1. 11
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

2. 22
A New Dawn
www.corlanhafren.co.uk

3. 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

4. 44
Global CO2 Concentration
Steep increase
since 1800
Roughly constant for
hundreds of years
Source - Met Office

5. 55
Predicted Future CO2 LevelsCO2concentration(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

6. 66
Predicted Mean Temperature Rise
Globaltemperaturerise,degreesC
High emissions
Medium-high emissions
Medium-low emissions
Low emissions
Source - Met Office

7. 77
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

8. 88
Boscastle - Picturesque Village in U.K.

9. 99
Boscastle - August 2004 (1:400 yr flood)

10. 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

11. 1111
The Perfect Storm  2030

12. 1212
UK Challenges - Population Growth
Population growth
not just a challenge
for developing
countries: UK issue

13. 1313
Planned Renewable Energy Provision
EU target of 20% carbon reduction by 2020
Considerable
Scope to increase

14. 1414
Mean Spring Tidal Stream Resource
Source – DTI Atlas of
Marine Renewable
Energy Resources

15. 1515
Mean Spring Tidal Range Resource
Source – DTI Atlas of
Marine Renewable
Energy Resources

16. 1616
WalesWales
EnglandEngland
Severn EstuarySevern Estuary

17. 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

18. 1818
Potential Power from Tides
2
µPower A H
H = level difference across barrage / lagoon
A = wetted surface area upstream of barrage
 For tidal barrages and impoundments:-
3
µPower V
V = mean free-stream tidal current
 For tidal stream turbines:-

19. 1919
Tidal Stream Turbines
DeltaStream SwanTurbines
• Rotor diameter ≥ 15m 
depth ≥ 25m to operate
• Nominally ≈ 1.2MW/unit

20. 2020
Cardiff Turbine Design
Flow
• Turbine will operate in any flow depth
• Design in its infancy – long way to go

21. 2121
Tidal Lagoon Concept
Source – University
of Colorado
Swansea Bay Lagoon
takes over 8hr to empty

22. 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
Swansea
Harbour
Swansea
Bay
Source – Tidal
Electric Ltd
Turbine
Housing

23. 2323
Original Proposals
80 km2
Impoundment
Environmental Impact?

24. 2424
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

25. 2525
Government Short Listed Proposals

26. 2626
Severn Barrage - 1849
First proposed by Thomas Fulljames - 1849

27. 2727
The Other Challenge

28. 2828
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 paSlide – courtesy
of STPG

29. 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 – courtesy
of STPG

30. 3030
Construction: Prefabricated Caissons
Slide – courtesy
of STPG

31. 3131
Turbine Installation
Slide – courtesy
of STPG
Slide – courtesy
of STPG

32. 3232
Tidal Power Generation
Slide – courtesy
of STPG

33. 3333
Proposed Operation - Ebb Generation
Slide
courtesy
of STPG

34. 3434
Proven Technology - La Rance
La Rance Barrage, France, has reliably
generated tidal power for over 35 years

35. 3535
Barrage Effect on Tides
Estuary Bed
Tide Enters
Severn Estuary
Flow through
turbines
Barrage

36. 3636
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 km2
are relatively small

37. 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

38. 3838
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 - 276Bewick’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
Bird Species in SPA Citation

39. 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

40. 4040
Severn Estuary Hydraulic Model

41. 4141
Severn Barrage - Grid Configuration
Inner Barrage
Cardiff

42. 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

43. 4343
(a)
Velocity Field Around Barrage
2 m/s
water level(m)
-4 -3 -2 -1 0 1 2 3
Frame 001  12 Apr 2008  Hydrodynamic Results in Nodes
2 m/s
water level(m)
2 2.5 3 3.5 4
Flood
Ebb

44. 4444
Level of water inside
impoundment
Option 1: Generate over ebb tide only
Proposed: One Way Generation

45. 4545
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

46. 4646
Three Modes of Operation Studied
Waterlevel(m)
Filling Generating
Holding Holding
Filling
Hmin
Hst
(a) Ebb Generation
A
B
C
D
C
D
Time(h)
Ebb only
Time(h)
Waterlevel(m)
Generating
Holding Holding
Hmin
Hst
(b) Flood generation
A
D
B C
D
Releasing Releasing
Flood only
Time(h)
Waterlevel(m)
FillingGenerating
Hmin
Hst
(c) Two-way generation
Generating GeneratingReleasing Filling
HoldingHolding
A
B
C
D
Two-way
Model predictions resulted
in peak power output for:-
Starting Head = 4.0 m
Minimum Head = 2.0 m

47. 4747
Maximum Water Levels - Ebb Only
Without Barrage
Maximum Water Level (m)
Tenby
Cardiff
Minehead
Weston
Ilfracombe
Barry
Swansea
Gloucester
Newport
Bristol
Avonmouth
N
4.0
4.5
5.0
5.5
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
Reduced
flood risk

48. 4848
Without Barrage
With Barrage
Maximum Water Levels - Two-Way
Reduced
flood risk

49. 4949
Peak Water Levels
0
1
2
3
4
5
6
7
8
020406080100120140160180200
Existing
Cardiff-Weston Barrage
Fleming Lagoon
Shoots Barrage
Swansea
Minehead
Newport
Avonmouth
Beachley(M48)
Sharpness
Cardiff
Distance from Gloucester (km)
HighWaterLevel(m)
(DatumrelativetoAvonmouth)
Epney
Newnham

50. 5050
Maximum Tidal Currents - Ebb Only
Without Barrage
Maximum Velocit y(m/s)
Tenby
Cardiff
Minehead
Weston
Ilfracombe
Barry
Swansea
Gloucester
Newport
Bristol
Avonmouth
N 0.3 0.7 1 1.3 1.7 2
Frame 001  05 Nov 2009  Maximum Water Level
With Barrage

51. 5151
Maximum Currents - Ebb and Two-Way
Maximum Velocit y(m/s)
Tenby
Cardiff
Minehead
Weston
Ilfracombe
Barry
Swansea
Gloucester
Newport
Bristol
Avonmouth
N 0.3 0.7 1 1.3 1.7 2
e 001  05 Nov 2009  Maximum Water Level
Ebb Only
Two-Way

52. 5252
Water levels and Power Output
I II III II
I=Filling (4.3h)
II=Holding (1.6h+1.0h)
III=Generating (5.5h)
4m
2m
(a)(a)
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

53. 5353
High Suspended Sediment Levels
Dynamic region of
high turbidity

54. 5454
Suspended Sediment Levels
Mean Flood
Without Barrage With Barrage
Mean Flood - Spring Tide
Reduced sediment
levels & clearer water

55. 5555
Effects of Turbidity Changes
But what type of birds?
Dunlin or other birds?

56. 5656
Riverine and WwTW Source Inputs?
RiversRivers
WwTWsWwTWs

57. 5757
EU Bathing Water Directive

58. 5858
Diffuse Pollution Effects?
Wales Population: Humans - 2.75m Sheep - 10.5m

59. 5959
Enteric
bacteria
water column
Wastewater
outfalls
Catchment runoff
Water birds
input
Advection with
diffusion/dispersion
output
Overall reduction
Decay
Adsorption
Deposition
Sediment re-suspension
and desorbed into water
Enteric Bacteria Flux

60. 6060
Enterococci T90 Experiments
 Samples taken from 5
sites along estuary
 Dark and irradiated
microcosms tested
4 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

61. 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

62. 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

63. 6363
Mean Ebb
Bacteria Levels
Without Barrage With Barrage
Mean Ebb - Rivers in Flood
Reduction in
bacteria levels

64. 6464
Welsh Grounds Lagoon

65. 6565
2 2.5 3 3.5 4 4.5 5 5.5 6
2 m/s
Water level (m)
Flood
ame 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

66. 6666
I – Filling
II – Holding
III – Generating
I II III
Predicted Power Generation

67. 6767
Shoots Barrage
Shoots Barrage
Second Severn
Crossing 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

68. 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

69. 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

70. 7070
UK Relative Water Stress
High water
stress
Low water
stress

71. 7171
Severn Barrage: More than a Renewable
Energy Project

72. 7272
BBC Documentary on Barrage
by
Jonathan Porritt

73. 7373

74. 7474
Addendum

75. 7575
The ChallengeThe Challenge
For engineers and scientists to deliverFor engineers and scientists to deliver
UK’s marine renewable energy targetsUK’s marine renewable energy targets
The OpportunityThe Opportunity
For UK to deliver renewable energyFor UK to deliver renewable energy
with minimal environmental impactwith minimal environmental impact

76. 7676
Thank YouThank You
Professor Roger A. Falconer
Email: FalconerRA@cf.ac.uk