asfpm conference – may 2010 1 shifting our focus from maps to risk william l. coulbourne, p.e....

ASFPM Conference – May 2010 1

Shifting Our Focus from Maps to Risk

William L. Coulbourne, P.E.Applied Technology Council

(ATC)


Topics of Discussion

Background Proposed modifications to our current

approaches to floodplain management Flood design information must include risk Risk must reflect probability of the event Need to consider mitigation measures in

addition to elevation All flood insurance is not equal

Conclusions and Recommendations


Background Last 20 years we’ve experienced many major

flood events 1993 – Midwest floods 1997 – Red River floods – ND/MN 2005 – Hurricane Katrina 2008 – Midwest floods 2008 – Hurricane Ike 2009 – Red River floods

NFIP has over 20,000 participating communities and 5.5 million policies

Represents $1 trillion in exposure NFIP program is $19 billion in debt


Background Current mitigation to reduce losses is really

just: Elevation Relocation

There are currently many ways to “ignore” the property location LOMR – remove the land from the floodplain Levee – protected by a manmade structure Adjacent to a ‘100-year’ floodplain and you are out Live in a house built pre-FIRM, you’re subsidized


Background (and the smell test)

Mapping standards require flood plain delineations to 1/10th ft. and then are shown on maps drawn to 1:600 – 1:700 scale (from paper titled: Demonstrating Floodplain Uncertainty Using Flood Probability Maps)

How much sense does that make? Width of the boundary line could be 25 ft. Conclusion I draw is the current strategy

is not working


Considerations for the Program

Flood design must include risk – now the risk is “read” as all the same everywhere in the flood plain

Risk must reflect the probability of the event The only feasible mitigation solution is

elevation above the ‘design event’ – need more options

All flood insurance must be actuarial and represent the risk


Flood Design Must Include Risk

Risk = probability x consequences Low risk = high probability x low

consequences High risk = low probability x high

consequences Not all development in the flood plain is

equal (unequal consequences to the community)


Generic plot of risk


Possible Risk Levels Very High Risk:

Property in coastal high hazard area Economic impact is great if damaged Affects more than 50,000 people Recovery would require more than 3 mos. Property is behind flood protection barrier

not inspected within last 5 years Iconic buildings could be flooded Flood depths could exceed 5 ft, velocities 5

fps


Possible Risk Levels

High Risk: Flood protection barrier inspected within last

5 years Flood depths could be 3 ft but not likely to

exceed 5 ft. Important buildings could be impacted but

community has plan for continued operations

Population affected 10,000 – 50,000


Possible Risk Levels Moderate Risk:Moderate Risk:

Last floodplain study less than 2 years old Flood depth will not exceed 3 ft. Population affected less than 10,000 Property might be on fill and thus cut off by

floods No community-important buildings affected


Possible Risk Levels Low Risk:

Property outside mapped flood plain Flood depth less than 2 ft. No property is isolated by flooding Population affected less than 5,000 No community-important buildings affected


Example – Cedar Rapids, IA 2008


Example – Cedar Rapids, IA 2008

Very High Risk

Very High Risk

High Risk


Risk Must Reflect Probability

It seems that many floods in last few years are exceeding the mapped probability (1% annual chance)

Maybe these floods are not really 1% annual events but something greater

Maybe our standard is to low (Dutch – 10,000-yr recurrence interval)

Continued development in/near floodplains will continue to increase flood probabilities (always changing condition)


Need Options to Elevation

Elevate to what elevation? 100-year event? 500-year event?

Engineer to resist floods Perhaps elevation is not economically feasible

– but actuarial flood rates are feasible Dry floodproofing? Wet floodproofing?


Stop Encouraging Development

Areas behind flood protection structures should be classified High Risk

Properties elevated within the designated floodplain are “not out of the floodplain”

Some places should be no build areas – coastal high hazard areas, floodways, areas where flood velocity > 5 fps

Properties within flood boundaries are either insured or do not receive federal assistance if damaged


Floodplain or not?


All Flood Insurance is not Equal

Premiums should be based on risk – not just elevation +/- BFE or in/out of 100-yr floodplain

Premiums should be higher when closer to the flood source

Premiums should account for installed mitigation measures of all sorts


Conclusions & Recommendations

Making a shift from maps to risk-based floodplain approach will not be easy or fast

Making a shift is imperative if we ever need for this program to be self-sufficient

Must broaden the pool of flood insurance contributors at the same time that the basis changes to risk

Must have insurance be actuarial at the same time the basis changes to risk

Questions?

asfpm conference – may 2010 1 shifting our focus from maps to risk william l. coulbourne, p.e....

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