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

Not a Bore? Issues of Tidal Power in the

Severn EstuaryAgenda

University of the West of England30th June 2008

AGENDA6 - 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

Low head housed turbines as used in tidal range barrages and lagoons – e.g. La Rance – are production technology

Tidal stream technology is now at prototype development stage

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 sitesCardiff – 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?’Not a Bore?’A Barrage of LegislationA Barrage of Legislation

[email protected] LecturerLaw Lecturer

How does the law view the estuary?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 estuaryRights in the estuary

• Public right to navigate

• Public right to fish• Private fishing rights• Private drainage

rights

The effect of human rightsThe effect of human rights

• Compensation for interference with those rights

• Difficult to assess at this stage

Environmental legislationEnvironmental legislation

• Habitats Directive• Severn candidate

‘Special Area of Conservation’

• Requirement to form compensatory habitat for protected features lost to power scheme

Not that difficult?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

SedimentsHow 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 quicklyMay 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] BiologistEnvironmental Biologist

Estuaries are one of the world’s most productive natural ecosystems

Estuaries support huge numbers of invertebrates – but few species

Lugworm(Arenicola marina)

Ragworm(Hediste diversicolor)

Baltic tellin(Macoma balthica)

Edible cockle(Cerastoderma edule)

Estuaries support huge numbers of invertebrates – but few species

Mud snails (Hydrobia ulvae) – density may exceed 35,000 m-2

Brown shrimp (Crangon crangon) estimated population ~10000 million shrimps

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

Used as a migratory corridor by some species

Sprat Herring

European eelRiver lamprey

Invertebrates & fish support an average wading bird population of 88,500 individuals

Golden plover(Pluvialis apricaria)

4,0004,000

Ringed plover(Charadrius hiaticula)

3,8003,800Dunlin

(Calidris alpina)

44,44544,445

Knot(Calidris canutus)

6,6006,600

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

• 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?