Wrecking the Sea Bed with Offshore Wind (Part 2)

This is the second in a series of posts about the damage done to the sea floor by offshore "Wind Parks" . Data has been taken from the proposed Navitus bay wind park consultation document.Document reference link below. On the DVD the main file is: PEI3_Ch2_NavitusBayWindParkProject.pdf

Undersea Cabling, Trenching, Ploughing and Encasement.

In order for an offshore wind park to show a semblance of operational ability, it requires a massive amount of undersea cabling. This cabling not only connects to land, but runs turbine to turbine and from turbine to substation, substation to substation and finally  substation to land. (Link: Navitus Bay PE13 Chapter 2 Section 2.6.10)

To protect these cables, they need to be buried. As a result, the sea bed will be variously trenched, ploughed and then backfilled. In some places these cables need to be secured to the sea floor by further encasing them in rock and/or concrete.

We are not talking about narrow little furrows here. This gouging through the seabed will involve hundreds of miles of trenches, many meters across and up to two meters deep.

Here are the main tables taken from the Navitus DVD itemising some (but not all) of the cabling.

NOTE: for export cables the "construction zone width" is missing however
para 6.116 indicates it is 10m

There is also a potential 70 Km of  of inter-substation cabling. The documentation indicates that this will be similar to the export cabling (para 2.106) so I assume 10m wide "construction zone"

Using the proposed trench/plough construction width multiplied by the length of the trench we find that if the trenching/ploughing was done as a continuous block, the trenched/ploughed area would amount to just over 4 square kilometres. That is around 1000 acres of virgin seabed, immediately off the World Heritage Jurassic Coast, completely ploughed up or covered with trenching spoil, then backfilled.

To get a feel for this vandalism, imagine excavating a trench across the New Forest. A gash that runs all the way from Bournemouth to Southampton - about 25 miles. The "construction zone" for this trench (i.e the trench itself, plus piles of debris, plus machine access) will be 100 meters wide. Then when you are done you roughly backfill it. 100 meters is incidentally just short of three times the width of an eight lane motorway.

Cable Protection

About 30% of the inter-array cabling and inter-substation cabling will require rock armouring. If you use the figures in the Navitus DVD, you will find that there will be a seven meter wide strip, one meter high (para 2.137) piled on top of some cables for a distance of over 27 Km ( 17 miles ).

 If you figure that out as a contiguous area of sea-bed smothered in foreign rock to a depth of one meter it comes out at over 47 Acres. 47 Acres of seabed immediately off the Jurassic coast. To achieve this encasement will require over a third of a million tonnes of rock debris (340,200 Tonnes of imported rock debris @ 1.8 tonnes per cubic meter)

Another way of viewing this mountain of rock debris is by imagining Bournemouth square filled with a cone of rock debris 100 meters across with a height of 77 meters (230 feet) in the middle. That is 25 feet higher than Westminster Abbey.

All this so a small intermittent power facility can operate at a wholesale cost of about three times that of the base electrical wholesale price.

Did I say it gets worse?

Well, sadly it does. Tomorrow we talk about foundations, piling and waste dumps. (The 3rd post is HERE)