Using Transas Pisces II simulation software, TML first modelled the path that the oil would take over the days following the arrival of the crippled ship in Falmouth Bay. By changing the position of the anchorage and re-running the simulation, the team was able to advise on mitigating the initial effects of the spill. Despite this, the model, which was based on the actual weather forecast, indicated that by day three the Helford River would be in danger of being polluted by significant amounts of oil.

TML recommended using their new concept of V shaped oil trap, which was developed with the Council’s support under the EU Cycleau project. The TML oil trap is different in several key respects from the current generation of anchored oil booms. It is a moored system which can be deployed in very precise geometries, enabling the spilled oil to be collected whilst still afloat. This means that there is no need to choose a deployment site with road access and that the oil is not deflected on to a “sacrificial beach”. In the case of the Helford, this allowed the environmentally sensitive seaward end of the estuary to be protected as well as the upstream oyster beds and wetlands. Collection of the oil at sea also means that large recovery resources such as barges and skimmers can be used. The recovered oil can then be recycled rather than having to be dumped in scarce and expensive licensed sites.

With just 48 hours to protect the Helford estuary, TML used their new software to design the V shaped oil trap and to determine its optimum position in the estuary. A significant feature of the design approach is that it uses surface water flow data from earlier surveys to predict very accurately the flow direction and velocity under the anticipated weather conditions.

The boom is then positioned and the arms angled in order to ensure that oil is deflected to the collection pool and that the boom is not overwhelmed. This allows effective deployment in areas of high current flow.

The TML design software automatically produces a complete list of the equipment needed for the deployment. This was all immediately loaded on to the Portree II, a multi-purpose work boat chartered from Mojo Maritime for the exercise. Precise mooring block co-ordinates, chain lengths and buoy positions were downloaded directly into the Portree’s survey software from TML’s oil trap design package, and within five hours of starting work, the moorings had been laid.

On this occasion the Falmouth Harbour Commissioners’ boats and staff were also available to provide practical help and advice. The next day 17 sections of 25m boom were deployed and linked to the pre-installed moorings. With the oil trap in place, oil arriving anywhere in the estuary mouth would be deflected along the boom to a catch pool at the point of the V, from where it would be removed by skimmer.

Day three saw weather conditions much worse than had been predicted, with the East facing estuary buffeted by force 6 easterly winds. Two to three metre waves were rolling through the river mouth and it was raining heavily but the oil trap successfully held its geometry and the boom remained in place.

MJ Information No: 21220