Paul Evans - Cardiff University The Tidal Regime of the Severn Estuary Paul Evans graduated from Cardiff University in 2006 with a 2:1 in Marine Geography. During his time at Cardiff University, Paul worked at HR Wallingford as part of an optional Year in industry where he worked on a number of commercial projects as a coastal hydraulic physical modeller. Paul subsequently studied for a Masters in Coastal Engineering at The University of Plymouth and completed a dissertation researching the protective capabilities of seawalls. Between 2007 and 2008, Paul was employed as a Research Assistant at Cardiff University (School of Earth and Ocean Sciences) where he undertook various tidal resource assessments for potential tidal stream turbine sites. In July 2008, Paul joined Waterman Transport and Development Ltd. as a Graduate Engineer in the Cardiff Office. Paul has over 4 years experience in hydrology and flood risk analysis, using FEH hydrological modelling techniques and 1D, 2D hydraulic modelling software, namely HEC-RAS and TUFLOW packages. Paul is currently a Research Assistant at Cardiff University (as part of the Low Carbon Research Institute (LCRI) convergence programme) to again investigate the resource potential at various sites along the Welsh coastline, namely Ramsey Sound. He has been working closely with Tidal Energy Limited to help choose the most suitable location within Ramsey Sound to install their delta-shaped tidal turbine in terms of suitable substrate, a flat seabed and sufficient tidal flow. Paul uses his GIS skills to map and model various sites in order to visualise and interpret the tidal flow data collected onboard Cardiff University’s Research Vessel Guiding Light. Paul is also studying for a PhD into the hydrodynamics of significant bathymetric features. With the second highest tidal range in the world, the Severn Estuary has a unique tidal regime. This will be the main focus of this presentation, introducing the science behind such a unique tidal range and how the physical environment of the Severn Estuary can alter or may be altered in the future.

1. The Tidal Regime of the Severn Estuary:
The Practicalities of Monitoring Tidal Flow
Paul Evans, Research Assistant & PhD Researcher – LCRI Marine
School of Earth and Ocean Sciences, Cardiff University

2. Overview
• Tidal Regime of the Severn Estuary
• Tidal Energy in Wales
• Case Study 1: Tidal flow Monitoring in the
Irish Sea
• Case Study 2: Tidal flow Monitoring in the
Severn Estuary
• Further Work

3. Severn Estuary Tidal Regime
• Partially enclosed body of tidal waters – 250km
• Hypertidal (MTR>6m); ca. 7m mouth of Channel, ca.
12m upper reaches
• Semi-Diurnal
Uncles (2010)

4. Severn Estuary Tidal Regime
• Fast tidal currents = Strong vertical and horizontal mixing,
and large bed stresses = Horizontal dispersion, near vertical
homogeneity in salinity, temperature and phytoplankton
• Max. mean spring and neap tide in the vicinity of Flat Holm =
3.0 ms-1 and 1.0ms-1
Uncles (2010) Uncles (2010)

5. Severn Estuary Tidal Regime
• Hydrostatic head at the
mouth and the landward
extent of the estuary
during flood and ebb
conditions create a tidal
flow – peaks lag behind
the high and low tides by
ca. 3 hours
• Newport Deep (NE flood)
• Bristol Deep – SW ebb –
greater tidal flow (narrow
and sinuous) Cotter (1975)
Flat Holm
Steep
Holm
Bristol
Deep
The
Wolves

6. Tidal Range vs. Tidal Stream
• Tidal range – impounding high tide level water
behind a barrage or in a lagoon can create a head
above the lower tidal water outside, which can be
run through turbines when releasing the impounded
water. This technology is likened to damming a
reservoir once or twice daily.
• Tidal stream involves extracting kinetic energy
directly by use of turbines from the horizontal tidal
current generated by the movement of the tidal
bulge as the earth rotates.

7. Tidal Range Technologies
Xia et al. (2010)
Natural Condition
Xia et al. (2010)
Cardiff to Weston Barrage
• Cardiff to Weston Barrage –
Installed capacity = 8640 MW; Annual
electricity supply = 17 TWh;
Generation of 5% of UK’s electricity
Xia et al. (2010)

8. Tidal Range Resource
Xia et al. (2010)
Fleming Lagoon
Xia et al. (2010)
Shoots Barrage
• Fleming Lagoon – Installed capacity =
1500 MW; Annual electricity supply = 3.2
TWh
• Shoots Barrage – Installed capacity =
1050 MW

9. Tidal Stream Resource
Ebb tide – HW+3 (Milford Haven)Flood tide – HW-3 (Milford Haven)

10. Welsh Tidal Stream
Resource
Potential Areas:
– Anglesey
– Pembrokeshire
– Bristol Channel
Source: Renewables Energy Atlas

11. Marine Renewable Energy
in Wales
Welsh Government Policy:
– 40GW marine renewable energy
potential
– Capture 10% of wave and tidal stream
energy off the Welsh Coastline by
2025 (equates to 4GW potential)
LCRI Marine:
– Cutting edge research to support
industrial development
– Tidal resource assessment

12. Marine Current Turbines – ‘SeaGen’
• Skerries Tidal Stream Array
• 9 SeaGen devices array with a total capacity of
up to 10MW
Tidal Energy Limited – ‘DeltaStream’
• Demonstration project in Ramsey Sound,
Pembrokeshire – capacity to provide electricity
for up to 1000 homes
• LCRI Marine survey data used to inform site
selection
Tidal Stream Devices in Wales
http://www.tidalenergyltd.com/?page_id=640

13. 13
Case Study 1: Irish Sea

14. 14
The Bishops and Clerks – a historical hazard to
navigation
“The Bishop and these his clerkes preache deadly doctrine to their winter
audience" George Owen, 1552-1613.
.
RNLI Lifeboat Joseph Soar – south end of Ramsey Island
RNLI Lifeboat Swn-Y-Mor alongside World Concord, 27th
November 1954
Case Study 1: Irish Sea

15. • Rock Outcrops
• Small Islands
• Underwater
pinnacles
• Deep channel
• Large island
http://www.ramseyisland.co.uk/ramsey-and-the-outer-islands/ramsey-island/
Case Study 1: Irish Sea

16. The Bitches
Horse Rock
Whitesand Bay
Case Study 1: Irish Sea

17. • Fast spatial and temporal
varying flow
• Varying location of shear line
between eddies
• Up- and down-welling
Case Study 1: Irish Sea

18. Case Study 1: Irish Sea

19. Case Study 1: Irish Sea

20. Slack
Slack+1
Slack+2
Slack+3
Slack+4
Slack+5
Case Study 1: Irish Sea

21. HWHW+0.5
Case Study 1: Irish Sea

22. Case Study 2: Severn Estuary
Survey Area
Flat Holm Island
The Wolves

23. Case Study 2: Severn Estuary

24. Case Study 2: Severn Estuary

25. Case Study 2: Severn Estuary

26. Further Work
• Analysis and interpretation of flow data
• Laboratory experiments – wake studies downstream of cone
• Numerical model validation
• Further surveys in vicinity of Flat Holm
• http://www.lcrimarine.org.uk/

27. Thank You
for
Listening
27