Flood-CBA (more complex) case · PDF file@fhrc_mdx Benefit appraisal route map 1. Receptor data in the benefit area 2. Property threshold surveys 3. Depth damage data for property

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Flood-CBA (more

complex) case study

@fhrc_mdx

Flooding in Filey: North Yorkshire

@fhrc_mdx

July 18th 2007: Flash floods in Filey

Flash flooding affected over 100 homes and a number

of commercial properties

Over 50 homes were evacuated

These events have been common and increasing in

occurrence since 2000

Flood risk management is required to alleviate the effects

of torrential runoff from surrounding agricultural land

A Cost-Benefit of flood mitigation options is presented

@fhrc_mdx

The flood event

• Depths of flooding

were up to 1 to 1.5

metres, though

many properties

were flooded to

just a few

centimetres.

• Rescue and

evacuation were an

important part of

Incident

management

@fhrc_mdx

The options for flood mitigation

Scarborough Borough Council

and their consultants

discussed options, with a short

list as follows:

• Do Nothing

• Do Minimum - maintenance

• Do Minimum - demountable

& temporary solutions

• Do Something - earth bund

and storage

option (without

environmental

enhancements)

• Do Something - earth bund

and storage option

(with environmental

enhancements)

@fhrc_mdx

Benefit appraisal route map

Stages in the evaluation of the benefits

of the earth bund and storage

option without environmental

enhancements

11 stages in the appraisal process

@fhrc_mdx

Benefit appraisal route map

1. Receptor data in the benefit area

2. Property threshold surveys

3. Depth damage data for property

4. Flood modelling of all potential flood events

5. Improving flood modelling

6. Validation of modelling against other data sources

7. Calculation of annual average damages (AAD)

8. Estimation of option costs

9. Benefit cost summary

10.Visualisation of results for transparent decision making

11.Partnership funding

@fhrc_mdx

Stage 1: Receptor data in the benefit area

• Obtain receptor data within the area at risk from a range of potential

flood events.

• The Environment Agency has a National Receptor Database (NRD)

georeferencing all property, infrastructure and environmental

assets

NRD stores data on:

• Property type

• Footprint area

• Address

• Damage function

code

• Grid co-ordinates

• Data quality rating Full auditability against all results means

greater process transparency and simpler

scheme justification

Receptor data relates to

property, land,

infrastructure and

environmental assets

@fhrc_mdx


• One of the properties suffering minor flooding is 47 off

Scarborough road (A semi detached property). We will follow

this property through the benefit analysis process

Semi-automated tools such as Google

Street View make auditing of data and

gap filling fast and efficient

@fhrc_mdx


People data

• Social justice may require to weight investment decisions in

favour of more socially deprived households where coping

strategies are weakened following a flood shock

• Social deprivation statistics assist with this decision

• Lower social deprivation ranking may mean greater allocation

of National flood risk budgets

Social deprivation Ranking from

Office of National Statistics

Super Output Areas data :

Highest rankings equate to least

social deprivation

None of the benefit area is in the lowest ranking of social deprivation.

@fhrc_mdx

Stage 2: Property threshold surveys

• The property threshold (the point at which flood damage begins,

usually the door step or air brick where property has suspended

floors) is required for every property:

• to enable flood depths to be calculated for any flood event

scenario in stage 4.

• To match these flood depths to property damage in stage 3

• This needs to be estimated or measured during field survey.

IZ ground level

Property threshold levelThreshold 0.25m

Flood depth-

damages

accrued

Cost £

0m

Onset of damage -0.3m

Property

MCM

depth-damages

tables

@fhrc_mdx

Stage 3: Depth – damage data for property

• Depth damage data for all property types, including the semi

detached property at #47, is extracted from MCM Online data.

-

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000-0

.3 0

0.0

5

0.1

0.2

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7 3

Damage (£)

Depth (m)

Sector Average

Detached

Semi-detached

Terrace

Bungalow

Flat

@fhrc_mdx


• The data from MCM - [“Flood and coastal erosion risk

management: A manual for economic appraisal, 2013”] shows

semi-detached property [highlighted yellow] MCM code

Property Type -0.3 0 0.05 0.1 0.2 0.3

1 Residential Sector Average

1,031

1,031

6,578

10,488

17,698

21,598

11 Detached

937

937

8,627

14,204

24,494

30,433

12 Semi-detached

1,254

1,254

6,095

9,670

16,266

19,854

13 Terrace

1,089

1,089

5,653

8,806

14,961

18,161

14 Bungalow

875

875

9,240

14,729

23,696

28,583

15 Flat

731

731

5,898

9,488

16,154

19,645

0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3

26,669

29,059

32,106

34,630

37,664

40,216

42,589

48,048

50,598

36,947

40,793

45,144

49,168

53,835

57,682

60,915

68,226

72,059

24,547

26,611

29,523

31,909

34,835

37,440

40,059

45,339

47,921

22,552

24,385

26,933

28,893

31,291

33,260

35,254

40,152

42,162

35,071

38,802

43,228

47,375

52,227

56,372

60,154

67,677

71,672

24,587

26,604

28,965

30,635

32,684

34,279

35,477

39,646

41,289

Data

highlighted in

yellow used

for # 47 at

modelled

depths in

stage 4

Metres above threshold

Damage in (£)

@fhrc_mdx


• Depth-damage data is also available for all non residential

data types for different characteristics of flooding (short and

long duration/with and without flood warning):

0

500

1,000

1,500

2,000

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00

Damage (£/m²)

Depth (m)

Non-residential properties fluvial short duration

Retail

Offices

Warehouses

Leisures

Public Buildings

Industry

NRP sector average

@fhrc_mdx


Other data is available in MCM on:

• Emergency services costs

• Evacuation and temporary accommodation costs

• Damage to vehicles and traffic disruption

• Infrastructure losses

• Agricultural losses

• Recreation and ecosystem services

These are

included in the

benefit

analysis

proportionate

to their

importance in

the benefit

area

This stage by stage route map will follow the process for evaluating

residential property damages and link the results to other receptor

losses and damages contributing significant further loss or damage.

@fhrc_mdx

Stage 4: Flood modelling of selected flood events

• The 2007 flood was only one of a potential series of greater or

lesser flood events.

• Mathematical modelling (in this case a product called InfoWorks) is

used to simulate the flood depths for a range of these flood events.

• The threshold flood is where flooding commences and damages

are zero.

• A range of successive floods allows the estimate of Annual Average

Damage for all floods over a long time period.

• Six such flood events were modelled for Filey:

@fhrc_mdx


• 5 year flood with an annual probability of 20%

Flood depth

high (0.6m)

Flood depth

low (0m)

#47

Seadale

@fhrc_mdx



Flood depth

high (0.6m)

Flood depth

low (0m)

#47

@fhrc_mdx


• 30 year flood with an annual probability of 3.33%

Flood depth

high (1.0m)

Flood depth

low (0m)

#47

@fhrc_mdx



Flood depth

high (1.4m)

Flood depth

low (0m)

#47

@fhrc_mdx



Flood depth

high (1.5m)

Flood depth

low (0m)

#47

@fhrc_mdx


• 200 year flood with an annual probability of 0.5%

Flood depth

high (1.5m)

Flood depth

low (0m)

#47

@fhrc_mdx

Stage 5: Improving flood modelling

• Robustness analysis: Visualisation allows auditing of errors in

modelling

30 year depth shallower than 10 year depth

Model results

need detailed

audit and

truthing prior

to progressing

to Stage 7.

For Filey,

serious

calibration of

model was

required

@fhrc_mdx

Stage 6: Validation of modelling against other data sources

Validation data

Many data

sources can be

applied to ground

truth the veracity

of the modelling:

• Historic flood

maps

• Insurance data

• Web sources

(flicker, you

tube)

• Anecdotal

evidence

2007 Selected insurance data

Checking the modelled damages against reality is difficult, if not

impossible, as by no means all modelled flood events have

occurred, usually just one as in 2007 case. Using insurance

claims and historic data can assist to some degree. Though

insurance data uses financial replacement costs whilst MCM

damages do not include VAT (a transfer payment) or betterment

(it is assumed that all damaged goods are approximately half way

through their lives, therefore economic loss is about 50%.)

@fhrc_mdx

Stage 7: Calculation of annual average damages (AAD)

For every property including #47 off Scarborough Road we now have:

• A property type

• A threshold level where flood water enters the property

• A flood depth for each of the modelled return periods, and as a result:

• A damage for every property for every flood depth for every return period

• Every input and calculation is stored against every

property

• Every stage of process can be visualised to assist

decision making

• AAD can now be calculated:

AAD is the theoretical damage expected each year on average from a

sequence of flood events with different annual occurrences of flooding

@fhrc_mdx


• Individual ‘event’ property damage for each residential property under ,

• ‘Do Nothing’ scenario using EA standard spreadsheets (Seadale sub area)

Asset Annual Average Damage - Residential Sheet Nr.

Client/Authority

Project name Option:

Project reference -

Base date for estimates (year 0) Aug-11 Prepared (date) 22/09/2011

Scaling factor (e.g. £m, £k, £) £ Printed 12/05/2014

Discount rate 3.5% Prepared by JC

Checked by

Applicable year (if time varying) Checked date

Average waiting time (yrs) between events/frequency per year Average waiting time (yrs) between events/frequency per year

2 5 10 30 50 100 200 infinity

0.500 0.200 0.100 0.033 0.020 0.010 0.005 0

Residential property Damages £ Annual Damage

£/ year

10BAY CRESCENT 0 0 13907 20194 33368 33368 33,368 1,292

12UNNAMED ROAD 0 0 0 13907 27971 33368 38,765 636

18BAY CRESCENT 0 0 13907 3032 27971 33368 38,765 1,065

17BAY CRESCENT 0 0 0 20194 20194 33368 46,541 670

19BAY CRESCENT 0 0 0 20194 20194 33368 46,541 670

22BAY CRESCENT 0 0 13907 20194 13907 27971 42,034 1,141

67CLARENCE DRIVE 0 0 0 33368 3032 27971 52,909 684

4PADBURY AVENUE 0 13907 27971 27971 27971 27971 27,971 3,024

5BAY CRESCENT 0 0 0 13907 27971 27971 27,971 582

16BAY CRESCENT 0 0 13907 20194 0 27971 55,941 1,072

46CLARENCE DRIVE 0 20194 20194 20194 20194 27971 35,747 3,107

47UNNAMED ROAD 0 0 0 0 0 3032 6,064 30

12UNNAMED ROAD 0 0 3032 0 20194 20194 20,194 424

3UNNAMED ROAD 0 0 0 0 13907 20194 26,482 271

2UNNAMED ROAD 0 0 0 0 13907 20194 26,482 271

6UNNAMED ROAD 0 0 0 0 3032 20194 37,357 217

5UNNAMED ROAD 0 0 0 0 3032 20194 37,357 217

4UNNAMED ROAD 0 0 0 0 3032 20194 37,357 217

46GRANGE AVENUE 0 0 3032 3032 13907 13907 13,907 365

44GRANGE AVENUE 0 0 3032 3032 3032 13907 24,781 311

9BAY CRESCENT 0 0 0 3032 3032 13907 24,781 190

63CLARENCE DRIVE 0 0 0 20194 3032 13907 24,781 390


Filey Flood Alleviation Strategy: Seadale only Do Nothing

#47

(yellow)

indicates

no

flooding

until the

200 year

event

Modelling of 16 Bay Crescent is still erroneous with 100

year flood event showing zero damage

@fhrc_mdx


• Calculation of ‘Do Nothing’ annual average damages (Seadale) and Present

value of damages (PVd) with other receptor damage/disruption included

(e.g. temporary accommodation, commercial and road damage).

• #47 is part of the residential aggregation Summary Annual Average Damage Sheet Nr.

Client/Authority

Project name Option:

Project reference -

Base date for estimates (year 0) Aug-11 First year of damage: 0 Prepared (date) 22/09/2011

Scaling factor (e.g. £m, £k, £) £ Last year of period: 99 Printed 12/05/2014

Discount rate 3.5% PV factor for mid-year 0: 29.813 Prepared by JC

Checked by

Applicable year (if time varying) Checked date

Average waiting time (yrs) between events/frequency per year Total PV

1 2 5 10 30 50 100 200 Infinity £

0.500 0.200 0.100 0.033 0.020 0.010 0.005 0

Damage category Damage £

Residential property - - 51,040 148,019 356,100 446,081 798,274 1,150,466 731,651

Ind/commercial (direct) - - - - - 7,578 7,578 8,588 3,464

Ind/comm (indirect) - -

Traffic related - -

Emergency services - - 2,858 8,289 19,942 25,405 45,128 64,907 41,166

- 3,025 12,705 37,510 58,685 64,130 69,575 75,020 145,044

Alt. Accommodation 3,348 6,078 12,156 25,546 52,326 85,801 119,276 91,820

Road Damage 2,376 12,277 51,390 85,973 100,848 121,407 141,966 187080

Total damage £ - 8,749 84,958 257,364 546,245 696,367 1,127,762 1,560,223

Area (damagexfrequency) - 1,312 4,685 11,411 5,357 6,213 4,560 6,720

Total area, as above 40,259

PV Factor, as above 29.813

Present value (assuming no change in damage or event frequency) 1,200,225 1,200,225

Notes

Area calculations assume drop to zero at maximum frequency.

Default value for the highest possible damage assumes continuation of gradient for last two points, an alternative value can

be entered, if appropriate.

One form should be completed for each option, including 'without project', and for each representative year if profile changes

during scheme life (e.g. sea-level rise)

Residential property, Industrial / commercial (direct), and Other damages are itemised in Asset AAD sheet and automatically linked

to this sheet


Filey Flood Alleviation Strategy: Seadale only Do nothing

Extra Heating

AAD for all

receptors =

£40,259

PVd =

£1,200,225

PVd uses the fixed Treasury discount

rate and a 100 year time horizon.

PVd adds AAD each year

and discounts to a

common price base

@fhrc_mdx


• The area under the loss probability curve calculates the £40,259

annual average damages:

Project: Filey Flood Alleviation Strategy: Seadale only Option: Do nothing

Frequency 0.000 0.500 0.200 0.100 0.033 0.020 0.010 0.005 0.000

Damage £ 0 0 8748.5 84958.1027 257363.5571 546245.2198 696367.4288 1127761.92 1560223.33

0

200000

400000

600000

800000

1000000

1200000

1400000

1600000

1800000

0.000 0.100 0.200 0.300 0.400 0.500 0.600

Frequency

Damage £

The curve

visualises a

‘good fit’. If the

curve is not

asymptotic to

both axes then

the annual

average

damages are

more than likely

to be

overestimated. The model is then run to establish the residual annual

average damages with each option as it is unlikely that any

option will eliminate all flooding completely.

For schemes with 100 year or more standard of protection it

is unlikely that residual damages will be more than 5% to

10% of Do Nothing damages. For simplicity in the case of

Filey they are assumed to be zero.

@fhrc_mdx

Stage 8: Costs of options

• Though benefits were separated for the 3 sub areas (Wharfedale,

Seadale and Weardale) the costs for each option were

amalgamated and divided in 3 equal parts

Option 1a Option 1b Option 2a

(Do nothing)

Do Nothing (Health and Safety compliance)

Do Minimum - Maintenance

PV total costs £0 £29,955 £1,336,655

Option 2b Option 3c Option 3d

Do Minimum - Demountable & Temporay Solutions

Do Something - Earth bund and storage option (without env.enhancements)

Do Something - Earth bund and storage option (with env.enhancements)

£1,542,762 £3,930,321 £4,373,164

Costs include capital, maintenance and operational costs

over a 100 year period (adhering to Government ‘long

termism’ for major infrastructure schemes) discounted

using Treasury discount rates. A 60% optimism bias is

usually added at initial appraisal stage to reduce Optimism

bias (the difference between appraisal and outturn costs

after the scheme is complete).

@fhrc_mdx

Stage 9: Benefit cost summary

• #47 property is

part of the

Seadale sub area

and Option 3c

costs (preferred

option) were

divided equally

between the 3 sub

areas.

• The benefit cost

summary

indicates that on

its own using UK

appraisal rules

the Seadale

scheme is not

cost beneficial for

any of the options

with a 0.9:1 ratio

for Option 3c.

Project Summary SheetClient/Authority Prepared (date) 22/09/2011

Printed 12/05/2014

Project name Prepared by JC

Checked by

Project reference Checked date

Base date for estimates (year 0) Aug-2011

Scaling factor (e.g. £m, £k, £) £ (used for all costs, losses and benefits)

Year 0 30 75

Discount Rate 3.5% 3.00% 2.50%

Optimism bias adjustment factor 60%

Costs and benefits of options

Option number Option 1a Option 2a Option 2b Option 3c Option 3d

Option name Do Nothing

Do Minimum -

Maintenance

Do Minimum -

Demountable &

Temporay

Solutions

Do Something -

Earth bund and

storage option

(without

env.enhanceme

nts)

Do Something -

Earth bund and

storage option

(with

env.enhanceme

nts)

COSTS:

PV capital costs 0 0 100,000 0

PV operation and maintenance costs 0 1,308,281 1,308,281 0

PV other 0 16,333 32,667 0

Optimism bias adjustment 0 794,768 864,568 0

PV negative costs (e.g. sales) 0 98,000 275,973 0

PV contributions

Total PV Costs £ excluding contributions 0 2,021,383 2,029,543 1,300,000 0

Total PV Costs £ taking contributions into account 0 2,021,383 2,029,543 1,300,000 0

BENEFITS:

PV monetised flood damages 1,200,225 1,200,225 1,200,225 -

PV monetised flood damages avoided 0 0 1,200,225 1,200,225

PV monetised erosion damages 0 0 0 0 0

PV monetised erosion damages avoided (protected) 0 0 0 0

Total monetised PV damages £ 1,200,225 1,200,225 1,200,225 0 0

Total monetised PV benefits £ 0 0 1,200,225 1,200,225

PV damages (from scoring and weighting)

PV damages avoided/benefits (from scoring and weighting)

PV benefits from ecosystem services

Total PV damages £ 1,200,225 1,200,225 1,200,225 0 0

Total PV benefits £ 0 0 1,200,225 1,200,225

DECISION-MAKING CRITERIA:

excluding contributions

Based on total PV benefits ( includes benefits from scoring and weighting and ecosystem services)

Net Present Value NPV -2,021,383 -2,029,543 -99,775 1,200,225

Average benefit/cost ratio BCR 0.0 0.0 0.9

Incremental benefit/cost ratio IBCR

Highest bcr


Costs and benefits £

Filey Flood Alleviation Strategy: Seadale only

Benefits of each option are ‘Do Nothing’ damages

minus residual damages (here assumed zero)

@fhrc_mdx

Stage 10: Visualising of results for transparent decision making • Property damage contribution and highest

contributing properties Benefits are capped

per property when the

annual average

damage accrued over

the time horizon of any

improvement scheme

are greater than the

market price of the

property (taking

average Regional

prices per property

type). No property can

have more damage

than the total value of

the property.

Properties capped

Properties below capping threshold

Commercial Properties affected

@fhrc_mdx

Stage 10: Visualising of results for transparent decision making

• Movement between flood risk zones with flood mitigation

Very Significant to Moderate risk

Very Significant to Low risk

Significant to Moderate risk

Significant to Low risk

Moderate to Low risk

Area of most

severe flooding

moves from

very significant

(>5%) risk to

Low risk (<1%)

with option 3c

The more properties with reduced risk before and after the

preferred option the better chance for scheme justification

@fhrc_mdx

Stage 10: Visualising of results for transparent decision making • Heat map of damage density for ‘Do Nothing’ scenario for

the 3 sub areas

Walldale Seadale

Wharfdale

#47

Damage

per square

metre

£550

£550

£0

#47 is on the

extremity of

flood risk in

Seadale

which alone

would not

justify a flood

management

option

@fhrc_mdx

Stage 10: Visualising of results for transparent decision making

• Visualisation of ‘Do Nothing’ present value of damages

(Wharfdale, Wooldale and Seadale)

@fhrc_mdx

Stage 11:CBA Summary and partnership funding

Key

Summary: prospect of FDGiA funding

"FDGIA Contribution":

"Raw OM Score": Scheme Benefit to Cost Ratio: 15.84 to 1

Cost saving and/or external contribution required: Effective return to taxpayer: 15.84 to 1

Less scheme contributions secured: Effective return to area: n/a to 1

"Adjusted OM Score":

Result:

FDGiA required for next phase(s):

1. Scheme details

Who will maintain asset?

PV Whole-Life Costs: million

PV Whole-Life Benefits: million

Cash cost of next phase(s): million

Duration of Benefits: years

Average flood damages: per household

Construction phase?

2. Qualifying benefits under Outcome Measure 2: households better protected against flood risk

Number of households in: Before After

20% most deprived areas - - - - - - 0 0 0

21-40% most deprived areas 361 230 119 333 161 - -28 -69 -119

60% least deprived areas 266 264 839 40 85 - -226 -179 -839

At: Moderate Significant Very Moderate Significant Very Moderate Significant Very

risk risk significant risk risk significant risk risk significant

risk risk risk

Annual damages avoided, compared with a household at low risk 150£ 600£ 1,350£

Change in household damages, in: Per year Over lifetime of scheme Qual. benefits (discounted)

20% most deprived areas OM2 (20%)

21-40% most deprived areas OM2 (21-40%)

60% least deprived areas OM2 (60%)

206,250-£

Change due to scheme

20,625,000-£ 6,159,319£

-£

38,044,432£ 1,273,950-£ 127,395,000-£

-£

2,826,000£

2.82600£

100

30,000£

62.6890£

LA

Yes - costs for approval include construction

-£

-£

265.66%

Potential candidate for FDGiA funding dependant upon funding availability

265.66%

FDGiA Calculator, based on interim funding arrangements announced 23rd May 2011ePublications Catalogue Product Code - FLHO0511BTXS-E-E

Filey Flood Alleviation Strategy Study - Option 3c (ALL SCHEME)Project Name/ref:

3.9570£

Input cells

Calculated cells

10,511,974£

Combining Weardale, Walldale and Weardale into a single FRM Strategy

BCR = 16:1

Costs = £3.95m

Benefits = £62m

Change in

flood risk for

households

at high,

medium and

low social

deprivation

Scheme meets

National funding

criteria

Threshold for National Funding set each year. Any shortfall to

be made up by local beneficiaries

@fhrc_mdx

In summary, the 11 steps in the appraisal process are:

1. Collect receptor (property, etc) data in the flood prone area

2. Obtain property thresholds through estimates or surveys

3. Extract depth damage data for all property from MCM

4. Undertake flood modelling for a range of flood events

5. Improve flood modelling through careful audit

6. Validate modelling against other data sources

7. Calculate annual average damages (AAD)

8. Estimate option costs

9. Present benefit cost summary

10.Visualise (GIS) results for transparent decision making

11.Negotiate partnership funding where benefits using MCM

appraisal methods and data fall far short of National funding

Documents

Flood-CBA (more complex) case · PDF file@fhrc_mdx Benefit appraisal route map 1. Receptor data in the benefit area 2. Property threshold surveys 3. Depth damage data for property