Tung et al., 2000). A number of reports have since recommended applying V-zone construction standards to the coastal A zone, defined as subject to breaking waves between 1.5 and 3 feet (ASCE, 2005a, 2005b; FEMA, 2005a, 2006c, 2006d; Wetmore et al., 2006).

The insurance losses in the coastal A zone following Hurricane Opal and recommendations to apply V zone construction standards suggest that the current zone boundaries do not adequately capture true coastal flood risk. Possible solutions include the following:

  1. Lower the V zone boundary definition to a 1.5-foot breaking wave, which would expand V zone insurance rates and construction standards across the coastal A zone.

  2. Retain the breaking wave threshold of 3 feet in the V zone and formally define the coastal A zone as areas subject to breaking waves between 1.5 and 3 feet.

FEMA is exploring both options. The first maps to include the extent of 1.5-foot waves were released in preliminary form for three coastal Mississippi counties in 2007. The boundary, called the “limit of moderate wave action delineation,” is not labeled a zone because it has no regulatory or insurance function, but simply provides guidance for reconstruction. Although this approach improves the portrayal of flood hazard in coastal A zones, it would not change construction standards and thus would not lower the risk of damage.


Recommendation. FEMA should redefine the V zone boundary based on a 1.5-foot breaking wave rather than the present 3-foot wave.

Coastal E Zone

The National Flood Insurance Program has the authority to identify erosion (E) zones in coastal and riverine environments but has not acted on it. A 1990 National Research Council (NRC) report recommended mapping coastal E zones to more accurately reflect the hazards of storm-induced and long-term erosion (NRC, 1990). Following debate in the House and Senate in 1994, Congress declined to approve FEMA erosion mapping and directed FEMA to study the coastal erosion problem.2 In 2000, the Heinz Center recommended that “Congress should instruct the Federal Emergency Management Agency to develop erosion hazard maps that display the location and extent of coastal areas subject to erosion” (Heinz Center, 2000). To date, Congress has taken no action on this recommendation and FEMA has not moved on its own.

A coastal E zone would be a special area within the V zone, and its seaward side would define the area where significant flood-related and long-term beach and dune erosion is expected to occur. This area is partially identified in the course of FEMA’s modeling procedures but is not currently drawn on the resulting coastal flood maps. Long-term erosion is measured by state or federal government agencies, but is not factored into flood maps, even when erosion rates are high compared to the lifetime of buildings. For example, the average rate of oceanfront erosion in North Carolina has been about 2 to 3 feet per year over the last 50 years.3

Flood-related and long-term erosion increases wave heights, so buildings in erosion zones need deeper and higher foundations than buildings outside erosion zones. However, current standards call for foundations to extend to a minimum depth of –10 feet orth American Vertical Datum 1988 (NAVD 88) for the entire V zone (ASCE, 2005b). As a result, foundations may be overdesigned (and more costly than necessary) in areas of low erosion and potentially underdesigned in areas of high erosion. This problem is likely to become more acute with climate change, which is expected to lead to sea level rise and more frequent or intense storms and thus to increase coastal erosion (IPCC, 2007). Similarly, insurance premiums are uniform throughout the V zone, but studies have shown that flood damage is greater in areas subject to both erosion and waves than areas further inland that are subject to waves alone (Rogers, 1990; USACE, 2005). Mapping an E zone could yield more actuarially realistic flood

2

Congressional Record, National Flood Insurance Reform Act of 1994, House of Representatives, May 3, 1994; Congressional Record, Community Development Banking and Financial Institutions Act of 1993, Senate, March 17, 1994.

3

Based on data from <http://dcm2.enr.state.nc.us/Maps/ER_1998/SB_Factor.htm>.



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