determined from either a pressure record and equation (12.43) or 
from a record of the free surface. The computation of the energy 
flux from the "significant" height and period is completely meaning- 
less, especially for "sea" conditions. 
If the beach has contours parallel to a straight shoreline, and 
if the waves have infinitely long crests (as in equation (7.36)) 
which are parallel to the shore, then the wave power intezrated over 
depth and averaged over time is given by equation (12.50) on the 
left in the transition zone and on the right in deep water. The 
energy flux in this case only, is equal at both points. Equation 
(12.50) is the extension of usual refraction theory considerations 
to Gaussian systems. Equations (12.51) and (12.52) are the analogues 
to (12.50) for the discrete case. They are given by Sverdrup and 
Munk [1944b] and Mason [1951]. 
One of the unsolved problems of wave forecasting and wave anal- 
ysis theory in terms of "significant" height and period was the 
problem of the combination of wave systems from two different storms 
either in deep water or in the transition zone. In terms of power 
spectra and the methods developed in this paper, the problem can 
easily be solved. It is easy to prove that the power spectrum of 
the sum of two different disturbances equals the sum of the power 
spectra of the two different disturbances. From this, it follows 
that all other properties combine in the same way, and the pressure, 
velocity components, and energy flux of combined wave systems can be 
found immediately. If the sum of the two power spectra yields a power 
*This section is also a proof of the statement made on page 260. The 
argument is given for two superimposed small spectra, but it would 
also follow for two adjacent spectra, (page 260 of Part I). 
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