The Severn Barrage

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The Severn Barrage Presentation to Institute of
Physics 1st June 2006 David Kerr Sir Robert
McAlpine Severn Tidal Power Group Sir Robert
McAlpineTaylor WoodrowBalfour BeattyAlstom
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Content of Presentation 1. Project Outline 2.
Electricity Generation Demand 3. Environmental
Effects 4. Flood Protection 4. Transport
Aspects 5. Construction Methods and Employment 6.
Economics of the Project 7. Conclusion
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• Location
• Bristol Channel/ Severn Estuary
• Downstream of Cardiff to Weston-super-Mare
• 16 km length

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Bondi study (EP46 - 1981) was the first major
studyTripartite study (EP57 - 1989) defined the
present schemeCould produce power by 2017 if
progressed soon
History of Severn Tidal Power Studies
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Tidal Power

• The Barrage impounds the tide, then the water
  is released through a turbine to generate
  electricity
• Proven Technology La Rance in France has
  generated tidal power reliably for over 35 years

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Barrage Operation
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Barrage Layout (1989 Report)

• 216 Turbines, 40MW each, 8640MW total
  
• 166 Sluices 35,000m2
• Ship Locks
• Small Locks
• Public Road

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Flow Patterns with Barrage
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Facts and Figures

• Annual Output 17 TWh (5 of UK consumption)
• Installed Capacity 8640 MW
• Savings of CO2 emissions 15Mt per year
  compared to Coal (equivalent to 3 of total
  UK Carbon emissions)
• Renewables Obligation
• 15 by 2015 (50-55TWh) - Barrage cannot
  contribute
• 20 by 2020 would require a further 17TWh.
  Barrage could contribute all of this - if
  sanctioned soon
• Capital Cost 8Bn 1989 gt 14Bn 2005 needs
  re-estimate
• Security of supply benefit

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Energy Generation (Spring Tide)
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Energy Generation (Neap Tide)
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Flexibility of Output
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Modes of operation Ebb Generation Preferred for
Severn ( for most other tidal barrages) Flood
Generation Less usable water volume Two Way
Generation No extra Energy Higher cost of Energy
due to more complex turbines Energy is spread
over more of the day
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Storage Possibilities
2nd Basin option from Bondi Report of 1975
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• Environmental Studies 1989
• A total of 70 studies, with a budget of 2M,
  covering
• Hydrodynamics (tides, currents, waves)
• Sediments, Salinity, Water Quality, Drainage
• Ecology, Birds, Fish

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Existing Estuary Environment

• Tide Range 14m on springs, 7m on neaps
• High tidal currents large inter-tidal areas
• 30Mt sediment suspended on springs, 4Mt on neaps
• Little sunlight penetration through the water
  column
• Low dissolved oxygen levels
• Ecology
• Harsh regime
• Very little life on the seabed
• Bird numbers per sq km lower than other
  estuaries but still substantial because of the
  large total area

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Sediment Types
Rock Gravel Sandy Area -5m OD Contour
Line Muddy Area
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• The Changing Environment
• Climate Change
• Temperature rise effects on ecology and birds
• Sea level rise flooding
• Water Quality
• Cleaner Sewage Discharges
• Reduction in Nutrients effect on birds
• Legislation
• Requires assessment against the present
  environment inappropriate for such a long term
  project should be assessed against the
  predicted future environment

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Main effects of the Barrage

• Tide Range reduced from 14m to 7m (springs)
• A smaller inter-tidal area upstream of barrage
• Reduced currents, leading to-
• A large reduction in suspended sediment
• Sunlight penetration through the water column
• An increase in dissolved oxygen to more normal
  levels
• A more stable seabed
• Expected to result in colonisation by a wider
  range of estuarine organisms and an increase in
  most bird species and numbers

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Areas at Risk from Flooding
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Flood protection in the Severn Estuary and Rivers

• Flooding in the estuary can occur when extreme
  high tides coincide with storm surges
• Flooding in the rivers can occur when these
  same sea conditions coincide also with high river
  flows
• The water level in the basin can be controlled
  -
• To prevent the flooding in the estuary (upstream
  of the barrage)
• To avoid obstruction to river flow caused by
  high tides

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Use Of Barrage for Flood Protection
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Environmental Balance ?

• Loss of the unique harsh environment
• Some birds (Dunlin) will lose part of their
  habitat
• Marine life and most bird species will increase
• Flood protection to estuary and rivers
• Carbon Saving
• The environmental assessment needs to be updated
  to account for the changes in the Estuary since
  the 1980s, predicted future changes and the
  changes in legislation

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Transport Key Issues

• Ports and Shipping
• Forecast Shipping Movements
• Size of Locks to suit Avonmouth docks
• Road and Rail
• Cost-benefit of a Barrage Crossing

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Construction Prefabricated Caissons
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• Caisson Construction Sites
• 1989 report identified potential UK sites shown
• Potential Sites in Europe
• Project and Employment Benefits of using many
  Sites

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Construction Sequence (1989 Report)
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Turbine Installation
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9m Diameter Bulb Turbine
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Employment(1989 report)

• 200,000 man years for construction
• 35,000 jobs at construction peak, distributed
  over the UK, about half in the Severnside
  region
• 10,000 - 40,000 permanent jobs in the region

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Cost Price relationship
ROC recycle ROC buyout Wholesale electricity
price
p/kWh April 2005 money
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Value of Externalities
These indicative values are a key part of the
project value
p/kWh
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Outline Programme for Implementation
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Conclusion
The Severn Barrage should be re-assessed as part
of the Energy Review