Sedimentary Dynamics and Geomorphic Evolution of the Laizhou Shoal

Based on field work and historical geomorphic analysis, and supported by GIS and RS, this paper has researched the geomorphic dynamic characteristics and evolution rules and the artificial effects on erosion and deposition of the Laizhou shoal since 1958, when many reservoirs were built, and a great amount of sand began to be reduced. The results show that the Laizhou shoal has been moving northward while the nearby Diaolongzui spit moving northward because of the geomorphic-dynamics between them since the mid-19th century. The sand made up of the shoal has come directly from the Diaolongzui coast, and ultimately from the rivers which empties into the Bohai Sea across the NE direction stretching coast from the Diaolongzui spit to the Qimudao island. There are two main depositional dynamic mechanisms, which have been controlling the shoal erosion and deposition processes. One is that when the ebb tidal current from the south-west Laizhou bay is retarded by the shoal, it turns to flow along the west-northern striking shoal with a secondary transverse circulation made up of shoalward currents in the bottom and upwelling currents near the shoal. So, erosion took place on the SW part, and deposition on the top part of the shoal, which led to the shoal migrating toward NE as a whole. Another is that the centrifugal effect of tidal currents around the pointed end of the shoal causes a secondary circulation made up of shoalward currents in the bottom and upwelling currents in the upper. So, the suspended sand deposits on the NW part of the shoal.