4.4　Storm Surge Set-up

4.4.1　For the design basis floodforcoastalsites，theset-upcausedbymaximum possible storm surge shall be analyzed.The cause and type of storm surge shall be determined based on the site location，climatic characteristics，and historical hydrometeorological conditions.

4.4.2　The verified mathematical model for storm surge shall be used to calculate the set-up caused by maximum possible tropical cyclone.The parameter P0 of maximum possible tropical cyclone should be calculated by the probabilistic method and deterministic method.

The maximum wind radius of maximum possible tropical cyclone shall be determined based on the aircraft sounding Pacific Northwest typhoon data and the value of P0.The typhoon speed in all directions shall be determined according to the typhoon yearbook data.

4.4.3　The maximum set-up shall be determined by comparing the long series data of tidal level measured by nearby stations with hourly astronomical tide process line calculated through harmonic analysis on the basis of tidal level data of long series.

4.4.4　The probabilistic method shall be used to obtain the maximum annual set-up series of the same storm type at the reference station，or historical typhoon data in yearbook and storm surge models can be used to obtain long series set-up at the site.At least two different statistic methods shall be used for frequency calculation to ascertain the storm surge set-up at frequencies of 2%，1%，0.1% and 0.01% and their corresponding confidence interval.The most reasonable results shall be determined through analysis and comparison.

4.4.5　The calculation of set-up using the probabilistic method shall cover a series of more than 30 years，and as long as possible.No matter how long a series the measured data covers，the historical storm surge flood shall be investigated and verified.

4.4.6　To determine the storm surge set-up，the weather system which caused storm surge as recorded in historical data shall be analyzed to understand the type，duration，intensity，route，and landing point of tropical and extratropical cyclones.This analysis shall be done in conjunction with astronomical tide and storm surge set-up process.

4.4.7　The calculated design storm surge set-up at the reference station may be used to ascertain the storm surge set-up at the plant site.

4.4.8　A verified mathematical model which is determined based on the type and characteristics of storm surge shall be used in the calculation of maximum storm surge set-up by the deterministic method.

4.4.9　The atmospheric pressure value and wind speed and direction at grid points shall be given in the calculation of tropical cyclone storm surge values.The model parameters shall be calibrated and verified against measured data.

4.4.10　In numerical simulation of storm surge set-up，historical storm surge set-up processes shall be simulated based on the measured meteorological and hydrological data to verify if the model is correct.

4.4.11　The maximum possible storm surge set-up at the plant site shall be determined as a set-up caused by an assumed group of extreme storm types that may occur at the site when moving to a certain location.The sensitivity of typhoon parameters shall be analyzed.

4.4.12　The extratropical cyclone parameters may be calculated by the frequency analysis method.

4.4.13　The density of typhoon landing paths shall be calculated at an angle not greater than 22.5°.

4.4.14　For a partially enclosed or enclosed water body，the maximum possible storm surge caused by moving squall line shall be analyzed.The two-dimensional storm surge model used to determine the storm surge water level caused by maximum possible tropical cyclone and maximum possible extratropical storm surge can be used to estimate the maximum possible storm surge water level caused by moving squall line upon adjustment.