Slick operations

OIL spills in the Mississippi River pose a unique set of problems for vessel operations and oil spill responders. The typical oil spill is more likely to be caused by collision than grounding as the river bottom is soft silt, and therefore unlikely to cause hull damage unless a vessel is unfortunate enough to find an underwater obstruction. Both collisions and groundings are more likely to occur during times of high river current, as are oil spills. Immediate containment is difficult to impossible, as oil is swiftly carried away by a three-to-five-knot current. Variable local weather conditions also dictate whether the oil is carried on downriver or trapped in pockets along the bank. Two fairly recent oil spill incidents, one moderate and the other quite large, illustrate this point.

In February 1999, the US Coast Guard ordered the tanker Hyde Park, which had just completed engine repairs and a class inspection in the New Orleans general anchorage, to proceed to the tanker anchorage area several miles downriver for further inspection. During the turning manoeuvre, at night and in high current, the ship struck a barge tow. Its bunker tanks were punctured by the corner of a barge, causing a fuel spill of between 70 and 100 barrels. The current swiftly took the oil downriver where, after about 40 miles, a crosswind blew some of the oil into a wooded area on the east bank, where much river debris had accumulated. Over the next few days the river dropped, stranding the oil in a large, temporarily swampy area which was choked with debris. As a result, the clean-up operation was painstakingly slow, requiring three weeks to complete, with most of the work being done by hand.

About a year and a half later, in November 2000, the loaded single-skin tanker Westchester was northbound on the Mississippi River about 35 miles below New Orleans when it suddenly lost power. While attempting to anchor, its number one starboard tank was punctured with the loss of about 1,700 barrels of crude oil. Although the river was at low stage, there was still enough current to carry the oil downstream quicker than containment gear could be put out. While a much larger spill than the Hyde Park, this time the weather was more favourable. A north-east wind held most of the oil in against the west bank of the river, away from the east bank, where there were much more sensitive wetlands and vegetation. The clean-up was lengthy, with the river being closed intermittently for about three days. The spill resulted in a number of claims but the ecological impact was not severe as the west bank levee system acted as part of the containment.

There are a number of lessons to be learned. Firstly, wind and weather are unpredictable factors when a spill on the Mississippi River is carried downstream by the current. Secondly, sometimes the spill is blown into sensitive or challenging removal areas, while at other times the wind will assist by holding the oil in an area where clean-up is unobstructed and concentrated. The river levee system tends to keep oil in relatively low-impact areas, but once oil is carried below the levee system into the marshlands of the river delta where wildlife sanctuaries, oyster beds and fishing grounds are located, the situation is much more tenuous, although typically the oil slicks have broken up by that time.

A repeat of the Westchester casualty will become less likely as double-bottom tankers replace single-skin vessels, but a sudden loss of power can put any ship into a precarious position, even during low river stage. In the Hyde Park incident, while ship handling factors were obviously involved, the risk in requiring a tanker to turn and head downriver at night during high river exceeded the risk of remaining a few more hours in the dry cargo anchorage before proceeding upriver.