SURFACE TENSION 



determmed by a thermometer in an instrument 

 shelter. 



surface tension — (also called surface energy^ sur- 

 face free energy, capillary forces, interfacial 

 tension). A phenomenon peculiar to the sur- 

 face of liquids, caused by a strong attraction to- 

 wards the interior of the liquid acting on the 

 liquid molecules in or near the surface in such 

 a way to reduce the surface area. An actual 

 tension results and is usually expressed in dyne 

 per centimeter or erg per square centimeter. 



(5) 

 surface water — See mixed layer, 

 surface wave — A progressive gravity wave in 



which the disturbance (that is, the particle 

 movement in the fluid mass as well as the sur- 

 face movement) is confined to the upper limits 

 of a body of water. Strictly speaking this term 

 applies to those progressive gravity waves whose 

 celerity depends only upon the wavelength 

 (73) 



surf beat — Irregular oscillations of the nearshore 

 water level, with periods of the order of several 

 minutes. (61) See beating. 



surf zone — The area between the outermost 

 breaker and the limit of wave uprush. (61) 



surge — 1. The name applied to wave motion with 

 a period intermediate between that of the ordi- 

 nary wind wave and that of the tide, from about 

 1/^ to 60 minutes. It is of low height, usually 

 less than 0.3 foot. (61) 



2. Horizontal oscillation of water with com- 

 parative short period accompanying a seiche. 

 ( 73 ) See storm surge. 



3. See ship motion. 



surge channel — A transverse channel cutting the 

 outer edge of an organic reef in which the water 

 level fluctuates with wave or tidal action. (2) 



surging breaker — See breaker. 



surveillance — The systematic observation of air, 

 surface, or subsurface areas by visual, electronic, 

 photographic, or other means. 



suspended load — See load. 



suspension current — See turbidity current. 



sverdrup — A unit of volume transport equal to 

 one million cubic meters (35.313 million cubic 

 feet) per second. (45) 



Swallow float — A tubular buoy, usually made of 

 aluminum, that can be adjusted to remain at a 

 selected density level to drift with the motion 

 of that water mass. The float is tracked by 

 shipboard listening devices and current veloci- 

 ties can be determined. 



swash — (or ufrush, run-up). 1. The rush of 

 water up onto the beach following the breaking 

 of a wave. 



2. A narrow channel or sound within a sand- 

 bank, or between a sandbank and the shore. 

 (68) 



3. Also a bar over which the sea washes. (68) 

 swash channel — 1. On the open shore, a channel 



cut by flowing water in its return to the parent 

 body (that is, a rip channel) . 



2. A secondary channel passing through or 

 shoreward of an inlet or river bar. {See figure 

 for bars.) 

 (61) 

 swash mark — The thin wavy line of fine sand, 

 mica scales, bits of seaweed, etc., left by the up- 

 rush when it recedes from its upward limit of 

 movement on the beach face. (61) 



10 



^^^^ 



SCHEMATIC DIAGRAM OF WAVES IN THE BREAKER ZONE 



1. Surf or Breaker zone; 2. Tronslatory waves; 3. Inner line of 

 breakers; 4. Peaked up wove; 5. Reformed oscillatory wove; 

 6. Outerline of breakers; 7. Still water level; 8. Waves flatten 

 again; 9. Waves break up but do not break on this bar at high 



tide; 10. Limit of uprush; 11. Uprush; 12. Backrush; 13. 

 Beach face; 14. Inner bar; 15. Outer bar (inner bor at Low 

 tide); 1 6. Deep bar (outer bar at low tide); 1 7. Mean lo¥r«r 

 low water (MLLW); 1 8. Breaker depth g 1 .3 height 

 1 9. Plunge point 



160 



