Research Of Dynamic Geomorphological Characteristics Of Sand-mud Transition On The Beach

The study of SMT(sand-mud transition)based on the investigation of the sandymuddy transitional beach in the coastal of Fujian province and analyzed the characteristics of the coastal dynamic geomorphology of the SMT.Field survey measured to collecting the location,topographic geomorphology data of sandy-muddy transitional beach,also the morphology and profile data.For understand the characteristics of SMT sediments,the formation and development of its changes were discussed,soil mechanics were tested,also the indoor analysed.Field measurements of28 sandy-muddy transitional beaches indicated that two categories: the source control type which mainly distribute in the estuary,and the dynamic control sandy-muddy transitional beach which distribute in the low-energy bay.And two kinds of SMT categories are estuary controlled SMT and low-energy bay SMT.Over the estuary area,there are overlying sand layer on the SMT,its difficult to distinguish.But on the lowenergy bay,it is muddy layer on the surface of SMT,obviously it is easier to distinguish.SMT distributed in parallel with the shoreline roughly,but when the shoreline changes or there is runoff on the beach or the sand bar appears,the SMT changed and offset.In addition,the results show that the SMT are roughly parallel to the beach shoreline,while their elevations display clear difference with a range of 0.6 m.In order to understand the development mechanism of SMT,2 typical sandymuddy transitional beach(Zuokeng beach,CL-ZK;Nantaiwu Beach,ZZ-NTW)were selected and investigated,six sediment columns were collected,and soil mechanics experiments(particle size experiment and geotechnical experiment)were carried out on sediment columnar samples.It combined with coastal dynamic deposition?dynamic geomorphology knowledge,deeply search for typical sandy-muddy transitional beach and its SMT development process.Due to the seasonal sedimentation and scour of estuary district,the mud interlayer soil is formed below at estuary controlled SMT sediments,but it is highly compressible and discrete shear strength.The sediments of SMT in low-energy bay are transformed into sand mud mixtures during the gradual deposition of mud,which is pure sand before;its shear strength has some regularity.And with the content of mud in mixture grow up to a certain extent,its shear strength decreases rapidly and the compressibility becomes larger.The migrations of SMT location and changes of SMT elevation are mostly ascribed to the both supply variations of sand and mud and wave hydrodynamic conditions.That corresponds to two SMT development modes,one of which is the periodic change of deposition or separation of sediment,mainly because of seasonal change of source condition.The other one is the muddy particles are deposited on the beach with low-energy,and formed a mixture of sand and mud.And SMT changes year by year,until the balance is re-reached.The last,when actual doing the survey,the SMT could not be distinguished according to the GMD(Geometric mean diameter)and mud content quickly,it needs to combine with auxiliary means.