Severn barrage controversy

Sian reports from the Green Party conference in Swansea

Green Party Spring Conference this week. We're in Swansea, soon to be the scene of the election of our first Welsh Assembly member. Rhodri Griffiths, our lead candidate for South Wales West region, opened proceedings with a thoughtful attack on the ruling Labour Party in Wales. First Minister Rhodri Morgan having handed us a gift recently by saying that he sees global warming as a bit of a business opportunity for Wales - perhaps a flourishing wine industry may emerge? Hmmmm.

Exposing ignorance of the global scale of the problem apart, our Green Rhodri was keen to point out that Welsh Labour's lack of care and ethics would have the early pioneers of the Labour Party turning in their graves. It was after all here in South Wales a century ago that Keir Hardie became the first Labour MP, after all.

Rhodri also reminded us that 250 years ago, it was here that the industrial revolution took hold and that, if any country in the world has a duty to make up for the consequences and take a lead in reducing carbon emissions, it should be Wales.

The first panel session of conference followed, and it was a contentious one, also with huge relevance to the area. How do we make use of the tidal energy of the Severn Estuary? It's clear there is enormous potential for generating clean, renewable and, crucially, predictable energy from the flow of the tide in and out of the Severn but it's also one of the most rare and unique habitats in the world, so we have to be careful.

How exactly to harness the energy while doing the least damage to this environment is the big question, and something the government's Sustainable Development Commission is looking at now. It will assess the different options (based on existing evidence) and publish its conclusions later this year.

The question is the subject of disagreement between environmental groups and is also a hot debate within the Green Party, so we have had a special Working Group on the case for the past six months. They are now putting a pair of motions to this conference on Friday to allow us to decide on our position.

The controversy and debate surrounds whether or not to completely enclose the Severn - along with nearly 200 square miles of estuary - with a hydroelectric barrage. The potential for power generation through this route is massive - equivalent to around three new nuclear power stations. However, the plan is guaranteed to permanently disrupt the wetlands and mud flats behind the barrage, reducing the range between high and low tides by half.

Today's panel discussion heard from both sides of the argument.

Insisting he didn't represent 'a plan for a barrage' but calling strongly for a more detailed government-funded review of the Severn, we heard from Jim Redman of the Severn Tidal Power Group, which includes several large engineering companies such as McAlpine and Balfour Beatty.

He did have a lot to say in favour of a barrage though, pointing out the predictability of the energy source, the lack of carbon emissions, the fact no fuel from abroad is needed, and the fact that, with carbon credits at the level currently provided to wind power (via the current Renewables Obligation, or feed-in tariffs as we would prefer - see previous blogs) private-sector energy companies would be willing to fund it. His call for a closer look at the options is supported by Greenpeace.

Peter Jones, from the RSPB for Wales, spoke in a personal capacity about the dangers to the environment of a barrage. His view is shared by Friends of the Earth the RSPB and WWF. The uniqueness of the Severn Estuary, with the second highest tidal range on earth, and home to tens of thousands of birds, means that, legally, for any barrage plan to get approval it would have to show there was no alternative and that there was an over-riding public interest at stake.

A possible alternative was outlined by Peter Ullman of Tidal Electric, a company specialising in enclosed tidal lagoons. He was keen to stress that there is nothing experimental or revolutionary about what his company does - everything used was a 'mature' technology back in the 1920s. The principle is simple - a barrier encloses a small area of shallow water, filling up at high tide, and then the water is let out of the lagoon via turbines when power is needed. A more complex arrangement of interlinked pools is able to make power available for longer than a barrage - around 80% of the time - and the environmental effects are negligible outside the pool itself.

There are well-developed plans for a lagoon in Swansea Bay that would enclose two square miles and generate around 30MW of power. Brig Oubridge, the Green Party member most famous for organising the annual Big Green Gathering, is proposing that the Swansea project is run as a 'public-public partnership' through a company backed by regional and local government with local people as significant investors. He estimates a down payment of £24 million needs to be raised, and that bank loans can complete the £81 million budget. With profits of £13 million a year expected after the loans are repaid, this could generate useful long-term cash for the local community.

To give a sense of the reduced environmental impact of lagoon projects, Peter Ullman superimposed little blue blobs on a photo from Google Earth to show that only fifty square miles within the estuary would have to be enclosed to generate the same amount of power as a barrage enclosing nearly 200 square miles.

Interestingly, the two technologies are not mutually exclusive. Although the area upstream of a barrage would be less viable for lagoon power, the dynamics of the tides mean that, downriver of a barrage, the amount of energy provided by each enclosed area would be increased. The debate is very complex and, even though I grew up around the Severn and am very attached to it - not least to the exciting tidal bore that rushes up river when tides are highest - I'm still not 100% sure how I will vote when the policy motions come up tomorrow.

Sian Berry lives in Kentish Town and was previously a principal speaker and campaigns co-ordinator for the Green Party. She was also their London mayoral candidate in 2008. She works as a writer and is a founder of the Alliance Against Urban 4x4s
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Inside Big Ben: why the world’s most famous clock will soon lose its bong

Every now and then, even the most famous of clocks need a bit of care.

London is soon going to lose one of its most familiar sounds when the world-famous Big Ben falls silent for repairs. The “bonging” chimes that have marked the passing of time for Londoners since 1859 will fall silent for months beginning in 2017 as part of a three-year £29m conservation project.

Of course, “Big Ben” is the nickname of the Great Bell and the bell itself is not in bad shape – even though it does have a huge crack in it.

The bell weighs nearly 14 tonnes and it cracked in 1859 when it was first bonged with a hammer that was way too heavy.

The crack was never repaired. Instead the bell was rotated one eighth of a turn and a lighter (200kg) hammer was installed. The cracked bell has a characteristic sound which we have all grown to love.

Big Ben strikes. UK Parliament.

Instead, it is the Elizabeth Tower (1859) and the clock mechanism (1854), designed by Denison and Airy, that need attention.

Any building or machine needs regular maintenance – we paint our doors and windows when they need it and we repair or replace our cars quite routinely. It is convenient to choose a day when we’re out of the house to paint the doors, or when we don’t need the car to repair the brakes. But a clock just doesn’t stop – especially not a clock as iconic as the Great Clock at the Palace of Westminster.

Repairs to the tower are long overdue. There is corrosion damage to the cast iron roof and to the belfry structure which keeps the bells in place. There is water damage to the masonry and condensation problems will be addressed, too. There are plumbing and electrical works to be done for a lift to be installed in one of the ventilation shafts, toilet facilities and the fitting of low-energy lighting.

Marvel of engineering

The clock mechanism itself is remarkable. In its 162-year history it has only had one major breakdown. In 1976 the speed regulator for the chimes broke and the mechanism sped up to destruction. The resulting damage took months to repair.

The weights that drive the clock are, like the bells and hammers, unimaginably huge. The “drive train” that keeps the pendulum swinging and that turns the hands is driven by a weight of about 100kg. Two other weights that ring the bells are each over a tonne. If any of these weights falls out of control (as in the 1976 incident), they could do a lot of damage.

The pendulum suspension spring is especially critical because it holds up the huge pendulum bob which weighs 321kg. The swinging pendulum releases the “escapement” every two seconds which then turns the hands on the clock’s four faces. If you look very closely, you will see that the minute hand doesn’t move smoothly but it sits still most of the time, only moving on each tick by 1.5cm.

The pendulum swings back and forth 21,600 times a day. That’s nearly 8m times a year, bending the pendulum spring. Like any metal, it has the potential to suffer from fatigue. The pendulum needs to be lifted out of the clock so that the spring can be closely inspected.

The clock derives its remarkable accuracy in part from the temperature compensation which is built into the construction of the pendulum. This was yet another of John Harrison’s genius ideas (you probably know him from longitude fame). He came up with the solution of using metals of differing temperature expansion coefficient so that the pendulum doesn’t change in length as the temperature changes with the seasons.

In the Westminster clock, the pendulum shaft is made of concentric tubes of steel and zinc. A similar construction is described for the clock in Trinity College Cambridge and near perfect temperature compensation can be achieved. But zinc is a ductile metal and the tube deforms with time under the heavy load of the 321kg pendulum bob. This “creeping” will cause the temperature compensation to jam up and become less effective.

So stopping the clock will also be a good opportunity to dismantle the pendulum completely and to check that the zinc tube is sliding freely. This in itself is a few days' work.

What makes it tick

But the truly clever bit of this clock is the escapement. All clocks have one - it’s what makes the clock tick, quite literally. Denison developed his new gravity escapement especially for the Westminster clock. It decouples the driving force of the falling weight from the periodic force that maintains the motion of the pendulum. To this day, the best tower clocks in England use the gravity escapement leading to remarkable accuracy – better even than that of your quartz crystal wrist watch.

In Denison’s gravity escapement, the “tick” is the impact of the “legs” of the escapement colliding with hardened steel seats. Each collision causes microscopic damage which, accumulated over millions of collisions per year, causes wear and tear affecting the accuracy of the clock. It is impossible to inspect the escapement without stopping the clock. Part of the maintenance proposed during this stoppage is a thorough overhaul of the escapement and the other workings of the clock.

The Westminster clock is a remarkable icon for London and for England. For more than 150 years it has reminded us of each hour, tirelessly. That’s what I love about clocks – they seem to carry on without a fuss. But every now and then even the most famous of clocks need a bit of care. After this period of pampering, “Big Ben” ought to be set for another 100 or so years of trouble-free running.

The Conversation

Hugh Hunt is a Reader in Engineering Dynamics and Vibration at the University of Cambridge.

This article was originally published on The Conversation. Read the original article.