| 摘要: |
| 在海洋工程建设(如港口建设、沿岸工程和海上平台建筑等)中,必须对正常条件(即作业条件)和极端条件(即恶劣环境条件)下的海洋环境参数作出估计。对于海洋水位而言,如《港口工程规范》(以下简称《规范》)中的设计水位和乘潮水位等即属于前者,校核水位即属于后者。正常条件下的水位参数比较容易确定,因为这种条件下的观测数据比较容易获得,有比较丰富的已知资料。极值水位是指若干年内オ有可能出现的高水位或低水位,例如在《规范》中要求50年一遇的水位作为校核水位。所以如依靠直接观测,必须具备至少几十年的观测资料,这一要求只有在有长期验潮站的港口オ能达到。如资料系列不够长,则必须采用一定的方法对它们的数值作出估计。
在有相当长期观测资料的情况下,常常采用极值分布的方法,即每年取一个最高(或最低)水位,然后拟合某种理论或经验的分布曲线,从而得出不同重现期的极高(或极低)水位。这种方法所得结果比较可靠(但也不是没有问题,详见第五节),但对资料要求高，特别在新建港口或海上工程,常常不能采用。
在有数年观测资料的情况下,可以采用同步差比法(见《规范》)。当拟建港和主港潮汐性质和风暴潮特性相近,特别是两地距离较近时,这种方法常常能给出良好的结果,不失为一种有效的方法,但其应用受到一定的条件限制
近年来,国外提出了一种“联合概率法”(Pugh and Vassie,1978,1980)。这种方法把水位中的潮汐水位(这里指的是可用调和方法预报的潮位,其中也包括周期性的气象潮)和余水位(即实测水位减去预报水位)分开,分别求其分布,然后再用联合概率法回过来求合成水位的分布,从而得出极值水位高度。这种方法的优点是能够充分利用水位观测资料,因而可以在观测时间较短的情况下得出比传统方法更稳定的结果。在Pugh和Vassie所提出的方法中,潮汐和余水位被看作是互相独立的。这一假定在深水海区较接
近实际,但在某些浅海区则与实际有较大出入。例如Pugh和Vassie发现,对位于泰晤士河的绍森德港,由联合概率法按上述假定得出的百年一遇的高水位比由传统极值分布方法得出的数值大约高60cm;而传统方法的结果与49年期间观测到的最高水位较接近。Pugh和Vassie在后来的文章中对绍森徳港的问题作了专门处理,得出较合理的结果,但基本上是采用经验的方法,在一般实际中使用是困难的。
为了考虑潮汐和余水位的这种相关性,我们曾将联合概率法予以推广,提出了条件分布联合概率法(方国洪、王骥,1987)。这种方法不论潮汐和余水位是否相互独立均可应用,具有更强的适应性。本文根据该文的基本想法,选择了我国沿海资料较长,并具有较好代表性的10个长期验潮站共286年的潮汐逐时记录,进行了分析研究,对该文提出的方法作了修改和补充。 |
| 关键词: 联合概率法、海洋工程、极值水位 |
| DOI： |
| 分类号: |
| 基金项目:中国科学院海洋研究所调查研究报告第2146号 |
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| A METHOD FOR ESTIMATING EXTREME SEA LEVELS BASED ON TIDE-SURGE JOINT PROBABILITY IN OCEAN ENGINEERING |
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Fang Guohong1, Wang Ji2, Jia Shaode2, Jiao Zongfeng2, Ye Anle3
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1.Institute of Oceanology, Academia Sinica;2.Institute of Marine Scientijic and Technological Information, SOA;3.Qingdao Ocean University
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| Abstract: |
| Extreme sea levels are traditionally estimated from extrapolation of observed annually maximum (or minimum ) sea level heights, by fitting an extreme-value distribution. This approach needs long-term observation, which is often not available for some newly developing areas.
Pugh and Vassie (1978) proposed combining the probability distributions of tide and surge to obtain the probability distribution of tota (tide plus surge) sea level. In that study, tide and surge were regarded as independent. I ater, Pugh and Vassie (1980)studied the extreme sea level at Southend and concluded that the interaction between tide and surge was important for estuarine areas.
In the present study the dependence of the probability distribution of surge on tidal level is examined. It is shown that for some Chinese coastal areas the statistical characteristics of surge in the case of lower tidal level can be twice as large as that for higher tidal level. This is attributted to the meteorological effects. The strong northerly monsoon in winter can cause larger surges and lower the tidal level at the same time.
In order to take into account the dependence of the surge distribution on tidal level, the conditional distribution of surge versus tide is introduced. The marginal distribution of tide can be simply obtained through the statistics of the predicted tidal heights for a period of 19 years. The distributions of surge corresponding to different tid levels are considered as"similar”, that is, the normalized distributions of surge corresponding to different tidal levels are considered as identical to each other and are the same as the normalized marginal distribution
of surge. Thus, the conditional distribution of surge can be calculated from the normalizedmarginal distribution and the standard deviation of surge corresponding to different tidal level. From the joint distribution of tide and surge the distribution of total sea level can be obtained.
The extreme sea levels obtained from the joint probability method are compares with those obtaind from the traditional method. It is shown that general consistency is achieved if the observational sea level series are long, and the former results are much more stable than the latter if the observational sea level series are short. |
| Key words: EXTREME SEA LEVELS,JOINT PROBABILITY,OCEAN ENGINEERING |
