Abstract: Using the 3-D estuarine coastal and ocean numerical model ECOM in the north branch of Changjiang estuary, combined with oil film drift and diffusion module, the current change due to Chongqi bridge project, and the area, thickness, trace of oil film were studied after the oil spill accident happened at the sea-route in waterway. The results of model calculation showed that the main influence on current concentrated on bridge hollow and piers after bridge construction. The current was less influenced as the distance from the bridge increases. The current speed increased about 48 cm/s on the waterway and reduces on the piers. In the case of southeast wind with 4 m/s, with ebb tidal current the oil film drifted to downriver area of north branch during spring tide. To the 6 hr. oil film diffused to the mouth of north branch. During flood tide, to the 6 hr. oil film reached to the middle of Xinchunsha. Moreover, the change of wind speed and direction has a significantly influence on the oil film trajectory and pollution extent in the port.

Key words: numerical simulation, current change, drift and diffusion of oil film, Chongqi bridge, numerical simulation, current change, drift and diffusion of oil film