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USGS Open-File Report 2005-1027, An Operational Mean High Water Datum for Determination of Shoreline Position from Topographic Lidar Data

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Data Sets & Methods


The National Assessment of Coastal Change Hazards Project of the U.S. Geological Survey, Coastal and Marine Geology Program, is using lidar mapping technology to determine shoreline position for the Nation's open ocean coasts with sandy beaches. The lidar mapping provides elevations relative to the NAVD88 fixed vertical datum. The shorelines determined from lidar-derived beach profiles are defined as an operational Mean High Water (MHW) contour, and therefore the elevation of the MHW tidal datum must be known relative to NAVD 88. The elevation of the MHW tidal datum varies relative to NAVD 88 along the coast as a function of the local tide range and mean tide level. National Oceanic and Atmospheric Administration (NOAA) tide station data were studied and compiled to tabulate MHW, Mean Higher High Water, and Mean Tide Level elevations along the East, West, and Gulf Coasts. In all, 136 tide stations were chosen: 93 along the East Coast, 19 along the West Coast, and 24 along the Gulf Coast. Although open coast tide stations were preferable for determining MHW, some stations that were not fully on the open coast were used to fill gaps where few or no open coast stations were available. The East, Gulf, and West coastlines were divided into "MHW Zones". These zones are sections of coast to which one MHW elevation is assigned. This operational MHW elevation, which is the average of MHW from all tide stations in the zone, is the elevation used for all lidar shorelines derived within that zone. Twenty-seven zones were created in all: twenty on the East Coast, three on the Gulf Coast, and four on the West Coast.

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