ROENTGEN EQUIVALENT PHYSICAL 



breaker line. {See figure for nearshore cur- 

 rent system.) 



rip feeder current — See feeder current. 



ripple — ^1. Tlie ruffling of the surface of water, 

 Iience a little curling wave or undulation. (61) 

 2. A wave controlled to a significant degree by 

 both surface tension and gravity. 



ripple marks — Undulating surface features of 

 various shapes produced ni unconsolidated sedi- 

 ments by wave or current action. Compound 

 ripples are characterized by systematically offset 

 crests and are produced by simultaneous inter- 

 fei'ence of wave oscillation witli current action. 

 Metaripples are asymmetrical sand ripples. As 

 size increases, ripples grade into sand waves, 

 sand ridges, sand dunes, and migratory sand- 

 banks or shoals. 



rips — A turbulent agitation of water generally 

 caused by the interaction of currents and wind ; 

 in nearshore regions rips may also be caused by 

 currents flowing swiftly over an irregular 

 bottom. 



rip surf — See rip current. 



rip tide — See rip current. 



rise — 1. A long, broad elevation that rises gently 

 and generally smoothly from the sea floor. (62) 

 2. The water level height measured above 

 chart datum. 



rise of the tide — The height of the tide measured 

 above chart datum, (50) 



rising tide — (sometimes called jiood tide). The 

 portion of the tide cycle between low water and 

 the following high water. (5) 



river discharge — (also called river outflow, river 

 runojf) . The rate of flow of water past a point 

 in a stream, expressed as volume per unit time 

 (usually cubic feet per second, cfs). More 

 specifically, the volume of river water that flows 

 into the sea, usually measured in cubic kilo- 

 meters, cubic miles, cubic meters, or cubic feet, 

 and sometimes acre-feet. 



River discharge may affect tidal currents con- 

 siderably, especially during rainy seasons, by in- 

 creasing th% strength and duration of ebb and 

 decreasmg the strength and duration of flood. 



river ice — Any ice formed in or carried by a 

 river. (68) 



river outflow — See river discharge. 



river runoff — See river discharge. 



Roberts radio current meter — An electro- 

 mechanical current meter which measures cur- 

 rent speed and direction. This meter can be 

 suspended below an anchored buoy or ship which 

 is equipped with a radio transmitter that trans- 

 mits the current measurements to a ship or shore 

 based monitor station. 



rock — The naturally occurring material that 

 forms the firm, hard, and solid masses of the 

 ocean floor. Also a collective term for masses 

 of hard material generally not smaller than 266 

 millimeters. See acid rock, basic rock. 



rock barnacle — Sec acorn barnacle. 



rock borer — A meml)er of any one of several 

 families, including tlio MytiJidae, Saxicavidae, 

 and tlie Pholadidae, of bivalves that live in 

 cavities they bore in soft rock, concrete, and 

 other materials. Boring generally is accom- 

 plished by rotating tlie shell, which bears 

 tootlied or rasplike projections; chemical solu- 

 tion of the rock may be a method used addi- 

 tionally by some. See marine borer. 



rock flour — Finely ground rock particles, chiefly 

 silt size, resulting from glacial abrasion. A 

 component of marine deposits off' glacial stream 

 mouths. (2) 



rockweed — (or wrack). One of a group of 

 marine plants, principally of an order (Fucales) 

 of the brown algae, mostly multibranched and 

 leatliery, which grow attached to rocks in the 

 intertidal zone by means of an organ called a 

 holdfast. The rockweed of the New England 

 clambake belongs to the genera Fucusi and 

 Aficophyllwm. 



rocky area — ( or foul area) . An area with a rocky 

 bottom. 



roentgen — (abbreviated r). An exposure dose 

 of X- or gamma radiation such that the associ- 

 ated corpuscular emission per 0.001293 grams of 

 air produces, in air, ions carrying 1 electrostatic 

 unit of quantity of electricity of either sign. 

 (70) 



Roentgen equivalent man — (abbreviated rem). 

 A measure of any ionizing radiation to body 

 tissue in terms of its estimated biological effect 

 relative to a dose of one roentgen (r) of X-rays. 

 The relation of the rem to other dose units 

 depends ujaon the biological effect under consid- 

 eration and upon the conditions of the irradia- 

 tion. Practically speaking each of the following 

 is considered to be equivalent to a dose of one 

 rem: (1) A dose of 1 roentgen due to X- or 

 gamma radiation ; (2) A dose of 1 rad due to X-, 

 gamma, or beta radiation ; (3) A dose of 0.1 rad 

 due to neutrons or high energy protons; and (4) 

 A dose of 0.5 rad due to particles heavier than 

 protons. (As defined by the Atomic Energy 

 Omn.mission.) See radiation absorbed dose. 



Roentgen equivalent physical — (abbreviated 

 rep) . The rep is defined as the quantity of cor- 

 puscular radiation which produces in tissue, per 

 gram of tissue, ionization equivalent to the 

 quantity of ionization of 1 roentgen of gamma 

 radiation in air. However, in early practice 

 the rep was widely accepted as a unit of absorbed 

 dose representing 93 to 97 ergs per gram of soft 

 animal tissue. Although the rep unit is still 

 being used in some food irradiation studies and 

 other miscellaneous radiation experiments, it is 

 quite rajDidly being replaced by the more easily 

 defined rad units. (70) See radiation 

 absorbed dose. 



137 



