The MIKE model application to overtopping risk assessment of seawalls and levees in Shanghai

This article used MIKE 21 models to evaluate the overtopping risk of seawalls and levees from the combined effect of land subsidence, storm tide, and sea level rise in Shanghai. Typhoon storm tides are the primary natural hazard affecting the Shanghai area. The worst storm tide in recent history was No. 9711, which produced a high tide of 5.99 m. Projections indicate that sea level will rise by 86.6 mm, 185.6 mm, and 433.1 mm by 2030, 2050, and 2100, respectively. The combined impact of these hazards threatens to flood large parts of the Shanghai area in the future. By 2030, 4.31 percent of the total length of the seawalls and levees in Shanghai will be at risk to being overtopped. By 2050, 27.55 percent of all seawalls and levees are likely to be overtopped. By 2100, overtopping will increase to 45.98 percent. The high risk of seawall and levee exposure to overtopping is closely related to the functional impact of land subsidence on the height of existing seawalls and levees. We propose specific engineering measures for Shanghai based on the results of our overtopping simulations.