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The Severn Barrage and Other Options: Hydro-environmental
Impact Assessment Studiesby
Roger A. Falconer FREngHalcrow Professor of Water Management
Hydro-environmental Research CentreCardiff School of Engineering, Cardiff University
22
A New Dawn
www.corlanhafren.co.uk
33
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
44
Global CO2 Concentration
Steep increasesince 1800
Roughly constant forhundreds of years
Source - Met Office
55
Predicted Future CO2 LevelsC
O2 c
once
ntra
tion
(ppm
) 750
650
550
450
350
2501990 2010 2030 2050 2070 2090
Year
50% 1990emissions
Constant 1990emissions
Businessas usual
Source: IPCC
66
Predicted Mean Temperature RiseG
loba
l tem
pera
ture
rise
, deg
rees
C High emissionsMedium-high emissionsMedium-low emissionsLow emissions
Source - Met Office
77
Predicted Mean Rainfall Changes
For Wales / SWPresent day wet events with a 5 yr return period are predicted to occur between 1.5 & 8.5 times more often
Source - Met Office
88
Boscastle - Picturesque Village in U.K.
99
Boscastle - August 2004 (1:400 yr flood)
1010
Hurricanes: Link to Climate Change
Source - Jorg Imberger Hurricanes inject large amounts of CO2 into upper atmosphere
By 2034 predicted there will be 50 more category 4 & 5 storms
1111
The Perfect Storm 2030
1212
UK Challenges - Population Growth
Population growthnot just a challengefor developingcountries: UK issue
1313
Planned Renewable Energy Provision
EU target of 20% carbon reduction by 2020
Considerable Scope to increase
1414
Mean Spring Tidal Stream Resource
Source – DTI Atlas ofMarine RenewableEnergy Resources
1515
Mean Spring Tidal Range Resource
Source – DTI Atlas ofMarine RenewableEnergy Resources
1616
WalesWales
EnglandEngland
Severn EstuarySevern Estuary
1717
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
1818
Potential Power from Tides
2Power A HH = level difference across barrage / lagoonA = wetted surface area upstream of barrage
For tidal barrages and impoundments:-
3Power VV = mean free-stream tidal current
For tidal stream turbines:-
1919
Tidal Stream TurbinesDeltaStream SwanTurbines
Rotor diameter 15m depth 25m to operate
Nominally 1.2MW/unit
2020
Cardiff Turbine Design
Flow
Turbine will operate in any flow depth Design in its infancy – long way to go
2121
Tidal Lagoon Concept
Source – University of Colorado
Swansea Bay Lagoontakes over 8hr to empty
2222
Embankment wall length over 9 km
Plan area 5km2
= 1000 football fields
Mean spring tidal range 8.5 m
Energy output of 124 GWh/yr
Severn Barrage 135 tidal lagoons
Cost £200 m (?)
Key details:
Shape and Scale - Swansea Lagoon
Plan Area
5km2
SwanseaHarbour
SwanseaBay
Source – TidalElectric Ltd
TurbineHousing
2323
Original Proposals
80 km2 ImpoundmentEnvironmental Impact?
2424
EIA Studies Needed for LagoonsModel 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
2525
Government Short Listed Proposals
2626
Severn Barrage - 1849
First proposed by Thomas Fulljames - 1849
2727
The Other Challenge
2828
Severn Barrage Proposal SiteSome 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 – courtesyof STPG
2929
Barrage Layout (1989 Report)Key facts:
216 turbines each 40 MW 17 TWh pa
166 sluices
Ship locks
Fish pass?
Public road & railway
Slide – courtesyof STPG
3030
Construction: Prefabricated Caissons
Slide – courtesyof STPG
3131
Turbine Installation
Slide – courtesyof STPG
Slide – courtesyof STPG
3232
Tidal Power Generation
Slide – courtesyof STPG
3333
Proposed Operation - Ebb Generation
Slidecourtesyof STPG
3434
Proven Technology - La Rance
La Rance Barrage, France, has reliably generated tidal power for over 35 years
3535
Barrage Effect on Tides
Estuary Bed
Tide Enters
Severn Estuary
Flow throughturbines
Barrage
3636
Existing Estuarine Environment Tide Range - 14 m on springs, 7 m on neaps
High tidal currents and large inter-tidal areas30 Mt sediment suspended on springs, 4 Mt neapsLittle sunlight penetration through water columnReduced saturation dissolved oxygen levels
EcologyHarsh estuarine regime with high currentsLimited aquatic life in water column / bedBird numbers per km2 are relatively small
3737
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
3838
Wigeon - 8,062Pochard - 880Ringed Plover - 665Curlew - 2,545Whimbrel - 222Spotted Redshank - 10
Wigeon - 3,977Pochard - 1,686Ringed Plover - 227Curlew - 3,096Whimbrel - 246Spotted Redshank - 3
Nationally important bird populations
Shelduck - 3,272Dunlin - 23,312Redshank - 2,566European Goose - 942
Shelduck - 2,892Dunlin - 41,683Redshank - 2,013European Goose - 3002
Internationally important populations of migratory birds
Bewick’s Swan - 276Bewick’s Swan - 289Internationally important populations of Annex 1 species
Species numbers between 2000 – 05(Red - Less, Blue - More)
Species numbers between 1988 - 93Citation category
Source - RSPB
Bird Species in SPA Citation
3939
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
4040
Severn Estuary Hydraulic Model
4141
Severn Barrage - Grid Configuration
Inner Barrage
Cardiff
Frame 001 16 Apr 2008 Initial bathymetry
4242
Grid Refinement Around Barrage
Shipping locks
80 Sluices
12 Sluices
Sub-stations
168 Turbines
48 Turbines
Sub-stations
74 Sluices
Embankment
Flat Holm
Steep Holm
Embankment
Cardiff
Weston
Frame 001 16 Apr 2008 Initial bathymetry
4343
(a) Velocity Field Around Barrage
2 m/swater level(m)
-4 -3 -2 -1 0 1 2 3
Frame 001 12 Apr 2008 Hydrodynamic Results in Nodes
2 m/swater level(m)
2 2.5 3 3.5 4
Frame 001 12 Apr 2008 Hydrodynamic Results in Nodes
Flood
Ebb
4444
Level of water inside impoundment
Option 1: Generate over ebb tide only
Proposed: One Way Generation
4545
Alternative: Two Way Generation
Level of water inside impoundment
Option 2: Generate over full tideRapid filling and
emptying of basin required at either end of tidal cycle
4646
Three Modes of Operation Studied
Wat
er le
vel (
m)
Filling GeneratingHolding Holding
Filling
Hmin
Hst
(a) Ebb Generation
A
BC
D
C
D
Time(h)
Ebb only
Time(h)
Wat
er le
vel (
m)
Generating
Holding Holding
Hmin
Hst
(b) Flood generation
AD
B C
D
Releasing ReleasingFlood only
Time(h)
Wat
er le
vel (
m)
FillingGenerating
Hmin
Hst
(c) Two-way generation
Generating GeneratingReleasing Filling
HoldingHolding
Sea level Basin level
A
B
C
D
Two-way
Model predictions resulted in peak power output for:-Starting Head = 4.0 mMinimum Head = 2.0 m
4747
Maximum Water Levels - Ebb Only
Without BarrageMaximum Water Level (m)
Tenby
Cardiff
Minehead
Weston
Ilfracombe
Barry
Swansea
Gloucester
Newport
BristolAvonmouth
N
4.0
5.5
3.5 4 4.5 5 5.5 6 6.5 7 7.5
Frame 001 05 Nov 2009 Maximum Water Level
With Barrage
Reducedflood risk
4848
Without Barrage
With Barrage
Maximum Water Levels - Two-Way
Reducedflood risk
4949
Peak Water Levels
0
1
2
3
4
5
6
7
8
020406080100120140160180200
Existing
Cardiff-Weston Barrage
Fleming Lagoon
Shoots Barrage
Sw
anse
a
Min
ehea
d
New
port
Avo
nmou
th
Bea
chle
y(M
48)
Sha
rpne
ss
Cardiff
Distance from Gloucester (km)
Hig
h W
ater
Lev
el (m
)(D
atum
rela
tive
to A
vonm
outh
)
Epn
ey
New
nham
5050
Maximum Tidal Currents - Ebb Only
Without BarrageMaximum Velocit y(m/s)
Tenby
Cardiff
Minehead
Weston
Ilfracombe
Barry
Swansea
Gloucester
Newport
BristolAvonmouth
N 0.3 0.7 1 1.3 1.7 2
Frame 001 05 Nov 2009 Maximum Water Level
With Barrage
5151
Maximum Currents - Ebb and Two-Way Maximum Velocit y(m/s)
Tenby
Cardiff
Minehead
Weston
Ilfracombe
Barry
Swansea
Gloucester
Newport
BristolAvonmouth
N 0.3 0.7 1 1.3 1.7 2
Frame 001 05 Nov 2009 Maximum Water Level
Ebb Only
Two-Way
5252
Water levels and Power Output Wa
terLe
vel(m
)
Powe
routp
ut(G
W)
0 2 4 6 8 10 12 14 16 18 20 22 24-10
-9-8-7-6-5-4-3-2-10123456
0
2
4
6
8
10
12
14
16
Time (hour)
Water level (m)Upstream of the barrage
Water level (m)Downstream of the barrage
Power Generation Power Generation24.4 Gwh 24.4 Gwh
I II III II
I=Filling (4.3h)
II=Holding (1.6h+1.0h)
III=Generating (5.5h)
4m
2m
(a) (a)
Water
Leve
l(m)
Powe
routp
ut(G
W)
0 2 4 6 8 10 12 14 16 18 20 22 24-10
-9-8-7-6-5-4-3-2-10123456
0
2
4
6
8
10
12
14
16
Time (hour)
Water level (m)Upstream of the barrage
Water level (m)Downstream of the barrage
PowerGeneration
PowerGeneration
8.3 Gwh 8.3 Gwh15.9 Gwh 15.9 Gwh
I II
Releasing (0.8h+1.1h)
II=Holding (2.0h+1.3h)
III=Generating (2.8h+4.4h)
4m
2m
III III (d)
I=Filling and
(c)
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
5353
High Suspended Sediment Levels
Dynamic region ofhigh turbidity
5454
Suspended Sediment LevelsMean Flood
Without Barrage With Barrage
Mean Flood - Spring Tide
Reduced sedimentlevels & clearer water
5555
Effects of Turbidity Changes
But what type of birds?Dunlin or other birds?
5656
Riverine and WwTW Source Inputs?
RiversRivers
WwTWsWwTWs
5757
EU Bathing Water Directive
5858
Diffuse Pollution Effects?
Wales Population: Humans - 2.75m Sheep - 10.5m
5959
Enteric bacteria
water columnWastewater outfallsCatchment runoffWater birds
input
Advection with diffusion/dispersion
outputOverall reduction
DecayAdsorptionDeposition
Sediment re-suspensionand desorbed into water
Enteric Bacteria Flux
6060
Enterococci T90 Experiments Samples taken from 5
sites along estuary
Dark and irradiated microcosms tested4 times for each site
Cellulose diacetate bandpass filter
Mixing unit
Chiller/heater Matt black lining
Artificial light source calibrated to provide average radiation conditions during July and August
6161
Relationship with Turbidity/SS Empirical relationships developed between turbidity and
suspended solids and T90 values Real-time T90 included in numerical model - varying with
time, location, predicted SS level and radiation patterns
6262
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
6363
Mean Ebb
Bacteria Levels
Without Barrage With Barrage
Mean Ebb - Rivers in Flood
Reduction inbacteria levels
6464
Welsh Grounds Lagoon
6565
2 2.5 3 3.5 4 4.5 5 5.5 6
2 m/s
Water level (m)
Flood
Frame 001 01 Sep 2008 Hydrodynamic Results in Nodes
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
2 m/s
Water level (m)
Ebb
Frame 001 01 Sep 2008 Hydrodynamic Results in Nodes
Velocity Field Around Lagoon
(a) During Filling Mode (b) During Generating Mode
6666
Water
Level
(m)
Powe
routp
ut(M
W)
0 2 4 6 8 10 12 14 16 18 20 22 24-10
-9-8-7-6-5-4-3-2-10123456
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Time (hour)
Water level (m)Upstream of the lagoon
Water level (m)Downstream of the lagoon
Power Generation Power Generation
I – FillingII – HoldingIII – Generating
I II III
Predicted Power Generation
6767
Shoots Barrage
Shoots Barrage
Second SevernCrossing M4
Severn Bridge
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
6868
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
6969
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
7070
UK Relative Water Stress
High water stress
Low water stress
7171
Severn Barrage: More than a Renewable Energy Project
7272
BBC Documentary on Barrage by
Jonathan Porritt
7373
7474
Addendum
7575
The ChallengeThe Challenge For engineers and scientists to deliver For engineers and scientists to deliver UK’s marine renewable energy targetsUK’s marine renewable energy targets
The OpportunityThe OpportunityFor UK to deliver renewable energy For UK to deliver renewable energy with minimal environmental impactwith minimal environmental impact
