2tt 



Substituting the value for w, taking the shallow-water approximation 

 that the factor [1 - M(H/L)^] — 1, and evaluating L from linear theory by 



T^ tanh (?li) 



L = 5.12 T^ tanh (-[;-) (C-4) 



equation (C-2) becomes 



P = 41 TH^ n tanh I— — j t sin a cos a (foot-pounds per day per foot) (C-5) 



Note that Watts (1953) computes Pj^g in units of foot-pounds per day per foot 

 of beach front, which is converted in the SPM to units of foot-pounds per sec- 

 ond per foot of beach front. 



Significant wave height and period were taken from the analysis of the wave 

 records (a 12-minute record every 4 hours) of a pressure gage installed at the 

 seaward end of the Palm Beach pier, located 17.7 kilometers (11 miles) north of 

 south Lake Worth inlet, in approximately 5.2 meters (17 feet) of water. Wave 

 direction was obtained from twice daily observations using an engineer's transit 

 with sighting bar and auxiliary sights from an elevated point 5.6 kilometers 

 (3.5 miles) north of the inlet. No mention is made of how the quantities d 

 and L are evaluated. 



There are six data points listed in Caldwell (1956) . One of these six data 

 points is not plotted in Figure 4-37 of the SPM. That point represents a con- 

 dition where the measured longshore transport and the computed longshore energy 

 flux are in opposite directions. The longshore transport rate, Q, was meas- 

 ured by comparing successive sets of surveys of the beach out to the 6.1- meter 

 (20 feet) depth contour at 152.4-meter (500 feet) intervals along the 3.4- 

 kilometer (11,000 feet) study area immediately south of the jetties at Anaheim 

 Bay, California. The longshore component of wave energy flux, P^g , was com- 

 puted from equation (C-5) and, as before, converted to units of foot-pounds per 

 second per foot of beach front for use in the SPM. Significant wave height and 

 period were taken from analysis of the wave records of a step-resistance wave 

 gage, supplemented by hindcasting when necessary, and checked by a float-type 

 wave gage. The gages were installed on the seaward end of the Huntington Beach 

 pier, located about 10 kilometers (6 miles) south of Anaheim Bay. Wave direc- 

 tion was obtained from wave hindcasting and wave refraction analysis using 

 synoptic weather charts. Again, no mention is made of how d and L are 

 evaluated. 



One data point is taken from an observation in Moore and Cole (1960) . The 

 longshore transport rate, Q, was measured by comparing two surveys marking 

 the growth of a spit across the outlet to Tasaychek Lagoon, Alaska. The long- 

 shore energy flux, P^g , was computed by Saville (1962) using the following 

 equation (T. Saville, CERC, personal communication, 1974) 



„ wLH^ t . rr c^ 



