SWELL - Wind-generated waves that have traveled out of their generating ^ 



area. Swell characteristically exhibits a more regular and longer fl 



period, and has flatter crests than waves within their fetch ^ 

 (SEAS) . 



SYNOPTIC CHART - A chart showing the distribution of meterological 



conditions over a given area at a given time. Popularly called 

 a weather map. 



SYZYGY - The two points in the moon's orbit when the moon is in con- 

 junction or opposition to the sun relative to the earth; time of 

 new or full moon in the cycle of phases. 



TERRACE - A horizontal or nearly horizontal natural or artificial topo- 

 graphic feature interrupting a steeper slope, sometimes occurring 

 in a series. 



THALWEG - In hydraulics, the line joining the deepest points of an 

 inlet or stream channel. 



TIDAL CURRENT - See CURRENT, TIDAL. 



TIDAL DATUM - See CHART DATUM and DATUM PLANE. 



TIDAL DAY - The time of the rotation of the earth with respect to the 

 moon, or the interval between two successive upper transits of the 

 moon over the meridian of a place, approximately 24.84 solar hours A 

 (24 hours and 50 minutes) or 1.035 times the mean solar day. (See ^ 

 Figure A-10.) Also called lunar day. 



TIDAL FLATS - Marshy or muddy land areas which are covered and un- 

 covered by the rise and fall of the tide. 



TIDAL INLET - (1) A natural inlet maintained by tidal flow. (2) 



Loosely, any inlet in which the tide ebbs and flows. Also TIDAL 

 OUTLET. 



TIDAL PERIOD - The interval of time between two consecutive like phases 

 of the tide. (See Figure A-10.) 



TIDAL POOL - A pool of water remaining on a beach or reef after reces- 

 sion of the tide. 



TIDAL PRISM - The total amount of water that flows into a harbor or 

 estuary or out again with movement of the tide, excluding any 

 freshwater flow. 



TIDAL RANGE - The difference in height between consecutive high and low 

 (or higher high and lower low) waters. (See Figure A-10.) 



A-38 



