BOTTOM (nature of). The composition or character of the bed of an ocean or 

 other body of water (e.g., clay, coral, gravel, mud, ooze, pebbles, rock, 

 shell, shingle, hard, or soft). 



BOULDER. A rounded rock more than 10 inches in diameter; larger than a 

 cobblestone. See SOIL CLASSIFICATION. 



BREAKER. A wave breaking on a shore, over a reef, etc. Breakers may be 

 classified into four types (see Figure A-4): 



SPILLING — bubbles and turbulent water spill down front face of wave. The 

 upper 25 percent of the front face may become vertical before breaking. 

 Breaking generally occurs over quite a distance. 



PLUNGING — crest curls over air pocket; breaking is usually with a crash. 

 Smooth splash-up usually follows. 



COLLAPSING — breaking occurs over lower half of wave, with minimal air 

 pocket and usually no splash-up. Bubbles and foam present. (See Figure 

 2-77). 



SURGING — wave peaks up, but bottom rushes forward from under wave, and 

 wave slides up beach face with little or no bubble production. Water 

 surface remains almost plane except where ripples may be produced on the 

 beachface during runback. 



BREAKER DEPTH. The still-water depth at the point where a wave breaks. Also 

 called BREAKING DEPTH. (See Figure A-2). 



BREAKWATER. A structure protecting a shore area, harbor, anchorage, or basin 

 from waves. 



BULKHEAD. A structure or partition to retain or prevent sliding of the 

 land. A secondary purpose is to protect the upland against damage from 

 wave action. 



BUOY. A float; especially a floating object moored to the bottom to mark a 

 channel, anchor, shoal, rock, etc. 



BUOYANCY. The resultant of upward forces, exerted by the water on a submerged 

 or floating body, equal to the weight of the water displaced by this body. 



BYPASSING, SAND. Hydraulic or mechanical movement of sand from the accreting 

 updrift side to the eroding downdrift side of an inlet or harbor 

 entrance. The hydraulic movement may include natural movement as well as 

 movement caused by man. 



CANAL. An artificial watercourse cut through a land area for such uses as 

 navigation and irrigation. 



CANYON. A relatively narrow, deep depression with steep slopes, the bottom of 

 which grades continuously downward. May be underwater (submarine) or on 

 land (subaerial). 



A-5 



