Study On Erosion And Siltation Of Tidal Flats In The North Part Of The Hangzhou Bay And Its Respone To Shanghai Chemical Industy Park

To the late 80's, the Nanhui section had experienced accretion to erosion to accretion, and the Fengxian section had experienced accretion to erosion, and the Jinshan section had experienced erosion to accretion. Since the 90's, due to the reclamation works on large scales along the Nanhui tidal fiat and the decreasing of sediment fluxes from the Yangtze River. Overall the Nanhui section in the east part of Hangzhou Bay has been mostly in siltation state, and the Fengxian section has experienced erosion on the whole, and the Jinshan section in the west part is now in relative steady state.Because of the a series of humans projects, the higher part of beach in the Nanhui section was surrounded and the lower part was siltation, and the underwater slopes were extrapolated and became more stabilized. The change of the beach and the slope make the field flow to adjust and make the beach erosed. The point of the trend was changed to move to the west side, making the Nanhui section accreted, but due to the decreasing of sediment fluxes from the Yangtze River, the accretion was weaker.The Fengxian section has been still in siltation state with a series of projects near the Nanhui section that cause the point of the trend move to the west. The year of 2003 is the most important year that the strong erosion has changed to the weak erosion in the Fengxian section. Because of the erosion, beach the slope of the beach become steeper, and the higher part of beach has been lost, and the shape of the profile has changed from convex to concave.The Jinshan section in the west part is now in relative steady state. The underwater slope include the narrow beach, the steep slopes, the flat sea-bed and the deep groove. The beach has been always stable in recent years. In the east of the Jinshan section, because of the series of projects, the sea line has been changed and the beach has been accreted.Overall, because the hundred years of standard seawall for the artificial stable shoreline was constructed along the north shore of Hangzhou Bay, there is almost no change in shoreline; erosion mainly happened in the beach under the solar eclipse, such as 0m depth line,5m depth line erosied no less than 0m depth line in the east part of the area.In the year 2003, the second SCIP project has been implemented. The embankment was laid near 0m water depth line. The flow field was changed by the construction, formating the upper and lower two washout zones, sandwiched between a deposition zone; in the year 2005, the second project has been finished, setting up a new flow field. Now it enter into a new balance period between the geomorphology and water power. Underwater topography of the adjustment period has not been over yet. Maybe it is at the end of adjustment, and local micro-washed and the local micro-deposition phenomenon will occur.Based on sediment were analyzed, the results were shown that most of sediment samples located in the research areas consist of clay silt. The change of sediments in the research area can be summarized as follows:grain size in sediments was from coarse to fine along the transverse direction seaward, and sand contribution within sediments was alternative change along the longitude direction. Furthermore, utilizing the principal component analysis, we have obtained finding a finding that the principal dynamic control factor of the sediment in the research district is the wave action and the subordinate dynamic control factor of the sediment is the tide action. Because of using Sato formula,5m water depth lines can be a boundary line. The grain size of tidal flat sediment in north coast of Hangzhou Bay is generally small, and silty clay is the main sediment types in this basin. Maybe the sediment of this basin is mainly supplied from the Yangtze River.Comparing the sediment trends graph with Circulation Model of the Hangzhou Bay Figure, the sediment enter into the Nanhui section firstly, and along the Nanhui beach the sediment have trend to move to the shore, showing a trend of accretion. In Fengxian section the sediment move away from the shore, indicating that the Fengxian section is still in erosion state. Because of the chemical project in the Jinshan section, the sediment which move to the south of Hangzhou Bay was retarded. Otherwise there is still some sediment transporting through the circulation system of Hangzhou Bay to the East China Sea.