Knowledge Base

RACE — (1) A strong or swift current of water. (2) The channel of such a current. Also, an artificial channel built to transport water and use its energy; a Raceway.

RACEWAY — A rectangular fish rearing unit that has a continuous flow of freshwater to maintain suitable oxygen, temperature, and cleanliness for intensive production.

RADIAL DRAINAGE — An arrangement of stream courses in which the streams radiate outward in all directions from a central zone or inward from all directions to a central area.

RADIAL FLOW — The flow of water in an aquifer toward a vertically oriented well.

RADIUS OF INFLUENCE — The radial distance from the center of a well bore to the point where there is no lowering of the water table or Potentiometric Surface (the edge of its Cone of Depression).

RAIN — Water falling to earth in drops that have been condensed from moisture in the atmosphere. Generally larger than 0.02 inches (0.05 cm) in diameter and which fall in still air at velocities usually greater than 10 feet (3.0 meters) per second.

RAIN AREA — (1) The area indicated on a weather map over which rain fell within a certain period of time. (2) The area over which rain is falling. (3) The most rainy portion of a cyclonic storm.

RAINDROP — A drop of rain.

RAINFALL — (1) A shower or fall of rain. (2) The quantity of water that falls as rain in a specified area and time interval. Not strictly synonymous with Precipitation.

RAINFALL COMPONENT — That part of the flow of a channel attributed to rain falling directly on the surface of the channel.

RAINFALL DURATION — The period of time during which rainfall occurs, exceeds a given intensity, or maintains a given intensity.

RAINFALL, EXCESS — That part of the rain in a given storm which falls at intensities exceeding the Infiltration Capacity of the land. The volume of rainfall available for direct runoff. It is equal to the total rainfall minus Interception, Depression Storage, and Absorption.

RAINFALL FREQUENCY — The frequency, usually expressed in years, at which a given rainfall intensity and duration can be expected to be equaled or exceeded.

RAINFALL (PRECIPITATION) INTENSITY AREA CURVE — A curve which expresses the relation between average rainfall or precipitation depth (or the rate) and the area over which it occurs for a given storm duration. Each curve generally covers a period of years during which the intensities shown will not, on the average, be exceeded more than once.

RAINFALL (PRECIPITATION) INTENSITY-DURATION CURVE — A curve showing the relationship between average rainfall or precipitation depth (or the rate) and storm duration in a given area.

RAINFALL (PRECIPITATION) INTENSITY-DURATION-FREQUENCY CURVE — Curves showing the relationship between rainfall or precipitation intensity and duration for different levels of frequency; each curve represents the rainfall intensity-duration which will be equaled or exceeded once in a certain number of years, indicated as the frequency of that curve.

RAINFALL (PRECIPITATION) INTENSITY FREQUENCY — The average time interval between the occurrence of the rainfall or precipitation of a given or greater intensity.

RAINFALL, MAXIMIZATION — (1) Moisture Maximization — The process of adjusting precipitation upward to a theoretical value that would have pertained if the moisture content of the air had been at the maximum with other storm conditions remaining unchanged. (2) Sequential Maximization — Reducing the observed elapsed time between storms to develop a hypothetical severe precipitation sequence. (3) Spatial Maximization — Reducing the distance between precipitation storms for a hypothetical severe sequence.

RAINFALL RATE — The amount of precipitation occurring in a unit of time; generally expressed in inches per hour.

RAINFALL (PRECIPITATION), RESIDUAL — Rain (or precipitation) that falls at the end of a storm at a rate less than the infiltration capacity.

RAINWATER — Water that has fallen as rain and contains little dissolved mineral matter.

RAPIDS — A part of a stream where the current is moving with a greater swiftness than usual and where the water surface is broken by obstructions, but without a sufficient break in slope to form a water fall, as where the water descends over a series of small steps. It commonly results from a sudden steepening of the stream gradient, from the presence of a restricted channel, or from the unequal resistance of the successive rocks traversed by the stream.

RAPID SAND FILTER — Generally a concrete basin filled with graded gravel and coarse sand. Filtration rates are about 40 times higher than in a slow sand filter, and cleaning is via a backwash operation.

RATING CURVE — (1) A graphic representation of a Rating Table (see below). (2) A curve showing the relation between Gage Height and discharge of a stream or conduit at a given Gaging Station. (3) A curve showing the relation between the discharge of a gage, meter, or other hydraulic structure or instrument and the pertinent hydraulic conditions affecting the discharge, such as pressure, hydrostatic head, and velocity of approach. If more than one condition affects discharge, a family of curves is needed to represent the rating.

RATING TABLE — (1) A table showing the relation between two mutually dependent quantities or variables over a given range of magnitude. (2) A table showing the relation between the Gage Height and the discharge of a stream or conduit at a given Gaging Station. (3) A table showing the relationship between the stage in a reservoir and its volume.

RAW SEWAGE — Untreated domestic or commercial wastewater.

RAW SLUDGE — The material settled out during the primary clarification of sewage.

RAW WATER — (1) Water that is direct from the source — ground or surface water — without any treatment. (2) Untreated water, usually that entering the first unit of a water treatment plant.

REACH (OF RIVER) — (1) Most generally, any specified length of a stream or conveyance. (2) A length of channel which is uniform in its discharge depth, area, and slope. (3) A length of channel for which a single gage affords a satisfactory measure of the stage and discharge. (4) The length of a river between two gaging stations.

REASONABLE PUMP LIFT — A determination of the rate and volume of water to be pumped from an aquifer. The reasonable pump lift (rate of withdrawal) would include consideration of:
[1] water quality in the aquifer or the basin, including sea water intrusion, base of fresh water, and lateral or vertical migration of contaminants;
[2] the ground water management program;
[3] the thickness of the aquifer;
[4] the depth of existing wells;
[5] the capital cost of new wells;
[6] the net cash flow; and
[7] the total amount of ground water that can be extracted during one water year by the total number of existing wells.

RECESSION HYDROGRAPH (CURVE) — A Hydrograph which shows the decreasing rate of runoff following a period of rain or snowmelt. Since Direct Runoff and Base Runoff recede at different rates, separate curves, called direct runoff recession curves, are generally drawn. Use of the term Depletion Curve in the sense of base runoff recession is not recommended.

RECHARGE (HYDROLOGIC) — The introduction of surface or ground water to groundwater storage such as an aquifer. Recharge or replenishment of groundwater supplies consists of three (3) types:
[1] Natural Recharge which consists of precipitation or other natural surface flows making their way into groundwater supplies;
[2] Artificial or Induced Recharge which includes actions by man specifically designed to increase supplies in a groundwater reservoirs through various methods such as water spreading (flooding), ditches, and pumping techniques; and
[3] Incidental Recharge which consists of actions, such as irrigation and water diversion, which add to groundwater supplies but are intended for other purposes.
Recharge may also refer to the amount of water so added.

RECHARGE AREA — The area in which water reaches the Zone of Saturation by surface infiltration. Infiltration moves downward into the deeper parts of an aquifer in a recharge area.

RECHARGE, ARTIFICIAL — The designed (as opposed to the natural or incidental) replenishment of ground water storage from surface water supplies. There exist five (5) common techniques to effect artificial recharge of a groundwater basin:
[1] Water Spreading consisting of the basin method, stream-channel method, ditch method, and flooding method, all of which tend to divert surface water supplies to effect underground infiltration;
[2] Recharge Pits designed to take advantage of permeable soil or rock formations;
[3] Recharge Wells which work directly opposite of pumping wells although have limited scope and are better used for deep, confined aquifers;
[4] Induced Recharge which results from pumping wells near surface supplies thereby inducing higher discharge towards the well; and
[5] Wastewater Disposal which includes the use of secondary treatment wastewater in combination with spreading techniques, recharge pits, and recharge wells to reintroduce the water to deep aquifers thereby both increasing the available groundwater supply and also further improving the quality of the wastewater.

RECHARGE BASIN — A surface facility, often a large pond, used to increase the infiltration of surface water into a ground water basin.

RECHARGE BOUNDARY — An aquifer system boundary that adds water to the aquifer. Streams and lakes are typical recharge boundaries.

RECHARGE, INCIDENTAL — Ground water recharge (infiltration) that occurs as a result of human activities unrelated to a recharge project, for example, irrigation and water diversion (unlined canals).

RECHARGE, NATURAL — The replenishment of groundwater storage from naturally-occurring surface water supplies such as precipitation and stream flows.

RECHARGE RATE — The quantity of water per unit of time that replenishes or refills an aquifer.

RECHARGE WELL — Used in conjunction with artificial or induced ground water recharge techniques, the recharge well works directly opposite of pumping wells to induce surface water into the ground water system. Based on the nature of the soil and rock being recharged, the use of recharge wells typically have limited scope and are better employed for recharging deep, confined aquifers.

RECHARGE ZONE — A land area into which water can infiltrate into an Aquifer relatively easily. The infiltration replenishes the aquifer. The location is also referred to as a Recharge Area.

RECIRCULATED WATER — Water that is used more than one time before it passes back into the natural hydrological system or discharged into a wastewater system. Also referred to as Recycled Water.

RECIRCULATION — Water reused within a plant unit. Sometimes, it also means water discharged by one unit and reused by other units in the same plant.

RECLAIMED SEWAGE — Wastewater treatment-plant effluent that has been diverted or intercepted for use before it reaches a natural waterway or aquifer.

RECLAIMED WASTE WATER — Waste water that becomes suitable for a specific beneficial use as a result of treatment or brackish water demineralized for use. General types of reclaimed waste water include:
[1] Primary Effluent — reclaimed water that only has had sewage solids removed and is typically used only for surface irrigation of tree, fodder, and fiber crops;
[2] Secondary Effluent — reclaimed water that has had sewage solids removed and has been oxidized and disinfected and is used to irrigate golf courses and cemeteries and provide water for pasture and food crops; and
[3] Tertiary Recycled Water — water produced by conventional sewage treatment followed by more advanced procedures including filtration and disinfection, providing it with the broadest range of uses.

RECLAIMED WATER — Refers to water that has received at least Secondary Wastewater Treatment and is reused after flowing out of a wastewater treatment facility.

RECLAMATION — (1) The process of land treatment that minimizes water degradation, air pollution, damage to aquatic or wildlife habitat, flooding, erosion, and other adverse effects from surface mining operations including adverse surface effects incidental to underground mines, so that mine lands are reclaimed to a usable condition which is readily adaptable for alternate land uses and creates no danger to public health or safety. The process may extend to affected land surrounding mining lands, and may require backfilling, grading, resoiling, revegetation, soil compaction, stabilization, and other measures. (2) May also apply to other land uses and land types, for example, the reclaiming of waste, desert, marshy or submerged land for cultivation, preservation, reuse, etc.

RECLAMATION OF WASTEWATER — The process of treating salvaged water from municipal, industrial, or agricultural waste water sources for beneficial uses, whether by means of special facilities or through natural processes.

RECLAMATION WITHDRAWAL — A withdrawal of public lands in connection with a reclamation project.

RECONDITIONING (WATER WELL) — The deepening, reaming, casing, recasing, perforating, reperforating, jetting, swabbing, installing of liner pipe, packers and seals or any other significant change in the design or construction of a water well.

RECORDER, STEAM FLOW — A mechanical apparatus which records a continuous record of a water level or other hydrologic factors such as water temperature, flow rates, etc.

RECYCLED WATER — Water that is used more than one time before it passes back into the natural hydrologic system.

REFERENCE WETLAND — A wetland within a relatively homogeneous biogeographic region that is representative of a specific hydrogeomorphic wetland type.

REGIMEN OF A STREAM — The system or order characteristic of a stream, i.e., its habits with respect to velocity and volume, form and changes in channel, capacity to transport sediment, and amount of material supplied for transportation. The term is also applied to a stream which has reached an equilibrium between corrosion and deposition or, in other words, to a graded stream.

REGULATION — (Hydrology) The artificial manipulation of the flow of a stream.

REGULATION RESERVOIR — A reservoir used in canal and irrigation systems to reduce the mismatch between downstream demands and upstream water supplies in order to maintain a balanced operation.

REIMBURSABLE COSTS — Those costs associated with a water project that are expected to be recovered, usually from direct beneficiaries, and repaid to the funding entity.

REJUVENATION — A change in condition of erosion that causes a stream to begin more active erosion and a new cycle.

RELATIVE HUMIDITY — The ratio of the amount of water vapor in the atmosphere to the amount necessary for saturation at the same temperature. Relative humidity is expressed in terms of percent and measures the percentage of saturation.

RELEASE — Any spilling, leaking, pumping, pouring, emitting, emptying, discharging, injecting, escaping, leaching, dumping, or disposing into the environment of a hazardous or toxic chemical or extremely hazardous substance.

RELICTION — A recession of the sea or other water body leaving land uncovered. Also, the land so left uncovered.

RELIEF WELLS (of a Dam) — A vertical well or borehole, usually downstream of impervious cores, grout curtains, or cutoffs, designed to collect and direct seepage through or under a dam to reduce uplift pressure under or within the dam. A line of such wells forms a relief well curtain.

REMOTE SENSING — The measurement or acquisition of information of some property of an object or phenomenon by a recording device that is not in physical or intimate contact with the object or phenomenon under study. Also, the utilization at a distance (as from aircraft, spacecraft, satellites, or ships) of any device and its attendant display for gathering information pertinent to the environment, such as measurements of force fields, electromagnetic radiation, infrared sensing, land use, water bodies, etc. Such systems typically employ devices such as cameras, lasers, radio frequency receivers, radar systems, infrared detectors, sonar seismographs, gravimeters, magnetometers, and scintillation counters.

RENEWABLE ENERGY — A source of energy that is replaced by natural phenomena, such as firewood or the water held by a dam and used for hydroelectric purposes. Conversely, fossil fuels are a nonrenewable source of energy.

RENEWABLE (NATURAL) RESOURCE — Natural resources that continuously can be replenished in the course of natural events within the limits of human time.

REPRESENTATIVE SAMPLE — A portion of material or water that is as nearly identical in content and consistency as possible to that in the larger body of material or water being sampled.

"REPURIFIED WATER" — Denotes reclaimed or recycled wastewater that is treated far beyond the most stringent standards current in force and then remixed with fresh water to augment existing water supplies. Typically, such waters would undergo extensive Tertiary Wastewater Treatment and then be stored in a reservoir (say, for up to one year), subsequently blended with fresh water supplies and then undergo further disinfection through conventional drinking water treatment before being distributed to municipal water users.

RE-REGULATING RESERVOIR — A reservoir for reducing diurnal (daily) fluctuations resulting from the operation of an upstream reservoir for power production.

RESERVATION — A withdrawal usually of a more or less permanent nature; also, any federal lands of the U.S. government which have been dedicated to a specified public purpose such as a national forest, wildlife refuge, or wilderness area.

RESERVATION OR WITHDRAWAL OF WATER — The withholding of water from appropriation. A reservation or withdrawal of water in order to preserve instream values would have the same affect as a Minimum Flow Appropriation for that purpose: The only essential difference is the procedure used.

RESERVE CAPACITY — Extra treatment capacity built into solid waste and wastewater treatment plants and interceptor sewers to accommodate flow increases due to future population growth.

RESERVE SUPPLY — Developed but presently unused surface water supply available to certain portions of a hydrologic study or planning area (as defined) to meet planned future water needs; the supply is not usually available to other areas needing additional water because of a lack of physical facilities and/or institutional arrangements.

RESERVOIR (Water) — A pond, lake, or basin, either natural or artificial, for the storage, regulation, and control of water.

RESERVOIR AREA — The surface area of a reservoir when filled to controlled retention water level.

RESERVOIR, MULTIPURPOSE — A reservoir constructed and equipped to provide storage and release of water for two or more purposes such as flood control, power development, navigation, irrigation, pollution abatement, domestic water supply, etc.

RESERVOIR, RE-REGULATING — A reservoir used to regulate the outflow from an upstream reservoir.

RESERVOIR, RETARDING — An ungated reservoir for temporary storage of floodwater. Sometimes called a Detention Reservoir.

RESERVOIR, SINGLE-PURPOSE — A reservoir planned to serve only one purpose.

RESERVOIR SURFACE — The surface of a reservoir at any level.

RESIDENTIAL WATER USE — Water used normally for residential purposes, including household use, personal hygiene, and drinking, watering of domestic animals, and outside uses such as car washing, swimming pools, and for lawns, gardens, trees and shrubs. The water may be obtained from a public supply or may be self supplied. Also referred to as Domestic Water Use.

RESIDENT POPULATION — The number of persons who live within a state or other political subdivision (county, city, etc.) who consider it their permanent place of residence. College students, military personnel, and inmates of penal institutions are counted as permanent residents. According to this definition, tourist and seasonal or part-time residents are considered nonresident population.

RESIDUAL AVERAGE ANNUAL FLOOD DAMAGES — Those flood damages which are not prevented by a flood control project or by other structural or nonstructural flood damage prevention measures.

RESIDUAL DEPRESSION STORAGE — Depression storage existing at the end of a period of excess rain.

RESIDUAL DETENTION STORAGE — Detention storage existing at the end of a period of excess rain.

RESIDUAL DISCHARGE — Direct surface discharge at the end of a period of excess rain.

RESIDUAL FLOOD DAMAGES — Those flood damages which are not prevented by a flood plain management program. They may or may not be preventible by other flood control measures (including both structural and nonstructural means).

RESOURCES — That which is, or may be, readily available as a source of supply or support. Also, the total amount of any rock, mineral, or fuel in the crust of the earth. Compare to Reserves.

RESOURCE MANAGEMENT SYSTEM — A combination of conservation practices identified by the primary use of land or water that, if effected, will at a minimum protect the resource base by meeting tolerable soil losses, maintaining acceptable water quality, and maintaining acceptable ecological and management levels for the selected resource use. Such systems may include conservation practices that provide for quality in the environment and quality in the standard of living.

RESOURCE MONITORING — The act of continually or periodically observing resources to determine changes and trends in their status and condition.

RETARDING RESERVOIR — Ungated reservoir for temporary storage of flood water.

RETENTION — That part of the precipitation falling on a drainage area that does not escape as a surface streamflow, during a given period.

RETENTION BASIN — A permanent lake or pond used to slow stormwater runoff.

RETURN FLOW — (1) That part of a diverted flow which is not consumptively used and returns to its original source or another body of water. (2) (Irrigation) Drainage water from irrigated farmlands that re-enters the water system to be used further downstream. Such waters may contain dissolved salts or other materials that have been leached out of the upper layers of the soil.

RETURN FLOW (IRRIGATION) — Irrigation water applied to an area which is not consumed in evaporation or transpiration and returns to a surface stream or ground water aquifer.

RETURN FLOW CREDIT — The concept of water use allocations based only on actual Consumptive Use; waters returned to the system are credited, in whole or part, against the original allowable allocations.

RETURN PERIOD (or RECURRENCE INTERVAL) — In statistical analysis of hydrologic data, based on the assumption that observations are equally spaced in time with the interval between two successive observations as a unit of time, the return period is the reciprocal of 1 minus the probability of a value equal to or less than a certain value; it is the mean number of such time units necessary to obtain a value equal to or greater than a certain value one time. For example, with a one-year interval between observations, a return period of 100 years means that, on the average, an event of this magnitude, or greater, is not expected to occur more often than once in 100 years.

RETURN SEEPAGE — Water which percolates from canals and irrigated areas to underlying strata, raising the ground-water level, and eventually returning to natural channels.

REUSE (of Water) — Water that is discharged by one user and is used by other users. Sometimes, it also means water discharged by one unit and used by other units in the same plant.

REUSE SYSTEMS — Refers to the deliberate application of reclaimed water for a beneficial purpose. Reuse may encompass landscape irrigation (such as golf courses, cemeteries, highway medians, parks, playgrounds, school yards, nurseries, and residential properties), agricultural irrigation (such as food and fruit crops, wholesale nurseries, sod farms and pasture grass), aesthetic uses, ground-water recharge, environmental enhancement of surface water and wetland restoration, fire protection, and other useful purposes.

REUSE WATER — Water used repeatedly.

RIGHT ABUTMENT — That part of the right-hand side of a valley side wall against which a dam is constructed. The right abutment is viewed by an observer looking downstream.

RIGHT BANK — The right-hand side of a stream, river, or channel when facing in the direction of the flow.

"RIGHT OF FREE CAPTURE" — The idea or concept that the water under a person's land belongs to that person and they are free to capture and use as much as they want. Also called the "law of the biggest pump." Does not apply where both surface water and ground water is regulated.

RIPARIAN — Pertaining to the banks of a river, stream, waterway, or other, typically, flowing body of water as well as to plant and animal communities along such bodies of water. This term is also commonly used for other bodies of water, e.g., ponds, lakes, etc., although Littoral is the more precise term for such stationary bodies of water. Also refers to the legal doctrine (Riparian Doctrine and Riparian Water Rights) that says a property owner along the banks of a surface water body has the primary right to withdraw water for reasonable use.

RIPARIAN AREAS (HABITAT) — Land areas directly influenced by a body of water. Usually such areas have visible vegetation or physical characteristics showing this water influence. Stream sides, lake borders, and marshes are typical riparian areas. Generally refers to such areas along flowing bodies of water. The term Littoral is generally used to denote such areas along non-flowing bodies of water.

RIPARIAN DOCTRINE — The system for allocating water used in England and the eastern United States. Under the Riparian Doctrine, ownership of land along a stream or river (i.e., riparian lands) is an absolute prerequisite to a right to use water from that body of water and each such landowner has an equal right to the water (whether or not he is presently using it or not).

RIPARIAN HABITAT — Areas adjacent to rivers and streams with a high density, diversity, and productivity of plant and animal species relative to nearby uplands.

RIPARIAN LAND — Land situated along the bank of a stream or other, generally flowing bodies of water.

RIPARIAN OWNER — One who owns land bounding upon a river or water course.

RIPARIAN VEGETATION — Plants adapted to moist growing conditions found along waterways and shorelines. They are frequently important to wildlife habitat because of their greater density and succulence.

RIPARIAN WATER RIGHTS — The rights of an owner whose land abuts water. They differ from state to state and often depend on whether the water is a river, lake, or ocean. The doctrine of riparian rights is an old one, having its origins in English common law. Specifically, persons who own land adjacent to a stream have the right to make reasonable use of the stream's natural flow on those lands within the watershed. (The emphasis on natural flow means that riparian rights cannot be claimed for long-term storage of water in a reservoir.) Riparian users of a stream share the streamflow among themselves, and the concept of priority of use (Prior Appropriation Doctrine) is not applicable. Under drought conditions, the users share shortages. Riparian rights cannot be sold or transferred for use on nonriparian land. Riparian rights to the waters of a lake, as opposed to a flowing stream, are often referred to as Littoral Water Rights.

RISER — A vertical pipe as for water.

RISING SLUDGE — (Water Quality) The rising of previously settled solids in the settling tank of an activated sludge system. The immediate cause is denitrification, resulting in the formation of nitrogen gas and buoyancy of the sludge mass. The result is that solids are carried away with the effluent.

RIVER — A natural stream of water of considerable volume, larger than a brook or creek. A river has its stages of development, youth, maturity, and old age. In its earliest stages a river system drains its basin imperfectly; as valleys are deepened, the drainage becomes more perfect, so that in maturity the total drainage area is large and the rate of erosion high. The final stage is reached when wide flats have developed and the bordering lands have been brought low.

RIVER BANKS — The portion of the channel cross section that restricts lateral movement of water at normal discharges. Banks often have a gradient steeper than 45 degrees and exhibit a distinct break in slope from the stream bed.

RIVER BASIN — A term used to designate the area drained by a river and its tributaries.

RIVER BASIN DEVELOPMENT — A program to develop the use of the water and land resources of a river basin, so coordinated as to obtain a greater efficiency of use than would be possible if the resources were developed by uncoordinated, multiple-purpose projects.

RIVER BASIN PLAN — A plan for the development of water and related land resources to make the best use of such resources to meet the basin needs and make the greatest long-term contribution to the economic growth and social well-being of the people of the basin and the nation.

RIVER CHANNELS — Natural or artificial open conduits which continuously or periodically contain moving water, or which forms a connection between two bodies of water.

RIVER FLOODING — Inundation of a normally dry area along a river (usually the mainstem) due to increased water level or discharge. Because the drainage areas of mainstem rivers are large, they do not Flash Flood as their smaller tributary streams do. River flooding occurs more than a few hours after the causative event (usually widespread heavy precipitation and/or snowmelt) of the flood. In many cases, the end of flash flooding along tributary streams may be followed by or coincident with river flooding (i.e., heavy precipitation which initially causes flash flooding on tributaries goes on to cause river flooding on the larger rivers). Because of the longer time factor, river flooding usually can be forecast with much greater accuracy than flash flooding.

RIVER FLOW MODEL — A simulation, generally mathematical, of a river's or drainage basin's Hydrologic Cycle, through a series of mathematical equations quantifying system inflows and outflows. Whenever possible, actual flow measurements for calibration purposes will be used.

RIVER GAGE REACH — That stretch of a river on which the stage and/or flow at a particular gage is characteristic of stage and/or flow along that entire reach. Consequently, streamflow, depth, drainage area and slope are fairly uniform along this stretch and there are no major inflows, diversions, dams, etc.

RIVERINE — Relating to, formed by, or resembling a river including tributaries, streams, brooks, etc.

RIVER REACH — Any defined length of a river.

RIVERS, CLASSIFICATIONS — Classifications of waterways included in the National Wild and Scenic Rivers System are as follows:
[1] Recreational Rivers — Rivers or sections of rivers that are readily accessible by road or railroad, that may have some development along their shoreline, and that may have undergone some impoundment or diversion in the past.
[2] Scenic Rivers — Rivers or sections of rivers that are free of impoundments, with shorelines or watersheds still largely primitive, and shorelines largely undeveloped but accessible in places by roads.
[3] Wild Rivers — Rivers or sections of rivers that are free of impoundments and generally inaccessible except by trail, with watersheds or shorelines essentially primitive and waters unpolluted.

RIVER STAGE — The elevation of the water surface at a specified station above some arbitrary zero datum (level).

RIVERWASH — Barren alluvial land, usually coarse-textured, exposed along streams at low water, and subject to shifting during normal high water.

RIVULET — A small stream or brook; a streamlet.

ROCKFILL DAM — An Embankment Dam in which more than 50 percent of the total volume comprises compacted or dumped pervious natural or crushed rock.

ROOT PRESSURE — Pressure exerted in the roots of plants as the result of Osmosis, causing exudation from cut stems and Guttation of water from leaves.

ROOT ZONE — The subsurface zone from the land surface to the depth interwoven by plant roots.

ROTATION — (Irrigation) Water delivery where a relatively constant supply flow is rotated to different users at varying times.

RUN — (1) To flow, especially in a steady stream. (2) A pipe or channel through which something, i.e., water, flows. (3) A fall or slide, as of sand or mud. (4) The migration of fish, especially in order to spawn; a group or school of fish ascending a river in order to spawn, i.e., the seasonal upstream migration of Anadromous fish. (5) (Irrigation) The distance of gravity flow from the point of release to the end of the area to be watered. (6) (Nautical) To sail or steer before the wind or on an indicated course. (7) (Geology) A vein or seam, as of ore or rock.

RUNNEL — (1) A rivulet; a brook. (2) A narrow channel or course, as for water.

RUNNING WATER — Water distributed through pipes and fixtures as a house with hot and cold running water.

RUNOFF — (1) That part of the precipitation, snow melt, or irrigation water that appears in uncontrolled surface streams, rivers, drains or sewers. It is the same as streamflow unaffected by artificial diversions, imports, storage, or other works of man in or on the stream channels. Runoff may be classified according to speed of appearance after rainfall or melting snow as direct runoff or base runoff, and according to source as surface runoff, storm interflow, or ground-water runoff. (2) The total discharge described in (1), above, during a specified period of time. (3) Also defined as the depth to which a drainage area would be covered if all of the runoff for a given period of time were uniformly distributed over it.
Meteorological Factors Affecting Runoff:
[1] Type of precipitation (rain, snow, sleet, etc.);
[2] Rainfall intensity;
[3] Rainfall amount;
[4] Rainfall duration;
[5] Distribution of rainfall over the drainage basin;
[6] Direction of storm movement;
[7] Antecedent precipitation and resulting soil moisture; and
[8] Other meteorological and climatic conditions which affect evapotranspiration such as temperature, wind, relative humidity, and season.
Physical Basic Characteristics Affecting Runoff:
[1] Land use;
[2] Vegetation;
[3] Soil type;
[4] Drainage area;
[5] Basin shape;
[6] Elevation;
[7] Slope;
[8] Topography;
[9] Direction of orientation;
[10] Drainage network patterns; and
[11] Ponds, lakes, reservoirs, sinks, etc. in the basin which prevent or alter runoff from continuing downstream.

RUNOFF, ADJUSTED MEAN ANNUAL — Average annual runoff adjusted for length of record by comparison with record at pivot stations.

RUNOFF, AVERAGE ANNUAL — Average of water year runoff in inches or acre-feet for the total period of record.

RUNOFF CYCLE — That portion of the Hydrologic Cycle between incident precipitation over land areas and its subsequent discharge through stream channels or Evapotranspiration.

RUNOFF, DIRECT — The runoff entering stream channels most immediately after rainfall or snowmelt. It consists of surface runoff plus interflow and forms the bulk of the Hydrograph of a flood. Direct runoff plus Base Runoff compose the entire flood hydrograph.

RUNOFF, GROUND-WATER — That part of the runoff which has passed into the ground, has become ground water, and has been discharged into a stream channel as spring or seepage water.

RUNOFF PERCENTAGE — Runoff expressed as a percentage of the precipitation.

RUNOFF PLOTS — Areas of land, usually small, arranged so the portion of rainfall or other precipitation flowing off and perhaps carrying soluble materials and soil may be measured.

RUNOFF RATE — The volume of water running off in a unit of time from a surface, expressed as inches of rainfall per hour, cubic feet per second, or other units.

RUNOFF, SURFACE — (1) That part of the runoff which travels over the soil surface to the nearest stream channel. (2) That part of the runoff of a drainage basin that has not passed beneath the surface since precipitation. Surface runoff is not the same as direct runoff.

RUN-OF-RIVER DAM — A hydroelectric generating power plant that operates based only on available streamflow and some short-term storage (hourly, daily, or weekly). Compare to Storage Reservoir.

RUNS — An area of swiftly flowing water, without surface agitation or waves, which approximates uniform flow and in which the slope of the water surface is roughly parallel to the overall gradient of the stream reach.

RURAL — DOMESTIC WATER — The rural domestic category includes water uses for domestic needs, stock watering, yard irrigation, etc., of individual homes, farms or ranches, and rural centers with a population of typically less than about 250 people.

RURAL WATER USE — Water used in suburban or farm areas for domestic and livestock needs. The water generally is self supplied (i.e., not supplied by a Public Water Supply System) and includes domestic use, drinking water for livestock, and other uses, such as dairy sanitation, evaporation from stock-watering ponds, and cleaning and waste disposal. Uses may also include suburban developments such as apartment houses, or trailer courts with their own wells, and tracts of homes served by a central cooperatively owned well, or small water company for which no other source is available.