencies of duration can be used as the DHW and DLW respectively.For esturay harbors without obvious tidal actions during flood preiod,the water levels with 1% and 98% of accumulated frequencies of duration shall be used as the DHW and DLW respectively.For determination of DHW and DLW,the accumulated frequencies of high waters,low waters and tidal water levels with certain duartion shall be satistically calculated with the tide level data obtained from observation for one or several complete years.No matter with the accumulated frequencies of high waters and low waters,or with the accumulated frequencies of tidal levels with certain duration,the DW are estimated with the plot curve by hand in port engineering design.Based on daily observed data of both high and low tide levels,Dong and Yao adopted Modified Maximum Entropy Distribution（MMED）to calculate design water levels in 2010.The computation accuracy is higher and the shortage of traditional method is overcome.However,the cumulative curve plotted by MMED does not fit tide duration very well.It makes sense to put forward a suitable statistical distribution to quickly estimate correct design tide levels.Collecting 12-year observed tide elevation data at Lianyungang Port,4kinds of distributions,such as Normal distribution,Log-normal distribution,Traditional maximum entropy distribution,and MMED,are candidate theoretical distributions for frequency analysis.Corresponding estimating approaches are given for the unknown parameters of these distributions.The K-S test and Root Mean Square Error are provided for optimal curve selection.Through statistical calculation and result comparison,the conclusions are given as follows：（1）TMED is suitable to estimate design high and low tide level for coastal port engineering.（2）The calculation accuracy by TMED is almost the same as that by MMED.（3）The histogram of tide duration shows its two peaks,but the probability density function of MMED only has one peak.MMED is not suitable to fit tide duration curve.On the contrary,TMED has a 2-peak probability density function,which can fit tide duration curve very well.