grid cell number 
N = number of grid cells 
110. If Ydiff is multiplied by the grid cell width (50 m), the devia- 
tion between measured and calculated shoreline positions can be expressed as a 
total net plan shape area. 
Calibration 
111. Calibration of the GENESIS model was performed using the measured 
shorelines for 1971 and 1982, with 1971 data representing the initial shore- 
line position. After 11 simulated years, the calculated 1982 shoreline posi- 
tion was compared to the measured position. 
112. By assigning different values to the transport parameters, K, 
and Ky in Equation 3, and making numerous calibration trial runs, a minimum 
difference indicator of Ydiff = 597 m was found between the measured and 
simulated 1982 shorelines. The resultant optimized values of the transport 
parameters K, and Ks, were 0.41 and 0.10, respectively. A plot of the mea- 
sured 1971 and 1982 shorelines, and the simulated 1982 shoreline, are shown in 
Figure 16. These optimal values were obtained for a variable depth of closure 
(Equation 2) given as a function of the wave conditions at each time step. 
113. The average value of the depth of closure from Equation 2, 
excluding zeros associated with calm days of no longshore sediment transport, 
was found to be 1.35 m for the 3-year wave hindcast data set. However, in the 
long term, the beach profile is active to a much greater depth. Kraus and 
Harikai (1983) have discussed alternative definitions of the closure depth. 
In the present case, a representative value of the maximum depth of closure 
calculated from the wave data was found to be 6.0 m. A larger value of the 
depth of closure requires a larger value of Ky, (and, possibly, K5) in 
the calibration to maintain the same time scale of shoreline change. A 
larger value of K, produces a higher longshore sediment transport rate 
(Equation 3). 
114. In order to check the sensitivity of the model to depth of clo- 
sure, the calibration procedure was twice redone, once with a constant depth 
of closure of 1.35 m, and again with a constant depth of closure of 6.0 m. 
These values represent the average and approximate maximum depths of closure, 
respectively, calculated from the input wave time series and Equation 2. In 
the case of a constant depth of closure of 1.35 m, the 1982 shoreline was sim- 
ulated with Ky = 0.28 and K = 0.15 . The difference indicator for the 
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