Abstract
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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