If beach survey profiles for the target beach are available, it is recommended 

 that the modeler use the curves in Figure 7 as templates to determine an 

 effective median grain size. The effective grain size, if supplied to 

 GENESIS, will produce an A- value that will give the most representative 

 profile shape. If profile survey data are lacking, the median grain size of 

 the surf zone sand should be used. 



121. The average nearshore slope tan/? for the equilibrium profile 

 defined by Equation 6 is calculated as the average value of the integral of 

 the slope 3D/3y from to y LT , resulting in tan/9 - A(y LT )~ 1/3 , in which 

 y LT is the width of the littoral zone, extending seaward to the depth D LTo . 

 Since by definition, y LT — (D LTo /A) 3/2 , the average slope is calculated to be 



««*- [,&]"* <*> 



Depth of closure 



122. The depth of closure, the seaward limit beyond which the profile 

 does not exhibit significant change in depth, is a difficult parameter to 

 quantify. Empirically, the location of profile closure D c cannot be iden- 

 tified with confidence, as small bathymetric change in deeper water is 

 extremely difficult to measure. This situation usually results in a depth of 

 closure located within a wide range of values, requiring judgment to be 

 exercised to specify a single value. Often profile surveys are not available 

 to a sufficient depth and with sufficient vertical and horizontal control to 

 allow comparisons of profiles to be made. Figure 8a shows the standard devia- 

 tion of depth values from five wide -scale bathymetric surveys plotted as a 

 function of mean depth for Oarai , a Pacific Ocean beach in Japan (Kraus and 

 Harikai 1983). Figure 8b shows a similar plot composed of data from multiple 

 profile surveys made over a 4-year period along nine transects at Oceanside, 

 California. Changes in the profile fall off at a depth of about 6 m for the 

 case of Oarai and at about 30 ft National Geodetic Vertical Datum (NGVD) for 

 the case of Oceanside. These values were used as the depths of closure in the 

 respective shoreline response models. 



57 



