SEASHORE - The SHORE of a sea or ocean. 



SEAWALL - A structure separating land and water areas, primarily 



designed to prevent erosion and other damage due to wave action. 

 See also BULKHEAD. 



SEICHE - (1) A standing wave oscillation of an enclosed water body that 

 continues, pendulum fashion, after the cessation of the originating 

 force, which may have been either seismic or atmospheric. (2) An 

 oscillation of a fluid body in response to a disturbing force having 

 the same frequency as the natural frequency of the fluid system. 

 Tides are now considered to be seiches induced primarily by the 

 periodic forces caused by the sun and moon. (3) In the Great Lakes 

 area, any sudden rise in the water of a harbor or a lake whether or 

 not it is oscillatory. Although inaccurate in a strict sense, this 

 usage is well established in the Great Lakes area. 



SEISMIC SEA WAVE (TSUNAMI) - A long-period wave caused by an underwater 

 seismic disturbance or volcanic eruption. Commonly misnamed 

 "tidal wave". 



SEMIDIURNAL TIDE - A tide with two high and two low waters in a tidal 



day with comparatively little diurnal inequality (See Figure A-10.) 



SET OF CURRENT - The direction toward which a current flows . 



SETUP, WAVE - Superelevation of the water surface over normal surge 

 elevation due to onshore mass transport of the water by wave 

 action alone. 



SETUP, WIND - See WIND SETUP. 



SHALLOW WATER - (1] Commonly, water of such a depth that surface waves 

 are noticeably affected by botrtom topography. It is customary to 

 consider water of depths less than one-half the surface wavelength 

 as shallow water. See TRANSITIONAL ZONE and DEEP WATER. (2) More 

 strictly, in hydrodynamics with regard to progressive gravity waves, 

 water in which the depth is less than 1/25 the wavelength. Also 

 called VERY SHALLOW WATER. 



SHEET PILE - See PILE, SHEET. 



SHELF, CONTINENTAL - See CONTINENTAL SHELF. 



SHELF, INSULAR - See INSULAR SHELF. 



SHINGLE - (1) Loosely and commonly, any beach material coarser than 

 ordinary gravel, especially any having flat or flattish pebbles. 

 (2) Strictly and accurately, beach material of smooth, well-rounded 

 pebbles that are roughly the same size. The spaces between pebbles 

 are not filled with finer materials. Shingle often gives out a 

 musical sound when stepped on. 



A-32 



