period does not vary in the refraction process. The results from all model 
runs were compiled into one random access file keyed on input wave period and 
direction. Knowledge of the deepwater wave height associated with each set of 
WIS wave conditions allows rapid calculation of nearshore wave properties. 
Plots showing the results of selected refraction model runs were made to 
further verify proper operation of the model and to give a visualization of 
the results. Selected plots are contained in Appendix C. 
Time series processing 
58. A program was developed to link the 3-year time series of the 
hindeast wave results at the 18.29-m depth to the results of the wave model 
runs to create a time series of wave height, period, and direction at the 3-m 
depth at each longshore grid line. The program reads one record of WIS data 
(height, direction, and period of sea and swell components) and defines a key, 
based on input period and direction, for both the sea and swell component. 
The keys are then used to enter the random access file and extract transformed 
wave conditions. The transformed wave height at each grid line at the 3-m 
depth is obtained as the product of the transformation coefficient and the 
deepwater wave height in the WIS record. The sea component is limited by the 
calculated TMA limit (Hughes 1984), which is the maximum wind sea that can 
occur at a given depth and period. (The acronym "TMA" derives from locations 
of field experiments used to verify the theory.) 
59. The shoreline change model requires input wave conditions at 6-hr 
intervals. Therefore, every other record of the hindcast time series was 
analyzed. To conserve computer memory and file space, only the component (sea 
or swell) with the greater energy flux per unit length of shoreline was saved 
in the output file. If both components had wave heights of less than 20 cm 
(0.66 ft) at the seaward boundary of the grid, no results were saved because 
neither component is expected to have sufficient energy to produce significant 
longshore sediment transport. In the shoreline model, this condition was 
treated as a calm wave condition of effective zero wave height. This tech- 
nique of imposing a threshold, although somewhat arbitrary, resulted ina sig- 
nificant reduction in calculation time. Analysis of the original and pro- 
cessed time series showed that the energy flux of the processed series was 
24 percent less than that of the original series due to the removal of the nu- 
merous low wave energy events. Field experiments performed by CERC subsequent 
to the present study support the concept of a threshold in longshore sediment 
36 
