Research On The Activity Of Sand Waves Bedforms In The Yangzi Shoal

The continental currents can make the sea bottom sand to all kinds of seabed forms. The seabed form,which grows paralled to the main current,is called the submarine current ridges,and sand dunes or sand waves,which are developed vertical to the main current. The sand dunes are the typical forms on the sand seabed. The migration and movement of sand dunes can empty the sand overlaying the pipes or bury the pipes leading to the base destabilization of building,and are the marks of the sea environmental changes. The current ridges and sand waves have closed relationship with the marine engineering,navigation and military affairs,so they have been a major research focus in geosciences.The study area is located in the east of changjiangriver in East China Sea(30.7o～32.6oN,122.5o～125oE),which water deep 30~50m and an area of 3×104sqmeters.By the six investigate reports about the study area and partially pressed papers,we can know that the motion of sand waves in Yangzi Shoal have the closed relationship with the hydrology and geology of the area. In usual day,sand waves can be drived by the tidal current,which derection is consistent with the major tidal current orientation. However,the bigger and harmed move distance of sand waves is aroused by the typhoon or cold waves. By the collect of hydrology and typhoon data and calculation of mathematics fomula,we gained the move distance of sand waves in the usual day and typhoon. Because orientation observation is difficult,so by the collect of sediment grain,tidal current and typhoon data,we made use of the different hydrological fomulas and drew the conclution about the distance in the usual and typhoon state. Because the two formulas used the different parameters,the conclusions is different.However,both of the formulas's results can explain that the distance of sand waves in ususl states is small than in the typhoon states.At the same time,we also calculate the transfer velocity of the sand waves'in the Dongfang of South Sea,and we also drew the similar conclusions In typhoon or cold wave states sand waves can transfer bigger distance. This show that the primary factor which can induce the sand waves'transference is typhoon or cold waves.