Limit of Moderate Wave Action (LiMWA)

Effects on Floodplain Management

RECAP

COASTAL MAPPING METHODOLOGY

Effects on Property Owners

Why LiMWA?

7. FIRM Production

2. Hazard-Induced Water Level Analysis

1. Defining Base Topography

6. Coastal Flood Hazard Mapping

4. Storm-Induced Erosion

3. Define Cross-Shore Transects

5. Overland Wave Modeling including Wave Runup and Overtopping

High storm surge and wave runup during Hurricane Isabel caused widespread

Topography and Bathymetry Data Image of Nantucket Island, Massachusetts,Credit: National Geophysical Data Center, NOAA

The analysis may include mean sea level, the astronomic tide, wave setup, and storm surge

FEMA uses the Primary Frontal Dune (PFD) designation to determine coastal flood zones

-Structural fill should not be used in Coastal A Zone. Should be built with pilings or column foundations.

-ASCE 24-14 DFE applies

-Communities that adopt VE standards in the Coastal A Zone and reference the LiMWA area receive CRS credits under activity 430 High Regulatory Stds

-Encourage to build safer and higher to minimize the risk to life and property

-NFIP premiums currently do not account for a building's location relative to the LiMWA.

Post-Storms field visit and laboratory tests have confirmed that the wave height as small as 1.5 ft can cause significant damage to structures constructed without considering coastal hazards

-FEMA PM-50

Flood Time!

What is LiMWA?

FEMA PM 50 (2008)

-Defines LiMWA as Informational Layer (non-mandatory).

-Coastal A Zone (CAZ) flood hazards associated with waves and debris that can erode and scour building foundations

LiMWA is Limit of Moderate Wave Action or Landward limit of waves 1.5 feet in height.

FEMA Procedure Memorandum No. 50 – Policy and Procedures for Identifying and Mapping Areas Subject to Wave Heights

Greater than 1.5 feet as an Informational Layer on Flood Insurance Rate Maps (FIRMs)

LiMWA

Limit of Moderate Wave Action (LiMWA)

-LiMWA is getting increased visibility from the States and the communities that are utilizing LiMWA as a regulatory tool in floodplain management.

-LiMWA is tied closely to the definition of Coastal A Zone in the Building Codes.

-FEMA is the only agency to have guidance on defining, mapping and officiating the LiMWA

By Howard Critchfield, Floodplain Coordinator

Bi-Monthly FPM Staff Meeting