value of the exact energy flux for sinusoidal wave heights with a Rayleigh
distribution. Since this means that P£s is proportional to energy flux
and not equal to it, P£S is referred to as the longshore energy flux
factor in Table 4-8 and the following sections.
Longshore energy flux in this general case (P&) i-s given by équation 4-27. This is an exact équation for the longshore component of
energy flux in a single small-amplitude, periodic wave. This équation
is good for any specified depth, but because the wave refracts, P& will
hâve different values as the wave moves into shallower water. The value
of Pj, in Equation 4-27 can be manipulated through use of small-amplitude
wave theory to obtain the four équivalent formulas for P& shown in Table4-7.
In order to use P^ for longshore transport computations in the surf
zone, it is necessary to approximate P^ for conditions at the breaker
position. These approximations are shown as P^s in Table 4-8, evaluated
in foot-pound per second units. The bases for these approximations are
shown in Table 4-9. Measurements show that the longshore transport rate
dépends on P£S. (See Figures 4-36 and 4-37.)
As implied by the définition of P&s, the energy flux factors in
Figures 4-36 and 4-37 are based on significant wave heights. The plotted
P£s values were obtained in the following manner. For the field data of
Watts (1953) and Caldwell (1956), the original references give energy flux
factors based on significant height, and these original data (after unit
conversion) are plotted as P^g in Figures 4-36 and 4-37. Similarly, the
one field point of Moore and Cole (1960), as adopted by Saville (1962),
is assumed to be based on significant height. (See Figure 4-37.) Finally,
the field data of Komar (1969), are given in terms of root-mean-square
energy flux. This energy flux is multiplied by a factor of 2 (Das, 1972),
converted to consistent units, and then plotted in Figure 4-36 and 4-37.
For laboratory conditions (Fig. 4-36 only), waves of constant height
are assumed. When these heights are used in the équations of Table 4-8,
the resuit is an approximation of the exact longshore energy flux. In
order to plot the laboratory data in terms of an energy-flux factor consistent with the plotted field data, this energy flux is multiplied by 2
before plotting in Figure 4-36.
loi the purpose of this section, it is assumed that the shoaling coefficient, Ks, for nearshore breaking waves is équivalent to the breaker
height index, Hfc/Ho*, found from observation. (See Figure 2-65.)
The choice of équations to détermine P^s dépends on the data available. The right hand columns of Tables 4-7 and 4-8 tabulate the data
required to use each of the formulas. An example using the second Pog
formula is given in Section 4.533.
Possible changes in wave height due to energy losses as waves travel
over the Continental Shelf are not considered in these équations. Such
4-96
distribution. Since this means that P£s is proportional to energy flux
and not equal to it, P£S is referred to as the longshore energy flux
factor in Table 4-8 and the following sections.
Longshore energy flux in this general case (P&) i-s given by équation 4-27. This is an exact équation for the longshore component of
energy flux in a single small-amplitude, periodic wave. This équation
is good for any specified depth, but because the wave refracts, P& will
hâve different values as the wave moves into shallower water. The value
of Pj, in Equation 4-27 can be manipulated through use of small-amplitude
wave theory to obtain the four équivalent formulas for P& shown in Table4-7.
In order to use P^ for longshore transport computations in the surf
zone, it is necessary to approximate P^ for conditions at the breaker
position. These approximations are shown as P^s in Table 4-8, evaluated
in foot-pound per second units. The bases for these approximations are
shown in Table 4-9. Measurements show that the longshore transport rate
dépends on P£S. (See Figures 4-36 and 4-37.)
As implied by the définition of P&s, the energy flux factors in
Figures 4-36 and 4-37 are based on significant wave heights. The plotted
P£s values were obtained in the following manner. For the field data of
Watts (1953) and Caldwell (1956), the original references give energy flux
factors based on significant height, and these original data (after unit
conversion) are plotted as P^g in Figures 4-36 and 4-37. Similarly, the
one field point of Moore and Cole (1960), as adopted by Saville (1962),
is assumed to be based on significant height. (See Figure 4-37.) Finally,
the field data of Komar (1969), are given in terms of root-mean-square
energy flux. This energy flux is multiplied by a factor of 2 (Das, 1972),
converted to consistent units, and then plotted in Figure 4-36 and 4-37.
For laboratory conditions (Fig. 4-36 only), waves of constant height
are assumed. When these heights are used in the équations of Table 4-8,
the resuit is an approximation of the exact longshore energy flux. In
order to plot the laboratory data in terms of an energy-flux factor consistent with the plotted field data, this energy flux is multiplied by 2
before plotting in Figure 4-36.
loi the purpose of this section, it is assumed that the shoaling coefficient, Ks, for nearshore breaking waves is équivalent to the breaker
height index, Hfc/Ho*, found from observation. (See Figure 2-65.)
The choice of équations to détermine P^s dépends on the data available. The right hand columns of Tables 4-7 and 4-8 tabulate the data
required to use each of the formulas. An example using the second Pog
formula is given in Section 4.533.
Possible changes in wave height due to energy losses as waves travel
over the Continental Shelf are not considered in these équations. Such
4-96