Field Research Facility located at Duck, North Carolina (Howd and Birkemeier 

 1987). Five multi-day storm events were simulated, and model calibration 

 parameters were examined for applicability to field conditions. For these 

 simulations, the input consisted of measured time series of wave height, wave 

 period , and water level , thereby greatly reducing the number of degrees of 

 freedom in the model and increasing confidence in the calibration. The model 

 performed well in simulating bar movement through the course of the storms 

 (Larson, 1988; Larson, Kraus, and Sunamura, 1988). 



Bars generated in the large wave tank experiments and simulated with the 

 numerical model for constant monochromatic wave and water level conditions 

 were much steeper than bars in the field. An important result of the field 

 simulation was that the model successfully reproduced gentler bar slopes 

 observed in the field, obtained under realistic conditions of time-varying 

 wave height, wave period, and water level. The field -calibrated model was 

 used in the present study of beach fill adjustment. 

 Wave Calculation 



Transport relations used in the model require the wave height at fixed 

 calculation points across the surf zone. Linear wave theory is applied from 

 the seaward end of the grid, located far offshore, to the break point. 

 Shoreward of the break point, the numerical wave simulation model of Dally 

 (1980) is used to calculate the broken and reformed wave height. 



Location of the depth-limited break point and breaking wave height are 

 important parameters in the model. The slope of the seaward face of a bar, 

 which changes in time as the bar grows and moves, will feed back to modify the 

 breaking waves, since the breaker index (ratio of wave height to water depth 

 at breaking) depends on bottom slope and wave steepness. For use in the 

 model, the breaker index was evaluated using 121 pairs of breaking wave 

 height/depth values from the large wave tank tests. The average breaker index 

 was found to be 1.00, with a standard deviation of 0.25, maximum of 1.79, and 

 minimum of 0.58. Note that the average is about 20 % greater than the 

 commonly applied value of 0.78. The breaker index was expressed as 



"b 



— - 1.14 C°' 21 (2) 



\ 



92 



