Pigrrre 1 presents the results. The maximum speed 

 of oscillation is given as a function of depth for each month. 



The eq\iations for the orbital diameter of particle 

 motion are; 



D =-2A cosh k(z+h) sin(lDc -crt) for inter- 

 sinh kh 

 mediate water and 



D = - 2A sin(loc -crt) for shallow. 

 kh 



These in turn reduce to: 



^ = H (Intermediate) and 

 3 Inh 2 ir d 

 L 



D = HL (Shallow) for the length of the hori- 

 2 7r d 



zontal oscillation at the bottom. Figiore 2 shows these lengths 

 as a fvmction of depth of water for each month. 



Table I gives the data from which the graphs (Fig, 1 

 and 2) were drawno It should be pointed out that the calcula- 

 tions express the upper limits of conditions since Seiwell's 

 "wave meter was located in 75 feet of water and, therefore, did 

 not record waves of less than l50 ft, in length, Bigelow's 

 observations were of surf and were probably "significant waves'- 

 (Munk 19hh)' It is therefore logical to assume that these 

 graphs (Fig, 1 and 2) present the results of the average month-ly 

 significant waves. 



SUMMARY 



Figures 1 and 2 show the maximum speeds and lengths 

 of bottom oscillations due to surface waves as a function of 

 the depth of water for each month (except June) off South 

 Beach, Martha^s Vineyard. 



The calculations for December show large values of 

 speed and length due to the very high wave height average 

 reported by Sciwell. The average wave length for December 

 was the lowest for the entire year, hov;ever, which leads to 

 the conclusion that the condition was caused by one or more 

 local storms during the month. The curves for December, 

 therefore, probably give abnormally large values. 



"M-"" S^ife^^ — -irn-H.. 



