CAY - See KEY. 



CELERITY - Wave speed. 



CENTRAL PRESSURE INDEX (CPI) - The estimated minimum barometric pressure 

 in the eye (ap'proximate centev) of a particular hurricane. The CPI 

 is considered the most stable index to intensity of hurricane wind 

 velocities in the periphery of the storm; the highest wind speeds 

 are associated with storms having the lowest CPI. 



CHANNEL - (1) A natural or artificial waterway of perceptible extent 

 which either periodically or continuously contains moving water, 

 or which forms a connecting link between two bodies of water. 



(2) The part of a body of water deep enough to be used for 

 navigation through an area otherwise too shallow for navigation. 



(3) A large strait, as the English Channel. (4) The deepest 

 part of a stream, bay, or strait through which the main volume 

 or current of water flows. 



CHARACTERISTIC WAVE HEIGHT - See SIGNIFICANT WAVE HEIGHT. 



CHART DATUM - The plane or level to which soundings (or elevations) or 



tide heights are referenced (usually LOW WATER DATUM) . The surface 

 is called a tidal datum when referred to a certain phase of tide. 

 To provide a safety factor for navigation, some level lower than 

 MEAN SEA LEVEL is generally selected for hydrographic charts such 

 as MEAN LOW WATER or MEAN LOWER LOW WATER. See DATUM PLANE. 



CHOP - The short-crested waves that may spring up quickly in a moderate 

 breeze, and break easily at the crest. Also WIND CHOP. 



CLAPOTIS - The French equivalent for a type of STANDING WAVE. In American 

 usage it is usually associated with the standing wave phenomenon 

 caused by the reflection of a nonbreaking wave train from a structure 

 with a face that is vertical or nearly vertical. Full clapotis is one 

 with 100 percent reflection of the incident wave; partial clapotis is 

 one with less than 100 percent reflection. 



CLAY - See SOIL CLASSIFICATION. 



CLIFF - A high, steep face of rock; a precipice. See also SEA CLIFF. 



CNOIDAL WAVE - A type of wave in shallow water (depth of water is less 



than 1/8 to 1/10 the wavelength). The surface profile is expressed 

 in terms of the Jacobian elliptic function on u; hence the term 

 cnoidal . 



COAST - A strip of land of indefinite width (may be several miles) that 

 extends from the shoreline inland to the first major change in 

 terrain features. (See Figure A-1.) 



A-6 



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