Estimating extreme sea levels in Yangtze Estuary by quadrature Joint Probability Optimal Sampling Method

Effective estimation of extreme sea levels is of primary importance for coastal construction and coastal hazard mitigation. To predict 100-year and 200-year Annual Maximum Water Levels in Yangtze Estuary, simulation studies using the Quadrature Joint Probability Method-Optimal Sampling (JPMOSQ) to generate a set of optimal synthetic typhoons and river discharges combined with numerical hydrodynamic models capable of accurately simulating sea levels were conducted. During the synthetic simulation combination generation process, astronomical tide was also taken into account based on the Monte Carlo method. After a series of model validations, which showed that this model performed well to reflect the characteristics of the typhoon field, wave height, and sea level in the studied region, this model was implemented to predict extreme sea levels. Through simulation, 100-year and 200-year Annual Maximum Water Levels at Wusong station were predicted to be +6.08 m (Wusong Datum, WD) and +6.28 m WD, respectively, while these two values for Baozhen station were predicted to be +6.12 m WD and +6.33 m WD, respectively. Also, the 100-year and 200-year Annual Maximum Water Levels at Hengsha station were predicted to be +5.99 m WD and +6.13 m WD, respectively. Comparisons with former studies showed that the JPMOSQ method can be used to forecast extreme sea levels during typhoons in Yangtze Estuary. Estimating results from this study would be conducive to risk assessment in coastal areas as a reference.