Abstract: The erosion-accretion characteristics and the underlying mechanisms of the Shanghai Petrochemical Complex(SPC) offshore seabed in 2000-2013, together with the stability evaluation of the seawall was studied with GIS software. Results indicate that: (1) Most areas of the seabed were in state of accretion in 2000-2013, but there emerged a great scouring intensity in the Jinshan Trough. Among them, the evolution of study areas was given priority to erosion in 2000-2004 and 2004-2008, with an average annual net erosion rate of 5.27 cm and 10.52 cm, respectively. But it was in accretion state in general in 2008-2012, with an average annual net accretion rate of to 8.50 cm. The study areas were mostly in steady state in 2012-2013, accounting for 76.04% of the total. (2) Analyses on the 8 cross sections showed that the terrain in the north was in relatively steady state. The terrain in the middle of the deep trough (section Ⅴ) was stable, but the Jinshan Trough was scoured southward in the west (section Ⅰ and Ⅱ) and east (the section Ⅶ and Ⅷ). And the areas shallower than 15 m were given priority to accretion in the south of study areas. (3) The seawall stability evaluation showed that the seawall was in primary and secondary stability level centrally distributed on the sixth coastal levee. For more than a decade, the erosion-accretion characteristics of the SPC offshore seabed was closely related to the loss of sand transport in Jinshan flood trough, and wading engineering constructions such as city beach and large-scale deposition promotion projects in Nanhui. New wading tourism development project is under developing, which still need much more concern.

Key words: erosion-accretion characteristics of the seabed, seawall stability, Shanghai Petrochemical Complex, Hangzhou bay