boundary was implemented with a land boundary resolution ranging from 1 km
to 7 km depending on location. Along the Atlantic coastline element sizes were
2 km, along the Gulf of Mexico coastline resolution was 2-4 km, with the excep-
tion of 1 km along southern Louisiana, 2-5 km along the northern South
American coastline, and 1-4 km in the Caribbean Sea with the exception of
Haiti/Dominican Republic with 4-7 km. Improved grid resolution also allowed
the inclusion of islands previously neglected in the Eastcoast 1995 grid due to
the relative size of the island to the element size. Many of these islands have
been added in the vicinity of the Bahamas as well as in the Caribbean basin and
will be expected to have a significant impact in directing the path of the tidal
flow through these areas and into the Caribbean Sea and the Gulf of Mexico.
The islands added include Aruba, Curacao, Bonaire, Isla Margarita, Trinidad and
Tobago, St. Vincent and the Grenadines, Saint Lucia, and the Cayman Islands in
the Caribbean; Turks and Caicos Islands in the West Indies; and the Exuma Cays
in the Bahamas.
Grid Development
A systematic methodology to discretize the WNAT domain is necessary to
create a more accurate and computationally efficient mesh. Grid refinement is
desired in four fundamental areas: (a) shallow waters, (b) coastline, (c) conti-
nental slope, especially at the shelf break, and (d) in regions with significant 2-D
response structures (including resonant basins). Fine resolution is necessary in
shallow waters to correctly resolve tidal waves while additional resolution is
necessary near the coastline to represent its changing geometry with sufficient
accuracy. In the deep ocean, since the hydrodynamic response is small and
slowly varying and the wavelengths are large, larger element sizes can be used.
As the waves approach the shelf, the change in bathymetry forces the wave-
lengths to shorten. To accurately capture this effect, a sufficient density of nodes
is required on the continental slope, and especially at the continental shelf break
(Hagen, Westerink, and Kolar 2000; Hagen et al. 2001). In resonant basins, such
as the Gulf of Mexico and the Caribbean Sea, long-term stability problems which
are related to resolution can occur over the course of time, thus requiring addi-
tional resolution in deeper waters within these basins as well (Hagen 1998; Roe
1998).
In the development of the previous Eastcoast 1991 and Eastcoast 1995
databases, a wavelength to grid size ratio (λ/∆x) criterion with a defined mini-
mum and maximum grid size was applied to construct the mesh. Extensive
numerical analysis and experimentation has demonstrated a need for additional
resolution in regions where bathymetric gradients are significant (Hagen,
Westerink, and Kolar 2000; Hagen et al. 2001). This can be easily accomplished
by considering the TLS criterion in combination with the wavelength to grid-size
ratio criterion.
The wavelength to grid-size ratio is a scalar parameter, which serves as a
criterion for one-dimensional, linear, frictionless, constant bathymetry flow and
is defined as:
10
Chapter 3 Eastcoast 2001 Grid Development
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