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CURRENT, RIP - See RIP CURRENT. 



CURRENT, STREAM - A narrow, deep, and swift ocean current, as the Gulf 

 Stream. Opposite of CURRENT, DRIFT. 



CURRENT SYSTEM, NEARSHORE - See NEARSHORE CURRENT SYSTEM. 



CURRENT, TIDAL - The alternating horizontal movement of water associated 

 with the rise and fall of the tide caused by the astronomical tide- 

 producing forces. Also CURRENT, PERIODIC. See also CURRENT, FLOOD 

 and CURRENT, EBB. 



CUSP - One of a series of low mounds of beach material separated by- 

 crescent- shaped troughs spaced at more or less regular intervals 

 along the beach face. Also BEACH CUSP. (See Figure A- 7.) 



CUSPATE BAR - A crescent-shaped bar uniting with the shore at each end. 

 It may be formed by a single spit growing from shore and then turn- 

 ing back to again meet the shore, or by two spits growing from the 

 shore and uniting to form a bar of sharply cuspate form. (See 

 Figure A-9.) 



CYCLOIDAL WAVE - A steep, symmetrical wave whose crest forms an angle of 

 120 degrees. The wave form is that of a cycloid. A trochoidal wave 

 of maximum steepness. See also TROCHOIDAL WAVE. 



DAILY RETARDATION (OF TIDES) - The amount of time by which corresponding 

 tidal phases grow later day by day (about 50 minutes). 



DATUM, CHART - See CHART DATUM. 



DATUM, PLANE- The horizontal plane to which soundings, ground elevations, 

 or water surface elevations are referred. Also REFERENCE PLANE. 

 The plane is called a TIDAL DATUM when defined by a certain phase 

 of the tide. The following datums are ordinarily used on hydro- 

 graphic charts : 



MEAN LOW WATER - Atlantic coast (U. S.), Argentina, Sweden, 



and Norway; 

 MEAN LOWER LOW WATER - Pacific coast (U. S.); 

 MEAN LOW WATER SPRINGS - United Kingdom, Germany, Italy, Brazil, 



and Chile; 

 LOW WATER DATUM - Great Lakes (U. S. and Canada): 

 LOWEST LOW WATER SPRINGS - Portugal; 

 LOW WATER INDIAN SPRINGS - India and Japan (See INDIAN TIDE 



PLANE) : 

 LOWEST LOW WATER - France, Spain, and Greece. 



A common datum used on topographic maps is based on MEAN SEA LEVEL. 

 See also BENCH MARK. 



DEBRIS LINE - A line near the limit of storm wave uprush marking the 

 landward limit of debris deposits. 



A-9 



