storm induced coastal erosion for flood insurance …...storm induced coastal erosion for flood...
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Storm Induced Coastal Erosion for Flood Insurance Studies and Forecasting Coastal Flood Damage Impacts: Erosion, Runup & OvertoppingJeff Gangai- Dewberry
Tucker Mahoney – FEMA HQ
1
Introduction
▸Background
▸FEMA Storm Induced Erosion for FIS
▸Short-term and long-term needs
▸Disaster Response Forecasting erosion, runup,
and overtopping.
2
Background
• Early 1980’s used WHAFIS but no erosion was applied
• Storm surge study concerns in NC in early 1980’s identified the need for
erosion.
• Studies in 1985 and 1986 justified the need for erosion as well as other aspects
• Reports in 1987 and 1989 Identified procedure
• 1988 540 sq ft rule and Primary Frontal Dune (PFD) put in regulations
• FEMA guidelines and studies updated in 1990s
• 2004 Pacific Guidelines
• 2014 Great Lakes Guidelines
3
Background - Documentation History
• 1985_Review of Coastal Surge Model and Dune Erosion NC FIS
• 1986_Assessment_Of_Current_Procedures_Used_for_Identification_of_Coastal
_High_Hazard_Areas_compiled
• 1987_Relationship Between Frontal Dune Erosion And Storm Recurrence
Interval
• 1988_VZone-fr_finalrule
• 1988_CFR44_Definitions_and_Sec65.11
• 1989_Basis of Assessment Procedures for Dune Erosion in Coastal Flood
Insurance Studies
• 1999_bellomo-pajak-sparks
• 2004_D.4.6_Coastal_Erosion_Pacific
• 2005_Focus Study_ Erosion
• 2007_D.2.9_Coastal_Erosion_Atlantic_GC
• 2014_D.3.7_Coastal_Erosion_GtLakes
4
Erosion Recommendations
▸ Description and Assessment of Coastal Dune Erosion – 1986
1. Include, at a minimum, the primary frontal dune in the V Zone
2. For purposes of the wave analysis, consider that the primary frontal dune does not exist
(unless its cross-sectional area above the flood level and seaward of the dune crest
exceeds 540 square feet)
3. Incorporate an erosion model into the wave analysis model for use in areas of
appropriate applicability
4. Incorporate a routine in the wave height model to compute the effects of wave runup
5. Maintain the 3-foot breaking wave criteria for defining V zone inland of the primary
frontal dune
6. FIA should issue a comprehensive set of guidelines and specifications for wave analysis
and V zone mapping
7. Refine “Coastal High Hazard Area” for publication in the Federal Register
8. Offer insurance rate incentives to communities that have adopted and are enforcing
construction restrictions more stringent than NFIP minimum requirements
5
Erosion Recommendations 1986
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Erosion Recommendations 1986
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Erosion Recommendations 1986
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Regulations
▸ Final Rule
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NFIP Regulations
▸ Definitions in Section 59.1
• Coastal high hazard area means an area of special flood hazard extending from offshore
to the inland limit of a primary frontal dune along an open coast and any other area
subject to high velocity wave action from storms or seismic sources.
• Primary frontal dune (PFD) means a continuous or nearly continuous mound or ridge of
sand with relatively steep seaward and landward slopes immediately landward and
adjacent to the beach and subject to erosion and overtopping from high tides and waves
during major coastal storms. The inland limit of the PFD occurs as the point where there is
a distinct change from a relatively steep slope to a relatively mild slope.
▸ 60.3(e)(7)
• Prohibit man-made alteration of sand dunes and mangrove strands within Zones V1-30,
VE, and V on the community’s FIRM which would increase potential Flood damage.
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Present Methods
• Atlantic & Gulf Guidelines
• 540 Sq ft Dune Methods
Standardized Profile slopes
Primary Frontal Dune
• Bluff Retreat
• Pacific Guidelines – Historic Data
• Geometric profiles
• Bluff Retreat
• Great Lake Guidelines
• CSHORE Model
• Historic Data – Lacks guidance
11
TMAC Recommendation #9
“Scientific review and revision, as warranted, of the 540 sq ft criterion would help
ensure accurate identification of coastal food and erosion hazard areas and facilitate
community management and protection of dunes (including Primary Frontal Dunes, as
required by NFIP regulations).”
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Moving Forward
▸ Short Term
• How to use Historic Erosion guidance
• Update 540 with current local data, as well as profile shapes
• Guidance on altering profile shape
• Process based Model - CSHORE, SBEACH, XBEACH…
▸ Long Term
• 2D Modeling incorporation of erosion to Surge and Waves
• Removal of VE extension to PFD in regulations
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Use of Historic Data
Coastal Research Center
The Richard Stockton College of New Jersey
USGS
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Update 540 sq ft with Local Data
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▸1D cross-shore transect model
▸ Models near-shore processes simultaneously
• Sediment transport / erosion
• Wave setup
• Wave transformation and breaking
• Wave runup & overtopping
CSHORE Processes
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CSHORE Erosion
▸ USACE CSHORE model
• Applies real physics
• Near-shore wave processes
• Cross-shore and along shore
sediment transport
• Requires sediment grain size
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USACE CSHORE Model
▸ Applies real physics
▸ Near-shore wave
processes
▸ Cross-shore and along
shore sediment transport
▸ Time series input from
forecasted storm data
▸ Gives storm impacts to:
• Erosion
• Waves
• Runup
• Overtopping rate
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Hurricane Hermine
Hurricanes on the Approach
Hurricane Matthew
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Hurricane Hermine
▸ Landfall as a Category 1 near St. Marks, Florida
• First landfall hurricane since 2005
• Strong storm surge and damaging winds
▸ RFP received 3pm Friday 9/2 (Labor Day)
• Signed NTP by 7pm
Dora 1964
King 19501949
1935
Alma 1966
1941
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▸ Gages
▸ National Hurricane Center – SLOSH
▸ RENCI (Renaissance Computing Institute) – ADCIRC – Surge and Waves
Surge
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Hurricane Hermine
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Hurricane Matthew
Flood Depth Categories:• Affected < 2 feet
• Minor 2 – 5 feet
• Major 5 – 8 feet
• Destroyed > 8 feet
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Coastal Erosion and Overtopping
Sandy2015 & 2016 Winter
Storms
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CSHORE for Forecasting?
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▸ Ability to answer critical EM-related questions:
• How much erosion will occur?
• When will overtopping occur?
• Potential breaching areas?
• When will roads be impassable?
• When do homeowners need to be out?
▸ Potential EM/planning products
• Severity of beach erosion areas
• Potential overtopping and breaching areas
• High Velocity potential
• Wave damage potential areas
• Scenarios with probabilities
CSHORE for Forecasting?
Forecasting
& Analytics
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Questions?
Coastal Storm Erosion