BENCH MARK - A permanently fixed point of known elevation. A primaiy 

 bench mark is one close to a tide station to which the tide staff 

 and tidal datum originally are referenced. 



BERM, BEACH - See BEACH BERM. 



BERM CREST - The seaward limit of a berm. Also BERM EDGE. (See 

 Figure A-1.) 



BIGHT - A bend in a coastline forming an open bay. A bay formed by 

 such a bend. (See Figure A- 8.) 



BLOWN SANDS - See EOLIAN SANDS. 



BLUFF - A high steep bank or cliff. 



BOLD COAST - A prominent land mass that rises steeply from the sea. 



BORE - A very rapid rise of the tide in which the advancing water pre- 

 sents an abrupt front of considerable height. In shallow estuaries 

 where the range of tide is large, the high water is propagated in- 

 ward faster than the low water because of the greater depth at high 

 water. If the high water overtakes the low water, an abrupt front 

 is presented with the high water crest finally falling forward as 

 the tide continues to advance. Also EAGER. 



BOTTOM - The ground or bed under any body of water; the bottom of the 

 sea. (See Figure A-1.) 



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): 



Spitting - 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 across over 

 quite a distance. 



Ptunging - crest curls over air pocket; breaking is usually with 

 a crash. Smooth splash-up usually follows. 



Cottapsing - breaking occurs over lower half of wave. Minimal air 

 pocket and usually no splash-up. Bubbles and foam present. 

 (See Figure 2-69.) 



A-4 



