Surfrider Foundation: Mitigation Through Surf Enhancement

APPENDIX A
(Page 2 of 2)

    The first input is the name of the ASCII version of bathymetry array which must be entered in single quotes.
    The second input in the name of the output file. This file is always called output.dat and also single quoted.
    The grid dimensions mr and nr are the sides of your bathymetry grid which was 200 by 200 for all grids used in this study.
    The grid spacings dxr and dyr control the scale of your grid. Each grid cell in this study was 5 meters by 5 meters. The depth tolerance dt is a tolerance for steps in the bathymetry grid. Any vertical step larger than the tolerance reports an error. In this study all bathymetries had a step no larger than one, therefore 5 was used for convenience.

    The input iu: controls the units of the grids spacing. The metric system was used for this modeling.
    The dispersion relationship ntype selects the model option that is used for shallow water wave propagation. In this study the composite relationship, which is a Stokes-Hedges model (See Assumptions above), was always used because the wave propagated over shallow reef structures.
    The lateral boundary condition ibc was always open for this study. This creates "reasonably transparent" boundaries on the edges of the grid. It is suggested that the boundary condition is tested with the closed option to determine the potential amount of interference by waves "reflecting" off the lateral boundaries (Kirby and Dalrymple, 1994). In this study the model was run with the boundary condition closed with no noticeable effects.
    The input ispace and input nd control the number of subdivisions used by the model to iterate through the grid. The input ispace was always set to 0 allowing the program to pick the x spacing. It is important that there are at least 5 subdivisions in the y direction per wavelength for the model to operate correctly (Kirby and Dalrymple, 1994). In this study this was determined that 1 division still allowed for at least 5 subdivisions per wavelength for a 12 second wave.
    In the input iff controls the dissipation from three boundary layers: the turbulent boundary layer, bottom damping and laminar boundary layers. Because dissipation was not a concern in this study all boundary layer dissipations were turn off (set to zero). This suggests that wave heights after breaking are maximized for all cases.
    The subgrid features input isp allows a subgrid to be entered in the bathymetry grid with a finer resolution. Subgrids were not used in this study (isp = 0).
    The inputs iinput and ioutput allow for data for a separate model run to be incorporated into the current modeling run. Because all model runs were conducted in their entirety iinput and ioutput were always turned off (set to 1).
    Surface plots of propagated waves can be generated by setting isurface to 1. This was not typically done, however some surface plots were investigated.
    The input iwave controls the wave field type: discrete waves or a directional spreading model. In this study all models were run with a discrete wave (iwave = 1) with one frequency (nfreq = 1). The wave period controls the period of the propagating wave. Wave period is entered in seconds. A wave period of 12 seconds was determined to be the average period in El Segundo in surfable conditions. The tide stage input controls the water level on the bathymetry by either adding or subtracting the number of units input as tide stages. For example a tide stage of -2 would subtract two meters from the depths of the bathymetry. This was not used in this study. Instead the bathymetry was altered to represent different depths.
    The input nwavs controls the number of waves per frequency. This was always set to 1 wave. The input amplitude is the wave amplitude at the first set of offshore grid cells. It is important to remember that amplitude is one half the wave height (H). The direction controls the propagation direction relative the to the x-axis. This was usually set to zero.
    Once the model is run several ASCII files are generated with a resolution equal to that of the input bathymetry grid. The time it takes per model run is dependent on the grid size and computer speed. Some large grids can take up to an hour to run, the average run time for this study was approximately 3 minutes. The output files include height.dat, depth.dat, angle.dat which are discussed in Chapter 3. In addition several radiation stress files are created. These output files were not investigated in this study.

table of contents

Surfrider Foundation USA:
122 S. El Camino Real #67
San Clemente, CA 92672
tel. (949) 492-8170
fax (949) 492-8142

Email addresses:
Reef issues: cnelsen@surfrider.org
Other: info@surfrider.org

See our feedback page.
Surfrider Website INDEX