In this paper, a numerical model of the coupling between astronomical tide and storm surge based on a 3-D hydraulic model for estuary and coast (ECOMSED) is confirmed to be suitable for simulation of storm surge in the Bohai Bay. The maximum surges caused by typhoons from 1989 to 2008 are simulated; the yearly extreme water levels on grids and the spatial distribution of extreme water level of different return periods in the Bohai Bay are concluded. It shows that tidal range and surge increase from deep water to shallow water as a whole. Extreme water level in deep water are smaller than shallow water, the spatial distribution of extreme water level is influenced by topography. From the simulation result, the maximum surges at Tanggu and its adjacent sea area are 1.88m, 1.65m and 1.57m in 1992, 1997 and 2003, respectively. The maximum extreme water level of 50-year return period is about 4.35 m which mainly occurs in the adjacent area from reclamation district of north Tianjin Harbor to Dashengtang. The spatial pattern of extreme water level of 25-year return period and 100- year return period are similar to that of 50-year return period, the extreme water level also occur in the adjacent area of north Tianjin Harbor, but the areas of extreme water level of different return periods are different.
The change of bottom topography and coastlines has significant effects on storm surge, and strong storm surge often occurs in the nearby of sea coast. Therefore spatial distribution of yearly extreme water level is influenced by topography. Long term tidal gauge station data of minimum 19 years is so scarce that the spatial distribution of yearly extreme water level is needed to be calculated by numerical simulation.
