Communicating Moderate Wave Risk on Flood Insurance Rate Maps

Communicating Moderate Wave Risk on Flood Insurance Rate MapsConcurrent Session B8 Coastal Studies, LL2: Hanover F

June 2, 2015

Alex Sirotek, GISP, CFM

Communicating Moderate Wave Risk on FIRMs

LiMWA – Limit of Moderate Wave Action

• Moderate wave action = 1.5 – 3.0 foot waves• What’s important is the coastal AE zone

with waves behind the LiMWA– often known as the Coastal A Zone (CAZ)

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*From FEMA’s “Limit of Moderate Wave Action (LiMWA) Fact Sheet”


Brief History of the LiMWA and Coastal A Zone

• American Society of Civil Engineers (ASCE) have been using the “Coastal A Zone” since 1998– Minimum Design Loads for Buildings and Other Structures

(ASCE 7, 1998)

• FEMA’s Coastal Construction Manual has referred to the Coastal A Zone since 2000

• By around 2005, most sources started agreeing on a 1.5 foot wave height as the limit of this Coastal A Zone– This 1.5 foot boundary became the LiMWA

• Since 2006, the International Building Code (IBC) has required construction in the CAZ to meet VE standards

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Coastal A Zone, MoWA, LiMWA

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*From the May 2011 “Primary Frontal Dune VE Zone Study and Coastal Special Flood Hazard Area Study” prepared by AECOM in association with Christopher P. Jones, P.E., Deloitte Consulting, LLP, and Michael Baker Jr., Inc.


Coastal A Zone, MoWA, LiMWA

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• Table 5-2 of FEMA’s Coastal Construction Manual contains an exhaustive cross reference of all applicable standards


History of the LiMWA

• The LiMWA was first implemented by FEMA in Procedure Memorandum 50 – December 3, 2008

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LiMWA on Map Mod DFIRM

• Originally a dotted and dashed line

• Generally shown within the static AE zone

• “Coastal A Zone” is the area between the LiMWA and the VE zone

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• LiMWA symbology varies in practice, as it can overlap zone breaks

• It can be difficult to determine whichside of the LiMWA has 1.5 - 3 foot waves

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• The yellow highlighted areas indicates the Coastal A Zones

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Updates to LiMWA Symbology

• Updates to guidance suggest using a line with arrows to indicate the direction of the 1.5 – 3 foot wave area

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*From FEMA’s “Limit of Moderate Wave Action (LiMWA) Fact Sheet”


Updates to LiMWA Symbology

• The arrows can work well on a static FIRM, but symbology is dependent on the direction of the line

• If the data doesn’t contain the direction, they can appear random (like here)

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RiskMAP LiMWA Symbology

• Standard RiskMAP format is a black and red dotted line

• Arrows can still be used• Can obscure zone breaks

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RiskMAP LiMWA Symbology

• Region 1 has been using a slightly altered version

• Hollow LiMWA line so that the underlying zone or zone break can be seen

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Supplemental LiMWA Information

• More and more states and communities are adopting the Coastal A Zone or LiMWA as a regulatory standard

• In Region I, non-regulatory products have been created by FEMA and states to show the LiMWA and coastal A zone more clearly

• These can be shown in supplemental products and GIS layers, are not shownon the FIRM itself

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LiMWA/CAZ as an Informational Layer

• One solution would be to show the Coastal A Zone as an informational layer

• Drawback is that panels can begin to get quite busy

• Shown here with a Coastal Barrier Resources System informational layer

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LiMWAs – Stuck in the Middle

• Operating Guidance No. 14-13 (October 30, 2013)– PM 50 didn’t outline how to appeal or change LiMWA– LiMWA not technically appealable, as it is an informational layer– Changes to the LiMWA can be handled by a

Notice to User update• However, as it is directly tied to the coastal modeling,

a LOMR would likely be required

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What is simpler than a LiMWA?

• The concept of LiMWA/CAZ would be easier to explain as a zone than a boundary

• Replace the AE seaward of the LiMWA with the “AV” zone

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AV

* From FEMA’s “Limit of Moderate Wave Action (LiMWA) Fact Sheet”


“AV” Zone

• AV was chosen as it is an AE zone with VE qualities

• From a FEMA and mapping perspective, Coastal A Zone is confusing as it indicates an “approximate” study

• Coastal A Zone hasvarying definitions

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“AV” Zone Symbolized

• Clearly shows areas with wave action in a different color

• VE zones are solid purple• AV zones are purple and

blue stripes, indicating half-way betweenAE and VE

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Why a new zone?

• The “AV” zone could be treated exactly as an AE by FEMA• However, makes it much simpler for communities to adopt

the moderate wave action areas as a regulatory standard– No need to interpret what is and what isn’t a CAZ, or create

supplemental polygons

• Makes it much easier to query information and produce reports on moderate wave areas– Housing stock affected by moderate waves– Population affected by moderate waves

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Next steps…

• Get everyone to agree on terminology…

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*From the May 2011 “Primary Frontal Dune VE Zone Study and Coastal Special Flood Hazard Area Study” prepared by AECOM in association with Christopher P. Jones, P.E., Deloitte Consulting, LLP, and Michael Baker Jr., Inc.


Questions?

Alex Sirotek, GISP, [email protected]

6/2/1522

Government & Nonprofit

Communicating Moderate Wave Risk on Flood Insurance Rate Maps