Shore dunes ar-e the visual evidence of a sedimentation process and 

 occur as a result of a local climatic condition by which the sand trans- 

 porting wind loses its competence. This may occur by reduction in wind 

 velocity; by change in wind direction; or by sheltering, either natural or 

 induced artificially o 



So long as sand is available on the beach and local wind conditions 

 favorable to sand transport exist the process of deflation continues. 

 O'Brien and Rindlaub^ •'report rates of m.ovement as high as 2,200 pounds of 

 sand per foot of beach per day measured on Clatrop Spit at the mouth of the 

 Colum.bia River. In many areas the loss of sand from beaches by wind de- 

 flation is doubly troublesome, as at Hollywood feach near Port Kuenema where 

 dune formations induced by shore cottages threatens to engulf the buildings, 

 the structures acting as effective sand fences in promoting dune formation 

 and growtho In this area the loss of sand by -local wind action probably 

 approximates 50,000 cubic yards annually, which is more than sufficient to 

 maintain excellent beaches almost anywhere in the Great Lakes area where 

 annual littoral drift is smaller than on most ocean shores. 



The indirect effects of wind on the shore face are much more important 

 than the direct effects briefly discussed above. The case may be stated 

 in this fashion. If wind is assumed to blov;- over an initially rough water 

 surface energy will be transferred from the wind to the water by normal 

 pressure and frictional drag, thus generating wave motion. The area in 

 which this transfer occurs, i.e., the generating area, corresponds roughly 

 to the area of the wind system. Considering the wide extent of the re- 

 latively unobstructed water surface, and the possibility' in large bodies 

 of water that several wind systems may contribute to the energy of waves, 

 it, can be presumed that the energy carried to the shore by waves greatly 

 exceeds that which it is possible to obtain by the action of local winis. 



The' energy budget of wind generated waves has. been studied by Sverdrup 

 and TAinkO), who have stated that "It seems probable that the energy used 

 for wave formation represents only a small fraction of the wind energy 



which is dissipated below a height of 8 to 10 nsters. A very small 



fraction, about 1 per cent, of this amount is transferred to the sea for 

 maintaining the pure wind current and another fraction goes into formation 



and maintenance of waves. Analysis indicates that 10 per cent or less 



of the wind energy dissipated in the lowest layer (of wind) goes toward 

 increasing or maintaining the energy of the waves," Among other factors 

 to be considered are: that, 



1. The vraves existing at any monent are the result of wind 

 action in one or more generating areas; 



2,, Interference occurs between waves; 



3» The generating wind is variable in velocity, direction, 

 and duration; 



U, A T/ind of given velocity probably generates a spectrum 

 of waves of various periods and amplitudes. 



21 



(3) Wind Waves and ijwell-A Basic Theory for Forecasting, H. U. Sverdrup ^ 

 v.. H. TAink, Scripps Inst, of Oceanography, 7*'ave Rpt. No. 1, Sep 194.3. 



