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Spencer is delighted to report that, in a recent survey carried out for Thanet Offshore Wind Ltd and site developers Vattenfall, its work in laying export cables for a major wind energy project is shown to be environmentally sound. The survey vas carried out by independent engineering and environmental consultancy Royal Haskoning, who operate in 17 countries worldwide.
In February 2010, Spencer broke new ground when working with project developers Vattenfall on a landmark project that was to become the largest offshore wind energy installation in the world (see previous news story and case study). Using its highly efficient SpiderPlow pipe and cable-laying machine, fitted with a specially adapted feed mechanism, Spencer was able to install 1.1 kilometres of 225mm diameter export cable in less than four hours.
Now whilst these figures alone provide impressive reading, one year on and another impressive statistic is beginning to emerge: The installation was across a mudflat saltmarsh in Pegwell Bay, a stretch of coastline that is regarded as an ecologically sensitive area. As well as laying cables quickly and efficiently, it was the SpiderPlow’s process of installation that provided a benefit which was even more significant than that of its speed and precision.
Whereas more traditional methods require excavators to dig a trench along the cable corridor, the SpiderPlow’s blade makes a narrow cut through the soil. Therefore, there is minimal disturbance to the geo-structure of the land and the surrounding area, with no need to back-fill and with only minor reinstatement required. This means that the top-soil stays at the top; a factor which is extremely significant for fertile land or, in this case, a sensitive ecological location.
Spencer further protected the parts of the saltmarsh on which it was working by the use of timber Bog Mats. These are wooden platforms that were laid as a roadway across the soft terrain to enable the transit of excavators and vehicles without damaging the surface with caterpillar tracks or wheels.
Following the installation of the export cable last February, the recovery of the saltmarsh has been carefully monitored by scientists to ensure that the land returns to its original natural state. Each month, from March to August, as requested by Vattenfall, a representative from Royal Haskoning visited the site, took photographs, recorded the progress of the recovery and then published a final report at the end of 2010.
The findings of the last site survey in August state:
In the previous month the saltmarsh vegetation had flourished, with vegetation in some areas reaching approximately one-metre high and reduced areas of bare mud. The vegetation was recorded as being very well established.
The saltmarsh vegetation along the cable route corridor has recovered very well over the monitoring period and recolonised effectively. It is therefore considered that the corridor has been successfully colonised by saltmarsh species and, given time, the plant species present will grow and spread in a similar way to the existing area.
The wind energy project’s main cable laying contractors were delighted that the work carried out had caused such little damage to the effected area and said it would recommend Spencer and its SpiderPlow for any similar installations in the future.
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