Wrecking the Sea Bed with Offshore Wind Part 5

This is the fifth and last 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 documents (Available On This Link) which are also available on a DVD. The main files are:
PEI3_Ch2_NavitusBayWindParkProject.pdf  ( Link HERE )
PEI3_Ch5_PhysicalProcesses.pdf  ( Link HERE )
PEI3-Ch_9_benthicecology.pdf (Link HERE)
PEI3_Ch_10_fishandshellfishecology.pdf ( Link HERE )

I hope I have shown in the first four posts (using the Navitus' own documentation) that the small power plant that would be Navitus Bay Offshore Wind park will involve massive damage to the seabed.

Just to summarise from previous posts: 

The foundations will  involve ripping up around one and a half million tonnes of seabed. This damage coupled with disposal of the spoil will wreck around 1000 acres of sea bed - or around a total of 4 square kilometers.  

Several hundred miles of undersea cabling will involve trenching, ploughing and jetting into the sea-floor. The debris will spray out, burying everything within a 5 -20 meter wide corridor. Though a plume of finer debris will extend much further. So another 1000 acres (or another four square kilometers) of sea bed will be trashed. 

On top of this cabling sea bed disturbance, there will be dumped  over a third of a million tonnes of rock debris to protect the cables from being accidentally trawled up.

But it does not stop there. There is even more rock debris required. This rock is known as anti-scour.

Anti Scour

The Navitus Wind Park (like any other offshore wind farm) will need thousands of tonnes of imported rock piled around the bases of turbines to prevent the foundations being undermined by scouring. 

This anti-scour rock debris will essentially form a foreign and unnatural marine environment around about 30% of the turbines. Typically, each anti-scour ring will measure  25 meters in diameter and be 2 meters thick. (para 2.70)

A ring that size will account for about 1000 tonnes of rock debris per turbine or around 70,000 tonnes in total for the proposed 30% of turbines (para 2.68) that will need the anti-scour.

In addition to this there is additional anti-scour to cover the cable entry points (this is in addition to the rock used for cable protection described in a previous post). This will be needed on an unspecified proportion of turbines requiring anti-scour (para 2.71). Assuming 40 turbines need this and it will be as thick as the anti-scour itself then this will be another 30,000 tonnes of rock debris.

In total the anti-scour alone will involve importing another one hundred thousand tonnes of foreign rock and dumping it into the marine environment directly off the World Heritage Jurassic Coast.

The suffocation of the natural environment around these turbines by building what are essentially artificial and foreign habitats will no doubt, over time, also import foreign wildlife into the area (as has happened elsewhere - para 9.121). With the excavation and  dumped spoil, this anti-scour will inevitably skew the current balance of the existing wildlife within the turbine area. No doubt some species will prosper. But others may collapse as they struggle to compete in what is to them an artificial and chaotically changed environment. Sadly though it does not end there.

Effect on Tidal Flows

Although the potential gains from this scheme are pitifully poor, it will still be a huge artificial structure. In fact a structure so enormous and so intrusive on the natural environment that it will actually slow down the tidal flow rate by 7% within the turbine area and cause a flow speed increase outside. In an area already suffering from considerable marine coastal erosion, having a structure that speeds up tidal flows north (i.e. landward) of this structure would appear to be careless - to say the least. (para 5.325)

Finally I'll point out that this thing is so big and intrusive on the natural environment it could actually cause a change of tidal phase where the peak rate of flow may be retarded by a full 10 minutes (para 5.325).

Finally I would like to bring up a topic nobody is talking about although I suspect it is a topic many involved with this project are fully aware of.

Sea-bed Methane Release

Coastal sediments can potentially hold large quantities of Methane ( see paper Reindl & Bolalek link - Here ) & ( paper Mascharka, Montross, & Pierrehumbert link - Here )

Whenever you disturb ancient coastal sediments you are guaranteed to release trapped seabed Methane. Large Dredgers (as an example) are usually fitted with methane extraction and venting equipment to prevent the risk of explosion (See The Art of Dredging - Here ). But here the problem is not so much tied up with an explosion risk as to the fact that methane is a green house gas 20 times as potent as CO2. 

It would be high farce for this monstrosity to be built only to do more damage to the atmosphere than it is optimistically slated to offset. It is difficult to see how that trenching and ploughing an area equating to 1000 acres then excavating a million and a half tonnes of seabed can do anything but release copious quantities of trapped coastal seabed methane. 

Somehow this possibility appears to have been missed out of the Navitus documentation altogether.

So finally - What Exactly will be the Environmental Gain?

Sadly the pillage and destruction described here are just the tip of the ice-berg. 

In these few posts I have dealt solely with a sub-set of the sea-bed damage caused by offshore wind farms. Nobody seems to have publicly paid much attention to this, although to be fair English Heritage has raised the alarm (table 9.2). Perhaps the surface calamities threatened by these offshore projects are so awful they push other unseen destruction to the back of people's minds.

A very good site detailing other major problems with offshore wind (particularly Navitus) is on this link - Challenge Navitus - Here 

Most of all though, let us just remember that all this destruction and upset to a fragile and internationally recognised coastal region is to provide a SMALL intermittent power supply of typical daily output of 250 MWe or less.

Even then, simply to be viable, this offshore wind farm will have to be paid around three times the typical electricity wholesale cost.

If we leave aside the quasi-religious zeal, the vacuous fashionability and the endemic greed that drives this foolishness, can anyone really give a good reason to desecrate this coast (or any other) for so little gain? 

Wrecking the Sea Bed with Offshore Wind (Part 4)

This is the fourth 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 documents (Available On This Link) which are also available on a DVD. The main files are:
PEI3_Ch2_NavitusBayWindParkProject.pdf  ( Link HERE )
PEI3_Ch5_PhysicalProcesses.pdf  ( Link HERE )
PEI3-Ch_9_benthicecology.pdf (Link HERE)
PEI3_Ch_10_fishandshellfishecology.pdf ( Link HERE )

Foundations and Waste - adding it up

Yesterday I looked at the devastation wrought on the sea bed by a single gravity base turbine. In that scenario the spoil from the foundation excavations were dumped nearby.

There is an alternative to this. Instead of dumping the spoil on site it can be dumped elsewhere. Maybe at a nominated disposal site within the Solent itself.

Of course, for a single turbine, the disposal of several thousand tonnes of seabed spoil, whether locally or to a waste dump is unlikely to cause significant problems to the area as a whole. When regarded as a single entity, the waste issues caused by an individual turbine (while lamentable) are negligible within the bigger picture. 

The problems come when you add it all up.

Potentially, for the 213 turbines plus three substations a met mast and other assorted sea bed scrapings, the amount of displaced spoil comes in at well over one and half million tonnes. Even if they end up with a significant number of turbines that use foundation techniques that generate less spoil it is highly unlikely that the amount of seabed spoil will ever be less than about 1.2 million tonnes.

Remember this all gets excavated fairly rapidly over a four year period.

So how much is 1.6 million tonnes of sea-bed?

It has a volume of about 860,000 cubic meters. To give an idea of how much that is, let us build a solid cone of spoil sitting in Bournemouth Square. The base of this cone needs to be 100 meters across (325 ft). Now imagine building your cone upwards.

Do you remember from earlier how a 100m wide cone of rock debris (used to armour the cables) reached  beyond the height of Westminster Abbey?

Well, for this mountain of sea-bed spoil, that's kids stuff.

As you keep building it upward don't look back as you go past the height of Big Ben (96m - 300ft.) Keep going past the height of the London Eye (135m – 443ft).

You've got a helluva long way to go yet.

Keep going until you reach the height of the Shard in London (London's highest building 310m – 1017 feet). Take a quick breather if you like, but you are not there yet.

Keep on building up beyond the Eiffel Tower (324m) – but keep going.

You end up running out of spoil 40m short of the top of the Empire State Building in New York. The final height of your 100m wide solid cone of seabed spoil will be 344m - 1128 ft.

Now remember, if you plan dumping this mountain somewhere other than by your turbines, you will need to find a way of bringing it all back again during decommissioning. It will be needed to fill those craters left when you dig out the foundations of the defunct turbines. Or is there some other plan (if any) for this eventuality?

From the environmental assessments that form part of the Navitus documents, it appears that the disposal of this mountain of spoil will have a “negligible” affect on the environment. In fact “negligible” is a much used word in this documentation. It vies with “imperceptible” for popularity.

A Little Parallelism for you.

If I go to an ancient Oak forest and cut down and dig up an old Oak, the effect on the rest of the forest is probably “negligible”. The trashed area will no doubt recover in a few years. Then lets say, three days later, I do the same thing again. This is a large forest so again the effect is negligible. Then I do it again and again. I keep going for four years. Each Oak cut down makes a negligible change to the forest. But at the end of our four years of "negligible" destruction, we end up with a scene of desolation. A brutalised and trashed environment that will take, as a whole, very many years to recover (if at all).

I hope you can see the parallel with building an offshore wind park.

I was going to deal with heavy metal pollution and methane release from the spoil as well today but this post is too long already. That will come on another day. Sadly there is so much wrong with offshore Wind (and  Navitus Bay in particular) that I'm going to be at this for some time.

Wrecking the Sea Bed with Offshore Wind (Part 3)

This is the third 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 documents (Available On This Link) which are also available on a DVD. The main files are:
PEI3_Ch2_NavitusBayWindParkProject.pdf  ( Link HERE )
PEI3_Ch5_PhysicalProcesses.pdf  ( Link HERE )
PEI3_Ch_10_fishandshellfishecology.pdf ( Link HERE )

Foundations and Waste

While the sea bed is being dug up with hundreds of miles of cable trenching (see last post), the average offshore wind park will also be gouging out the seabed for the foundations for the turbines themselves. 

Take a single gravity base turbine. 

The concept appears to be that the sea bed is variously excavated, levelled and generally dug over and the 7600 Tonnes of spoil from these operations is shipped to the surface. The gravity base structure is then built on top of part of the excavated area. The final coup-de-grace to the area is then executed by rapidly dumping the spoil in the vicinity of the turbine base.

Over a period of a few minutes, directly below the spoil barge, a devils rain of 4800 tonnes of boulders, stones and gravel smash into the sea bed destroying everything in its path. As the waste piles up it will collapse and spread out, cascading outward like magma from a volcano. The area of destruction is likely to be well over 100 meters wide. 

Within this area everything dies. 

Flora, fauna, starfish, crabs, everything. It is unlikely that even fast swimming fish would escape the devils rain but even if they did, they are not going to live for long. Nature does not favour creatures evicted from their immediate habitat. Survival would be the exception rather than the rule.

That accounts for 4800 tonnes of the spoil. Then we have the remaining 2800 tonnes of mud and fine sand to consider.

The sea acts like a filter. The large rubble in the spoil falls directly to the sea bed leaving the smaller particles in suspension. The rate these fall to the sea bed is dictated by their size. A large opaque bloom of debris will spread out from the dump site flowing along with tidal direction. It will (mostly) sink as it travels. While some of this debris will remain in suspension for days, most will smear out a suffocating coat of mud over the sea bed extending out hundreds of meters from the dump site. Assuming a suffocation depth of 10cms and that 500 tonnes of the particulate matter is fine enough to remain in suspension, the remaining 2300 tonnes has the capability to extend the destroyed area by another 10,000 square meters.

So this single turbine has the potential to destroy an area of sea-bed equal to the excavated area (para 5.155) plus the area of the dump site and a further area suffocated by mud

2000 square meter excavated area
7500 square meters destroyed by large spoil
10000 square meters suffocated by mud

Thats not far short of 20,000 square meters of sea bed totally destroyed and left devoid of life - a ring of death with a diameter of over 150 meters.

From the documentation Navitus optimistically report that the environmental damage will take around 5 years to heal.


While this may be true for the mud polluted areas, it is difficult to see how areas covered with large amounts of immovable rock, shingle and boulders, piled haphazardly on the what was the sea bed will recover. You have dumped what amounts to 7600 tonnes of (at best) sub-soil on what was the sea bed.

Ask any gardener how well plants grow in mining spoil. Ask the older people in the valleys of South Wales how well vegetation grew on the spoil heaps that were imposed on them.

Truly, life is tenacious. It will in some form return to the devastated areas. But the likelyhood is that the balance of flora and fauna will at least be different and more likely to be diminished and enfeebled.

All of the above is for a single turbine. Navitus plan to build 213 of these things. 

The seabed “preparation” will be done at 3 day intervals. Every 15 working days another 100,000 square meters of sea bed will have been destroyed. This will go on for four years.

Even on their own reckoning, by the time they have trashed this 1000 Acres of sea-bed none of it will have had time to recover.

Now add this 1000 Acres of devastation to the 1000 acres of ruin brought about by the cable laying and the cable rock armour.

All this for a pitifully inadaquate, intermittent and massively expensive power generation technology.

Ruin upon ruin. 

But it does not stop there. Next I will look at the scale of the total amount of spoil produced and also some of the less desirable elements within that spoil that will be released into the marine environment.

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. 

Wrecking the Sea Bed with Offshore Wind (Part 1)

Just off the World Heritage Jurassic coastline there are plans for a large offshore wind farm called Navitus Bay. A consultation process ended last year. Most of the referenced data used in the following few posts has been dug out of the CDROM produced for this. An online link to the main document I use is HERE and on the CDROM it is PEI3_Ch2_NavitusBayWindParkProject.pdf

As Offshore windfarms go, there is nothing remarkable about Navitus Bay. Most of the data in the following few posts, shocking as it is, will equally apply to similar schemes elsewhere in the country.

But before I start, I feel I need to emphasise how poor offshore wind farms are at generating electricity. We need to keep this in mind when we look at the massive environmental damage done by their construction.

So first of all let us cut through some of the propaganda.

The first fantasy figure that gets promoted is the maximum output rating – a figure that is rarely (if ever) reached. Navitus Bay gets promoted as a 1GW+ plant. Or about the same capability as Sizewell B. Which is frankly, absurd.

There is an enormous difference between the maximum rating and the actual averaged yearly output (the Capacity Factor or CF). The documentation for this project optimistically touts a Capacity Factor of 35% or an annual averaged rating of around 350MW.

The actual national offshore CF from 2008 to 2012 is recorded by DECC 

Using the DECC recommended "unchanged configuration" table, an offshore geographically averaged CF of 35% has only ever been achieved once. But remember, Navitus Bay is near Bournemouth. This is not the Irish Sea. Navitus Bay will inevitably be performing at the lower end of the average. Those few per cent matter. If the final CF turns out to be 28% and not 35% then the averaged power rating will have been overstated by 25%. 

Even then, like all wind turbinery the typical daily output will be significantly less than the Capacity Factor. This is because the Capacity Factor gets inflated by unpredictable short duration high energy events. 

So bear in mind that while this is physically a large project, in reality, the final result would be a SMALL intermittent power plant.

In the next few posts I'll solely deal with the environmental damage done to the sea bed by offshore wind farms. Damage you will not be able to see. But damage that will take hundreds and maybe thousands of years to heal. And all for a puny amount of electricity, a vacuous feel good fashion statement and of course, lots and lots of money.

Tomorrow I start with undersea cabling and the required trenching ploughing and general trashing of the sea bed that goes with it. So how much undersea cabling am I talking about? Try 300 miles worth. And the trenches? how about up to 2 metres deep and 10 meters wide...