NO. 43 - December 1953 



II-A "On Ocean Wave Spectra and a New Method of Forecasting 

 Wind -Gene rated Sea" by Gerhard Neumann 



Based on recent observations of the composite nature 

 of wind -generated waves and on theoretical reasoning, 

 the spectrum of ocean waves is derived for a contin- 

 uous sequence of wave components. The properties of 

 the wave spectrum are developed, and it is shown that 

 the spectrum has an optimum band where most of the 

 spectral energy is concentrated, and that the product 

 of the frequency of the optimum band and wind speed 

 is constant. The range of periods with a significant 

 amount of energy, the width of the spectrum, deter- 

 mines the actual wave pattern. It depends upon the wind 

 speed and the state of development of the waves at 

 limited fetches and durations of wind action. For 

 practical purposes, a number E with dimensions (feet)^ 

 is introduced, which is proportional to the accumu- 

 lated energy in the wave spectrum. This value E is 

 derived by integrating the wave spectra, and permits 

 easy determination of height characteristics of the 

 composite wave motion. Results are presented in the 

 form of co-cumulative power spectra for convenient 

 use in practical wave forecasting. 



NO. 44 - ^une 1954 



II-C "Coast Erosion and the Development of Beach Profiles^ 

 E by Per Bruun 



The first part of this paper consists of a study of 

 the Danish North Sea coast including the following 

 factors: coastline development; development of beach 

 profiles including comparison for different wind/wave 

 conditions; coast erosion and quajitity of littoral 

 drift; and forecasting future development of shoreline 

 and beach profiles. Depth soundings since 1874 on 

 the Lime Inlet Barriers are used and treated statis- 

 tically, explaining development of these barriers and 

 adjacent coasts. The second part consists of a study 

 of the Mission Bay, California area, including study 

 of: development of beach profiles with comparison for 

 different wave conditions; seasonal fluctuations of 

 profiles; and comparison of Danish and California data. 



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