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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
NYS Department of Environmental Conservation
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
NYS Department of Environmental Conservation
-property owners inparticipating communities).
urance
urance
urance
urance
Evolution of NFIP
Mandatory Flood Insurance PurchaseRequirements
Extension of Floodplain Standards into
Buildin Codes
NYS Department of Environmental Conservation
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Floodplain Mapping
Analysis
More sophisticated mapping techniques
$1 Billion Map Modernization: 5-yearlan assed in 2003
NYS Department of Environmental Conservation
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.
NYS Department of Environmental Conservation
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
NYS Department of Environmental Conservation
, 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)
NYS Department of Environmental Conservation
Maximum Mapping Need = $169 Million
Realistic Mapping NeedExcludes Topo and Base Map
Maximum: $148 Million
Minimum: $37 Million
Planning Need: $93 Million
Remaining Counties
NYS Department of Environmental Conservation
ax mum: on
Minimum: $21 Million
Planning Need: $48 Million
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NYS Department of Environmental Conservation
But even new mapshave old studies!
8.7% of Statespopulation not yetin map production.
New map oftendoesnt mean newstudy.
NYS Department of Environmental Conservation
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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-
NYS Department of Environmental Conservation
: , 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
NYS Department of Environmental Conservation
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
NYS Department of Environmental Conservation
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Uncertainty
Topography
Hydraulics
Mapping precision
NYS Department of Environmental Conservation
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
-
NYS Department of Environmental Conservation
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
NYS Department of Environmental Conservation
.
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
NYS Department of Environmental Conservation
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.
NYS Department of Environmental Conservation
Without LiDAR, use USGS DEMs, usually10 meter horizontal, 5 10 verticalaccuracy.
Hydraulics
Hydrology and Topography
Assumptions:
Open channels, free flowing conditions
NYS Department of Environmental Conservation
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Mapping, Insurance,
Perceptions and Risk
binary.
In or out
Criticism ThatProgram is not
NYS Department of Environmental Conservation
Actuarially Sound.
Perceptions
.
Declining property values.
This is a government money grab.
When has it flooded here?
NYS Department of Environmental Conservation
. 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.
NYS Department of Environmental Conservation
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.
NYS Department of Environmental Conservation
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
NYS Department of Environmental Conservation
Preserve Flood Storage Areas
Reacquaint streams with their floodplains
Extend Freeboard Landward
BFE +2
NYS Department of Environmental Conservation
BFE
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Conclusions
.
Reform needed to avoid politicalbacklash against flood mapping.
Flooding is the risk, not insurance.
NYS Department of Environmental Conservation
development.
William Nechamen CFM
Chief, Floodplain ManagementNYS DEC, Floodplain Management Section
625 Broadway, 4th FloorAlbany, NY 12233-3504
NYS Department of Environmental Conservation