Severn Barrage
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Barrage locations considered over the years. Black indicates lines of
most interest, with associated peak power generation at that location.
The
Severn Barrage is any of a number of ideas for building a
barrage from the
English coast to the
Welsh coast over the
Severn tidal estuary. Ideas for
damming or barraging the
Severn estuary (and
Bristol Channel) have existed since the 19th century. The purposes of such a project has typically been one, or several of: transport links,
flood protection,
harbour creation, or
tidal power
generation. In recent decades it is the latter that has grown to be the
primary focus for barrage ideas, and the others are now seen as useful
side-effects. The UK Government is currently undertaking a
Severn Tidal Power Feasibility Study which will consider all tidal range technologies (including barrages, lagoons and others) in the Severn estuary.
The building of such a barrage would be a huge engineering feat,
comparable with some of the world's biggest construction projects. The
huge size and cost of most of the ideas over the years are what have
kept plans firmly on the drawing board.
[edit] History
There have been numerous proposed projects over the years, initially
to provide a safe harbour and more recently to generate electricity.
[edit] Early projects
Thomas Fulljames's own impression of his proposed Barrage
In 1849 Thomas Fulljames, a civil engineer and the county surveyor for
Gloucestershire proposed a barrage from
Beachley to
Aust (now the site of the first
Severn Bridge),
a span of just over 1 mile (1.6 km). Since this was before serious
electricity demand, the first proposals were based on the desire for a
large shipping harbour in the Severn Estuary, and also road and railway
transport and flood protection.
[1]
Diagram of a plan to harness tidal power on the River Severn circa 1921. Caption from
Popular Mechanics Magazine 1921
No action was taken on Fulljames's proposals and three quarters of a
century later, in 1925, an official study group was commissioned. An
awareness of the large
tidal range of 14 metres (46 ft),
[2] second only to
Bay of Fundy in
Eastern Canada,
[3][4] led to a proposal to generate 800
Megawatt (MW) of electricity at
English Stones and although considered technically possible, it was prevented on economic grounds (then costing £25 million).
[5] The viability was tested a few years later in 1931 when Paul Shishkoff, a
Russian immigrant, demonstrated a 300 horsepower (220 kW) prototype tidal generator at
Avonmouth.
[6]
It included a novel mechanism for spreading the power output over 24
hours. The full barrage was estimated at £5 million at the time.
In 1933 the Severn Barrage Committee Report (HMSO) from a committee chaired by
Lord Brabazon recommended that a 800 MW barrage across the English Stones area would be the best option.
[7] The work was interrupted by
World War II and then revived in 1945 when engineers predicted an output of 2.2 terawatt hours (
TWh) per year.
[8] A further government study looked at barrage options in 1948 and estimated the construction costs at £60 million.
[6] By the time of the next study in 1953 the estimated cost had risen to £200 million.
In 1971 a report by Dr Tom Shaw, a tidal Power expert and advocate proposed a barrage from
Brean Down to
Lavernock Point. The scheme was estimated to cost £500 million.
[9] In 1975 the Central Electricity Generating Board (
CEGB), published a study with evidence from
Bristol and
Salford universities for the Secretary of State’s Advisory Council on Research and Development for Fuel and Power.
[10]
As this was the era of cheap oil, the council established that a
barrage could not be economically viable unless the energy situation
deteriorated significantly.
[edit] Bondi Committee – 1981
Proposed location of Bondi Committee Barrage
After just such a deterioration (due to the
Iranian Revolution and
1979 energy crisis) the plans were reinvestigated by the
Severn Barrage Committee in 1981. This committee was known as the "Bondi Committee" (after Professor Sir
Hermann Bondi).
The committee investigated 6 possible barrage locations, from English
Stones at the top of the estuary, down to a location largely at sea in
the Bristol Channel between
Lynmouth in North Devon and
Porthcawl in South Wales. It produced a major energy paper,
[11]
which recommended a 10 miles (16 km) long barrage of concrete
powerhouse between Brean Down and Lavernock Point, sluice and plain
caissons together with sand and rock-fill embankments. It would have
generated 7,200 MW on the flow of the tides (the largest barrage
considered could have produced double that power output). This set of
plans was strongly built on a few years later by the Severn Tidal Power
Group.
In 1984 Wimpey Atkins proposed a smaller barrage at English Stones,
in the hope of creating a smaller more economically viable project that
would avoid the environmental impact of a large barrage.
[12]
[edit] Hooker or Shoots Barrage – 1987
Cross section of Shoots Barrage turbine housing
This Wimpey Atkins 1984 study was criticised because it did not tackle the issue of
silting and in 1987
Arthur Hooker OBE (a former partner of
WS Atkins) in conjunction with
Parsons Brinckerhoff prepared a revised barrage proposed at English Stones to better tackle this issue.
Parsons Brinckerhoff further updated their earlier proposal in 2006
and current estimates for this barrage (now known as the "Shoots
Barrage") would cost £1.4 to £1.8 billion to build, and generate
2.75 TWh of power per year.
[13] At the highest tidal range, it would develop a peak output of 1,050 MW, and 313 MW output on average throughout the year.
Cross section of embankment
The barrage would be located just below the
Second Severn Crossing – i.e. above
Cardiff and
Bristol on the estuary – and so much smaller locks would be needed for upstream access to
Sharpness and
Gloucester docks as the large ports of
Portbury and
Avonmouth would be unaffected.
Like the STPG proposal, Hooker generates only on the ebb tide.
Construction time would be four years. It would be built of rock fill
embankment at the coastal sides (more like the proposals for "Tidal
Lagoons"), but like the STPG would be sluice caissons and turbines with
powerhouse in the middle section.
In April 2009 the
Liberal Democrats produced a report called "A Tidal Solution - The Way Forward"
[14]
that backed the Shoots Barrage along with a number of additional
measures for power generation in the Severn Estuary. In September 2009
the report was adopted by the Lib Dem party conference as official party
policy.
[15]
[edit] Severn Tidal Power Group – 1989
The £4.2 million study by Severn Tidal Power Group (STPG) built on
the work of the Severn Barrage Committee, but also examined other
possible barrages, and produced another major energy paper.
[16]
They concluded that the 1981 plans were the best location for a
barrage, but calculated that the power output could be larger, at
8,640 MW during flow, or 2,000 MW average power. This would provide
17 TWh of power per year (about 6% of UK consumption), equivalent to
about 18 million tons of coal or 3
nuclear reactors.
The cost in 1989 was calculated to be about £8 billion (£12 billion in
2006 money – about the same as six nuclear reactors, but different
lifespan), and running costs would be £70 million per year (about the
same as 1.5 nuclear reactors).
[citation needed]
Diagram of the STPG Barrage
The barrage would use existing technology as used in the
Rance tidal barrage in France, the
Annapolis Royal Generating Station
in Canada and the Netherlands sea barrages. Power would be most
efficiently generated only in the flow direction, and this effect on
tidal range would mean that the tidal extent would be halved by losing
the low tide rather than the high tide. That is, that the tide would
only go out as far as the current tidal mid-point, but high tides would
be unaffected (unless the barrage was deliberately closed to prevent
flooding).
Construction in prefab caissons
The barrage would contain 216
turbines each generating 40 MW for the 8,640 MW total. Arrays of
sluices would let the
tide
in and then close to force it out through the turbines after the tide
has gone out some distance outside the barrage. This deliberate building
of a
head on the water builds pressure that makes the turbines more efficient.
[citation needed]
The barrage would contain a set of
shipping locks, designed to handle the largest
container vessels.
Construction would take about eight years and would require 35,000
employees at peak build time. The minimum lifespan of the barrage would
be 120 years (about three times that of a nuclear reactor), but could
easily be 200 years if decent maintenance was performed.
[citation needed]
Artist's impression of aerial view of STPG Barrage
The STPG appraisal concluded that the
electricity generated from the barrage would make the scheme economically viable if given certain "
green" advantages, and that the
environmental impact was acceptable.
[citation needed] Margaret Thatcher's government did not accept this, and shelved the plans. However, since then
global warming has radically altered the public perception of
environmental damage; and soaring
oil,
gas and energy costs have made the
economics of the barrage much more favourable.
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The advent of renewable energy discounts favours electricity generated from "green" sources; and in addition, much lower
interest rates make the cost of
loans
much lower, and long-term financing of such massive projects is now
more viable. Consequently, there have been renewed calls for these plans
to be re-appraised.
[edit] Severn Tidal Reef – 2007
Evans Engineering (Joseph Evans & Sons Limited) have released plans for what they call a Severn Tidal "Reef".
[17]
This is a novel structure which aims to overcome the environmental
side-effects of a barrage, and can be conceptualised as being half-way
between a barrage and a tidal "fence" (a linked string of tidal-stream
turbines). The designer, Rupert Evans, had previously worked on a tidal
fence proposal, but since dismissed it as unworkable. The reef reduces
environmental impact by working with a much smaller "head" of water—just
2 metres (6.6 ft)—thereby reducing the impact of the structure on the
estuary water and flow. The smaller head means that the water velocity
is much lower and more lower power turbines are required. The load
factor will be higher, partly because of the generation being both ebb
and flow and the total energy output should (according to a recent
report by W.S.Atkins commissioned by the
RSPB)
be significantly greater than for the Cardiff-Weston Barrage, and is in
part a result of siting the structure at the "outer" Minehead to
Aberthaw line, which roughly doubles the volume of tidal water
available.
[18]
[edit] Sustainable Development Commission – 2007
On 1 October 2007, the UK's
Sustainable Development Commission (SDC) published a report looking at the potential of
tidal power in the UK,
[19][20]
including proposals for a Severn barrage. The report draws on a series
of five evidence-based reports, one of which summarises all the
available evidence from previous studies on a number of Severn barrage
options, but focusing on the Cardiff-Weston and the Shoots schemes. The
SDC also commissioned a programme of public and stakeholder engagement,
which included a national opinion poll and a series of local and
regional workshops.
[21]
The SDC gave its support to the building of a Severn barrage, providing a number of strict conditions were met. These include:
- A Severn barrage should be publicly led as a project and publicly
owned as an asset to avoid short-term decisions and ensure the long-term
public interest
- Full compliance with the EU Habitats and Birds Directives is vital, as is a long-term commitment to creating compensatory habitats on an unprecedented scale
- Development of a Severn barrage must not divert Government attention away from much wider action on climate change
The SDC also raised the challenge of viewing the requirement for
compensatory habitat as an "environmental opportunity", through the
potential to combine a climate change mitigation project with the
adaptation that will be required to respond to the effects of climate
change. A publicly led project would enable the use of a low
discount rate
(2%), which would result in a competitive cost of electricity, and
would limit the economic impact of even a very large-scale compensatory
habitats package. Electricity production costs are not competitive if a
commercial discount rate is applied.
[edit] UK Government study announced – 2007
A two year feasibility study was announced in late 2007,
[22] a the terms of reference were announced on 22 January 2008,
[23]
following the publication of the Turning the Tide report from the
Sustainable Development Commission. This study builds upon past studies
and focuses on a variety of tidal range technologies including barrages
and lagoons, and innovative designs such as a tidal fence and a tidal
reef in the Severn estuary.
The study, previously lead by
John Hutton,
Secretary of State for Business, Enterprise and Regulatory Reform, is now being lead by
Ed Miliband,
Secretary of State for Energy and Climate Change.
The study aims to gather and assess evidence to enable the Government
to decide whether it could support a tidal power scheme in the Severn
Estuary and if so on what basis. Key work areas involved are:
- The environmental impacts on biodiversity and wildlife; flood management; geomorphology; water quality; landscape and compensatory habitat;
- Engineering and technical areas such as options appraisal; costs;
energy yield, design and construction, links to the National Grid and
supply chain;
- Economic considerations – financing; ownership and energy market impacts;
- The regional social, economic and business impacts;
- Planning and consents – regulatory compliance; and
- Stakeholder engagement and communication.
The feasibility study concluded its first phase when a public
consultation was launched on 26 January 2009. The consultation covered a
proposed short-list of potential tidal power project options from an
initial list of 10 schemes, processes that were undertaken during
shortlisting and the proposed scope of the Strategic Environmental
Assessment (SEA). The SEA is a formal environmental assessment of plans
or programmes which are likely to have significant effects on the
environment.
[24] A
consortium led by
Parsons Brinckerhoff
(PB) has been appointed to manage this part of the project. The process
is guided by a stakeholder steering group. The study will culminate in a
full public consultation in 2010.
[25]
In July 2009 the Government response to consultation confirmed
detailed study would be carried out in the second phase on the 5 schemes
that were proposed for short-listing in January. It also announced work
to bring forward 3 further schemes that are in the very early stages of
development. In September 2010,
The Observer
reported that the government intended to rule out the possibility of
public funding for a complete barrage, while recommending that further
feasibility studies be carried out on smaller projects.
[26]
[edit] Economic impact
[edit] Power generation potential
The Severn Barrage plans would provide a predictable source of
green energy during lifetime of the scheme, 5% of the UK's output from the 10-mile version.
[27]
This could reduce the cost of meeting UK’s renewable energy targets,
and help the UK to meet such targets, including those to tackle climate
change.
[19]
This is because of the few carbon emissions associated with the plan,
because unlike conventional power generation, the Severn Barrage plans
do not involve the combustion of
fossil fuels.
A consequence of this plan is that the carbon payback time—the time it
takes for saved carbon emissions (those produced by generating the same
amount of power in other ways) to outstrip those produced during
construction— could be as little as four-and-a-half months, although
likely to be around six.
[28]
It could continue to operate for around 120 years,
[19] compared with 30–40 years for nuclear power plants.
[29] An additional benefit would be to improve
energy security.
[19]
However, although power supply is predictable, peaks in generation
from the barrage do not necessarily coincide with peaks in demand. There
are two major
tidal cycles affecting power output:
- semi-diurnal cycle: the familiar daily rise and fall of the sea with
a full cycle every 24 hours and 50 minutes, with two high and low
tides, giving maximum power generation opportunities a few hours after
each of the two high tides;
- spring-neap cycle: a 29.5 day tidal range cycle with the lowest
power days producing about 25% of the power of the highest power days.[30]
Just under eight hours per day of generation time is expected.
[30]
This cyclic power generation pattern could negatively affect economics and efficiency of other power generators and additional
power transmission lines that will only be cyclically utilized.
[citation needed]
[edit] Construction costs
The estimated costs of the most recent plans are huge. Figures are as high as £23 billion.
[31] Recent studies
[32]
have suggested that the smaller short-listed options could be privately
financed, and so in effect the matter of cost and risk becomes a
private one between the building
consortium and their banks. Schemes of the scale of Cardiff-Weston are likely to require significant
Government involvement. If the
banks
feel that a smaller project is viable and decide to lend the money at
an acceptable cost of finance then the projects will go ahead (subject
to planning and other approvals). None of this cost would directly fall
on the
tax-payer but any support mechanism for the tidal power would be likely to fall on
consumers.
There would though be secondary knock-on costs from the tidal power
project that might be met by the tax-payer, such as modifying existing
ports,
provision of compensatory habitat and dealing with environmental
change. However, these would be offset by the positive knock-on effects,
such as
flood
protection - which would have otherwise also cost tax-payer money.
Whether the parties actually decided to exchange money for these
knock-on effects would be a matter for Government negotiation.
[edit] Local impact
Any large-scale barrage would create leisure-friendly water conditions behind it.
Flood protection would be provided by the barrage, covering the vulnerable Severn estuary from
storm surges from the sea. New road and/or rail
transport
links could be built across a barrage if demand rises in the future, as
outlined below. Any barrage could provide a boost to the local
economy — construction industry in the short term, tourism and infrastructure in the long term.
[33]
However,
shipping would have to navigate
locks,
and existing estuary industries, including fisheries, would be damaged
and jobs lost. All industrial discharges into the River Severn (e.g.
from
Avonmouth) would have to be reassessed.
[citation needed]
[edit] Environmental impact
The Severn Estuary is a
Special Area of Conservation
due to the European importance of its ecology. The inter-tidal area
provides food for over 85,000 migratory and wintering water birds, and
represents 7% of the UK's total estuaries.
[34] There are
nature reserves and
Site of Special Scientific Interest (SSSI) on the islands of
Flat Holm[35] and
Steep Holm.
[36]
The Barrage was not supported in the 2003 Energy Review due to
"strong environmental concerns" (The same paper also described nuclear
power as "an unattractive option").
[37]
The
RSPB
opposes any Severn Barrage because of the effect it will have the
feeding grounds 85,000 birds depend on, stating "The impact a barrage
would have is huge. This is one of the most important sites in the UK
for wild birds and the chances of them surviving if it went ahead are
fairly slim. There wouldn't be enough room left for all the birds and
there wouldn't be enough food for those that remained. The estuary is
one of the UK's most important sites for water birds and its wildlife
value must be taken fully into account."
[38]
Possible effect of turbidity reductions in Severn Estuary
The present strong
tidal currents in the estuary serve to lift up
silt sediment and so keep the water thick with fine particles. This blocks light-penetration and means that the Severn Estuary
marine environment is actually a relative
desert, in terms of both plant and
fish life.
[39]
The barrage will not create a "
lagoon"
- as both opponents and supporters have sometimes claimed. Tidal power
stations by definition require that the tide flows through the barrage,
but the tidal range in the Severn would be halved.
[38] There are claims that the migration of fish would be hampered, but these are contested. The
Severn bore would also be weakened or eliminated. Any barrage would be likely to stimulate
coastal erosion in some areas, and create a negative visual impact upon the landscape (subjective, similar to
wind turbines).
There would also be negative consequences of the huge amount of
concrete (and other materials) needed, with the quarrying of stone
likely to impact on other areas.
[citation needed]
DEFRA claims that the
environmental effects of the barrage still need more analysis before final conclusions can be drawn. The
Sustainable Development Commission
is investigating UK tidal resources, including tidal power in the
Severn Estuary and its environmental impact, and should report mid-2007.
[40]
[edit] Tidal lagoon alternative
Friends of the Earth
support the idea of tidal power, but oppose barrages because of the
environmental impact. They have proposed their own plans based on the
concept of
tidal lagoons,
[41] whereby man-made lagoons in the estuary would fill and drain through
turbines.
Their proposals would include lagoons covering up to 60% of the area
covered by the barrage, which in some smaller configurations would not
impound water in the ecologically sensitive inter-tidal areas of the
estuary. The lagoons could be sub-divided so power would be generated at
more states of the tide than a barrage, with lower peak output, giving
economic advantages to set against the higher construction cost of
longer barriers. This idea is based on a prototype now being designed at
Swansea bay. However leading figures in the construction industry are sceptical that the lagoons can be economic.
[42][43]
A set of Tidal lagoons known as the "Russell Lagoon concept" were
studied and dismissed by the 1981 Bondi Committee report, rejected on
the grounds of both economics and environmental damage. Studies
suggested that tidal currents around and between the lagoons would
become extremely fierce and damaging.
[edit] Effects of different site locations
One of the complicating factors in assessing the impacts of a barrage
is the large number of possible locations and sizes for the barrage.
Generally, the larger the barrage the bigger its environmental impact,
and the bigger the amount of energy it could create - and therefore the
bigger
carbon offset it could have by way of its renewable power generation.
The largest barrages (sited beyond
Hinkley Point and towards
Minehead on the English side and
Aberthaw
on the Welsh side) would significantly affect the entire Severn Estuary
and much of the Bristol Channel, but could generate 15 GW peak power
and protect the whole of the Somerset levels against flooding and
sea-level rise caused by Global Warming. The smallest barrages (sited at
Aust/
Chepstow) would affect only the river and estuary in Gloucestershire, but would also only generate perhaps 0.75 GW peak power.
