from the attack o£ the selected design wave and corresponding to aver- 

 age pressure intensities over the different vertical increments of the 

 vertical -wall parapet are: 



Vertical increment 



MSL 



Pressure 



(ft) 





(lb/ft2) 



to 5 





1,550 



5 to 10 





1,790 



10 to 15 





2,130 



15 to 20 





1,200 



20 to 23 





695 



These pressures are about three times those obtained from Sainflou's 

 (1928) equation, and are about one-sixth the pressures from Minikin's 

 (1963) equation. The type of structure developed for profile Y is 

 shown in Figure 6-46. Overtopping tests showed 7.3 cubic feet per sec- 

 ond of overtopping water per foot of seawall. Vertical-wall seawalls 

 were tested for the slip profile and the sea train profile; profile lo- 

 cations are shown in Figure 6-43. The elements of the test sections are 

 shown in Figures 6-47 and 6-48. The breaking and nonbreaking wave tests 

 determined that breaking waves would not occur on these structures for 

 wave periods less than about 6 seconds. Since the sheltering effects of 

 Snake Island protect the reaches from the longer-period waves, it was con- 

 cluded that these structures could be designed from Sainflou's equation 

 (for nonbreaking waves only), using waves of 3.5-second period and wave 

 heights from 2.5 to 6 feet, depending on the depths of water bayward of 

 the reaches corresponding to the slip and sea train profiles (Fig. 6-43). 



(5) Floating Breakwaters; Nonbreaking Waves . 



(a) Project . Proposed floating breakwaters. Oak Harbor, 

 Washington. 



(b) Reference . Davidson (1971a). 



(c) Laboratory . WES. 



(d) Test Period . September 1969 to March 1970. 



(e) Problem . A floating breakwater in combination with a 

 timber-pile and rubble-mound breakwater is proposed for protection of a 

 small-craft harbor at Oak Harbor, Washington. Oak Harbor is located on 

 Whidbey Island in Puget Sound about 50 miles north of Seattle, Washington 

 (Figs. 6-49 and 6-50). Water depths along the breakwaters range from 

 about 10 to 15 feet MLLW on the south side of the harbor and from about 



to 15 feet MLLW on the east side. The maximum tide elevation is +14.5 

 feet MLLW. The proposed small-craft harbor is exposed to short -period 

 wind waves from east clockwise to west. The maximum waves range to about 

 a 3.5-second period and a 2.0-foot height; wave heights in the mooring 

 areas of the harbor basin were not to exceed 0.5 feet. The floating 



415 



