Development And Analysis Of The Unstructured Numerical Model For Storm Surge In The Changjiang Estuary

The fatality induced by storm surge stands first on the list of marine disaster in China. The mouth of the Yangtze River and its adjacent areas, which are economically developed and heavily populated, have been struck by storm surges and suffered losses provoked by them almost every year. Therefore, it is with practical significance to conduct research of storm surge forecasting modeling for this area.An unstructured grid and high resolution model based on ADCIRC bidirectional coupled with SWAN is developed to simulate the storm surges in the Yangtze Estuary and its adjacent areas. Unstructured mesh grid is applied to fit the complex shoreline and topography of the estuarine and coastal areas. The grid size around the boundary of Shanghai reaches100-m. The effects of tide, wave and river discharge are considered. Observed data of tide and wave are adopted to test and calibrate the model.23storm surge events during1979-2008, with observed data of water elevations and wind speeds are used to validate the hindcasts performed by this model. The results show good agreement with observations. The model is also utilized to explore and testify the regular pattern of surge caused by two typical classes of typhoon tracks. Influencing factors of surge such as air pressure, wind stress, typhoon tracks, and interactions with tides are investigated by numerical experiments. Quantitative relations between surge range, pressure gradient and typhoon tracks are revealed by statistical analysis of typhoon tracks and observed surge records at the Waigaoqiao station. Interrelations of surge and tide phase are analyzed using statistical analysis of observed surge and tide data.The potential impacts of the sea level rise (SLR) on the storm surge at the Yangtze Estuary its adjacent areas are investigated by numerical experiments using this model. The model was applied to two typical typhoons for the present day sea-level as well as1.0m and0.483m SLR scenarios. Impacts exerted by SLR on the tide and waves are also discussed. The migration of the amphidromes caused by SLR causes the co-phase lines to defect relatively counterclockwise to those of the current near the Yangtze Estuary. The amplitude increases slightly at the inner mouth of the Yangtze River, and more notable increases are presented at the northern part of the Yangtze River Mouth. The amplitude decreases in adjacent areas of the Hangzhou Bay. Comparing the maximum wave height for each scenario, in the Changjiang Estuary and its adjacent areas, the wave height increase was found to be significant in shallow areas due to the increase in water depth; the breaking locations of the wave shift shoreward. The general patterns in wave height change are approximately determined by the typhoon path and topography. In different storm surge cases, the trend and extent of variations of peak value are not quite similar in the Changjiang Estuary and its adjacent areas, extents of peak elevations’variation and those of surge range from a few to a dozen centimeters, no more than25cm. The curves of surges and water elevations accelerate slightly relative to that of the control scenario. All the properties respond to sea level rise in a non-linear and spatially non-uniform manner.