Impacts Of The Geometrical Variations Of Jiaojiang Estuarv On Storm Tides

Storm tides occur frequently in the Jiaojiang Estuary,which is an enormous threat to the lives and property of local people.Multiple factors makes the dynamic mechanism of storm surge complex,among which estuarine geometry is an essential one.Meanwhile,owing to reclamation projects recently,the geometry of Jiaojiang Estuary changes significantly.Therefore,it's of great significance for coastal engineering disaster prevention and mitigation to explore the impacts of the geometrical variations of estuary on storm tides.Based on MIKE 21 flow model and parametric typhoon model,a numerical model coupling astronomical tide with storm surge was established for the Jiaojiang Estuary.The model was calibrated using predicted and observed water level data during Typhoon 9417 and 9711,as well as mearured flow data in April 2009,respectively.Counting on the idea of reclamation planning,a series of numerical experiments with different geometrical variations were designed,which can be divided into extension of north bank,extension of south bank and extension of both side.Based on the present estuarine geometry,the dynamic characteristics of astronomical tides and storm tides in the Jiaojiang Estuary during Typhoon 9711 were revealed.The amplitude of main constituent M2 is about 1.75m.Residual current is mainly seaward because of the discharge of the Jiaojiang River.During spring tide,maximum flood tide discharge of river entrance is 29715m3/s,while flood flux 2.88E+8m3.Typhoon 9711 moved from southeast to northwest and landed in Wenling,less than 100km south the Jiaojiang River.High storm tide level and high tide level occur at the same time,while storm surge peaks earlier.Distribution of high storm tide level is mainly controlled by wind field while the storm current field varies significantly from the tidal current field..Based on the experiments of various estuarine geometry,the variations of astronomical tide features with its mechanism were revealed.Along with extension of north bank,the amplitude and maximum velocity of M2 show a downward trend,as well as the flood tide discharge and flux of the entrance.Along with extension of south bank,the amplitude and maximum velocity of M2 also show a downward trend,while the flood discharge and flux reduce markedly.The impact of both banks extension can be roughly regarded as the combination of extension separately,only more severely.Tidal prism reduces along with the extension,which changes the features of tidal process.Tidal flat occupied by the extension weakens the shoaling effect,and then changes the tidal characteristics.Based on the experiments of various estuarine geometry,the variations of storm tide features with its mechanism were revealed.Along with extension of north bank,high tide level and high storm tide level reduce,while the estuary being narrowed and the hydrodynamic being weakened.Along with extension of south bank,high tide leve similarly reduces while high storm tide level lifting in river channel.Meanwhile,the orientation of river entrance deflection due to the extension.The impact of extension of both banks can also be roughly regarded as the combination of extension separately.Furthermore,controlled experiments were carried out using topography data measured in 1998 and 2013.Result shows that affection caused by seabed defomation can be neglected comparing to the geometrical variations.Through sensitivity numerical experiments,the contribution of different driving factors to storm tide was explored.Result shows that wind field contributes most,more than 70%at high storm tide level.Air-pressure surge is followed by 20%.Runoff tend to take effect at low water level.Besides,geometrical variation of estuary has little influence on the contribution,except the wind field contribution in river channel.