Estimation of the maximum and minimum surge levels at the Hanhikivi peninsula, Gulf of Bothnia

A combination of statistical and deterministic methods was used to calculate the flood level for the Hanhikivi peninsula on the northeastern coast of the Gulf of Bothnia, where a nuclear power plant is planned. An existing Baltic Sea numerical model (BSM-2010) solving the depth-averaged shallow water equations was used. Using formulas for an idealized storm field, wind and atmospheric pressure fields were assigned as forcing. The possible intensity of the extreme storm field was determined from the database of storm fields that passed over the northern hemisphere from 1958–2016. The modeling results show that the maximum water level rise at Hanhikivi occurs when an extreme storm field over southern Norway moves east-northeast with a velocity of 65 km h–1. Extreme water levels in Hanhikivi obtained with statistical and deterministic methods at a probability up to 0.01% (return period of 104 years) are +252 cm and –251 cm, respectively.