Percuil Oil Pollution Control Boom Deployment

Holidaymakers and residents of St. Mawes enjoying the last of the summer weather at the beginning of October, were intrigued by the sight of a large orange floating pipeline stretching across the River Percuil. One suggestion of what this could be for was the transmission of treacle from the last operating mine in this part of Cornwall across to the pumping station at St Mawes.

In fact, this supposition was far from the truth and the facts were a little more esoteric: after several previous attempts were aborted due to unusually bad weather- even for a Cornish summer - a team led by Cornwall County Council Emergency Planning Unit successfully placed a shore to shore oil pollution boom across the Percuil River, near St Mawes, as a prevention against oil entering the ecologically valuable estuary should a spill occur.

The Percuil River is part of the Fal Estuary, and, as well as being a Special Area of Conservation, it is one of the Cornwall Nature Conservation Sites and has several Sites of Special Scientific Interest. It is also part of the Heritage Coast and an Area of Outstanding Natural Beauty and therefore was identified as a high priority for protective booming. This led to the County Council selecting the Percuil as one of the ten estuaries that were most worthy of protection around the Cornish Coast.

Conventional booming methods were difficult to implement due to the number of anchors that would be required and also because of land access difficulties on the southern side of the estuary.

The Harbour Master at Falmouth, Mark Sansom, has become an acknowledged expert in the use of the Differential Global Positioning System since demonstrating his ability while laying the pontoons for the Tall Ships event in Falmouth in 1998. He believed that advancements in mooring techniques which he has developed over many years could be combined with the use of the DGPS to provided a practical solution to this problem.

The operation to deploy the moorings, and then subsequently the boom, involved a barge and a number of workboats. A large buoy on a riser identifies each mooring block. When the boom is to be deployed, a set of six chains is attached to each of the blocks. These chains are of individual pre-determined lengths and are colour coded to ensure they are positioned correctly.

This new method allows a straight-line boom to be deployed utilizing only six anchor points. It relies heavily on 2 precision elements: the accurate placement of the mooring blocks in the river and the subsequent attachment of six different chain lengths to each mooring block, each chain carefully calculated for its position in the system. Some booming experts had predicted that this new idea - the booming of an entire river estuary to protect it from sea borne oil pollution - would not be possible as the principle of this scheme relies on getting the boom in a straight line on the water. This is a result that has not been previously accomplished with any other system over such a length, although there have been booms placed on other estuaries, and even practice sessions on the Percuil using a few short boom lengths utilising the new principle.

The exercise - or more accurately 'test' - was to prove whether the innovative mooring system being used was practical and, most importantly, would give the boom the required straight line on the water. Although this seems a small step forward in fact it is quite a large one, relying as it does on precision which has only recently become possible with the advent of DGPS. This equipment, used correctly, enables a mooring to be placed to an accuracy of half a metre.

The trial proved to be a complete success; 700 metres of boom were deployed and anchored, in a straight line, across the Percuil.

The great advance made possible by this new system is that more boom layout designs are now possible, enabling more effective protection to be provided. It is hoped that one enormous benefit will be that we can bring the oil together in a position where it is under our control - but still afloat, and from where we can remove it without fouling the shore. This is, in itself, sufficient reason to carry on with the principles and there is an additional, strong, reason to consider this as progress - the spilled oil floating on the water is relatively uncontaminated and can be handled as an oil product, possibly with some value, rather than special waste which costs money to dispose of.

The team that carried out the trial were assembled from many agencies, including A & P Falmouth, Falmouth Harbour Commissioners, Falmouth Oil Services, Oil Spill Response Ltd, Sub Marine Services, Harbour Masters from Truro and St Mawes, and Cornwall County Council. These all supplied equipment, manpower or financial assistance according to their capability.

Now that the system has proved successful the Emergency Planning section of Cornwall County Council intends to offer the principles of this scheme to their partners in Europe who face the same potential oil spill risks on their coastlines which are, in many cases, similar to those in Cornwall.

John James

Extract from HVMCA newsletter No.26 Spring 2003