application, in meters. Water depths are defined as positive numbers and land
elevations are negative numbers. The depths are read with a free format. The
file begins with the depth at cell (1, NJ) and reads in the cross-shore direction
(I = 1 to NI). The read is repeated for J = NJ-1 (I = 1 to NI), and progresses to
J = 1. The default name for the bathymetry file is dep.in. In SMS, the file is
specified as project.dep. A sample bathymetry file is given in Appendix B.
The sample grid has 188 cells in the cross-shore direction and 236 cells in the
alongshore direction. The grid spacing is 25 m.
Incident Wave Spectra
Incident two-dimensional wave spectra are specified as energy density as a
function of frequency and direction. A single input spectrum is applied along the
entire offshore boundary of the STWAVE grid (the spectrum is set to zero for
any land points along the boundary). Thus, it is good practice to establish the
offshore boundary of the bathymetry grid along a depth contour where the wave
spectrum is fairly homogeneous (no large shoals or canyons offshore of the
boundary). The first line of the input spectra file describes the number of
frequency and direction bins in the spectra (read in free format):
NF = Number of frequency bins in the spectra. The number of frequency
bins determines how finely the calculated spectra are resolved. A large number
of frequency bins increases the computation time, and a small number of bins
reduces model resolution. Typically, 20-30 bins are used.
NA = Number of direction bins in the spectra. This value must be set to 35,
which gives 5-deg resolution in direction.
The next lines of the incident wave spectra file specify the frequencies for
model spectra (used for the input spectra, internal computations, and output
spectra), starting from the lowest frequency. There must be NF frequencies
specified. The frequencies are again read in free format and may occupy as
many lines as needed. These frequencies should span the frequency range where
significant wave energy is contained in the spectrum. This can be estimated by
inspecting the input spectrum or estimating the peak period expected using the
wave growth curves in the Coastal Engineering Manual (in preparation). A rule
of thumb is that the spectral peak should fall at about the lower one-third of the
frequency range (e.g., if the peak frequency is 0.1 Hz, the range may be 0.01 to
0.3 Hz). Wave frequencies higher (or periods shorter) than the highest frequency
bin or lower than the lowest frequency bin will not be resolved by the model.
Typically, frequency increments are on the order of 0.01 Hz, but the increment
need not be constant. West Coast applications will tend to require finer
resolution focused at lower frequencies (because of long wave periods), and Gulf
Coast or Great Lakes applications will tend to require coarser resolution covering
a broader range of frequencies (because of shorter wave periods).
Following specification of the frequency bins is a header line containing a
spectrum identifier, wind information, peak frequency, and water elevation
correction:
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Chapter 3 Input File Description
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