SINUSOIDAL WAVE - An oscillatory wave having the form of a sinusoid. 



SLACK TIDE (SLACK WATER) - The state of a tidal current when its velocity 

 is near zero, especially the moment when a reversing current changes 

 direction and its velocity is zero. Sometimes considered the inter- 

 mediate period between ebb and flood currents during which the veloc- 

 ity of the currents is less than O.I knot. See STAND OF TIDE. 



SLIP - A berthing space between two piers. 



SLOPE - The degree of inclination to the horizontal. Usually expressed 



as a ratio, such as 1:25 or 1 on 25, indicating 1 unit vertical rise 

 in 25 units of horizontal distance; or in a decimal fraction (0.04); 

 degrees (2° 18'); or percent (4%). 



SLOUGH - See BAYOU. 



SOIL CLASSIFICATION (size) - An arbitrary division of a continuous scale 



of grain sizes such that each scale unit or grade may serve as a con- 

 venient class interval for conducting the analysis or for expressing 

 the results of an analysis. There are many classifications used; 

 the two most often used are shown graphically on the next page. 



SOLITARY WAVE - A wave consisting of a single elevation (above the origi- 

 nal water surface), its height not necessarily small compared to the 

 depth, and neither followed nor preceded by another elevation or de- 

 pression of the water surfaces . 



SORTING COEFFICIENT - A coefficient used in describing the distribution of 

 grain sizes in a sample of unconsolidated material. It is defined as 



So = Qi/Q3> where Qi is the diameter (in millimeters) which has 



75 percent of the cumulative size -frequency (by weight) distribution 

 smaller than itself and 25 percent larger than itself, and Q3 is that 

 diameter having 25 percent smaller and 75 percent larger than itself. 



SOUND (noun) - (1) A wide waterway between the mainland and an island, or 

 a wide waterway connecting two sea areas. See also STRAIT. (2) A 

 relatively long arm of the sea or ocean forming a channel between 

 an island and a mainland or connecting two larger bodies, as a sea 

 and the ocean, or two parts of the same body; usually wider and more 

 extensive than a strait. 



SOUND (verb) - To measure the depth of the water. 



SOUNDING - A measured depth of water. On hydrographic charts the sound- 

 ings are adjusted to a specific plane of reference (SOUNDING DATUM). 



SOUNDING DATUM - The plane to which soiondings are referred. See also 

 CHART DATUM. 



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