EM 1110-2-1100 (Part II)
30 Apr 02
grid resolution is sufficiently high. This picture includes the geometry of crests and troughs as well as the
location of regions of high or low wave height resulting from short-crestedness of the wave field. Since
irregular waves in the field usually lead to a fairly smooth spatial variation in wave height estimates (after
statistical averaging), a more stringent test of model accuracy is provided by comparison to laboratory tests
with monochromatic waves. Parabolic models have been tested against data of this type in a number of
studies, including Berkhoff, Booij, and Radder (1982); Tsay and Liu (1982); Kirby and Dalrymple (1984),
Panchang et al. (1990), and Demirbilek (1994). The results showed that the higher-order parabolic
approximation, together with nonlinear correction to the wave phase speed, can correctly predict the
distribution of wave heights and nodal points in the evolving wave field. Figure II-3-10 shows the
bathymetry input to REF/DIF1 for a simulation of wave propagations at Revere Beach, MA. Figure II-3-11
shows the wave heights calculated by the models.
(7) Data requirements for REFDIF.
(a) REF/DIF 1 computes a grid-based wave evolution over an arbitrary bathymetry and current field.
To run the model, the user must provide, at minimum, an array of depth values h on a grid with regular
spacing in x and y. The model always assumes that x is the preferred direction, or the direction in which the
computation marches. No provision is made at present for relating the model coordinate system to a global
coordinate system. If the user wishes to include the effects of tidal currents in the model study, then arrays
of velocity components U and V must also be provided for the same regular grid used to specify h values.
This information establishes the geometry for the model run.
(b) The user must also specify the form of the wave train at the offshore boundary. This may be done
by specifying a combination of one or more monochromatic waves at the offshore boundary, or the offshore
wave field may be specified at the first grid row by means of input data. The user's manual provided in Kirby
and Dalrymple (1992) should be consulted for more details about the input data.
(c) The model provides the user with a grid of computed wave heights and directions on the same
geometric grid used for input. In addition, the complex amplitude values are provided and may be used to
reconstruct plots of the computed wave field, if these are desired and if the grid resolution is fine enough to
permit it. For larger-scaled model areas, this last step is often not feasible, as it requires 5 to 6 grid points per
modeled wave length in the input bathymetry grid. A version of REF/DIF capable of simulating wave spectra
has recently been released.
(a) STWAVE is a steady-state spectral model for predicting wave conditions in coastal areas. It solves
the complete radiative transfer equation (Equation II-3-1) including both propagation effects (refraction,
shoaling, diffraction, and wave-current interactions) and source-term effects (wave breaking, wind inputs,
and nonlinear wave-wave interactions). STWAVE was developed under the premise that waves in nature
should be treated as nonlinearly interacting stochastic wave components rather than as deterministic nonlinear
waves. This is particularly relevant when dealing with wave transformations over distances of hundreds of
thousands of wavelengths (typical of many coastal wave transformation studies). At much shorter distances
a deterministic, long-crested approximation can provide an appropriate framework for understanding and
interpreting wave behavior. At longer distances, theoretical and empirical evidence
Estimation of Nearshore Waves