A study of suspended sediment concentration in Yangshan deep-water port in Shanghai, China

Suspended sediment concentration (SSC) plays an important role in the estuarine environment. Its spatial or temporal variations in coastal zones and estuaries indicate that sediments are suspended, transported and deposited under various actions, such as the river discharge, waves, currents and local topography. Yangshan deep-water port is located in the Qiqu Archipelago with many islands and tidal channels. Taking Yangshan deep-water port sea area as an example, an analysis of distributions and variations in the SSC based on data measured in Oct. 1996, Jan. 1999, May 2006 and May 2007 and the surface SSC data measured during the period from 1998 to 2008, has been undertaken. Results from the study suggest that: (1) the yearly-averaged SSC decreased from 1998 to 2008; (2) the SSC has strong seasonal variations, the monthly-averaged SSC values are higher from November to April of the next year (the winter half year) than from May to October (the summer half year); (3) the periodic nature of the changes are obvious, which is consistent with a tidal semimonthly cycle of approximately 14.8 days; (4) the vertical distribution which is an e exponential distribution increase from the surface to the bottom. Furthermore, the data indicate that tidal currents are the most dominant factor affecting the SSC. Although the Yangtze River discharges abundant sediments to the study area, it does not directly affect concentration variations in seasonal time scales. But in yearly variation or long time scales, the SSC varying trend is coincident with sediment discharge change of the Yangtze Estuary. In addition, the construction projects, or dumping of sediments, have obvious effects on SSC and sedimentation for part of the area. " Strait-channel effects" have some degree of influence to the SSC distribution around islands.