| Strong onshore wind and inverse pressure effectcaused the water accumulation which leads to storm surge as typhoon makes landfall.The change of water level makes frequent disasterof overtopping a levee which leads to serious threat to life and property in estuary.Storm surge disaster is the most severe one in the oceanic disasters in China. It is a complex physical process when storm surge develops. Response of storm surge is notable as the external environmentchanges. It is significant to achieve forecast of storm surge accurately and warn coastal disaster effectively after accounting for the response of storm surge to different factors consideration.The conception, density of storm landfall defined as dN/dx, is proposed aiming to reflecting the landing frequency of storm. Based on statistical analysis of typhoon landfall on Zhejiang coastal during the last 63 years, it could be found that dN/dx appears to be decrease from the northern coast to the southern coast. dN/dx is 0.05n/km,0.1n/km and 0.18n/km along the north, center and south of Zhejiang coast. A nested model is utilized to simulate the interaction of astronomical tide and storm surge. Comparison of non-nested model and nested model in storm surge calculation would be presented. The result accuary of nested model is higher than those of non-nested model with obvious magnitude of 18-72cm in storm surge. Therefore, the nested model can improve the accuracy which is more suitable to simulation. In addition, study on influence of maximal wind radius (RMW) on storm surge indicates that before 24hours during 0608 typhoon landing, storm surge will increase by 3.6-6.2cm with RMW increment of 10km. Besides, based on the simulation results of storm surge during 32 typhoons, the tidal level of representative stations in the north, middle and south of Zhejiang coast will be extracted. The return periods of tidal level for these stations during storm surge landfall will be estimated by means of Pearson method.Nonlinear interaction actually exist nearshore, especially in the estuaries. The interaction then cause the difference of tidal level between the storm surge and astronomical tide up to 70cm-80cm in the estuaries of Zhejiang covered by the combination of strong tide and super typhoon; the difference is 14-36cm under combination of neap tide and super typhoon. Additionally, the influence of wave will contribute growth rate of 0.4%～2.5% in high water level in the estuaries.Runoff-storm surge model will be built to analyze runoff effects on the storm surge in southern Zhejiang. According to the time series process of runoff (Qt) during 9711 and 0608 typhoon, four cases with different (0.5Qt, Qt,3Qt and 5Qt) runoff schemes will be designed In all, with the runoff increasing, the difference of tidal range along both banks is raised, which result in increase of disaster risk; the tidal levels along southern bank are larger than those along the southern bank. Transverse gradient of tidal levels are greater in low tide. A correlation between surge and discharge could be obtained, that is The maximum surge is up to 60cm 45cin on condition of Q in Jiaojiang estuary and Oujiang estuary respectively. On condiction of 5Q, tidal level is raised by 3.7m and 2.8m in Jiaojiang and Oujiang estuaryrespectively.The study also makes a discussion on the variations of coastline changing in tidal levels during different typhoons landfall. The results show that high water levels increase but the low water levels decrease. Both changes lead to the tide curve beingstretched under the changes of coastline. The tidal range is raised mainly attributed to growth in high tidal level under combination of strong tide and super typhoon;for neap tide and super typhoon, both increase in high tidal level and decrease in low tidal level raise the tidal range. Additionally, research of cluster reclamation on storm surge is conducted. The maximum increment of tidal level is up to 22cm and the section of which tidal level larger than 7.5m is extend by 3km, which promote the disaster risk. Tidal levels along northern bank are greater than those along southern bank, and the maximum difference in tidal level is up to 17cm.Effects of SLR on storm surge in Jiaojiang estuary can be described as followed:with SLR increasing, increment of tidal level increase characterized as periodic fluctuation; process of such increment is one hour prior to tidal process; as SLR is 0.15m, the maximum increment upstream Niutou Necking is about 0.08m but it exerts few influence on tidal level. |
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