fema flood maps, flood risk and public perception

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  • 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

    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

    [email protected]