4. Empirical Relations. 
The expressions derived in the preceding paragraphs are used to set up the 
following empirical relations 
Tp = KP eb (15) 
and 
iy = athe (16) 
where K and K, are coefficients to be determined from the test data in 
this report. 
Equation (15) is based on the concept that the work done in moving the 
sand alongshore is proportional to the energy which approaches the beach. The 
units are consistent and K is dimensionless. 
Equation (16) is based on the concept that the sand transported alongshore 
depends on the alongshore force exerted by the wave motion on the bed inside 
the surf zone. By the equation of motion, this force is related to the change 
of momentum inside the surf zonee The alongshore momentum, S,., enters the 
surf zone through the breaker line but cannot exit through ‘the shoreline 
boundary. Therefore, the change in alongshore momentum is Sxy and equation 
(16) results. K, has dimensions of length over time. 
5- Surf Similarity Parameter. 
Kamphuis and Readshaw (1978) showed that K and K, are dependent upon 
the surf similarity parameter, 
Boe _tan B (17) 
1/2 
(H,/L,) 
in which tan 8 is the beach slope, Hp the breaker height, and Ly the 
deepwater (d/L > 1/2) wavelength. Ep reflects variations in beach shape, 
breaker type, and rate of energy dissipation. Using the results of laboratory 
tests, the following relationships were found by Kamphuis and Readshaw 
K 
P 
Ks OsO8Es foe Oath KB, < 1025 (19) 
rd 
0-7E, oie Wolk K BK hod (18) 
For values of €&, higher than the upper limits, Kp and K, become inde- 
pendent of €})- 
The surf similarity parameter is evaluated in this report to determine its 
effect on the longshore transport rate. 
III. EXPERIMENTAL SETUP 
This section discusses the setup in the SPTB (Figs. 2 and 3) and describes 
the wave generators, wave gages, and cameras and their positions. Also dis- 
cussed are the sand-moving system, the method for measuring the longshore 
current velocity, and the size distribution of the sand used in the experi- 
ment. The design of the setup was based in large part on Fairchild (1970). 
15 
