BOSS International


Estimating nearshore wind-wave growth and transformation is a critical component of most coastal engineering projects, e.g., predicting bathymetric and shoreline change, estimating navigation channel shoaling and migration, designing or repairing coastal structures, assessing navigation conditions, and evaluating natural evolution of coastal inlets or beaches versus consequences of engineering actions. Nearshore wave propagation is influenced by complex bathymetry (including shoals and navigation channels); tide-, wind-, and wave-generated currents; tide- and surge-induced water-level variation; and coastal structures. Use of numerical wave models has become widespread to represent wave transformation primarily because of their increasing sophistication and economy of application relative to the large expense of field measurements or physical model studies.

» Overview


STWAVE (STeady State Irregular WAVE Model) provides an easy-to-apply, flexible, and robust model for nearshore wind-wave growth and propagation. Recent upgrades to the model include wave-current interaction and steepness-induced wave breaking. STWAVE has also been incorporated into SMS (Surfacewater Modeling System), which provides a user interface and supporting software for grid generation, interpolation of current fields, generation of input spectra, and visualization of model output.

The purpose of applying nearshore wave transformation models is to describe quantitatively the change in wave parameters (wave height, period, direction, and spectral shape) between the offshore and the nearshore (typically depths of 20 m or less). In relatively deep water, the wave field is fairly homogeneous on the scale of kilometers; but in the nearshore, where waves are strongly influenced by variations in bathymetry, water level, and current, wave parameters may vary significantly on the scale of tens of meters. Offshore wave information is typically available from a wave gauge or a global- or regional-scale wave hindcast or forecast. Nearshore wave information is required for the design of almost all coastal engineering projects. Waves drive sediment transport and nearshore currents, induce wave setup and runup, excite harbor oscillations, or impact coastal structures. The longshore and cross-shore gradients in wave height and direction can be as important as the magnitude of these parameters for some coastal design problems.

STWAVE simulates depth-induced wave refraction and shoaling, current-induced refraction and shoaling, depth- and steepness-induced wave breaking, diffraction, wave growth because of wind input, and wave-wave interaction and white capping that redistribute and dissipate energy in a growing wave field.

To assist STWAVE users in generating input files and visualizing output files, a user interface has been built for STWAVE within SMS. The SMS interface supports grid generation, interpolation of current fields, generation of input spectra, visualization of wave heights, periods, and directions, and visualization of output spectra.

For coastal inlets, it is common to run the finite-element circulation model ADCIRC to calculate water-surface elevations and current fields, as well as to run STWAVE.

Example Application of STWAVE - Wave Propagation at Ponce de Leon Inlet

This example is based on a field site, Ponce de Leon Inlet, located on the east coast of Florida. The nearshore bathymetry at Ponce Inlet is complex because of the presence of the inlet, a navigation channel, jetties, and a large ebb shoal. Tidal currents at the inlet can exceed 1 m/sec. Engineering problems at Ponce Inlet that require information about the nearshore wave field include scour in the inlet throat near the north jetty, erosion of the north spit in the interior of the inlet, migration of the navigation channel, and possible breaching shoreward of the north jetty.

The bathymetry contours within the STWAVE modeling domain for Ponce Inlet.

The example application starts with an ADCIRC finite-element bathymetry grid and a current field generated by ADCIRC. These gridded data are converted to “scatter” data (random data points that are not associated with a grid, but with x and y locations). From these scatter data, a Cartesian bathymetry grid and current field are generated. Next, other required model input (input spectrum and model parameters) is entered and the model is executed. Finally, post-processing of the data is performed, including visualization of the bathymetry and wave heights, directions, heights, and spectra.

Contour plot of the wave heights over the entire STWAVE domain. The gray shade contours represent wave height, and the background line contours represent the bathymetry.

For these incident wave conditions, the wave-height variations closely follow the depth contours, because depth-limited breaking in the dominant process and thus the wave height contours mimic the depth contours. For cases with less extreme incident wave heights, the maximum wave heights are found on the ebb shoal, where energy is focused by refraction.