Calculating Erosion Rates: Using Long-Term Data to Increase Data Confidence

See related content

by Mark Crowell, Federal Emergency Management Agency, Washington, United States,
Michael K. Buckley, Federal Emergency Management Agency, Washington, United States,

Document Type: Proceeding Paper

Part of: Coastal Engineering Considerations in Coastal Zone Management

Abstract: Computer cartographic techniques were used to produce historical shoreline change maps for two study areas: (1) an eight kilometer section of Calvert County, Maryland; and (2) an eight kilometer section of Cape May County, New Jersey. The shorelines were digitized from historical Nation Ocean Service (NOS) T-sheets, and historical and current aerial photography. Erosion rates and concomitant uncertainty ranges (i.e., ± erosion rate error bars) were calculated from these data sets using pairs of endpoint shorelines spanning several different time-frames. For each time-frame, the total number of erosion rates falling within the error bars was tallied. The results demonstrate that: (1) the uncertainty range is usually less when calculating erosion rates from long-term (greater than 60 years) endpoint data, than when calculating rates from short- to medium-term (less than 60 years) endpoint data. This is true even though historical (pre-1930) T-sheets may have a greater potential for shoreline location error than do more modern data (such as post-1930 T-sheets and air photos); and (2) the percent of erosion rate data falling within the uncertainty range increases dramatically as time-frames are decreased. In summary, the confidence level of long-term erosion rate data will usually be much greater than the confidence level of short- to medium-term data.

Subject Headings: Erosion | Shoreline | Mapping | Uncertainty principles | Aerial photography | Ocean engineering | Shoals | Confidence intervals | North America | United States | New Jersey | Maryland

Services: Buy this book/Buy this article


Return to search