STWAVE vs. CGWAVE

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STWAVE vs. CGWAVE: What is the difference between these two numerical models? When do

you use one instead of the other? Both are used for wave modeling, but the relative scales are

different. Wave modeling can be grouped into three classes or relative scales: generation, transfor-

mation, and local scale. The generation scale deals with waves as they are formed or generated in

deep water. The transformation scale describes wave transformation in deep to intermediate level

water depths. The finite difference STWAVE model falls in this class of numerical models and

includes the coastal processes of refraction, shoaling, wave-current interaction, wave growth, and

depth-limited wave breaking. The local scale class is for nearshore or local modeling of intermediate

to shallow water. The finite element CGWAVE model is in this category. Thus, the STWAVE can

be used to transform deepwater waves to a depth coinciding with the offshore boundary of the

CGWAVE model.

CGWAVE PROCEDURE: The procedure for running CGWAVE within SMS can be divided into

four parts:

a. Create a conceptual model

b. Generate the finite element mesh

c. Run the model

d. Post-process the results

Each of these steps are discussed in the following paragraphs. Since SMS does not have an "undo"

function, it is a good idea to save your work early and often.

CREATE A CONCEPTUAL MODEL: To create the conceptual model, which SMS uses to

generate a mesh-based numeric model, you should (a) import and register a background image,

(b) gather coastline and bathymetric data, (c) determine the coordinate system and datum reference

for the project, and (d) conceptualize the study area with a CGWAVE coverage type.

Background Image. It is useful to have an aerial photograph or image of the project area to see if

the conceptual model is correct. Image data is input in the Map module in tiff or jpg formats using

the File|Open command. These images have to be registered or geo-referenced to state plane

coordinates, meters. The three registration points shown in Figure 2 must be moved to known

coordinate positions or a pre-existing GIS type "world file" must be read into SMS to geo-reference

the image. In this example, the *.jpg file was opened first and then the .jgw world file was input

using the Import World File button. If an SMS image file (.img) was previously saved, it can be

opened in lieu of the world file referencing. The ASCII image file tc_overlay_metric.img opens the

file Tedious_small.jpg and provides the proper registration information.

Coastline and Bathymetric Data. The CGWAVE model requires bathymetric and coastline

data. Bathymetric data is input in the Scatter module in an "xyz" file format, using the File|Open

command. The x and y coordinates should be in state plane and true north. All values of water depth

should be in meters and positive downward. Bathymetry should include the model domain and a