Not a Bore ? Issues of Tidal Power in the Severn Estuary. Agenda University of the West of England 30 th June 2008. 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
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University of the West of England
30th June 2008
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
Dr Mervyn Bramley
Visiting research fellow
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
From tidal range: Power ≈ k1A H2
H = level difference across barrage / lagoon
A = wetted surface area upstream of empoundment
From tidal stream: Power ≈ k2V3
V = mean free-stream tidal currentPotential tidal energy capture
Small commercial array up to 5 MW
Large array up to 30MW
Potential interference with shipping lanesTidal stream array
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 ≈ £250mTidal lagoon – Swansea
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 ≈ £15bnTidal barrage options – different sites
Concrete caissons towed to prepared foundations for sluiceways and turbines
Connection to national grid
Rail or road possibly, but adds considerably to width
200,000 person years of employment – Site worksCardiff – Weston barrage A mega engineering project
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?Issues for consideration
How does the law view the estuary? be applied at a significant scale in the Severn Estuary?
Capital engineering costs plus be applied at a significant scale in the Severn Estuary?
Compensation costs for people’s rights
Compensation for the environmentNot that difficult?
Sediment Distribution and Flood Risk
Sue Marriott and Chris Spencer
Sediment be applied at a significant scale in the Severn Estuary?
What types of sediments exist in the estuary and how are they distributed?
Where does the sediment come from?
Is the sediment contaminated?
Flood riskCurrent issues
Sediment be applied at a significant scale in the Severn Estuary?
McLaren et al. 1993
How will the barrage impact on sediments? be applied at a significant scale in the Severn Estuary?
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 estuarySediments
Flooding be applied at a significant scale in the Severn Estuary?
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 upstreamFlooding
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?Future Sea-Level Rise
Would a barrage result in changes to sediment distribution? increased erosion and increased flood risk
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?Issues for consideration
Edible cockle ecosystems
(Arenicola marina)Estuaries support huge numbers of invertebrates – but few species
Mud snails ( ecosystemsHydrobia ulvae) – density may exceed 35,000 m-2
Brown shrimp (Crangon crangon)
estimated population ~10000 million shrimpsEstuaries support huge numbers of invertebrates – but few species
1. Sand goby ecosystems
3. Whiting100+ fish species have been recorded from the Severn Estuary & Bristol Channel
Invertebrates & fish support an average wading bird population of 88,500 individuals
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
Will the evaluation make comparison with the potential impact and input of other low carbon energies such as wind and solar?
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?
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
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?
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
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?
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?Questions for the BERR Feasibility Study to Address