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Tidal Datums, Tidal Range, and Nuisance Flooding Levels for Chesapeake Bay and Delaware Bay

November 15, 2021

This U.S. Geological Survey data release provides data on spatial variations in tidal datums, tidal range, and nuisance flooding in Chesapeake Bay and Delaware Bay. Tidal datums are standard elevations that are defined based on average tidal water levels. Datums are used as references to measure local water levels and to delineate regions in coastal environments. Nuisance flooding refers to the sporadic inundation of low-lying coastal areas by the maximum tidal water levels during spring tides, especially perigean spring tides (also known as king tides). Nuisance flooding is independent of storm event flooding, and it represents a cumulative or chronic hazard. The data were obtained by following a consistent methodology and at sufficient spatial resolution to resolve the distinct and complex features of each bay system. Tidal water levels were simulated by using the ADCIRC model system for the entire 2016 year. The year 2016 was chosen because it corresponded with the maximum magnitude of the combined 18.6-year and 4.4-year tidal modulations. The estuarine and bay areas were resolved with horizontal resolutions on the order of tens to hundreds of meters. The ADCIRC simulations provide time series of water levels at each computational point of an unstructured grid that covers the entire area of interest—from the open ocean to overland areas up to approximately 15 meters above the North American Vertical Datum of 1988. The water-level time series were analyzed to provide estimates of tidal range (great diurnal range and mean range of tide), tidal datums (mean high water, mean higher high water, mean low water, and mean lower low water), and nuisance flooding (highest astronomical tide and monthly mean high water). The resulting data are provided at all points of the computational grid for Chesapeake and Delaware Bays and the surrounding coastal area.