EM 1110-2-1100 (Part II)
30 Apr 02
(4) The three models discussed below are all steady-state models. Time-dependent, shallow-water models
are available (Jensen et al. 1987; Demirbilek and Webster 1992a, 1992b). They are not discussed here
because they require extensive sets of meteorological data and cannot be easily applied. The basic
characteristics of the three models discussed are as follows:
(a) (RCPWAVE) RCPWAVE is a steady-state, linear-wave model based on the mild-slope equation and
includes wave breaking. It is applicable for open coast areas without structures. It is basically a
monochromatic-wave approach.
(b) (REFDIF1) REFDIF is a steady-state model based on the parabolic approximation solution to the
mild-slope equation. The model includes wave breaking, wave damping, and some nonlinear effects.
Although primarily used as a monochromatic wave model, a spectral version is available. The model can
simulate aspects of propagation associated with simple currents and can include structures.
(c) (STWAVE) STWAVE is a steady-state, linear wave model that computes the evolution of the
directional spectrum over space (Equation II-3-1). The model includes breaking, bottom friction, percolation,
and wind input and solves for the nonlinear transfers of energy within the wave spectrum. It has two modes
for handling diffraction of wave energy and the computational domain may include simple structures. The
models can handle aspects of propagation associated with simple currents.
(5) The three models are theoretically complicated and computationally demanding. All can be
effectively used on a powerful PC-type computer or work station. Each model has considerable strengths and
each can be an appropriate choice for wave transformation. However, none can be considered universally
applicable and the results from all can be inaccurate if the assumptions made in model development are
significantly violated. Users of any of the models must become thoroughly familiar with the model, its
assumptions, and limitations.
b. RCPWAVE.
(1) Introduction.
(a) The RCPWAVE model (Ebersole 1985; Ebersole, Cialone, and Prater 1986) was developed in the
early 1980's as an engineering tool for calculating the properties of waves as they propagate into shallow
water and eventually break. The theoretical basis for the model (linear-wave theory) and the types of
information generated by the model (wave height, period, and direction as a function of location) are
consistent with current theories and equations used by the engineering community to calculate potential
longshore sand-transport rates and shoreline and beach change. The model was designed to operate
efficiently for coastal regions that may be tens of kilometers in length, and to overcome deficiencies of
previously developed refraction models that could be applied on a regional scale. The wave ray refraction
models of Harrison and Wilson (1964), Dobson (1967), Noda et al. (1974), and others "failed" in regions of
strong wave convergence and divergence (i.e., highly irregular bathymetry), leaving users with no wave
solutions and little guidance for interpreting results in these regions. Berkhoff (1972, 1976) derived an
elliptic equation that approximately represented the complete transformation process for linear waves over
arbitrary bathymetry, where the bathymetry was only constrained to have mild slopes. Numerical solution
of this equation requires discretization of the spatial domain and subsequent computations with grid
resolutions that are a fraction of the wave lengths being considered (typically one tenth or smaller). This
requirement limits the utility of the approach for large regions of coastline.
(b) RCPWAVE is based on the mild-slope equation. An assumed form for the velocity potential
associated with only the forward scattered wave field is used with the mild slope equation to develop two
equations, one describing the conservation of wave energy (assuming a constant wave frequency) and the
II-3-20
Estimation of Nearshore Waves
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