fema flood maps, flood risk and public perception

8/11/2019 FEMA Flood Maps, Flood Risk and Public Perception

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FEMA Flood Maps, Flood Riskand Public Perception

NYS Department of Environmental Conservation

,

NYS DEC

Floodplain Management Section

The National Flood InsuranceAct of 1968

The National Flood Insurance Act created thee era nsurance m n s ra on an rec e

to:

Identify flood-prone areas within the U.S.

Establish flood-risk zones within those areas.

Require new and substantially improved


buildings be constructed in ways that minimizeflood damage.

Transfercost of private property flood lossesfrom taxpayer to property owner.


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The Three-Legged Stool The NFIP balances three

related program areas:

(mapping).

Floodplain Management(regulations such asbuilding codes and zoning).

Flood Insurance (provision

Flood

In

Flood

In

Flood

In

Flood

In


-property owners inparticipating communities).

urance

urance

urance

urance

Evolution of NFIP

Mandatory Flood Insurance PurchaseRequirements

Extension of Floodplain Standards into

Buildin Codes



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Floodplain Mapping

Analysis

More sophisticated mapping techniques

$1 Billion Map Modernization: 5-yearlan assed in 2003


Additional program RiskMAP to 2013

NYS Cooperating Technical Partnership

Has NFIP Prevented FloodDamage?

Structures Built to Standards Suffer75% Less Damage during Base Flood.

Program Saves $1-2 billion / year in

structural flood dama es.


Criticism of possible increase in at-risk

development.


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Mapping Needs

,

8,938 Map Panels

7,932 Detailed Stream/Shore Miles

18,401 Approximate Stream/Shore Miles


, 57 Counties plus NYC


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Mapping Needs

.

Base Map Acquisition: $550/Panel ($4.9 million,already funded)

Map Production: $1550/Panel ($13.8 Million)

Detailed Study Costs: $14,000/Mile ($120 million)


Maximum Mapping Need = $169 Million

Realistic Mapping NeedExcludes Topo and Base Map

Maximum: $148 Million

Minimum: $37 Million

Planning Need: $93 Million

Remaining Counties


ax mum: on

Minimum: $21 Million

Planning Need: $48 Million


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But even new mapshave old studies!

8.7% of Statespopulation not yetin map production.

New map oftendoesnt mean newstudy.



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Coastal Mapping

Nassau and Suffolk have new CoastalModels and Maps: 2009

Westchester, Orange, Ulster, Greenehave digital maps but no new LI Soundor Hudson River studies

FEMA plan: New coastal studies 2010-


: , es c es er, u sonEstuary

Great Lakes Mapping: 2010-2013

Public and Media Perception

How may people will be hurt by the maps?

Flood insurance can cost over $1,000/year

Perception of government scam

Perception of junk science

Maps are more precise. Are they more


accurate?

Maps show more, including imperfections.


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What is the Risk?

100-year flood?

per year

=26% chance over 30years

500-year flood?

6% over 30 years

But it hasnthappened here!

Flood Damages



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Uncertainty

Topography

Hydraulics

Mapping precision


Hydrology Varying hydrologic methods

Gau ed Streams:

Log Pearson Equations, include confidence intervals ((http://water.usgs.gov/osw/bulletin17b/bulletin_17B.htmlhttp://water.usgs.gov/osw/bulletin17b/bulletin_17B.html))

Ungauged Streams

Regional Regression Equations

-


One of the most comprehensive comparisons ofOne of the most comprehensive comparisons of

hydrologic methods for ungauged watersheds washydrologic methods for ungauged watersheds waspublished by the U.S. Water Resources Council inpublished by the U.S. Water Resources Council in1981.1981.


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Hydrologic Uncertainty

What is reasonable?

egress on equa ons can ave as mucas 40% standard error for 1% flood.

Rainfall runoff models deemed acceptableif within +- one standard error of USGS


.

Trends are not considered.

Topography

Detailed flood studies include surveyedcross sections and surveys of hardstructures

LiDAR : Remainder & Approximate Studies

2 contour interval for flat terrain, 1.2 accuracy


4 contour interval for hilly terrain, 2.4 accuracy

at 95% confidence level


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More on Topography

LiDAR is Most accurate, comprehensive,uickest and economical to o ra hical

mapping tool available: @ $350/mi2.

Parcel by parcel ground survey is moreaccurate but is prohibitively expensive est$800 million statewide.


Without LiDAR, use USGS DEMs, usually10 meter horizontal, 5 10 verticalaccuracy.

Hydraulics

Hydrology and Topography

Assumptions:

Open channels, free flowing conditions



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Mapping, Insurance,

Perceptions and Risk

binary.

In or out

Criticism ThatProgram is not


Actuarially Sound.

Perceptions

.

Declining property values.

This is a government money grab.

When has it flooded here?


. Distrust of government.


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Risk and Insurance

Mandatory Insurance PurchaseRequirements only in high risk zone.

Residual Risk.

Blocked bridges and culverts.

Ice jams.

Dams and levees.


Migrating Streams and Erosion.

Trends: Development & Climate Change.

Needs for Reform

.

Pre-FIRM policy subsidy.

Add mechanism to adjust rates based onfrequency and depth of flooding.


prove that they are an inch above the line.

Line width itself introduces error!


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Adapting to Risk

Need to extend elevation requirementslandward

Recognize At-Risk Locations


Preserve Flood Storage Areas

Reacquaint streams with their floodplains

Extend Freeboard Landward

BFE +2


BFE


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Conclusions

.

Reform needed to avoid politicalbacklash against flood mapping.

Flooding is the risk, not insurance.


development.

William Nechamen CFM

Chief, Floodplain ManagementNYS DEC, Floodplain Management Section

625 Broadway, 4th FloorAlbany, NY 12233-3504


[email protected]

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