Numerical Research On Beach And Dune Evolution Under Storm Conditions

Coastal erosion,especially for sand beaches,is a widespread challenge for waterfront regions.The beaches alternate between winter profile and summer profile periodically on annual time scale.The cross-shore sediment transport relates mainly to wave nonlinearity,undertow and infragravity motion.During storm period,wave impacts are focused on back-shore dunes due to high storm surge level,leading to huge erosion and sediment redistribution in several days.Comparing with traditional hard structure,the soft or sandy dunes is increasingly highlighted for coast protection in recent years.WRF-ARW,SWAN,ADCIRC as well as the process-based Xbeach model are employed to simulate the atmospheric & hydrodynamic field storm erosion process for the Pingtan beach nourishment project.Field data beach profile is adopted to validate the model.The responses of structure-protected and dune-protected beach profile during storm conditions are compared.For the cases of hard protection structures,the waves act directly on the seawall,causing converge of wave energy in front of the sea wall as well,and result in scouring in front of the structure.The hard structure may also enhance upstream accretion and downstream erosion by intervention of longshore sediment transport.In the case soft protection measures,the dunes often behave as erosion at the upper part of the cross-section and accretion at the downside part of the cross section and eroded sand deposits on the fore-beach.The capacity of sand supply will be enhanced for steeper dune faces.Dune erosion increases with wave period and infragravity wave plays an important role in dune erosion during storms.Dune erosion potential as well as sand supply capacity will also be influenced by storm surge.The first impact of the storm is more crucial in reshaping of the dune profile among the successive storms.