126 CHARACTER OF SURF 



and take advantage of the series of smaller breakers that succeed a 

 series of larger ones, when coining in to land. A cross sea also renders 

 the surf much worse than it would be otherwise, partly because it 

 disturbs the regularity of the wave pattern, but especially because 

 steep peaks may shoot upward along the breaker zone, when waves 

 coming from different directions chance to join just before breaking, 

 as happens offshore under similar conditions (p. 124). The resulting 

 surf may be so high and so confused that any attempt to land through 

 it would be much more dangerous than an observer offshore would 

 expect, if he did not detect the presence of the opposing trains of 

 waves. 



DEPTH OF WATER IN WHICH SURF DEVELOPS 



Waves of moderate steepness, generated in deep water, but then 

 advancing over a shoaling bottom in calm weather, have been found 

 from tank experiments and from field observations on the coast of 

 California to break when they reach the point where the depth is no 

 longer more than about 1.3 times as great as their own heights there, 

 which is close to the theoretical expectation. But common experience 

 in various localities is that the ratio between height of breaker and 

 depth of water where it breaks varies considerably, under different 

 conditions of wind, sea, and current (if there is any) . 



Thus, the surf at St. Augustine, Fla.. has been seen breaking where 

 the depth was only about 0.72 as great as the height of the breakers in 

 some cases, but where the depth was twice as great as the heights of 

 the breakers in others (Gaillard, 1904, p. 120). Measured waves have 

 also been seen to break in depths ranging from 1.3 to 1.7 times as great 

 as their own heights at South Beach, Martha's Vineyard; in depths 

 1 to 2.7 times their heights on Lake Superior (Gaillard, 1904, pp. 121- 

 122) ; and in depths of from 0.9 to 2.0 as great as their own heights at 

 La Jolla, California. Measured waves that were 26 feet high at the 

 7 or 8-fathom line have been seen breaking at the S^-fathom line 

 (i. e., in 33 feet of water) at Peterhead, Scotland; swells 5.5 to 8 feet 

 high have been seen breaking where the depth was 2.2 to 2.3 times as 

 great as that at Scarboro, England ; and ground swells 10 to 12 feet 

 high break commonly where the general low tide depth is about 10 

 fathoms (60 feet) on Riy Bank off South Africa, sometimes for days 

 at a time. Other striking cases of breakers in water considerably 

 deeper than the probable heights of the waves at the time are the surf 

 often reported at depths of 7 to 9 fathoms (42 to 54 feet), and some- 

 times to 10 fathoms (60 feet) on San Francisco Bar, and on the Co- 

 lumbia River Bar; at 90 feet at Cape Foulweather, Oregon; at 48 feet 

 off Port Orf Old, Oregon ; at 42 to 48 feet between Trinidad and Pilot 



