RIP CURRENT - A strong surface current flowing seaward from the shore. 

 It usually appears as a visible band of agitated water and is the 

 return movement of water piled up on the shore by incoming waves 

 and wind. With the seaward movement concentrated in a limited 

 band its velocity is somewhat accentuated. A rip consists of 

 three parts: the FEEDER CURRENTS flowing parallel to the shore 

 inside the breakers; the NECK, where the feeder currents converge 

 and flow through the breakers in a narrow band or "rip"; and the 

 HEAD, where the current widens and slackens outside the breaker 

 line. A rip current is often miscalled a rip tide. Also RIP SURF. 

 See NEARSHORE CURRENT SYSTEM. (See Figure A- 7.) 



RIP SURF - See RIP CURRENT. 



RIPPLE - (1) The ruffling of the surface of water, hence a little curling 

 wave or undulation. (2) A wave less than 2 inches long controlled 

 to a significant degree by both surface tension and gravity. See 

 WAVE, CAPILLARY and WAVE, GRAVITY. 



RIPPLES (BED FORMS) - Small bed forms with wavelengths less than 1 foot 

 and heights less than 0.1 foot. 



RIPRAP - A layer, facing, or protective mound of stones randomly placed 



to prevent erosion, scour, or sloughing of a structure or embankment; 

 also the stone so used. 



ROADSTEAD (Nautical) - A sheltered area of water near shore where vessels 

 may anchor in relative safety. Also road. 



ROLLER - An indefinite term, sometimes considered to denote one of a 

 series of long- crested, large waves which roll in on a shore, as 

 after a storm. 



RUBBLE - (1) Loose angular waterworn stones along a beach. (2) Rough, 

 irregular fragments of broken rock. 



RUBBLE-MOUND STRUCTURE - A mound of random-shaped and random-placed 



stones protected with a cover layer of selected stones or specially 

 shaped concrete armor units. (Armor units in primary cover layer 

 may be placed in orderly manner or dumped at random.) 



RUNNEL - A corrugation or trough formed in the foreshore or in the bottom 

 just offshore by waves or tidal currents. 



RUNUP - The rush of water up a structure or beach on the breaking of a 

 wave. Also UPRUSH. The amount of runup is the vertical height 

 above Stillwater level that the rush of water reaches. 



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A-30 



