Transcript Not a Bore? Issues of Tidal Power in the Severn Estuary

Not a Bore?
Issues of Tidal Power in the
Severn Estuary
Agenda
University of the West of England
30th June 2008
AGENDA
6 - 6.10 pm
Introduction and Welcome
Jim Longhurst and Eric Albone
6.10- 6.40 pm Presentations
Mervyn Bramley, Tom Appleby,
Chris Spencer and David Bird
6.40 - 7.20 pm Discussion at Tables.
One key issue for the Feasibility Study
7.20 -7.30 pm Report Back on one key issue for
the Feasibility Study
7.30pm
Close
Severn Tidal Power
‘Not a Bore?’
Engineering factors and technologies
Dr Mervyn Bramley
Visiting research fellow
Technologies – Tidal range and tidal stream
Tidal stream technology is now
at prototype development stage
Low head housed turbines as used in
tidal range barrages and lagoons – e.g.
La Rance – are production technology
Potential tidal energy capture
From tidal range:
Power ≈ k1 A H2
• H = level difference across barrage / lagoon
• A = wetted surface area upstream of empoundment
From tidal stream:
Power ≈ k2V3
• V = mean free-stream tidal current
Tidal stream array
• Prototype stage moving
to full-scale
demonstration
• Small commercial array
up to 5 MW
• Large array up to 30MW
• Potential interference
with shipping lanes
Tidal lagoon – Swansea
• Impoundment by 9 km
length embankment
• Plan area of 5km2
• Mean spring tidal range ≈
8.5 m
• Installed capacity 50MW
• Annual energy output
124 GWh
• Cardiff Weston barrage ≈
135 tidal lagoons
• Estimated cost ≈ £250m
Tidal barrage options – different sites
Cardiff – Weston Barrage
• Location: Lavernock Point
to Brean Down
• Length: 16 km (10 miles)
• Generating capacity: 8.6
GW or 8,600 MW
• Annual average output:
17 TWh or 17,000 GWh
• Percentage of UK
electricity supply: 4.4%
• Estimated cost ≈ £15bn
Cardiff – Weston barrage
A mega engineering project
• Concrete caissons towed to
prepared foundations for
sluiceways and turbines
• Some embankment
• Shipping lock
• Connection to national grid
• Rail or road possibly, but
adds considerably to width
• 200,000 person years of
employment – Site works
Issues for consideration
• Are the technologies sufficiently proven and appropriate to
be applied at a significant scale in the Severn Estuary?
• Can the environmental impact of a Severn tidal scheme
both during and after construction be adequately mitigated?
• Can the other uses of the Severn Estuary, in particular
ports, commerce and shipping, be accommodated?
• Could the UK finance and handle a project of the size of
the larger Severn barrage proposals?
• Can the carbon embedded in a Severn tidal scheme be
adequately offset by the low-carbon power it generates ?
• Can we envision a multi-functional scheme and a managed
changing environment, or is this our philosopher’s stone?
‘Not a Bore?’
A Barrage of Legislation
[email protected]
Law Lecturer
How does the law view the estuary?
• Law views it as land
covered by water
• Needs consent of the
owners of the seabed
• Otherwise
compulsory purchase
requirements
Rights in the estuary
• Public right to
navigate
• Public right to fish
• Private fishing rights
• Private drainage
rights
The effect of human rights
• Compensation for
interference with
those rights
• Difficult to assess at
this stage
Environmental legislation
• Habitats Directive
• Severn candidate
‘Special Area of
Conservation’
• Requirement to form
compensatory habitat
for protected features
lost to power scheme
Not that difficult?
• Capital engineering costs plus
– Compensation costs for people’s rights
– Compensation for the environment
Severn Barrage ‘Not a Bore?’
Sediment Distribution and Flood
Risk
Sue Marriott and Chris Spencer
Current issues
Sediment
 What types of sediments exist in the estuary
and how are they distributed?
 Where does the sediment come from?
 Is the sediment contaminated?
Flood risk
Sediment
McLaren et al. 1993
Sediments
How will the barrage impact on sediments?
 Circulation by tidal currents restricted to Bristol
Channel below barrage
 Fine sediment can settle in lagoon behind
barrage making water clearer, allowing
ultraviolet penetration therefore cleaner water
plus photosynthesis and phytoplankton blooms
 Contaminated sediment from floodplains may
build up
 Build up of sediment may reduce volume of
upper estuary
Flooding
 Flooding
What contributes to flood risk in the area?
 What will the effects of the barrage be?
 Lagoon will raise water tables so river water may not drain
away so quickly
 May cause extra deposition of mud in lower reaches of
rivers due to lower gradients reducing capacity
 Increased flood risk in lower reaches and backing upstream
Increased flood risk upstream?
Future Sea-Level Rise
• Sea-level rise will have impacts on coastal areas
due to increased erosion and increased flood
risk
• Would also cause backing up of river water in
lower reaches
• Barrage may be opened during high river flows
to move water out quicker
• Erosion energy will be reduced behind barrage
• Could a barrage help mitigate against future
sea-level rise?
Issues for consideration
• Would a barrage result in changes to sediment
distribution?
• Will changes have impacts in the Bristol Channel?
• What are the implications of raised water tables in the
surrounding areas?
• What is the likelihood of an increase in contamination of
estuarine sediment?
• What are the likely impacts on sediment and flood risk of
other tidal power generation options?
• Costs of extra coastal and flood defences needed due to
future sea-level rise vs cost of barrage?
Severn Barrage ‘Not a Bore?’
The Estuarine Ecosystem
[email protected]
Environmental Biologist
Estuaries are one of the world’s most
productive natural ecosystems
Estuaries support huge numbers of
invertebrates – but few species
Baltic tellin
Lugworm
(Macoma
balthica)
(Arenicola marina)
Edible cockle
Ragworm edule)
(Cerastoderma
(Hediste diversicolor)
Estuaries support huge numbers of
invertebrates – but few species
Mud snails (Hydrobia
ulvae) –(Crangon crangon)
Brown shrimp
density may
exceedpopulation
35,000 m-2 ~10000 million shrimps
estimated
 100+ fish species have been recorded from the
Severn Estuary & Bristol Channel
 just 10 species contribute to 90% of all fish
1. Sand goby
2. Bass
3. Whiting
 Important nursery for many marine species
Sprat
Herring
 Used as a migratory corridor by some species
River lamprey
European eel
Invertebrates & fish support an average wading
bird population of 88,500 individuals
4,000
6,600
44,445
3,800
Golden
plover
Knot
(Pluvialis
apricaria)
(Calidris canutus)
Ringed
plover
Dunlin
(Charadrius
hiaticula)
(Calidris alpina)
Issues for consideration:
 How do we balance the need for energy against
the potential for environmental damage?
 The ecosystem will not be destroyed – but it
will be changed – for better or worse?
 How do we put a value on species &
biodiversity – are salmon more important than
lampreys?
Questions for the BERR Feasibility Study to Address
• The following slides provide a list of questions for the BERR
Feasibility Study to address as formulated by the participants at the
Not a Bore Science Café Event.
• Some 85 people drawn from the Bristol hinterland attended the
Science Café event held at the University of the West of England on
30th June 2008.
• Following a series of short scene setting presentations participants
discussed the implications of tidal power from the Severn estuary.
• Arising from these discussions are a list of questions that the BERR
Feasibility Study should address.
Questions for the BERR Feasibility Study to Address
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Will the evaluation make comparison
with the potential impact and input of
other low carbon energies such as
wind and solar?
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Will the SEA evaluate the human costs
in the areas following changes arising
from an energy capture system in the
Severn?
Given that environmental impact is a
necessary consequence of whatever
system is put in place, rather than
compromise why not go for the project
that produces the most power and
maximises the low carbon energy
potential? Will the SEA evaluate such
a scenario?
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Why is tidal power from the Severn
back on the political agenda?
Will the SEA and Feasibility Study
consider implications for Human
Rights?
How will the proposed schemes affect
local communities?
How will a tidal power scheme benefit
the South West?
Will the preferred scheme be
evaluated against other forms of
renewable energy?
Is consideration being given to smaller
community based energy schemes?
How will the Feasibility Study ensure
that the selected tidal power scheme
will not be a white elephant?
Questions for the BERR Feasibility Study to Address
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How confident can we be that the
Feasibility Study methodology is not
biased in favour of any particular type
of technology or size of scheme and
that it takes account of the cost
effectiveness of non-tidal power
alternatives to put the study’s
conclusions in context?
What are the likely health impacts of a
barrage particularly in construction and
also through increased risk of flooding.
How are the cultural
aspects/damage/change to be costed?
The Severn bore is a unique natural
phenomenon – how can a monetary
values be put on it?
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If a barrage is the preferred option how
will sufficient aggregate be sourced to
build the structure?
Will the Feasibility Study identify the
responsible parties to undertake
environmental compensation?
What will be the impact of any
scheme on flood risks? Will the flood
scenarios considered actually be worst
case?
How will the commercial effect on the
Bristol's Docks be taken into account?
Questions for the BERR Feasibility Study to Address
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How is the lack of scientific and
engineering knowledge being
addressed?
Will ownership of a scheme be
considered in the feasibility study?
How certain are the cost estimates?
Are allowances made for the legal
compensation that will be required?
How seriously are the alternatives to a
barrage being considered?
How much energy conservation could
the likely cost of a Weston –
Lavernock Barrage buy?
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What is the payback period for the
carbon footprint?
What will be the impacts on the
ecology and how certain can we be
that the ecological compensation
schemes will be able to replace the
lost biodiversity?
How confident are we that a tidal
power scheme will be future proof?
Will a scheme be as efficient in 10
years time as the day it is
commissioned?
What effect will the discontinuous
operation of a tidal power scheme
have on the supply of electricity and
on the maintenance of the site?