Abstract:

The drift and diffusion of oil film after the oil spill accident will pollute the surrounding waters, and environmental sensitive protection targets. The study of oil film drift and diffusion after oil spill accident can provide theoretical guidance for the treatment of oil spill accident. Coupling the oil spill drift and diffusion module, the estuarine and coastal three-dimensional hydrodynamic model ECOM-si (semi-implicit estuarine, costal and ocean Model) was used to simulate and analyzed the drift and diffusion of oil film after the oil spill accident at the Baosteel wharf in the Changjiang Estuary, and its impact on the environmental sensitive protection targets in this paper. Based on the measured wind speed and direction data at weather station on the Chongming eastern shola in the Changjiang Estuary, the prevailing wind and unfavorable wind affecting the oil spill drift are given. Forced by the monthly mean river discharge of 11700 m³·s^-1, prevailing wind, three unfavorable winds and tide in January, the horizontal distribution of oil film, time of the oil film reaching and leaving the water intakes of four reservoirs and drinking water source protection areas, and other environmental sensitive protection targets, duration and maximum oil film thickness of oil film after the oil spill accident at the Baosteel wharf was numerically simulated and analyzed in detail. After the oil spill accident, the oil film oscillates upstream and downstream with the flood and ebb current, meanwhile the runoff transports the oil film to the sea, and the wind makes the oil film drift towards the wind direction. Under the action of the prevailing wind, northerly wind of 5.6 m³·s^-1, the oil film drifts and diffuses downstream along the south coast of the Changjiang Estuary, and a small part enters the south side of the North Passage. Under the unfavorable wind, southeasterly wind of 4.0 m³·s^-1, the oil film drifts in the northwest and accumulates on the north coast of the South Branch. Forced by the runoff, it is transported downstream on the middle and north side of the South Branch and the North Channel. Under the unfavorable wind, northwesterly wind of 4.8 m³·s^-1, it weakens the impact on the sensitive targets upstream of the oil spill accident site and the ones in the North Channel, outside Chongming eastern shoal, and aggravates the impact on the environmental sensitive protection targets in the North Channel and South Passage. Under the unfavorable wind, southwesterly wind of 3.2 m³·s^-1, most of the oil film drifts and diffuses downstream on the middle and north side of the North Channel, and a small part of the oil film is on the middle and north side of the North Passage. It weakens the impact on environmental sensitive targets upstream of the oil spill accident site and the downstream ones in the South Channel and South Passage, and aggravates the impact on the sensitive targets in the North Channel and outside Chongming eastern shoal. The distribution of oil film and its impact on the environmental sensitive protection targets are significantly different under the force of different wind directions, indicating that wind plays a very important role in oil film drift and diffusion.

Key words: oil film, drift and diffusion, prevailing wind, unfavorable wind, numerical simulation