Barrage or What?Engineering Options

Prof Colin Taylor CEng FICEProfessor of Earthquake EngineeringHead, Department of Civil Engineering

colin.taylor@bristol.ac.uk

The technical options

• Barrage• Lagoon• Tidal reef• Tidal fence• Tidal stream

Source: Marc Paish, Severn Tidal Fence Group

Barrage

Barrage turbine

Source: Roger Falconer

Tidal lagoon

Source: University of Colorado

Fleming lagoon flow computation

Filling Discharging

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

Source: Roger Falconer

Evans tidal reef

Source: Evans Engineering

Evans tidal reef

Low-head turbine for reef

Source: Rod Rainey, Atkins

Tidal fence

Source: Marc Paish, Severn Tidal Fence Group

Tidal stream

Source: DeltaStream Turbines

Source: Swanturbines

Short listed options

Severn Tidal Fence Group

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

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

Reef issues

• Unproven technology• Long development

period• Less loss of tidal

range• Lower efficiency?• Inhibits shipping

Source: Evans Engineering

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

Cost comparisons

Source DECC Analysis of Options report