A20 



a check on the acceptability of the wave data set, longshore sediment transport 

 rates using the data were computed. This computation resulted in a predicted 

 net longshore transport rate of -10,000 cu yd/yr, which compares favorably 

 with the -5,000 to -10,000 cu yd/yr net transport rate calculated during the 

 design studies and also inferred from an analysis of shoreline changes in aerial 

 photography of the site. This good comparison supports the use of this wave 

 data set for the modeling effort. 



Calibration and verification 



For the calibration and verification process for this project, the intent was 

 to vary the values of various calibration parameters to obtain agreement 

 between the measured shoreline of September 28, 1991 (initial beach 

 monitoring survey) and the calculated shoreline. Once reasonable agreement 

 was achieved between these two shorelines, the model would be verified by 

 comparing the measured and calculated shoreline of November 17, 1991. 



In the course of calibration, generally only one parameter at a time was 

 changed in order to evaluate its effect on the calculated shoreline portion. As 

 a first step, the value of the main parameter K, was varied to determine the 

 value that would result in a calculated overall net longshore transport rate 

 close to the previously determined values. Second, the parameter K 2 was 

 varied to improve the agreement between the measured and calculated 

 shoreline positions as well as the approximate magnitude of net inflow of sand 

 from the south. Next, the longshore locations of the breakwaters were 

 translated several grid cells to the north and south as required to improve the 

 agreement between the calculated and measured shoreline positions. Next, the 

 transmission coefficients of the breakwaters were varied to adjust the size of 

 the salients behind the breakwaters. Lastly, beach fill was added to simulate 

 the evolution of the storm berm that resulted in an increase in beach width. 



In total, 15 calibration simulations were conducted. Several of the initial 

 runs were conducted without any structures in place along the shoreline to 

 determine the value of K^ Evaluation of these runs indicated that Kj = 0.50 

 resulted in a calculated net longshore transport rate of -10,000 cu yd/yr (south 

 to north), which agreed with the previously determined rate of -5,000 to - 

 10,000 cu yd/yr. 



With K, = 0.5 and K2 = 0.25, an initial simulation with all breakwaters 

 in place was conducted. Results of this run, shown in Figure All, indicate 

 that the bayward limit and shape of most of the salients behind the 

 breakwaters are in reasonably good agreement with the measured salients. 

 However, the longshore locations of the calculated salients are displaced too 

 far to the north and the depths of the embayments are too great. The 

 calculated Calibration Verification Error (CVE) equals 10.44 ft. 



A number of additional simulations were made with the longshore locations 

 of the breakwaters translated both north and south several cells in an attempt 

 to improve the agreement between the longshore location of the calculated and 



Appendix A Case Design Example of Detached Breakwater 



