INFLUENCE FACTORS ON SCOURING IN SUBMARINE PIPELINE AREA: A CASE FORM CEZI ISIAND, ZHOUSHAN TO ZHENHAI, NINGBO

For buried submarine pipelines, local scour is one of the main reasons which may lead to pipeline exposure, free span in the seafloor and even failure in use. The submarine oil pipeline from Cezi Island, Zhoushan to Zhenhai, Ningbo, buried in 2005 and operated since 2006, was exposed heavily in several areas and even suspended during 2007—2012. Based on the data of geophysical survey carried out annually, we have good reason to believe that the pipeline’s situation was very bad and would be worse in the future because of the local scouring. The scour was caused mainly by natural process of scouring and siltation. However, other factors, such as extreme weather conditions, large-scale land reclamation, construction of bridges connecting the Zhoushan islands with the mainland, and the decrease in sediment input from the Yangtze River, should not be ignored.