COMRISK Sub-Project 8

Lincshore: Risk Management Options

Pete Floyd, Risk & Policy Analysts Ltd.,working with Halcrow and the

Environment Agency

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

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What has happened

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0 50 100 150 200 250-4

-3

-2

-1

0

1

2

3

4

5

Observed

Design

MSHW

MSL

MSLW

Chainage (m)

Lev

el (

m O

D)

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)

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Current Proposals

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Where do you place the sand? (Risk Management Options)

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● Locations of dVmax● Minimum standard of defence ● Risks to people ● Risks to property● Combination of above

Standard of Defence

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● 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!

Variations in Key Parameters

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83797571676359555147433935312723191511

0 10 20 30 40 50 60

Berm Width (m)

83797571676359555147433935312723191511

0 100 200 300

Seawall Overtopping (l/s/m)

Is Likelihood of Flooding a Function of Berm Width?

RPA0 10 20 30 40 50 60

0

25

50

75

100

125

150

175

200

225

250

275

609

16

59

75

79

71

82

39

80

10

35

23

40

12

15

72

70

24

52

67

7836

18

42

55

19

57

68

74371151

3344 22

6977

17

20

5048453149

7673

21

32

28

25

14

29

63

27

61

47

13

O'topping vs Berm Width

Berm Width (m)

O'to

pp

ing

(l/s

/m)

Risks to People

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● 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

Risks to Property

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● In Strategy Review, used ‘Risk Reservoirs’

● Damages calculated for residential, caravans, industrial and agricultural damages for each reservoir for each option under different conditions

Sample Damages by Reservoir

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Damages (£k) vs Return Period (Maintain Option)Reservoir 1 10 50 100 200 500R11 0 0 17 43 5,730 8,735R12 0 0 36 178 32,997 45,772R13 0 0 0 0 0 0R14 0 0 0 0 0 0R15 0 0 0 0 25 2,033R16A 8 41 1,264 2,095 13,008 24,334R16B 0 0 0 0 2,099 4,075R17 0 0 0 0 0 0R18 6 29 1,820 3,479 5,666 14,955R19 0 0 0 0 0 215R20 0 2 2,661 12,967 17,935 26,873R21 0 0 0 0 0 0R22A 0 0 2 2 37 777R22B 0 0 0 0 0 0R23 0 0 0 0 0 0R24 0 0 3 68 15,372 16,182R25 0 0 17 1,185 33,695 38,724Total Zone 2 14 73 5,818 20,017 126,565 182,674

Difficulties

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● 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

Conclusions

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● 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