would seem to give roughly the same frequencies -- i.e.3 a statistical 
summary of wave conditions at a point over a long period of time would pro- 
bably be similar regardless of which method was used. 
There appears to be no particular explanation for the 16-hour late 
arrival time of the waves forecast by the Darbyshire method, and there are, 
of course, not enough data to show whether this is abnormal, such large 
deviations occurring only infrequently, or is inherent in the method 
(resulting perhaps from a speed of travel of the wave components different 
from that predicted by the group velocity). Since the method has apparently 
been used quite satisfactorily by the British, it is probably the former. 
It is interesting to note that both methods show an increase in wave 
height from a secondary fetch following the - main storm. Apparently this was 
not recorded, and it is not known whether this was due to refraction (the 
gage is in a depth of about 80 feet) or to some other cause. 
The Darbyshire method is considerably more time consuming than that of 
Bretschneider (though undoubtedly short cuts in the computations would be 
found were the method to be adopted for extensive use), but the former does 
have the advantage of providing a picture of the wave spectrum. Since the 
different components of the wave train refract differently according to 
their periods, this spectrum can become very important in predicting inshore 
conditions. In the general case, results of sufficient accuracy can be ob- 
tained from the use of the significant period alone for refraction purposes, 
but in cases where there is a wide spectrum or the refraction conditions are 
complex, this may lead to significant errors. Asample of the predicted 
wave spectrum for the peak of the storm is shown in Figure 2. The peak height 
during the storm (11.9 feet) is the square root of the sum of the squares of 
the heights of the individual components shown. 
Recent work at New York University by Neuman and Pierson has resulted in 
a third method of forecasting waves, as yet unpublished. It is planned to 
make a similar forecast for this same storm by that method, when it becomes 
available. 
‘BIBLIOGRAPHY 
(1) Sverdrup, H. U, and W. H. Munk - Wind Waves and Swell, Principles in 
Forecasting, ice OS Malsies IP 27/ Sq aes 
(2) Bretschneider, C. L. - Revised Wave Forecasting Relationships, Proc. 
2nd Conf. on Coastal Engrg., Council on Wave Research, The Engineering 
Foundation, 1952. 
(3) Darbyshire, J. - The Generation of Waves by Wind, Proc. Roy. Soc. A, 
iio IMNAZ, Wo AilSs IPS2, 
(4) Bretschneider, C. L. - Revised Wave Forecasting Curves and Procedures, 
Inst. of Engrg. Res., Univ. of Calif., Ser. 29, Issue 155-7, 1951 
(unpublished). 
(5) Kaplan, K. - Analysis of Moving Fetches for Wave Forecasting, Beach Erosion 
Board, Technical Memorandum No. 35, 1953. 
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