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Ice midlands region warwick, 2010 Ice midlands region warwick, 2010 Presentation Transcript

  • The Severn Barrage and Other Options: Hydro-environmental Impact Assessment Studies by Roger A. Falconer FREng Halcrow Professor of Water Management Hydro-environmental Research Centre Cardiff School of Engineering, Cardiff University
  • A New Dawn www.corlanhafren.co.uk
  • General Challenges
    • Growing worldwide increase in energy demand - particularly in India and China
    • Tidal energy generation has advantage over wind and waves - in that tides are predictable
    • UK target of 15% of energy from renewables by 2020 - about 35% of electrical energy
    • Wales’ 2025 target for marine renewables energy is 14 TWh/yr - Barrage would generate over 60%
    • Severn Estuary basin is ideal for tidal energy
  • Global CO 2 Concentration Source - Met Office Steep increase since 1800 Roughly constant for hundreds of years
  • Predicted Future CO 2 Levels CO 2 concentration (ppm) 750 650 550 450 350 250 1990 2010 2030 2050 2070 2090 Year 50% 1990 emissions Constant 1990 emissions Business as usual Source: IPCC
  • Predicted Mean Temperature Rise Source - Met Office Global temperature rise, degrees C High emissions Medium-high emissions Medium-low emissions Low emissions
  • Predicted Mean Rainfall Changes For Wales / SW Present day wet events with a 5 yr return period are predicted to occur between 1.5 & 8.5 times more often Source - Met Office
  • Boscastle - Picturesque Village in U.K.
  • Boscastle - August 2004 (1:400 yr flood)
  • Hurricanes: Link to Climate Change Hurricanes inject large amounts of CO 2 into upper atmosphere By 2034 predicted there will be 50 more category 4 & 5 storms Source - Jorg Imberger
  • The Perfect Storm  2030
  • UK Challenges - Population Growth Population growth not just a challenge for developing countries: UK issue
  • Planned Renewable Energy Provision EU target of 20% carbon reduction by 2020 Considerable Scope to increase
  • Mean Spring Tidal Stream Resource Source – DTI Atlas of Marine Renewable Energy Resources
  • Mean Spring Tidal Range Resource Source – DTI Atlas of Marine Renewable Energy Resources
  • Wales England Severn Estuary
  • Proposed Tidal Devices for Severn
    • Tidal Stream Turbines - wind type turbines located in water column and energy created directly from tidal stream currents
    • Tidal Lagoons (OTIs) - enclosed embayment constructed offshore, creating tidal phased head difference - similar to barrage concept
    • Tidal Barrage - embankment across estuary - ideal for renewable energy with high tidal range and large upstream plan-surface area
  • Potential Power from Tides H = level difference across barrage / lagoon A = wetted surface area upstream of barrage
    • For tidal barrages and impoundments:-
    V = mean free-stream tidal current
    • For tidal stream turbines:-
  • Tidal Stream Turbines
      • Rotor diameter  15m 
      • depth  25m to operate
      • Nominally  1.2MW/unit
    DeltaStream SwanTurbines
  • Cardiff Turbine Design Flow
    • Turbine will operate in any flow depth
    • Design in its infancy – long way to go
  • Tidal Lagoon Concept Source – University of Colorado Swansea Bay Lagoon takes over 8hr to empty
    • Embankment wall length over 9 km
    • Plan area  5km 2 = 1000 football fields
    • Mean spring tidal range  8.5 m
    • Energy output of 124 GWh/yr
    • Severn Barrage  135 tidal lagoons
    • Cost  £200 m (?)
    Shape and Scale - Swansea Lagoon Key details: Plan Area  5km 2 Swansea Harbour Swansea Bay Source – Tidal Electric Ltd Turbine Housing
  • Original Proposals 80 km 2 Impoundment Environmental Impact?
  • EIA Studies Needed for Lagoons
    • Model studies needed to predict changes for:-
      • Tidal currents: - speed, levels, eddies, river plumes
      • Wave climate: - height, length, refraction, reflection
      • Suspended sediments: - distribution along channel
      • Sediment deposition: - in and out of impoundment
      • Coastal morphology:- changes to beach profiles
      • Water quality:- turbidity, nutrients, light penetration
      • Pre-/post-construction:- short & long term impacts
      • Mitigating measures:- changes to design/operation
  • Government Short Listed Proposals
  • Severn Barrage - 1849 First proposed by Thomas Fulljames - 1849
  • The Other Challenge
  • Severn Barrage Proposal Site
    • Some key facts:
    • 2nd highest spring tidal range  14 m
    • Cardiff to Weston
    • Length about 16 km
    • Generate  5% of U.K. electricity
    • Total cost  £20 bn
    • Save > 6.8 million tonnes carbon pa
    Slide – courtesy of STPG
  • Barrage Layout (1989 Report)
    • Key facts:
    • 216 turbines each 40 MW  17 TWh pa
    • 166 sluices
    • Ship locks
    • Fish pass?
    • Public road & railway
    Slide – courtesy of STPG
  • Construction: Prefabricated Caissons Slide – courtesy of STPG
  • Turbine Installation Slide – courtesy of STPG Slide – courtesy of STPG
  • Tidal Power Generation Slide – courtesy of STPG
  • Proposed Operation - Ebb Generation Slide courtesy of STPG
  • Proven Technology - La Rance
    • La Rance Barrage, France, has reliably generated tidal power for over 35 years
  • Barrage Effect on Tides Severn Estuary Estuary Bed Tide Enters Flow through turbines Barrage
  • Existing Estuarine Environment
    • Tide Range - 14 m on springs, 7 m on neaps
      • High tidal currents and large inter-tidal areas
      • 30 Mt sediment suspended on springs, 4 Mt neaps
      • Little sunlight penetration through water column
      • Reduced saturation dissolved oxygen levels
    • Ecology
      • Harsh estuarine regime with high currents
      • Limited aquatic life in water column / bed
      • Bird numbers per km 2 are relatively small
  • Changing Natural Environment
    • Climate Change
      • Temperature rise will affect ecology, birds etc
      • Sea level rise will lead to increased flood risk
    • Water Quality
      • Cleaner effluent discharges with EU WFD
      • Nutrient reduction will affect aquatic life
    • Legislation
      • Long term projects (>120 yr) require assessment against future - not just current - environment
  • Bird Species in SPA Citation Wigeon - 8,062 Pochard - 880 Ringed Plover - 665 Curlew - 2,545 Whimbrel - 222 Spotted Redshank - 10 Wigeon - 3,977 Pochard - 1,686 Ringed Plover - 227 Curlew - 3,096 Whimbrel - 246 Spotted Redshank - 3 Nationally important bird populations Shelduck - 3,272 Dunlin - 23,312 Redshank - 2,566 European Goose - 942 Shelduck - 2,892 Dunlin - 41,683 Redshank - 2,013 European Goose - 3002 Internationally important populations of migratory birds Bewick’s Swan - 276 Bewick’s Swan - 289 Internationally important populations of Annex 1 species Species numbers between 2000 – 05 ( Red - Less , Blue - More ) Species numbers between 1988 - 93 Citation category Source - RSPB
  • Main Effects of Barrage
    • Spring tide range reduced from 14 m to 7 m
      • Significant loss of upstream inter-tidal habitats
      • Reduced currents up & downstream of barrage
      • Reduced turbidity / suspended sediment levels
      • Increased light penetration through water column - with increased water clarity
      • Increased primary productivity and changed bio-diversity of benthic fauna and flora
    • Upstream tidal range of 7m is still relatively large compared to most deltas world-wide
  • Severn Estuary Hydraulic Model
  • Severn Barrage - Grid Configuration
  • Grid Refinement Around Barrage
  • (a) Velocity Field Around Barrage Fl ood Ebb
  • Proposed: One Way Generation Level of water inside impoundment Option 1: Generate over ebb tide only
  • Alternative: Two Way Generation Level of water inside impoundment Option 2: Generate over full tide Rapid filling and emptying of basin required at either end of tidal cycle
  • Three Modes of Operation Studied
    • Model predictions resulted in peak power output for:-
    • Starting Head = 4.0 m
    • Minimum Head = 2.0 m
    Ebb only Flood only Two-way
  • Maximum Water Levels - Ebb Only Without Barrage With Barrage Reduced flood risk
  • Maximum Water Levels - Two-Way Without Barrage With Barrage Reduced flood risk
  • Peak Water Levels
  • Maximum Tidal Currents - Ebb Only Without Barrage With Barrage
  • Maximum Currents - Ebb and Two-Way Ebb Only Two-Way
  • Water levels and Power Output
    • Ebb Only
    • 48.8 GWh/24.8h
    • 5.2 m mean tide
    • High tide 4.6 m
    • Two-Way
    • 48.4 GWh/24.8h
    • 4.4 m mean tide
    • High tide 3.2 m
    (a) (c)
  • High Suspended Sediment Levels Dynamic region of high turbidity
  • Suspended Sediment Levels Mean Flood Without Barrage With Barrage Mean Flood - Spring Tide Reduced sediment levels & clearer water
  • Effects of Turbidity Changes But what type of birds? Dunlin or other birds?
  • Riverine and WwTW Source Inputs? Rivers WwTWs
  • EU Bathing Water Directive
  • Diffuse Pollution Effects? Wales Population: Humans - 2.75m Sheep - 10.5m
  • Enteric Bacteria Flux Decay Adsorption Deposition Sediment re-suspension and desorbed into water Enteric bacteria water column Wastewater outfalls Catchment runoff Water birds input Advection with diffusion/dispersion output Overall reduction
  • Enterococci T 90 Experiments
    • Samples taken from 5 sites along estuary
    • Dark and irradiated microcosms tested
    • 4 times for each site
    • Artificial light source calibrated to provide average radiation conditions during July and August
    Cellulose diacetate bandpass filter Mixing unit Chiller/heater Matt black lining
  • Relationship with Turbidity/SS
    • Empirical relationships developed between turbidity and suspended solids and T 90 values
    • Real-time T 90 included in numerical model - varying with time, location, predicted SS level and radiation patterns
  • Sediment Associated Experiments 2
    • Two beakers incubated at 15˚C  one mixed and one allowed to settle - two sites tested
    Mixed beaker -concentrations remained constant Settled beaker – concentrations fell as finer particles settled
  • Bacteria Levels Mean Ebb Without Barrage With Barrage Mean Ebb - Rivers in Flood Reduction in bacteria levels
  • Welsh Grounds Lagoon
  • Velocity Field Around Lagoon (a) During Filling Mode (b) During Generating Mode
  • Predicted Power Generation
  • Shoots Barrage
    • Key facts
    • 30 x 7.6m diam 35 MW turbines  2.75 TWh/yr
    • Construction period ~ 4 yr
    • Less plan area
    • Slightly higher tidal ranges
    • Cost  £2.6 bn
    Shoots Barrage Second Severn Crossing M4 Severn Bridge
  • Other Issues to Consider
    • Barrage would bring jobs:
      • 30,000+ jobs at construction peak, distributed over UK - about half in Cardiff - Bristol region
      • 10,000+ permanent jobs in Severnside
    • Regional economic impact:
      • Availability of skilled labour and materials?
      • Local infrastructure needs - housing, schools etc
      • Concerns about supply chain, deep ports etc
      • Opportunities for expansion of Port Talbot etc
      • Considerable tourism and recreational potential
      • Road / rail links between Wales, London and EU
  • Summarising
    • Severn Barrage would have a lasting impact on a unique UK macro-tidal estuary:
      • Provide 5% of UK’s electricity from renewables
      • Reduce intertidal habitats by about 14,000 ha
      • Reduce flood peaks - upstream and downstream
      • Reduce tidal currents and suspended sediments - increasing light penetration and water clarity
      • Change ecology and benthic flora and fauna
      • Enhance opportunities for tourism and recreation
      • Two-way generation - enables optimal energy provision for minimal environmental change
      • Fish migration would remain a major challenge
  • UK Relative Water Stress High water stress Low water stress
  • Severn Barrage: More than a Renewable Energy Project
  • BBC Documentary on Barrage by Jonathan Porritt
  •  
  • Addendum
  • The Challenge For engineers and scientists to deliver UK’s marine renewable energy targets The Opportunity For UK to deliver renewable energy with minimal environmental impact
  • Thank You Professor Roger A. Falconer Email: FalconerRA@cf.ac.uk