1
Introduction
Background
An important component of most coastal and ocean engineering projects is
an accurate assessment of the wave climate at the project site. Typical applica-
tions include determination of siltation rates inside entrance channels and harbor
basins, determination of safe conditions for the loading/offloading of ships, opti-
mization of harbor layouts for both wind-generated and long-period infragravity
waves, design of structures such as breakwaters, and the evaluation of the impact
of coastal structures on adjacent shorelines. Nearshore wave conditions are norm-
ally determined from deepwater conditions because long-term wave data are
usually unavailable for most project sites. These offshore wave characteristics
have to be transformed to the project site taking into account the effects of wind-
wave generation, shoaling/refraction over seabed topography, energy dissipation
due to wave breaking and bottom friction, wave reflection/diffraction near struc-
tures, nonlinear wave-wave interactions, and wave interaction with current fields.
A number of mathematical models have been developed to simulate the prop-
agation and transformation of waves in coastal regions and harbors. The different
models are based on different assumptions, which limit the types of problems to
which they can be applied. Examples include spectral wind-wave models for
wave propagation in open water where the processes of wind input, shoaling, and
refraction are dominant; parabolic mild-slope equation models for wave propaga-
tion over large coastal areas when reflection is negligible; Helmholtz equation
ing depth; and Boussinesq models for nonlinear wave refraction-diffraction in
shallow water.
Numerical models available at the U.S. Army Corps of Engineers for pre-
dicting wave conditions in coastal regions and harbors include the spectral wind-
wave model STWAVE (Smith, Sherlock, and Resio 2001) and the elliptic mild-
slope model CGWAVE (Demirbilek and Panchang 1998). STWAVE is a wind-
wave propagation model based on the wave action conservation equation. It is a
phase-averaged model, i.e., it assumes that phase-averaged wave properties vary
slowly over distances of the order of a wavelength. This allows the efficient com-
putation of wave propagation over large open coastal areas. Due to the phase-
averaging procedure, STWAVE cannot accurately resolve rapid variations that
occur at subwavelength scales due to wave reflection/diffraction.
1
Chapter 1 Introduction
Previous Page
