COMRISK Sub-Project 8 Lincshore: Risk Management Options

1. Pete Floyd, Risk & Policy Analysts Ltd., working with Halcrow and the Environment Agency COMRISK Sub-Project 8 Lincshore: Risk Management Options

2. RPA Approach • Step 1: Review Halcrow Strategy Review • Step 2: Explore key risk issues • Step 3: Develop refined risk assessment methodology • Step 4: Disseminate results

3. What has happened

4. Why? Grain Size! • Simply stated: 0.2 mm (before) + 0.6 mm (emplaced) = 0.4 mm by 2001 • But mixture of grain sizes leads to natural sorting with mean sizes of 0.42 mm, 1.2 mm and 0.27 mm on upper, middle and lower beaches respectively • Slopes can be readily predicted using Dean expressions: h = A x 2/3 where A = 0.21 D0.48 • to give slopes of 1:19 and 1:52 for middle and lower beaches (as previous slide)

5. Current Proposals

6. Where do you place the sand? (Risk Management Options) • Locations of dVmax • Minimum standard of defence • Risks to people • Risks to property • Combination of above

7. Standard of Defence • Essentially, standard is function of wave climate, berm width, sea wall, etc. • Reviewed profiles from April 2002 and associated overtopping calculations (for 1 in 200 year event) • Difficult to reconcile!

8. Variations in Key Parameters

9. Is Likelihood of Flooding a Function of Berm Width?

10. Risks to People • Risks to people function of flood likelihood, wave depths/velocity, area vulnerability (type of housing), people vulnerability, etc. • Methodology being developed in parallel research for Environment Agency • BUT also need to resolve earlier issues relating to flood likelihoods

11. Risks to Property • In Strategy Review, used ‘Risk Reservoirs’ • Damages calculated for residential, caravans, industrial and agricultural damages for each reservoir for each option under different conditions

12. Sample Damages by Reservoir

13. Difficulties • Risk management of frontages will rely on being able to determine damages of events from each frontage rather than across whole coast • Clearly, would require extensive modelling work to generate ‘damage risk contours’ • As before still need to relate flood potential to beach profiles

14. Conclusions • 10 years on, beach profiles are not as designed due, primarily, to grain size distribution of emplaced sand • Modified profile accounted for in current proposals • However, developing practical risk management options has proved to be a complex process