Knowledge Base

CAISSON — (1) A watertight structure within which construction work is carried on under water. (2) A large box open at the top and one side, designed to fit against the side of a ship and used to repair damaged hulls under water. (3) A floating structure used to close off the entrance to a dock or canal lock.

CALCIUM CARBONATE — (CaCO3) The principal hardness and scale-causing compound in water. A white precipitate that forms in water lines, water heaters, and boilers in hard water areas; also known as scale. Also the principal chemical composition of Tufa, a calcareous and siliceous rock deposit of springs, lakes, or ground water.

CANAL — A constructed open channel for transporting water.

CANAL AUTOMATION — The implementation of a control system that upgrades the conventional method of canal system operation.

CANAL CHECK GATE STRUCTURE — A structure designed to control the water surface level and flow in a canal, maintaining a specified water depth or head on outlets or turnout structures. Most canal check structures have movable gates.

CANAL FREEBOARD — The amount of canal lining available above maximum design water depth.

CANAL POOL — Canal section between check structures

CANAL PRISM — The cross-sectional shape of a typical canal.

CANAL REACH — The segment of the main canal system consisting of a series of canal pools between major flow control structures.

CANAL SYSTEM OPERATION — Water transfer from its source to points of diversion for irrigation, municipal and industrial, fish and wildlife, and drainage purposes.

CANCELED WATER RIGHT — A water right that is invalidated due to the failure of the water right holder to comply with the terms and conditions of the permit.

CAPACITY, FIELD or SOIL — The amount of water held in a soil sample after the excess gravitation water has drained away.

CAPACITY, GROSS RESERVOIR — The total amount of storage capacity available in a reservoir for all purposes from the streambed to the normal maximum operating level. It does not include surcharge, but does include dead storage.

CAPE — (1) A point or head of land projecting into a body of water. (2) A rounded projection, out into the water, and either high land or low land. For inland lakes, cape rarely appears on maps as a place name and also only infrequently in descriptions. Point and head according to present usage appears to be preferred to cape.

CAPILLARITY — (1) The property of tubes or earth-like particles with hair-like openings which, when immersed in fluid, raise (or depress) the fluid in the tubes above (or below) the surface of the fluid in which they are immersed. (2) The interaction between contacting surfaces of a liquid and a solid that distorts the liquid surface from a planar shape. Also referred to as Capillary Action or Capillary Attraction.

CAPILLARY ACTION — (1) The action by which water is drawn around soil particles because there is a stronger attraction between the soil particles and the water molecules themselves. (2) The movement of water within the interstices of a porous medium due to the forces of adhesion, cohesion, and surface tension acting in a liquid that is in contact with a solid. Synonymous with the terms Capillarity, Capillary Flow, and Capillary Migration.

CAPILLARY ATTRACTION — The force that results from greater adhesion of a liquid to a solid surface than internal cohesion of the liquid itself and that causes the liquid to be raised against a vertical surface, as water is in a clean glass tube. It is the force that allows a porous material like soil to soak up water from lower levels.

CAPILLARY FRINGE — (1) The zone at the bottom of the Zone of Aeration (Vadose Zone) where ground water is drawn upward by capillary force. (2) The zone immediately above the Zone of Saturation (or Groundwater Table) in which underground water is lifted against gravity by surface tension (Capillary Action) in passages of capillary size.

CAPILLARY PHENOMENA — A phenomenon of water movement caused by Capillarity.

CAPILLARY POTENTIAL — The work required to move a unit mass of water from the reference plane to any point in the soil column.

CAPILLARY RISE — The height above a free water surface to which water will rise by Capillary Action.

CAPILLARY WATER — (1) Water held in the soil above the Phreatic Surface by capillary forces; or soil water above hydroscopic moisture and below the field capacity. (2) A continuous film of water found around soil particles.

CAPILLARY ZONE — The soil area above the water table where water can rise up slightly through the cohesive force of Capillary Action.

CAPTURE — (1) Water withdrawn artificially from an aquifer is derived from a decrease in storage in the aquifer, a reduction in the previous discharge from the aquifer, an increase in the recharge, or a combination of these changes. The decrease in discharge from an aquifer plus the increase in recharge. Capture may occur in the form of decreases in the ground-water discharge into streams, lakes, and the ocean, or from decreases in that component of Evapotranspiration derived from the Zone of Saturation. (2) Diversion of the flow of water in the upper part of a stream by the headward growth of another stream.

CAPTURE ZONE — The zone around a well contributing water to the well; the area on the ground surface from which a well captures water.

CARBONATED WATER — (1) Effervescent water, usually containing salts, charged under pressure with purified carbon dioxide gas, used as a beverage or mixer. Also referred to as soda water, club soda, or seltzer. (2) A solution of water, sodium bicarbonate, and acid.

CARBONATION, GROUNDWATER — The dissolving of carbon dioxide in surface water as it percolates through the ground. The carbon dioxide reacts with water to form carbonic acid, a weak acid that causes the water to have a slightly acidic pH.

CARRIAGE LOSSES (Water) — A term used to describe the operational losses associated with conveying water from its point of diversion to its point of use. These losses typically include spillage, seepage, evaporation, and phreatophyte usage along the water course, as applicable. Water rights applicants are entitled to water for transporting their entitlement to their proposed place(s) of use. Carriage losses are generally considered unavoidable, and are legally bearable so long as that extra water is used reasonably and economically in transporting the water to its destination.

CASCADE — A short, steep drop in stream bed elevation often marked by boulders and agitated white water.

CASCADE FLOW — Regulated flow through a series of flow control structures.

CATCHMENT — (1) The catching or collecting of water, especially rainfall. (2) A reservoir or other basin for catching water. (3) The water thus caught.

CATCHMENT AREA — (1) The intake area of an aquifer and all areas that contribute surface water to the intake area. (2) The areas tributary to a lake, stream, sewer, or drain. (3) A reservoir or basin developed for flood control or water management for livestock and/or wildlife. See also Drainage Area; Watershed. (4) The land (and including the streams, rivers, wetlands and lakes) from which water runs off to supply a particular location in a freshwater system. In North America, the term watershed is often used instead of catchment area. In the UK, watershed means the line separating two adjacent catchments.

CATCHMENT AREA (BASIN) — The area draining into a river, reservoir, or other body of water.

CATCHMENT BASIN — The entire area from which drainage is received by a river or a lake; most generally used in reference to surface runoff.

CENTRALIZED CONTROL (Canal) — Control of a canal project from a central location by the watermaster.

CENTRALIZED HEADQUARTERS (Canal) — Control of a canal project from a central location generally by a master station, communications network, and one or more remote terminal units (RTUs).

CENTRIFUGAL PUMP — A device that converts mechanical energy to pressure or kinetic energy in a fluid by imparting centrifugal force on the fluid through a rapidly rotating impeller.

CERTIFICATE OF WATER RIGHT — An official document which serves as evidence of a Perfected Water Right.

CERTIFIED WATER RIGHT — A state-issued document that serves as legal evidence that an approved application has been physically developed and the water put to beneficial use. The certificate establishes priority date, type of beneficial use, and the maximum amount of water that can be used. Before a water right can be certified, verification of the physical development must be provided to the state through a survey conducted by an approved water rights examiner. Even certified water rights are subject to occasional review to ensure continued beneficial use.

CHANNEL (LAKE) — In instances sub-lacustrine channels appear where a lake has been formed by the submergence of a valley, or the drowning of a river; the channels formed under subaerial conditions by stream cutting may remain unfilled by sediments, on the lake bottom. Channel is applied to a surface water way, either natural or artificial, which connects two lakes and provides for boat travel; to river distributaries and connecting water in a delta; and to trench-like excavations extended inland from a lake shoreline to provide water frontages and boat access for back lots.

CHANNEL (LAKE BASIN) — The deeper, narrow elogated or more sharply trenched part of a lake bottom.

CHANNEL (WATERCOURSE) — A natural stream that conveys water; a ditch or channel excavated for the flow of water. River, creek, run, branch, anabranch, and tributary are some of the terms used to describe natural channels, which may be single or braided. Canal, aqueduct, and floodway are some of the terms used to describe artificial (man-made) channels.

CHANNEL BANK — The sloping land bordering a channel. The bank has steeper slope than the bottom of the channel and is usually steeper than the land surrounding the channel.

CHANNEL CAPACITY — The maximum rate of flow that may occur in a stream without causing overbank flooding.

CHANNEL CONTROL — The condition under which the stage-discharge relation of a gaging station is governed by the slope, size, geometry, and roughness of the channel.

CHANNEL DENSITY — The ratio of the length of stream channels in a given basin to the area of the basin, expressed in feet per acre (meters per hectare).

CHANNEL INFLOW — Water which at any instant is flowing into the channel system from surface flow, subsurface flow, base flow, and rainfall directly on the channel.

CHANNEL LINING — Protection of the channel bottom and banks with concrete or Riprap.

CHANNEL MODIFICATION — The modification of the flow characteristics of a channel by clearing, excavation, realignment, lining, or other means to increase its capacity. Sometimes the term is used to connote Channel Stabilization.

CHANNEL REALIGNMENT — The construction of a new channel or a new alignment which may include the clearing, snagging, widening, and/or deepening of the existing channel.

CHANNEL STABILIZATION — Erosion prevention and stabilization of velocity distribution in a channel using jetties, drops, revetments, vegetation, and other measures.

CHANNEL STORAGE — The volume of water at a given time in the channel or over the flood plain of the streams in a drainage basin or river reach. Channel storage is sometimes significant during the progress of a flood event.

CHANNELED — Having one or more longitudinal grooves.

CHANNELIZATION — The artificial enlargement or realignment of a stream channel.

CHECK DAM — A small dam constructed in a gully or other small watercourse to decrease the streamflow velocity, minimize channel erosion, promote deposition of sediment, and to divert water from a channel.

CHECK GATE — A gate located at a check structure used to control flow.

CHECK IRRIGATION — A method of irrigation in which an area is practically or entirely surrounded by earth ridges.

CLEAN (Water) — Water that is free from foreign matter or pollution; not infected; unadulterated.

CLEAR WELL — A reservoir containing potable water which has been previously treated before entering the distribution lines.

CLIMATE — The sum total of the meteorological elements that characterize the average and extreme conditions of the atmosphere over a long period of time at any one place or region of the earth's surface. The collective state of the atmosphere at a given place or over a given area within a specified period of time.

CLIMATIC CYCLE — The periodic changes of climate, including a series of dry years following a series of years with heavy rainfall.

CLIMATIC YEAR — A period used in meteorological measurements. A continuous 12-month period during which a complete annual cycle occurs, arbitrarily selected for the presentation of data relative to hydrologic or meteorologic phenomena. The climatic year in the United States begins on October 1st and runs through September 30th. Similar to a Water Year.

CLOSED BASIN — A basin is considered closed with respect to surface flow if its topography prevents the occurrence of visible surface outflow. It is closed hydrologically if neither surface nor underground outflow can occur.

CLOSED-BASIN LAKE — A lake which has no outlet, from which water escapes only by evaporation.

CLOSED DRAIN — Subsurface drain, tile, or perforated pipe that receives surface water through surface inlets.

CLOSED LAKES — Those that do not have an effluent in contrast to drainage lakes or open lakes which do have outlet streams. Closed lakes are common in arid and semi-arid regions where they usually contain saline or brackish water.

COAGULANT — (1) An agent that causes a liquid or sol to coagulate. (2) (Wastewater Treatment) A chemical compound, such as Alum (aluminum sulfate), used to produce coagulation.

COEFFICIENT OF ROUGHNESS — Factor in fluid flow determination expressing the character of a surface and its fractional resistance to flow. Also referred to as Roughness Coefficient.

COEFFICIENT OF RUNOFF — Factor in the rational runoff formula expressing the ratio of peak runoff rate to rainfall intensity.

COEFFICIENT OF STORAGE — The volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in head.

COEFFICIENT OF TRANSMISSIVITY (t) — The rate at which water of the prevailing kinematic viscosity is transmitted through a unit width of the aquifer under a unit Hydraulic Gradient. It is equal to an integration of the hydraulic conductivities across the saturated part of the aquifer perpendicular to the flow paths. Also, the rate at which water is transmitted through a unit width of an aquifer under a unit hydraulic gradient. Transmissivity values are given in gallons per minute through a vertical section of an aquifer 1 foot wide and extending the full saturated height of an aquifer under a hydraulic gradient of one in the English Engineering System; in the Standard International System, transmissivity is given in cubic meters per day through a vertical section of an aquifer 1 meter wide and extending the full saturated height of an aquifer under hydraulic gradient of one. It is a function of properties of the liquid, the porous media, and the thickness of the porous media.

COLLECTION SITE — A stream, lake, reservoir, or other body of water fed by water drained from a watershed.

COLLECTOR SEWERS — Pipes used to collect and carry wastewater from individual sources to an interceptor sewer that will carry it to a treatment facility.

COLLECTOR SYSTEM — Conveys water from several individual sources such as groundwater wells and drains and surface inlet drains for rainstorm and snowmelt runoff to a single point of diversion. The collector system is associated with projects that increase water supply and decrease flood damage.

COLLECTOR WELL — A well located near a surface water supply used to lower the water table and thereby induce infiltration of surface water through the bed of the water body to the well.

COMPENSATION LEVEL — The level in a body of water, usually occurring at the depth of 1 percent light penetration, which forms the lower boundary of the Zone of Net Metabolic Production.

COMPENSATION POINT — The point under water at which plant photosynthesis just equals plant respiration. The water depth defines the lower boundary, where photosynthesis takes place, of the Euphotic Zone.

CONCENTRATION — The amount of Solute present in proportion to the total Solution. More specifically, a measure of the average density of pollutants or other constituents, usually specified in terms of mass per unit volume of water or other Solvent (e.g., milligrams per liter) or in terms of relative volume of solute per unit volume of water (e.g., parts per million).

CONCORDANT FLOWS — Flows at different points in a river system that have the same Recurrence Interval, or the same frequency of occurrence. It is most often applied to flood-flows.

CONCRETE — A mixture of water, cement, sand, and pebbles. The hydration of cement and drying of concrete causes it to become very hard.

CONCRETE-GRAVITY STRUCTURE — A type of concrete structure in which resistance to overturning is provided only by its own weight.

CONDITIONAL WATER PERMIT — An authorization for the permittee to construct any facilities (such as a well and irrigation system) and to begin utilization of the water. A water right and a water permit are not the same thing.

CONDUIT — (1) A natural or artificial channel through which fluids may be conveyed. (2) (Dam) A closed channel for conveying discharge through, under, or around a dam.

CONE OF DEPRESSION (COD)/CONE OF INFLUENCE (COI) — A cone-like depression of the water table or other piezometric surface that has the shape of an inverted cone and is formed in the vicinity of a well by withdrawal of water. The surface area included in the cone is known as the area of influence of the well. Also referred to as the Pumping Cone and the Cone of Drawdown.

CONFIDENCE LIMITS — (Statistics) Bounds of statistical probability, e.g., 95 percent, 98 percent, 99 percent, etc., established as part of the testing criteria. The confidence limits express the statistical probability associated with the acceptance of an econometric model's results.

CONFINED AQUIFER — An aquifer which is bounded above and below by formations of impermeable or relatively impermeable material. An aquifer in which ground water is under pressure significantly greater than atmospheric and its upper limit is the bottom of a bed of distinctly lower hydraulic conductivity than that of the aquifer itself. See Artesian Aquifer.

CONFINED GROUND WATER — A body of ground water covered by material so impervious as to sever the hydraulic connection with overlying ground water except at the intake or recharge area. Confined water moves in pressure conduits due to the difference in head between intake and discharge areas of the confined water body.

CONFINED WATER (ARTESIAN) — Water under artesian pressure. Water that is not confined is said to be under water table conditions.

CONFINING BED — A body of "impermeable" material stratigraphically adjacent to one or more aquifers. It may lie above or below the aquifer. In nature its hydraulic conductivity may actually range from nearly zero to some value distinctly lower than that of the aquifer. In some literature, the term confining bed has now supplanted the terms Aquiclude, Aquitard, and Aquifuge.

CONFLICTING USES (OF LAKE) — Uses that act to the detriment of other users. Technically, conflicts of use may exist only between riparians because all acts of others would be in the realm of trespass.

CONFLUENCE — (1) The act of flowing together; the meeting or junction of two or more streams or rivers; also, the place where these streams meet. (2) The stream or body of water formed by the junction of two or more streams or rivers; a combined flood.

CONFLUENT GROWTH — (Water Quality) A continuous bacterial growth covering all or part of the filtration area of a membrane filter in which the bacteria colonies are not discrete. In coliform testing, abundant or overflowing bacterial growth which makes accurate measurement difficult or impossible.

CONJUNCTIVE MANAGEMENT — The integrated management and use of two or more water resources, such as a (ground water) aquifer and a surface water body.

CONJUNCTIVE OPERATION — The operation of a ground water basin in combination with a surface water storage and conveyance system. Water is stored in the ground water basin for later use by intentionally recharging the basin during years of above-normal water supply.

CONJUNCTIVE (WATER) USE — The combined use of surface and ground water systems and sources to optimize resource use and prevent or minimize adverse effects of using a single source.

CONNECTING STREAM — A stream connecting a lake with another lake or stream.

CONNECTOR SYSTEM — Conveys water from a single source to a different location typically without intermediate collection of diversions. The connector system is associated with regulation reservoirs and intakes to pumping plants or powerplants.

CONSERVATION — (1) Increasing the efficiency of energy use, water use, production, or distribution. (2) The careful and organized management and use of natural resource, for example, the controlled use and systematic protection of natural resources, such as forests, soil, and water systems in accordance with principles that assure their optimum long-term economic and social benefits. Also, preservation of such resources from loss, damage, or neglect.

CONSTANT HEAD ORIFICE TURNOUT (Canal) — A calibrated structure containing an adjustable orifice gate and a gate downstream to control a constant head differential across the orifice gate to divert and measure water from a main irrigation canal to a distributing canal.

CONSTANT VOLUME OPERATION METHOD (Canal) — A canal operation that maintains a relatively constant water volume in each canal pool.

CONSTRUCTION — The process of building.

CONSTRUCTION JOINT (of a Dam) — The interface between two successive placings or pours of concrete in a dam's structure where a bond, and not a permanent separation, is intended.

CONSUMABLE WATER SUPPLY — That amount of river water available for consumption at a given point on the river after existing prior water rights have been met.

CONSUMPTION, DOMESTIC — The quantity or quantity per capita (person) of water consumed in a municipality or district for domestic uses during a given period, usually one day. Domestic consumption is generally considered to include all uses included in "municipal use of water," in addition to the quantity of water wasted, lost, or otherwise unaccounted for. Also see Consumption, Municipal; Municipal Use of Water.

CONSUMPTION, INDUSTRIAL — The quantity of water consumed in a municipality or district for mechanical, trade, and manufacturing uses during a given period, usually one day.

CONSUMPTION, MUNICIPAL — The quantity of water consumed through use in developed urban areas. Also see Consumption, Domestic; Consumptive Use.

CONSUMPTIVE IRRIGATION REQUIREMENT (CIR) — The quantity of irrigation water, exclusive of precipitation, stored soil moisture, or ground water, that is required consumptively for crop production.

CONSUMPTIVE USE (LAKE WATERS) — Implies withdrawal of water for such purposes as irrigation, power generation and industrial, municipal and domestic water supplies. Destructive use, such as for waste disposal or as a carrier for sewage, is considered consumptive. Nonconsumptive uses (those that do not reduce the supply) are: recreational, bathing, fishing, boating and hunting, navigable waterways and for aquaculture.

CONSUMPTIVE WASTE — Water that returns to the atmosphere without providing benefit to humans.

CONSUMPTIVE WATER USE — (1) A use which lessens the amount of water available for another use (e.g., water that is used for development and growth of plant tissue or consumed by humans or animals). (2) The portion of water withdrawn from a surface or groundwater source that is consumed for a particular use (e.g., irrigation, domestic needs, and industry), and does not return to its original source or another body of water. The terms Consumptive Use and Nonconsumptive Use are traditionally associated with water rights and water use studies, but they are not completely definitive. No typical consumptive use is 100 percent efficient; there is always some return flow associated with such use either in the form of a return to surface flows or as a ground water recharge. Nor are typically nonconsumptive uses of water entirely nonconsumptive. There are evaporation losses, for instance, associated with maintaining a reservoir at a specified elevation to support fish, recreation, or hydropower, and there are conveyance losses associated with maintaining a minimum streamflow in a river, diversion canal, or irrigation ditch.

CONSUMPTIVE WATER USE, IRRIGATION — The quantity of water that is absorbed by the crop and transpired or used directly in the building of plant tissue, together with that evaporated from the cropped area. Does not include runoff or deep percolation in support of the Crop Leaching Requirement.

CONSUMPTIVE WATER USE, NET — The consumptive use decreased by the estimated contribution by rainfall toward the production of irrigated crops. Net consumptive use is sometimes referred to as the Crop Irrigation Requirement.

CONSUMPTIVE WATER USE REQUIREMENT (CROP) — The annual irrigation consumptive use expressed in feet or acre-feet per acre.

CONTAMINATION (WATER) — Impairment of the quality of water sources by sewage, industrial waste, or other matters to a degree which creates a hazard to public health. Also, the degradation of the natural quality of water as a result of man's activities. There is no implication of any specific limits, since the degree of permissible contamination depends upon the intended end use, or uses, of the water. See Pollution.

CONTENTS (STORAGE) — The volume of water in a reservoir. Unless otherwise indicated, reservoir content is computed on the basis of a level pool and does not include bank storage.

CONTOUR — A line on a map that indicates a line of equal elevation on the land or water in feet over mean sea level. A line of equal thickness of water depth, soil or sediment thickness, or geologic structure thickness.

CONTOUR DITCH — An irrigation ditch laid out approximately on the contour, or elevation of the land.

CONTOUR FLOODING — Irrigation method resulting in flooding fields from Contour Ditches.

CONTOUR-FURROW IRRIGATION — The application of irrigation water in furrows that run across the slope with a forward grade in the furrows.

CONTOUR FURROWS — Furrows plowed approximately on the contour on pasture and rangeland to prevent runoff and increase infiltration; also, furrows laid out approximately on the contour for irrigation purposes.

CONTOUR PLOWING — A soil tilling technique that follows the shape of the land to minimize erosion.

CONTOUR STRIP FARMING — A kind of contour farming in which row crops are planted in strips, between alternating strips of close-growing, erosion-resistant forage crops.

CONTOUR TRENCHING — Development of water storage Detention or Retention Facilities along the contour by excavation and placement of soils as an embankment along the downstream side. Intervals vary with precipitation, slope, and soil.

CONTRIBUTING AREA — That portion of a watershed which contributes to measured runoff under normal conditions.

CONTROL — A natural constriction of the channel, a long reach of the channel, a stretch of rapids, or an artificial structure downstream from a Gaging Station that determines the Stage-Discharge Relation at the gage. A control may be complete or partial. A complete control exists where the stage-discharge relation at a gaging station is entirely independent of fluctuations in stage downstream from the control. A partial control exists where downstream fluctuations have some effect upon the stage-discharge relation at a gaging station. A control, either partial or complete, may also be shifting. Most natural controls are shifting to a degree, but a shifting control exists where the stage-discharge relation experiences frequent changes owing to impermanent bed or banks.

CONTROL DAM — A dam or structure with gates to control the discharge from the upstream reservoir or lake.

CONTROL POINTS (Horizontal and Vertical) — Small monuments that are securely embedded in the surface of a dam and used to detect any movement with respect to Permanent Monuments placed away from the dam itself.

CONTROL SCHEME (Canal) — The collection of methods and algorithms brought together to accomplish control of a canal system.

CONTROL STRUCTURE (LAKE LEVEL) — Dam, dike, pump or any structure built for the purpose of controlling the water level of a lake or pond.

CONTROL SYSTEM (Canal) — An arrangement of electronic, electrical, and mechanical components that commands or directs the regulation of a canal system.

CONTROLLED DRAINAGE — (Irrigation) Regulation of the water table to maintain the water level at a depth favorable for optimum crop growth.

CONTROLLED VOLUME OPERATION METHOD (Canal) — An operation in which the volume of water within a canal reach between two check structures is controlled in a rescribed manner for time variable inflows and outflows such as off-peak pumping or canal-side deliveries.

CONVENTIONAL METHOD (Canal) — Where operations personnel (ditchrider and watermaster) control the canal system onsite. Labor-saving devices and machinery may be used to assist in the control of the canal facilities.

CONVENTIONAL SYSTEMS — (Water Quality) Systems that have been traditionally used to collect municipal wastewater in gravity sewers and convey it to a central primary or secondary treatment plant prior to discharge to surface waters.

CONVENTIONAL WATER — A natural freshwater supply as opposed to desalted or brackish water.

CONVEYANCE LOSS — Water that is lost in transit from a pipe, canal, conduit, or ditch by leakage, seepage, evaporation, or evapotranspiration. Generally, these conveyance losses are not available for further use; however, leakage from an irrigation ditch, for example, may percolate to a ground-water source and be available for further use.

CORRELATIVE ESTIMATE — A discharge or stream flow estimate determined by Correlation, or comparisons to other, possibly influencing factors, e.g., rainfall, snowpack, levels of upstream lakes and reservoirs, etc. A correlative estimate represents a likely value of the discharge or flow for any particular period — commonly a month — according to a specified method of analysis and the explanatory variables chosen.

CORRELATIVE (WATER) RIGHTS — Certain rights of land owners over a common ground water basin are coequal, or correlative, so that any one owner cannot take more than his share even if the rights of others are impaired. Where a source of water does not provide enough for all users, the water is reapportioned on the basis of prior water rights held by each user.

CORROSIVE — A substance that deteriorates material, such as pipe, through electrochemical processes.

CORRUGATION IRRIGATION — Spreading water by directing it into small channels across the field.

CRITICAL DRY PERIOD — As a general definition, describes a series of water-deficient years, usually a historical period, in which a full reservoir storage system at the beginning is drawn down to minimum storage at the end without any spill.

CRITICAL DRY YEAR — A dry year in which the full commitments for a dependable water supply cannot be met and deficiencies are imposed on water deliveries.

CRITICAL FLOW — (1) The flow conditions at which the discharge is a maximum for a given specific energy, or at which the specific energy is a minimum for a given discharge. (2) In reference to Reynolds' critical velocities, the point at which the flow changes from streamline or non-turbulent to turbulent.

CRITICAL LOW-FLOW — Low flow conditions below which some standards (Criteria) do not apply. The impacts of permitted discharges are typically analyzed at critical low-flow.

CRITICAL SLOPE — That slope that will sustain a given discharge at uniform, Critical Depth in a given channel.

CRITICAL VELOCITY — Velocity at which a given discharge changes from tranquil to rapid flow; that velocity in open channels for which the specific energy (the sum of the depth and velocity head) is a minimum for a given discharge.

CROP — (1) Plants, seeds, flowers and root tubers that are grown to be used as food or to be sold for profit. (2)Total amount of plants of one type harvested.

CROP COEFFICIENT — The ratio of evapotranspiration occurring with a specific crop at a specific stage of growth to potential evapotranspiration at that time.

CROP CONSUMPTIVE USE (Crop Requirement) — Often called Evapotranspiration. The amount of water used by vegetative growth of a given area by transpiration and that evaporated from adjacent soil or intercepted precipitation on the plant foliage in any specified time (acre-feet/acre).

CROP IRRIGATION REQUIREMENT — The amount of irrigation water in acre-feet per acre required by the crop; it is the difference between Crop Consumptive Use, or Crop Requirement, and the effective precipitation for plant growth. To this amount the following items, as applicable, are added: (1) irrigation applied prior to crop growth; (2) water required for leaching; (3) miscellaneous requirements of germination, frost protection, plant cooling, etc.; and (4) the decrease in soil moisture should be subtracted.

CROPLAND — Land currently tilled, including cropland harvested, land on which crops have failed, summer fallowed land, idle cropland, cropland planted in cover crops or soil improvement crops not harvested or pastured, rotation pasture, and cropland being prepared for crops, or newly seeded cropland. Cropland also includes land planted in vegetables and fruits, including those grown on farms for home use. All cultivated (tame) hay is included as cropland. Wild hay is excluded from cropland and included in pasture and range.

CROP ROTATION — A pattern of changing the crops grown in a specific field from year to year in order to control pests and maintain soil fertility.

CROP SUBSIDY — A price support paid to farmers by the government.

CURRENT CANAL — The current caused by an influent (inlet) or effluent (outlet) stream may effectively limit the growth of aquatic plants and create canal-like openings through weed beds.

CURRENT METER — An instrument for measuring the velocity of water flowing in a stream, open channel, or conduit by ascertaining the speed at which elements of the flowing water rotate a vane or series of cups.

CUTBACK IRRIGATION — Water applied at a faster rate at the beginning of the irrigation period and then reduced or cutback to a lesser rate, usually one-half the initial rate or that amount to balance with the intake rate.