6
Discussion and
Conclusions
The Eastcoast 2001 is the new and improved tidal database for the WNAT
data throughout the domain. Computed harmonic constituents compare to
measured amplitude data to within 6 to 13 percent and to measured phase data to
within 7 to 13 deg on a globally averaged basis. In general, comparisons to
measured data are the best in the Atlantic Ocean and the worst in the Caribbean
Sea. This is not entirely surprising since the bathymetric data is least accurate in
the Caribbean Basin, particularly on the continental shelves and near the Lesser
Antilles Ridge, which controls the Atlantic-Caribbean coupling. In general, the
dominant tidal constituent in a given basin is the most accurately modeled
constituent. Thus, on average the M2, N2, and S2 constituents compare to
measured amplitude data to within 6 to 7 percent and to measured phase data to
within 4 to 8 deg in the Atlantic. The K1 and O1 constituents on average compare
to measured amplitude data to within 10 to 11 percent and measured phase data
to within 6 to 9 deg in the Gulf of Mexico. Considering potential measurement
data error estimates puts the computed to measured data agreement into perspec-
tive. Typically, measured data error estimates are half of the computed to
measured data errors. Since the computed to measured data errors include the
uncertainty in the measured data, it is clear that a substantial portion of the
reported computed to measured data errors originate from the errors in the
measured data.
Improvements made to the Eastcoast 2001 tidal database stem from a highly
detailed grid, updating the coastline boundary with greater detail and precision
and applying an improved bathymetric database. The Eastcoast 2001 database
computations applied a 254,629-node grid based on a combination of the widely
used wavelength to grid-size ratio and the topographic length scale criteria.
Together these criteria produced a state-of-the-art grid to accurately capture the
change in the wavelength's energy as it travels from the deep ocean over the
shelf break onto the continental shelf and to the shore. Maximum grid resolution
was defined as 25 km, and minimum resolution was defined as 1 to 4 km.
Although it appears that elements in deep waters can be larger than 25 km from
an accuracy perspective, potential long-term stability problems led to the use of
this level resolution in all deeper waters.
The coastline boundaries were updated with the World Vector Shoreline
database. Significant islands could be added in the Bahamas as well as in the
21
Chapter 6 Discussion and Conclusions