The shoreline essentially follows the 8 foot contour line, except where the
ortho offered further clarification. That 8 foot contour line matches closest
to what NAVD88 shows as "mean high water" (see official definition
below) at 7.97 feet. MEAN HIGH WATER (MHW): "A tidal datum. The average of
all the high water heights observed over the National Tidal Datum Epoch. For
stations with shorter series, simultaneous observational comparisons are made
with a control tide station in order to derive the equivalent datum of the
National Tidal Datum Epoch." Source "The MHW line along the tidal shoreline is represented by the contour line
that is 8.0' above the NAVD 88. The MHW elevation is not necessarily an
equipotential (level) surface, but the variation from a level surface is not
significant for this project. The determination of MHW is based on 18 yrs of
tidal data and represents the latest official National Tidal Epoch of
1960-1978. The Seattle Tide Station (Sta No 944-7130) is located at the
downtown ferry terminal." Source: From paper by Nick Bodnar 10/18/1993
Some other definitions regarding these shorelines (from Nick Bodnar,
10/18/1993): LAKES UNION AND WASHINGTON SHORELINE (18.6' above NAVD 88) The
approximation of "ordinary high water"; the level of Lk Washington
varies from 17.0'-18.6' during the year; the max lake elevation is 18.8' as
controlled by Corps of Engineers (COE) at Hiram Chittenden Locks. The NAVD 88
lake elevations have been converted from the U.S. Engineers Datum. This zero of
NAVD 88 is 3.25' above the Locks Datum at the common bench mark P-7. The
shoreline contour of 18.8' above NAVD 88 should be used from the Locks,
upstream through Lk Union and Lk Washington. The COE has performed various
studies that show the level of Lk Wash to approximate an equipotential surface
that can be represented by a single contour elevation for mapping purposes.
OTHER LAKES The shoreline around Green Lake and all other lakes are delimited
by the water/land interface as seen on the aerial photography.
Displays data from CARTO.SHORE_LNUpdated as needed.