Researches on characteristics and dynamic mechanism of short-term scouring and silting changes of the tidal flat on Nanhui Spit in the Changjiang Estuary in China

To some extent,scouring and silting evolution of tidal flat may reflect the relationship and interaction between dynamic effect and geomorphologic characteristics.On the basis of Shanghai coastal zone investigation project,acontinuous observation was made at the intertidal zone of three sections on Nanhui Spit from June 2006 to June 2007,in order to research the properties of short-term scouring and silting changes as well as its influencing factors.The results show that(1) recently,the tidal flat of Nanhui Spit mostly has a scouring posture,and seasonal difference of flat variation in the year is relatively obvious;affected by it slocation,the respective section shows different developing properties,for example,scouring and silting changes of section one are the most obvious of all,the amount of which is both above 10cm; (2) acted by waves and tidal current,the surface sediment of this zone is easy to be stirred,and the existence of sediment circulation system is favorable for the suspended sediment to settle in shallow water area,which becomes the sediment source of tidal flat;(3) influenced by the storm surge caused by typhoon "Bilis",drastic scouring as well as silting happened in this zone.All of these have proved that the scouring and silting changes of tidal flat were affected by several kinds of dynamic conditions.