where C is the wave phase velocity, C the wave group velocity, and E 
the wave energy density © 
2 
pgH 
= rms 
Re (5) 
where H is the root-mean-square (rms) wave height. The term in paren- 
theses in equation (4) is the flux of wave energy per alongshore distance, 
F,, assuming straight and parallel bathymetric contours. When zero wave 
energy dissipation is assumed, 
F = EC_ cosa = constant (6) 
x & 
In this report, dissipation is assumed to be zero up to the breaker zone; 
therefore, F is constant from deep water to the breaker zone. Since the 
ratio of sina to C is constant due to Snell's law, equation (4), which 
represents the alongshore wave momentum entering the surf zone, is constant 
seaward of the breaker zone. 
Equation (4) can be revised for application of monochromatic waves, as in 
this reporte For such wave conditions, the average wave height, H, measured 
during the tests (and discussed later in Section IV) is equal to H.j.- By 
rewriting equation (4), 
og sina 
Chey = 8 a cosa} ——— (7) 
S is now defined for use with laboratory monochromatic wave data. Note 
that equation (4) is valid for any wave condition; equation (7) is valid only 
for conditions where H equals Hems* 
2. Energy Flux. 
In literature, the longshore transport rate has been empirically related 
most frequently to a term found by multiplying both sides of equation (4) by 
the wave phase velocity, C, to yield 
Bye (EC, cosa) sina (8) 
Unlike Sy. 5 Po is not constant seaward of the breaker line; therefore, 
specifying where P, is being calculated is necessary. This report, follow- 
ing convention, determines Pp at the breaker line, 
Pie (EC, cosa), sina, (9) 
representing the value of Pp, at the point closest to where the longshore 
transport is occurring. The subscript b denotes breaker values. MThe term 
13 
