Title: Primary Frontal Dune Coastal High Hazard Area Mapping Requirements
Author: Darryl Hatheway
Short Story [for Coastal Beat]:
In the California Coastal Analysis and Mapping Project Open Pacific Coast study area there are
many primary frontal dunes (PFD) which will be included in the Coastal High Hazard Area
(CHHA), also known as a VE Zone on FEMA flood maps. Although this is not a new FEMA
hazard zone designation, these areas have not previously been incorporated within FEMA coastal
flood studies in California. The mapping criteria for these zones was adopted by FEMA in 1988,
after most California coastal flood studies were last updated. This VE Zone criteria and mapping
requirement will only influence the hazard zone mapping in coastal areas with PFDs. –Continue
Reading-Long Story [to be posted on the website]:
In the California Coastal Analysis and Mapping Project Open Pacific Coast study area there are
many Primary Frontal Dunes (PFD) which will be included in the Coastal High Hazard Area
(CHHA), also known as a VE Zone on FEMA flood maps. Although this is not a new FEMA
hazard zone designation, these areas have not previously been incorporated within FEMA coastal
flood studies in California. The mapping criteria for these zones was adopted by FEMA in 1988,
after most California coastal flood studies were last updated.
Prior to 1988, coastal dunes and especially the PFD were typically mapped outside of any
regulatory flood hazard zone. Figure 1 illustrates the coastal flood hazard zones prior to the 1988
PFD requirement. The VE and AE Zone limits were a function of the calculated wave height or
wave run-up above the 100-year stillwater elevation (SWEL). The remainder of the dune ridge
would typically be mapped outside the special flood hazard area. This increased the vulnerability
of these critical natural resources and allowed new structures to be constructed on the dunes
without specific building standards or consideration of the risk of potential erosion and
overtopping.
REGULATED PRIO RTO 1988
X Zone
AE Zone
VE Zone
Wave Crest Profile
100-year SWEL
Mean sea level
Figure 1. Illustration of coastal flood hazard zones prior to the 1988 PFD requirement.
Because the PFD is a natural frontline defense during coastal flood events, FEMA identified a
need to establish definitive guidance for dune erosion and protection. In May 1988, FEMA
adopted new regulations and VE Zone mapping requirements for the PFD that consider wave
action and erosion processes. The National Flood Insurance Program (NFIP) regulations were
revised to define the PFD and the requirement to map it within the CHHA. This revision
redefined the CHHA to include the PFD to a specific landward limit.
The PFD is defined as “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.” Therefore,
the PFD is now included in the CHHA by administrative definition and the CHHA is defined as
“an area of special flood hazard extending from offshore to the inland limit of the primary frontal
dune along an open coast and any other area subject to high velocity wave action from storms or
seismic sources.” Figure 2 shows typical zone designations following the May 1988 regulation
changes and inclusion of the PFD as part of the VE Zone hazard mapping criteria. Under the
PFD criteria, the mapped VE Zone is extended inland based on definitions of the PFD and not on
detailed wave calculations or modeling results.
REGULATED SINCE 1988
X Zone
VE Zone
Wave Crest Profile
Landward limit of storminduced erosion
100-year SWEL
Mean sea level
Landward
toe of dune
540 ft2
eroded
PFD Area VE Zone
Erosion VE Zone
Figure 2. Illustration of coastal flood hazard zones after the 1988 PFD requirement was adopted.
While the NFIP regulations provide a definition of the PFD, identification in the field is not
always easy. Dunes are often irregular features that may not be homogeneous. The figure below
shows an example of an area with a PFD in Santa Cruz County near the Pajaro Dunes
development. More details on PFD identification and mapping requirements can be found in the
Guidelines for Coastal Flood Hazard Analysis and Mapping for the Pacific Coast of the United
States, available on FEMA’s website.