Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

The Indicator

The condition of the U.S. coastline––whether it is managed or natural, and whether it is eroding, accreting, or stable––has become a matter of great concern. Not only can a wide sandy beach or broad expanse of coastal marshland be aesthetically pleasing, but it can also protect coastal homes from hazards such as storms and high tides. An eroding shoreline can translate into hundreds of million of dollars in damage to coastal property and loss of tourism revenues.

Management responses to erosion are also problematic. Replacing sand (“beach nourishment”) is costly and may have environmental impacts such as disturbance of fish and wildlife habitat and damage to dunes from heavy equipment. Construction of bulkheads and other structures (“armoring”) is generally a longer-term approach, but has very significant effects on fish and wildlife that use the shoreline or beach. Neither nourishment nor armoring necessarily stops erosion; however, armoring typically lasts longer than nourishment.

An accurate assessment of how much of the U.S. shoreline is eroding and how much is accreting or stable is necessary to determine how many coastal homes may be in jeopardy (see The Heinz Center 2000). It will also allow planners and officials to take action to protect existing homes from damage and help them manage future development of the coastal zone. Such assessments are complicated by the fact that erosion is a natural and naturally varying phenomenon. Erosion changes on a seasonal and multiyear basis; there will always be some areas that are eroding and some that are accreting, and these areas will shift over time.

The Data Gap

As discussed in the indicator text, guidelines will be necessary for classifying stretches of coastline as “accreting” or “eroding.” It is thought that the associated change in the horizontal movement of the shoreline will be in the range of one-half to several feet per year. In addition, the coastal management community will need to agree on impact to the shoreline of groins, which are erosion control structures typically built perpendicular to the shoreline. It is not a simple matter, as it would be for bulkheads, to assign a length of shoreline affected by a groin.

Most shoreline erosion and beach nourishment data are developed on a short-term, project-specific basis. Few long-term or regional studies have been carried out, and differences in data collection and analysis protocols make it difficult to compare site-specific reports and compile the data for either regional or national reporting. A study by Dolan et al. (1985) contains a compilation of erosion data from the 1960s, 1970s, and 1980s. This one-time study may be a model for future analyses.

Various methods have been used to determine whether shoreline locations are eroding, accreting, or stable. These include shoreline profiles, National Oceanographic and Atmospheric Administration’s (NOAA) National Ocean Service Topographic Survey Sheets, and aerial photographs, which can be geo-referenced or orthorectified. In addition, Light Detection and Ranging (LIDAR) has been an effective tool for measuring erosion and has been used in at least two different programs. The Airborne LIDAR Assessment of Coastal Erosion (ALACE) project was a partnership between NOAA, the National Aeronautical and Space Administration (NASA), and the U.S. Geological Survey that utilized LIDAR collected via aircraft to map a good portion of the sandy beaches of the lower 48 states; NOAA continues to utilize LIDAR for site-specific analyses of shorelines rather than broad surveys of the U.S. coastline in its Topographic Change Mapping program. (For further information on ALACE or the Topographic Change Mapping program, see http://www.csc.noaa.gov/crs/tcm/.)

Depending on what methods are used, comparison of site-specific reports may or may not provide an accurate regional or national assessment. For example, shoreline profiles may not be dense enough to provide results that can be compared with those of aerial photography. Another consideration in comparing site-specific erosion studies is the time period over which the change in shoreline condition is measured. Reporting on the extent of erosion nationally will require establishing parameters for comparison between various datasets.

Beach nourishment may be undertaken to control erosion, or it may be the by-product of harbor or inlet construction or maintenance, when the excavated material is placed on an adjacent beach. Nourishment that occurs as a by-product is typically not well documented.

References

Dolan, R., F. Anders, and S. Kimball. 1985. Coastal erosion and accretion. National atlas of the United States of America, Department of Interior, U.S. Geological Survey.

The H. John Heinz III Center for Science, Economics and the Environment. 2000. Evaluation of erosion hazards. Washington, DC: The Heinz Center. (available at http://www.heinzctr.org/publications.htm)