COMRISK Sub-Project 8 Lincshore: Risk Management Options Pete Floyd, Risk & Policy Analysts Ltd.,...
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Transcript of COMRISK Sub-Project 8 Lincshore: Risk Management Options Pete Floyd, Risk & Policy Analysts Ltd.,...
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
RPA
What has happened
RPA
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)
RPA
Current Proposals
RPA
Where do you place the sand? (Risk Management Options)
RPA
● Locations of dVmax● Minimum standard of defence ● Risks to people ● Risks to property● Combination of above
Standard of Defence
RPA
● 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
RPA
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
RPA
● 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
RPA
● 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
RPA
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
RPA
● 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
RPA
● 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