ERDC/CHL CHETN-I-64
September 2001
drive sediment transport and nearshore currents, induce wave setup and runup, excite harbor
oscillations, influence navigation, and impact coastal structures. The longshore and cross-shore
gradients in wave height and direction are often as important as the magnitude of these
parameters for sediment transport and nearshore current studies. Present field measurement
technology cannot provide such high-resolution nearshore fields of wave parameters. STWAVE
simulates depth-induced wave refraction and shoaling, current-induced refraction and shoaling,
depth- and steepness-induced wave breaking, wind-wave growth, and wave-wave interaction and
whitecapping that redistribute and dissipate energy in a growing wave field.
Model Assumptions: The assumptions made in STWAVE are as follows:
meaning that wave energy can propagate only from the offshore toward the nearshore
(87.5 deg from the x-axis of the grid, which is the approximate shore-normal direction).
Waves reflected from the shoreline or from steep bottom features travel in directions
outside this half plane and thus are neglected. Forward-scattered waves, e.g., waves
reflected off a structure but traveling in the +x direction, are also neglected.
b. Spatially-homogeneous offshore wave conditions. The spatial variation in the wave
spectrum along the offshore boundary of a modeling domain is rarely known, and for
domains on the order of tens of miles, is expected to be small. Thus, the input spectrum
in STWAVE is constant along the offshore boundary.
model. A steady-state formulation reduces computation time and is appropriate for wave
conditions that vary more slowly than the time it takes for waves to transit the
computational grid. For wave generation, the steady-state assumption means that the
winds have remained steady sufficiently long for the waves to attain fetch-limited or fully
developed conditions (waves are not limited by the duration of the winds). Winds are
assumed uniform over the model domain.
shoaling, thus does not represent wave asymmetry. Model accuracy is therefore reduced
(wave heights are underestimated) for large wave heights in shallow water (large Ursell
numbers).
e. Depth-uniform current. The wave-current interaction in the model is based on the
assumption that current is constant through the water column. If strong vertical gradients
in current occur, their modification of refraction and shoaling is not represented in the
model. For most applications, three-dimensional current fields are not available.
been a topic of debate in wave modeling literature. Bottom friction has often been
applied as a tuning coefficient to bring model results into alignment with measurements.
Although bottom friction is easy to apply in a wave model, determining the proper
friction coefficients is difficult. Also, propagation distances in a nearshore model are
relatively short (tens of miles), so that the cumulative bottom friction dissipation is small.
For these reasons, bottom friction is neglected in STWAVE.
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