Reports
Calvert County shore erosion rate verification
2009, Hennessee, E.L.
File Reports, Coastal and Estuarine Geology, File Report 2009-02
Abstract
The Calvert County Department ofPlanl1ing and Zoning is in a quandary as to which of two studies to rely on in making decisions about its coastal zone - one study by a graduate student at the University of Maryland and the other by the Maryland Geological Survey (MGS). To help resolve the problem, MGS compared the results of the two studies for two areas in Calvert County, Randle Cliff and Little Cove Point. MGS also compared a subset of its original digital shorelines for the county with either (a) shorelines derived from the same sources (T-sheets) but digitized by the National Oceanic and Atmospheric Administration (NOAA) or (b) shorelines digitized directly by MGS from original T -sheets, as opposed to derivative maps compiled from those originals.
MGS traced the inconsistencies between the two studies to two shortcomings in its own digital shoreline data set: (1) for the earliest shoreline, dating from the mid-ISOOs, the Survey chose to digitize, not the original T-sheets, but maps derived from them and (2) for the most recent shoreline, MGS chose to interpret the land/water interface from nontide- coordinated orthophotography - a different shoreline change reference feature than the (mean) high water line mapped on T -sheets. Based on this study, the combined effect of those two problems was to minimize shoreline displacement and, consequently, rates of shoreline change.
MGS strongly recommends that as soon as NOAA completes digitizing the historical Tsheets and the ca. 200S shoreline for the county, shoreline rates of change be recomputed. The digital shorelines will represent a consistent shoreline change reference feature, and the most recent shoreline will be based on tide-coordinated photography. Short of recompiling shorelines and recalculating rates of change, MGS recommends that Calvert County continue to use Downs's results, despite the fact that her report is based on shoreline positions that are now 40 years out of date.
