SHORELINE. The intersection of a specified plane of water with the shore or 

 beach (e.g., the high water shoreline would be the intersection of the 

 plane of mean high water with the shore or beach). The line delineating 

 the shoreline on National Ocean Service nautical charts and surveys 

 approximates the mean high water line. 



SIGNIFICANT WAVE. A statistical term relating to the one-third highest waves 

 of a given wave group and defined by the average of their heights and 

 periods. The composition of the higher waves depends upon the extent to 

 which the lower waves are considered. Experience indicates that a careful 

 observer who attempts to establish the character of the higher waves will 

 record values which approximately fit the definition of the significant 

 wave. 



SIGNIFICANT WAVE HEIGHT. The average height of the one-third highest waves of 

 a given wave group. Note that the composition of the highest waves 

 depends upon the extent to which the lower waves are considered. In wave 

 record analysis, the average height of the highest one-third of a selected 

 number of waves, this number being determined by dividing the time of 

 record by the significant period. Also CHARACTERISTIC WAVE HEIGHT. 



SIGNIFICANT WAVE PERIOD. An arbitrary period generally taken as the period of 

 the one-third highest waves within a given group. Note that the 

 composition of the highest waves depends upon the extent to which the 

 lower waves are considered. In wave record analysis, this is determined 

 as the average period of the most frequently recurring of the larger well- 

 defined waves in the record under study. 



SILT. See SOIL CLASSIFICATION. 



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 intermediate 

 period between ebb and flood currents during which the velocity of the 

 currents is less than 0.05 meter per second (0.1 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 percent). 



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 convenient 

 class interval for conducting the analysis or for expressing the results 

 of an analysis. There are many classifications used; the two most of en 

 used are shown graphically in Table A-1. 



A-32 



