Connecticut Shoreline Change Analysis
100 Years of Erosion and Accretion
Summaries provided here give a basic overview of the methods used in this project. For a more detailed presentation, please consult the final report.
A variety of datasets were used, but all came from two primary sources: USGS Topographic Quadrangle sheets (Quad Sheets) and NOAA Topographic Survey Sheets (T-Sheets). Both provided digital shoreline data representing various time frames and extents. Shoreline data from the 1880s, 1980s and 2006 were compiled statewide. Shoreline data from the 1900s, 1910s, 1930s, 1940s, 1950s, 1960s, 1970s, 1980s, and 1990s were only available for portions of the state. Since the data came from different sources, it is important to acknowledge these distinctions:
- NOAA T-Sheets: Shorelines are generally defined as Mean High Water (MHW.) On T-sheets from the Atlantic coast this was interpreted by trained topographers using the physical appearance of the beach, usually a line from the preceding high water limit. Map scales were generally 1:10,000 but varied between 1:5,000 and 1:20,000.
- USGS Quad Sheets: Shorelines are best described as the “wet/dry line” or the intersection of land and water as interpreted from the source material – typically aerial photos. Depending on the tide stage when the photography was taken, the wet/dry line and MHW can be expected to differ by varying amounts. Map scales were uniformly 1:24,000
Despite differing source material, USGS recommended that increasing the available amount of data to analyze can outweigh the drawbacks of disparate sources and formats. To help address this, information on data source and vintage is accompanied by a margin of error, effectively a “plus or minus” value that creates a zone along the shore where we can reasonably expect a shoreline might have been.