This layer is one of the South Atlantic LCC indicators in the beach and dune ecosystem. It is an index of altered beaches capturing impacts from hardened structures like jetties, groins, and infrastructure.
Reason for Selection
Altered beaches (including human developments along shorelines, jetties, groins, seawalls, revetments, and other structures) provide a measure of overall habitat alteration. Human infrastructure along shorelines generally stabilizes barrier islands, and thereby impedes beach migration and barrier island rollover processes. Additionally, seawalls are difficult to locate on aerial photography, and developed shorelines may act as a surrogate for unmapped shoreline armoring.
Groins, seawalls, jetties, and revetments have resulted in narrowing of beaches, or greater beach loss, compared to unstructured beaches (Dugan et al. 2008, Hall and Pilkey 1991, Mohanty et al. 2012, Pilkey and Wright III 1988). Jetties alter sand transport and may result in downdrift erosion, although effects are dependent on the context of the structure (Bruun 1995). Bruun (1995) showed examples ranging from 5-13 km.
-- Hard structures were digitally mapped with guidance from recent ocean shoreline evaluations (Rice 2012a,b). Shoreline parallel structures (e.g., revetments) were mapped by length and perpendicular structures (e.g., jetties, groins) were mapped as points. Overall, shoreline parallel structures totaled 22.3 km, and 148 perpendicular structures were mapped.
-- Spatial designations of the Coastal Barrier Resources System, as a result of the Coastal Barrier Resources Act (1982) and its update (1990), were used to set boundaries of undeveloped beaches (U.S. Fish and Wildlife Service 2016-03-14, accessed December 6, 2016). The Act designated relatively undeveloped barrier island segments as ineligible for Federal expenditures, such as Federal flood insurance.
Indicators that have not changed since Blueprint 2.0 were initially computed, or in the case of existing data, resampled to 1 ha spatial resolution using the nearest neighbor method. For computational reasons, we then used the Spatial Analyst-Aggregate function to rescale the resolution to 200 m. The aggregate function avoided loss of detail by taking the maximum value of each cell in the conversion (e.g., species presence).
1) Beaches outside of the Coastal Barrier Resources System were considered vulnerable to alteration.
2) We buffered perpendicular structures by 5 km and considered shoreline within this radius altered.
3) All beaches outward from parallel structures were considered altered.
Data were reclassified into the following rankings:
0 = Low (vulnerable to alteration, with/without nearby jetties/groins)
1 = Medium (less vulnerable with nearby jetties/groins)
2 = High (less vulnerable without nearby jetties/groins)
Defining the Spatial Extent of Ecosystems
This indicator has been clipped to the beach and dune ecosystem. Visit the Blueprint 2.1 ecosystem maps for an explanation of how each ecosystem’s spatial extent is defined.
-- The effect of perpendicular structures (e.g., groins, jetties) on beaches is not straightforward. We used a 5 km radius around these structures to consider beaches altered, but the effect on beaches may be directional and may be lesser or much greater than the 5 km radius we selected.
-- Data were digitized from known sources, but should be considered a minimum amount of hard structures in the region. Further mapping and checking for known structures is warranted.
-- We have considered all beaches outside of the Coastal Barrier Resources System to be altered by human development, which may not necessarily be true.
-- Changes to the designations continue annually, including further additions to the system. The Coastal Barrier Resources System dataset used in this indicator is from 2016.
-- Beach renourishment negatively affects some beach and dune species, and is not captured by this indicator.
Coastal Barrier Resources System (CBRS) digital boundaries in this mapper are only representations of the official CBRS boundaries and are not to be considered authoritative. In general, these digital boundaries can be considered accurate to within approximately 150 ft of the actual CBRS boundaries as shown on the official maps. Additionally, because CBRS units extend seaward out to either the 20- or 30-ft bathymetric contour (depending on the location of the unit), the true seaward extent of the units is not shown in this mapper. The Service is not responsible for any misuse or misinterpretation of this digital data set, including use of the data to determine eligibility for Federal financial assistance such as Federal flood insurance. Click here for information on obtaining an official determination of whether or not an area or specific property is located within the CBRS. Visit this link for information on project consultations. For information on the horizontal accuracy of this digital data set, please read the metadata.
Disclaimer: Comparing with Older Indicator Versions
While this indicator has changed since the version of unaltered beach used in Blueprint 2.0, this only reflects differences in the way it was calculated and should not be compared to measure change over time.
The South Atlantic ecosystem indicators serve as the South Atlantic LCC's metrics of success and drive the identification of priority areas for shared action in the Conservation Blueprint. To learn more about the indicators and how they are being used, please visit the indicator page. Check out the Blueprint page for more information on the development of the Blueprint, a living spatial plan to conserve our natural and cultural resources.
Bruun, P., 1995. The development of downdrift erosion. J. Coast. Res., 1242-1257.
Dugan, J.E., Hubbard, D.M., Rodil, I.F., Revell, D.L., Schroeter, S., 2008. Ecological effects of coastal armoring on sandy beaches. Marine Ecology 29, 160-170.
Hall, M.J., Pilkey, O.H., 1991. Effects of hard stabilization on dry beach width for New Jersey. J. Coast. Res., 771-785.
Mohanty, P.K., Patra, S.K., Bramha, S., Seth, B., Pradhan, U., Behera, B., Mishra, P., Panda, U.S., 2012. Impact of groins on beach morphology: a case study near Gopalpur Port, east coast of India. J. Coast. Res. 28, 132-142.
Pilkey, O.H., Wright III, H.L., 1988. Seawalls versus beaches. J. Coast. Res., 41-64.
Rice, T.M., 2012a. Inventory of Habitat Modifications to Tidal Inlets in the Continental U.S. Coastal Migration and Wintering Range of the Piping Plover (Charadrius melodus). Appendix 1b, in Comprehensive Conservation Strategy for the Piping Plover (Charadrius melodus) in its Coastal Migration and Wintering Range in the Continental United States. U.S. Fish and Wildlife Service, East Lansing, Michigan.
Rice, T.M., 2012b. The Status of Sandy, Oceanfront Beach Habitat in the Continental U.S. Coastal Migration and Wintering Range of the Piping Plover (Charadrius melodus), Appendix 1c in Comprehensive Conservation Strategy for the Piping Plover (Charadrius melodus) in its Coastal Migration and Wintering Range in the Continental United States. U.S. Fish and Wildlife Service, East Lansing, Michigan
U.S. Fish and Wildlife Service. March 2016. John H. Chafee Coastal Barrier Resources System Approximate Polygons Vector Digital Data Set. Falls Church, VA. < https://www.fws.gov/ecological-services/habitat-conservation/cbra/Maps/Boundaries.html>. (December 6, 2016).