122 CHARACTER OF SURF 



somewhat lower if they are coming in at an angle, because of their 

 refraction (as explained on p. 157). And high breakers are also 

 often caused by old swells, for while these are often much lower than 

 the storm waves that engendered them, they are so much longer that 

 they begin to pile up in much deeper water than would a storm wave 

 of equal height. Thus, a swell that was 1,500 feet long ( period of about 

 17 seconds) and 5 feet high would produce a 10-foot surf; and it is not 

 unusual for old swells to produce breakers more than twice as high as 

 their own deep water heights, for this reason. 



The breakers that form in moderate weather are ordinarily highest 

 at the instant that the overfall takes place, with the precise heights 

 governed chiefly by how high the parent waves are over deeper water 

 offshore, as compared with their lengths there, i. e., on their initial 

 steepness. And since waves vary almost infinitely in their lengths and 

 heights offshore, surf exhibits a corresponding range, from only an 

 inch or two high up to the heights of the largest storm waves. Breakers 

 have, for example, been measured from 2 inches up to 7 feet in height 

 at St. Augustine, Florida (Gaillard, 1904, p. 33) ; from a few inches up 

 to about 13 feet at South Beach, Martha's Vineyard; and from iy 2 

 feet up to 20 feet or so on the coast of Morocco (p. 69), after the 

 establishment of a swell that was fairly consistent in period for a num- 

 ber of hours. 



Some records of high surf, culled from available data, are the fol- 

 lowing: 



a. Rollers 12 to 20 feet high have been observed at the Island of 

 Ascension, at the 10-fathom line, during a period of violent surf that 

 was probably somewhat higher than this, because produced by a swell. 36 



b. The heavy swells that run in from storms at sea are described as 

 breaking about 20 feet high against the coral reefs of the Hawaiian 

 Islands. 37 



c. Near Peterhead, Scotland, measured waves that were 26 feet high 

 and 500 feet long in 7 to 8 fathoms crested and broke along the 5 1 /£- 

 fathom line, by which time they may be assumed to have attained a 

 height well over 26 feet. 



d. At Algoa Bay, South Africa, unbroken waves, measured from 

 a staging, were 21 feet high close in to the breaking line, where the 

 depth of water was 23 feet, indicating a deepwater height of perhaps 

 17 or 18 feet. 



e. Breakers which damaged the breakwater at Wick Bay, Scotland, 

 were estimated by the resident engineer to have a maximum height of 

 42 feet. 



39 Buchanan, J. Y. 1888. The exploration of the Gulf of Guinea. Scott, geogr. mag., 

 vol. 4, p. 235. 



37 Blake, Tom. 1935. Hawaiian surf board, Honolulu, Paradise of the Pacific Press, 

 p. 63. 



