1. Barrage or What? Engineering Options Prof Colin Taylor CEng FICE Professor of Earthquake Engineering Head, Department of Civil Engineering colin.taylor@bristol.ac.uk

2. The technical options Barrage Lagoon Tidal reef Tidal fence Tidal stream Source: Marc Paish, Severn Tidal Fence Group

3. Barrage

4. Barrage turbine Source: Roger Falconer

5. Tidal lagoon Source: University of Colorado

6. Fleming lagoon flow computation Filling Discharging Source: Roger Falconer

7. Evans tidal reef Source: Evans Engineering

8. Evans tidal reef

9. Low-head turbine for reef Source: Rod Rainey, Atkins

10. Tidal fence Source: Marc Paish, Severn Tidal Fence Group

11. Tidal stream Source: DeltaStream Turbines Source: Swanturbines

12. Short listed options

13. Severn Tidal Fence Group

14. Barrage issues Significant environmental impacts Reduction of water levels and tidal range Loss of inter-tidal habitats Impacts on bird and fish populations in the Severn Inhibits port traffic Protection from effects of storm surges, sea level rise Reduced turbidity Established technology La Rance, France

15. Lagoon issues Significant reduction in tidal range within the impounded area Loss of inter-tidal habitats Other environmental effects are similar to smaller barrages Less impacts on fish and navigation as not a full a barrier across the estuary Enclosure construction uncertain (e.g. embankment, caissons, innovative modular concrete/earth units?) Longer than barrage

16. Reef issues Unproven technology Long development period Less loss of tidal range Lower efficiency? Inhibits shipping Source: Evans Engineering

17. Fence issues Unproven technology Long development period Less loss of tidal range Lower efficiency? Less impact on shipping (but vulnerable to ship impact?) Source: Marc Paish, Severn Tidal Fence Group

18. Cost comparisons Source DECC Analysis of Options report