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What do you call that thing, you know, that whatchama call it with the dohickey on the end? Welcome to Irrigation Terms 101, where you'll learn the name of the whatchama call it, and what that dohickey on the end is called. The irrigation terms herein are used with permission from the Irrigation Association (, edited by Eugene Rochester, CID, certification consultant.

The terms have not been approved by the IA, or the IA Certification Board. The Irrigation Association (IA) is a nonprofit organization dedicated to improving the products and practices used to manage water resources and to help shape the irrigation industry. The IA's interest in water resources encompasses conservation, drainage, improvement and recovery of water for economic and environmental enhancement in agriculture, turfgrass, landscape and forestry.

AC pipe: Asbestos-cement pipe was commonly used for buried pipelines. It combines strength with light weight and is immune to rust and corrosion. (No longer made.)

adjusted sodium adsorption ratio: Index of permeability problems, based upon water quality.

advance ratio: Ratio of the time for the water to reach the end of the field to the total set time for an irrigation set on a furrow irrigation system. The ratio should be less than 0.5 to have a good distribution uniformity.

advance time:

  • Time required for a given stream of irrigation water to move from the upper end of a field to the lower end.
  • Time required for a given surface irrigation stream to move from one point in the field to another.

aeration capacity: Volume fraction of air filled pores in a soil at field capacity.


  • Group of primary soil particles that cohere to each other more strongly than to other surrounding particles.
  • Groups of individual soil particles, held together naturally and consisting of particles of sand, silt and clay separated from each other by pores, cracks or planes of weakness. The term, soil structure, refers to this arrangement of the soil in natural aggregates. Various types of soil structure are recognized (massive, platy, prismatic, blocky, granular).

alfalfa valve: Outlet valve attached to the top of a pipeline riser with an opening equal in diameter to the inside diameter of the riser pipe and an adjustable lid or cover to control water flow.

alkali soils:

  • Soils with pH greater than 7.0.
  • Soils with an exchangeable sodium percentage greater than 15%.
  • Soils with sufficient exchangeable sodium (alkali) to interfere with plant growth and cause dispersion and swelling of clay minerals.

allowable depletion:

  • Portion of plant available water that is allowed for plant use prior to irrigation based in plant and management considerations.
  • That part of soil moisture stored in the plant root zone managed for use by plants, usually expressed as equivalent depth of water in acre inches per acre, or inches.
  • Sometimes referred to as allowable soil depletion or allowable soil water depletion.

anion: Negatively charged ion, which during electrolysis is attracted toward the anode. The most common anions in soil extracts and waters are bicarbonate, sulphate, carbonate, chloride and nitrate ions.

atmospheric vacuum breaker: Backflow device configured with a single moving part, a float, which moves up or down to allow atmospheric air into the piping system. The AVB is always placed downstream from all shut-off valves. Its air inlet valve closes when the water flows in the normal direction. But, as water ceases to flow the air inlet valve opens, thus interrupting the possible backsiphonage effect. This type of assembly must always be installed at least six inches above all downstream piping and outlets. Additionally, this assembly may not have shut-off valves or obstructions downstream. A shut-off valve would keep the assembly under pressure and allow the air inlet valve (or float check) to seal against the air inlet port, thus causing the assembly to act as an elbow, not a backflow preventer. The AVB may not be under continuous pressure for this same reason. An AVB must not be used for more than 12 out of any 24-hour period. It may be used to protect against either a pollutant or a contaminant, but may only be used to protect against a backsiphonage condition.

Blaney-Criddle Method: Air temperature based method to estimate crop evapotranspiration.

border dike: Earth ridge or small levee built to guide or hold irrigation or recharge water in a field.

British thermal units: Amount of heat required to raise the temperature of one pound of water from 63 to 64 degrees Fahrenheit.

capillary water: Water held in the capillary, or small pores of the soil, usually with soil water pressure (tension) greater than 1/3 bar. Capillary water can move in any direction.

cation: Positively charged ion which during electrolysis is attracted towards the cathode. Sodium, potassium, calcium and magnesium are the most common cations in waters and soil extracts.

cation exchange capacity: The measure of the positively charged ions in a soil matrix. The sum of exchangeable cations (usually Ca, Ma, K, Na, Al, H) that the soil constituent or other material can adsorb at a specific pH, usually expressed in centimoles of charge per Kg of exchanger (cmol/Kg), or milli equivalents per 100 grams of soil at neutrality (pH = 7.0), meq/100g.


  • Process when pressure on a liquid falls momentarily below the vapor pressure of that liquid, causing a phase change from liquid to vapor, and then a pressure increase causes another phase change and the gas becomes a liquid again.
  • Process where pressure in the suction line falls below the vapor pressure of the liquid, vapor is formed and moves with the liquid flow. These vapor bubbles or "cavities" collapse when they reach regions of higher pressure on their way through pumps.

Certified Irrigation Contractor (CIC): The Certified Irrigation Contractor is an irrigation professional whose principle business is the execution of contracts and subcontracts to install, repair and maintain irrigation systems. The CIC must conduct business in such a manner that projects meet the specifications and requirements of the contract.

Certified Irrigation Designer (CID): The IA Certified Irrigation Designer engages in the preparation of professional irrigation designs. They evaluate site conditions and determine net irrigation requirements based on the needs of the project. The designer is then responsible for the selection of the most effective irrigation equipment and design methods. The objective of a CID is to establish specifications and design drawings for the construction of an irrigation project.

Certified Landscape Irrigation Auditor (CLIA): The Certified Landscape Irrigation Auditor is involved in the analysis of landscape irrigation water use. Auditors collect site data, make maintenance recommendations and perform water audits. Through their analytical work at the site, these irrigation professionals develop monthly irrigation base schedules. Prior to certification examination, auditors are required to take an Irrigation Association approved preparatory course.

Certified Landscape Irrigation Manager (CLIM): The Certified Landscape Manager is an irrigation professional familiar with all areas of turf irrigation design and construction management. CLIMs must be certified as CICs, CIDs (all specialty areas), and CLIAs. Certified Landscape Irrigation Managers have extensive experience in design, construction, construction management and auditing of turf irrigation systems.

Check Valves:

  • double check assembly: Two internally loaded, independently operating check valves together with tightly closing resilient seated shut-off valves upstream and downstream of the check valves. Additionally, there are resilient seated test cocks for testing of the assembly. The DC may be used to protect against a pollutant only. However, this assembly is suitable for protection against either backsiphonage or backpressure.
  • pressure vacuum breaker: Backflow device configured with a spring loaded float and an independent spring loaded check valve. Check valve which is designed to close with the aid of a spring when flow stops. It also has an air inlet valve which is designed to open when the internal pressure is one psi above atmospheric pressure so that no non-potable liquid may be siphoned back into the potable water system. Being spring loaded it does not rely upon gravity as does the atmospheric vacuum breaker. This assembly includes resilient seated shut-off valves and test cocks. The PVB must be installed at least 12 inches above all downstream piping and outlets. The PVB may be used to protect against a pollutant or contaminant, however, it may only be used to protect against backsiphonage. It is not acceptable protection against backpressure.
  • reduced pressure principle assembly: Two internally loaded independently operating check valves and a mechanically independent, hydraulically dependent relief valve located between the check valves. This relief valve is designed to maintain a zone of reduced pressure between the two check valves at all times. The RP also contains tightly closing, resilient seated shut-off valves upstream and downstream of the check valves along with resilient seated test cocks. This assembly is used for the protection of the potable water supply from either pollutants or contaminants and may be used to protect against either backsiphonage or backpressure.

chemigation: Application of chemicals (including fertilizers) to crops through an irrigation system by mixing them with the irrigation water.

class (pipe): Term generally used to describe the pressure rating of SDR-PR (standard dimension ratio-pressure rated) PVC pipe, e.g., class 200 pipe has a pressure rating of 200 psi. Term used to identify the physical characteristics of thermoplastic pipe.


  • arid: precipitation averages less than 10 inches per year.
  • semiarid: precipitation averages between 10 and 20 inches per year.
  • subhumid: precipitation averages more than 20 inches per year, but less than 40 inches per year.
  • humid: precipitation averages more than 40 inches per year.

dielectric union: Pipe connection (union) having an insulator between the two sides of the union for the purpose of reducing corrosion caused by galvanic action.

emission uniformity: Index of the uniformity of emitter discharge rates throughout a micro-irrigation system. Takes account of both variations in emitters and variations in the pressure under which the emitters operate.

emitter (continuous flushing): Micro irrigation system emitter designed to continuously permit passage of large solid particles while operating at a trickle or drip flow, thus reducing filtration requirements.

evapotranspiration: Combination of water transpired from vegetation and evaporated from the soil and plant surfaces.

evaporation pan: Standard U.S. Weather Bureau Class-A pan (48-inch diameter by 10-inch deep) used to estimate the reference crop evapotranspiration rate.

friable: The ease with which the soil aggregates may be crumbled (in the hand).

friction factor, Christiansen: Coefficient used in the Christiansen Procedure to determine pressure loss in a multiple outlet piping system.

furrow dike: Small earth dike formed in a furrow to prevent water translocation. Typically used with LEPA and LPIC systems. Also used in non-irrigated fields to capture and infiltrate precipitation. Sometimes called reservoir tillage.

high density polyethylene: One of several forms of polyethylene used to make pipe and other irrigation components.

hygroscopic water:

  • Water which is bound tightly by the soil solids at potential values lower than -31 bars.
  • Water that is tightly held by soil particles. It does not move with the influence of capillary action or gravity, and it is normally unavailable to plants.

internal manual bleed: Feature which allows an automatic valve to be opened manually (without controller) by releasing water from above the diaphragm to the downstream side of the valve. Useful during installation, system start-up and maintenance operations when it is undesirable for water to escape into the valve box.

basin irrigation: Irrigation by flooding areas of level land surrounded by dikes. Used interchangeably with level border irrigation, but usually refers to smaller areas.

drip/trickle/micro irrigation:

  • Micro irrigation system (low pressure and low volume) wherein water is applied to the soil surface as drops or small streams through emitters. Preferred term is drip irrigation.
  • Method of micro-irrigation wherein water is applied to the soil surface (or below the soil surface) as drops or small streams through emitters. Discharge rates are generally less than 2 gph for single-outlet emitters and 3 gph per meter for line-source emitters.

border irrigation: Irrigation by flooding strips of land, rectangular in shape and cross leveled, bordered by dikes. Water is applied at a rate sufficient to move it down the strip in a uniform sheet. Border strips having no down field slope are referred to as level border systems. Border systems constructed on terraced lands are commonly referred to as benched borders.

cablegation: Method of surface irrigation that uses gated pipe to both transmit and distribute water to furrows or border strips. A plug, moving at a controlled rate through the pipe, causes irrigation to progress along the field and causes flow rates from any one gate to decrease continuously from some maximum rate to zero.

check irrigation: Modification of a border strip with small earth ridges or checks constructed at intervals to retain water as the water flows down the strip.

check basin irrigation: Water is applied rapidly to relatively level plots surrounded by levees. The basin is a small check.

corrugation irrigation: Method of surface irrigation similar to furrow irrigation, in which small channels, called corrugations, are used to guide water across a field. No attempt is made to confine the water entirely to the corrugations.

leaching requirement: Quantity of irrigation water required for transporting salts through the soil profile to maintain a favorable salt balance in the root zone for plant development.

Low Energy Precision Application [LEPA]: A water, soil, and plant management regime where precision down-in-crop applications of water are made on the soil surface at the point of use. Application devices are located in the crop canopy on drop tubes mounted on low pressure center pivot and linear move sprinkler irrigation systems.

Low Pressure In Canopy [LPIC]: Low-pressure in-canopy system that may or may not include a complete water, soil and plant management regime as required in LEPA. Application devices are located in the crop canopy with drop tubes mounted on low-pressure center pivot and linear move sprinkler irrigation systems.


  • Device for measuring deep percolation from a soil profile, usually consisting of an enclosed volume of undisturbed soil with some means of collecting drainage water. It may also include some method of measuring changes in the volume of stored soil water.
  • Isolated block of soil, usually undisturbed and in situ, for measuring the quantity, quality, or rate of water movement through or from the soil.
  • Device and monitoring system used to measure the evapotranspiration (ET) rate using a container closed at the bottom and with the top flush with surrounding grade and planted with turf. After rainfall and irrigation application are accounted for, daily change in the weight of the lysimeter is directly related to ET.

manufacturer's coefficient of variation: Measure of the variability of discharge of a random sample of a given make, model, and size of micro-irrigation emitter, as produced by the manufacturer and before any field operation or aging has taken place; equal to the ratio of the standard deviation of the discharge of the emitters to the mean discharge of the emitters.


  • Pipeline that supplies water to the laterals.
  • Closely linked series of mainline piping supplying water to valves or laterals.

matric potential: Dynamic soil property, and will be near zero for a saturated soil. Matric potential results from capillary and adsorption forces. Formerly called capillary potential or capillary water.

median drop size:

  • Diameter where half the sprinkler's water volume falls in drops smaller, and half falls in drops larger than the median size.
  • Drop size where 50% of the water volume occurs in drops greater than this size.

net positive suction head: Head that causes liquid to flow through the suction piping and enter the eye of the pump impeller.

non-saline sodic soil: Soil containing soluble salts that provide an electrical conductivity of saturation extract (ECe) less than 4.0 mmhos/cm and an exchangeable sodium percentage (ESP) greater than 15. Commonly called black alkali or slick spots.

(permanent) wilting point: Moisture content, on a dry weight basis, at which plants can no longer obtain sufficient moisture from the soil to satisfy water requirements. Plants will not fully recover when water is added to the crop root zone once permanent wilting point has been experienced. Classically, 15 atmospheres (15 bars), soil moisture tension is used to estimate PWP.

  • Moisture content of the soil after the plant can no longer extract moisture at a sufficient rate for wilted leaves to recover overnight or when placed in a saturated environment.
  • Also known as wilting percentage, wilting coefficient or wilting point.

polyvinyl-chloride: PVC

potable water:

  • Domestic or drinking water. It can be used as a source of irrigation water, but once water enters an irrigation system (and passes through the backflow device) it is no longer considered potable.
  • Treated water which is meant for human consumption. It can be used for irrigation systems as long as protection is provided to prevent contamination of the domestic supply.

profile (sprinkler): Chart showing the application rates vs. distance of throw for a sprinkler head.


  • Centrifugal: Pump consisting of rotating vanes (impeller) enclosed in a housing
  • jockey: A small pump used to provide pressure and flow in a multi-pump system.
  • mixed flow: Centrifugal pump in which the pressure is developed partly by centrifugal force and partly by the lifting action of the impellers on the water.
  • multistage: Pump having more than one impeller mounted on a single shaft.
  • propeller: Pump which develops most of its head by the lifting action of vanes on the water.
  • radial flow: Centrifugal pump that uses diffuser vanes to transform the velocity head into pressure head. Commonly called a turbine pump.
  • trash: Designed to pump large sized particulate matter in addition to liquid.
  • PTO: Driven by a separate power supply connected to the pump by a power takeoff (pto) drive.
  • vertical turbine: Consisting of an impeller on a vertical shaft, surrounded by stationary and usually symmetrical guide vanes. Combines the energy-imparting characteristics of axial-flow and propeller pumps.

pump start circuit: Feature on automatic controllers which supplies 24 VAC, which can be used to activate a pump through an external pump start relay.

pump start relay: Low-amperage or electric switch designed for use with pump start circuits.

relative humidity: Ratio of the amount of water vapor present in the atmosphere to the amount required for saturation at the same dry bulb temperature.


  • Area of flowing streams that lies between the normal water line and some defined high water line.
  • Pertaining to the banks of a body of water; riparian owner is the one who owns the banks.
  • Riparian water right is the right to use and control water by virtue of ownership of the banks.

riser: Length of pipe which has male nominal pipe threads on each end and is usually affixed to a lateral or sub-main to support a sprinkler or anti-siphon valve.

shutoff head: Pressure head on the outlet side of a pump at which the discharge drops to zero. Maximum pressure a pump will develop at a given speed.

slide gate: Head control valve, which slides on rails, used to control drainage or irrigation water.

slip configuration or slip joint: Connection without threads (of PVC pipe or fittings) which is solvent welded.

sodic soil: Nonsaline soil containing sufficient exchangeable sodium to adversely affect crop production and soil structure.


  • gear drive: sprinkler containing gears as part of its rotational drive mechanism.
  • infiltrometer: Consists of a sprinkler head(s) that applies water to the soil surface at a range of rates of less-than to greater than soil infiltration rates. Maximum infiltration rates are observed and recorded.
  • impact drive: sprinkler which rotates using a weighted or spring-loaded arm which is propelled by the water stream and hits the sprinkler body, causing movement.
  • rotor: sprinkler that rotates, but may more specifically refer to a gear driven sprinkler.
  • spray head: sprinkler head that does not rotate.
  • valve-in-head: sprinkler head having an integrally mounted valve.

standard dimension ratio: diameter of a pipe to its wall thickness. Outside diameter is used for OD rated pipe; ID is used for ID rated pipe. Certain dimension ratios have been selected by convention and standards to be used for construction of pipe. These dimension ratios are referred to as standard dimension ratios.

static head: Vertical distance between water source and discharge water levels in a pump installation.

Station: Circuit on a controller which has the ability to be programmed with a run time unique and separate from other circuits and provides power to one or more remote control valves (or valve-in-head sprinklers).


  • Application of irrigation water below the ground surface by raising the water table to within or near the root zone.
  • Applying irrigation water below the ground surface either by raising the water table or by using a buried perforated or porous pipe system that discharges water directly into the plant root zone.

subsurface drip irrigation: Application of water below the soil surface through emitters, with discharge rates generally in the same range as drip irrigation. The method of water application is different from and not to be confused with sub-irrigation where the root zone is irrigated by water table control.

swing joint: Threaded connection of pipe and fittings between the pipe and sprinkler which allows movement to be taken up in the threads rather than as a sheer force on the pipe. Also used to raise or lower sprinklers to a final grade without plumbing changes.

system capacity, gross irrigation: Ability of an irrigation system to deliver the net required rate and volume of water necessary to meet crop water needs plus any losses during the application process. Crop water needs can include soil moisture storage for later plant use, leaching of toxic elements from the soil, air temperature modification, crop quality, and other plant needs.

Tensiometer: Instrument, consisting of a porous cup filled with water and connected to a manometer or vacuum gauge, used for measuring the soil-water matric potential.

thrust block: Normally, concrete poured in place at changes in direction of water flow in piping systems to prevent movement of the pipe.


  • Process of plant water uptake and use, beginning with absorption through the roots and ending with transpiration at the leaf surfaces. See also evapotranspiration.
  • Liquid movement of water from the soil, into the roots, up the plant stems, and finally out of the plant leaves into the air as vapor.

Turgid: State of a plant cell when the cell wall is rigid due to the hydrostatic pressure of liquid in the cell.

uniformity coefficient (Christiansen's): Measure of the uniformity of irrigation water application. The average depth of irrigation water infiltrated minus the average absolute deviation from this depth, all divided by the average depth infiltrated.


  • alfalfa: Outlet valve attached to the top of a short vertical pipe (riser) with an opening equal in diameter to the inside diameter of the riser pipe and an adjustable lid or cover to control water flow. A ring around the outside of the valve frame provides a seat and seal for a portable hydrant. Typically used in border or basin irrigation.
  • angle: Valve configured with its outlet oriented 90 degrees from its inlet.
  • air vent (air relief, air release): Device that releases air from a pipeline automatically without permitting loss of water.
  • air vacuum, air relief: Device that releases air from a pipeline automatically without permitting loss of water or admits air automatically if the internal pressure becomes less than atmospheric.
  • back flow prevention: Check valve that allows flow in one direction. ... (NRCS, 1997) See specific valve for details.
  • Ball: Valve in a pipeline used to start or stop flow by rotating a sealed ball with a transverse hole approximately equal to the diameter of the pipeline. Ball rotation is typically 90 degrees for a single-port control.
  • Valve with an internally mounted ball with a hole in the center for water to pass through. (Rotation of the ball one-fourth turn opens and closes the valve.)
  • Butterfly: Valve in a pipeline to start or stop flow by rotating a disk 90 degrees. The disk is about the same diameter as the pipeline.
  • Check: Valve used in a pipeline which allows flow in only one direction.
  • Chemigation: Valve especially designed to be used with the injection of chemicals in an irrigation system.
  • corporation stop: Quarter turn valve similar to a ball valve with two exceptions. Internally there is a circular disk rather than a ball, and there is no attached handle.
  • curb stop: Physically the same as corporation valve but used at a different location.
  • drain, automatic: Spring loaded valve that automatically opens and drains the line when the pressure drops to near zero.
  • float: Valve, actuated by a float, that automatically controls the flow of water.
  • foot: Check valve used on the bottom of the suction pipe to retain the water in the pump when it is not in operation.
  • flow control: Valve with automatically adjusts to provide a predetermined downstream flow.
  • flushing: Valve on the end of a line to flush out dirt and debris. May be incorporated into an end plug or cap.
  • gate: Valve in a pipeline used to start or stop water flow. May be operated by hand with or with mechanical assistance or by high or low voltage (solenoid) electric controlled mechanical assistance. Gate valves consist of seated slide or gates operated perpendicular to the flow of water. Head loss through a gate valve is typically less than a globe valve, but more than a ball or butterfly valve.
  • globe: Valve in a pipeline used to start or stop water flow. Globe valves stop flow by positioning a disk and gasket over a machined seat about the same diameter as the pipe. Globe valves are limited to smaller sizes because of the high velocities and very high head loss through the valve.
  • hydraulic: Irrigation zone valve which uses small flexible tubes and water under pressure to provide the actuation signal from the controller to the valve.
  • Isolation: Any mechanical valve used to isolate a section of a piping system.
  • master: Valve used to protect the landscape from flooding in case of a ruptured main or malfunctioning downstream valve. The master valve is installed on the mainline after the backflow preventer (in some systems).
  • orchard: Outlet valve installed inside a short vertical pipe (riser) with an adjustable cover or lid for flow control. Similar to an alfalfa valve, but with lower flow capacity. Typically used in basin irrigation.
  • pilot: Small valve used to actuate a larger one.
  • pressure regulating: Valve designed to automatically provide a preset downstream pressure in a hydraulic system.
  • pressure relief: Spring loaded valve set to open at a pressure slightly above the operating pressure, used to relieve excessive pressure and surges.
  • pressure sustaining: Valve designed to provide a minimum preset upstream pressure.
  • quick coupling: Permanently installed valve which allows direct access to the irrigation mainline. A quick coupling key is used to open the valve.
  • remote control: Valve which is actuated by an automatic controller by electric or hydraulic means. Synonymous with Automatic Control Valve.
  • surge: Device in a pipe T fitting to provide flow in alternate directions at timed intervals. Used in surge irrigation.
  • vacuum relief: Valve used to prevent a vacuum in pipelines and avoid collapsing of thin-wall pipe.

voids ratio: Ratio of the volume of voids (pores) to the volume of soil.

volute: Refers to the flow path of water and its associated pump casing as it leaves the impeller of a pump.

water hammer:

  • phenomenon which occurs when the velocity of water flowing in pipelines is rapidly changed, usually by a rapid or sudden gate or valve closure, starting or stopping of a pump, or sudden release of air. The resulting pressure waves pass through the water at high velocities and can produce very high momentary positive and/or negative pressures.
  • Shock wave created when the flow of water in a piping system suddenly stops (or changes speed). Usually the result of a fast-closing (or opening) valve.

weir: Flow measuring device for open-channel flow. Weirs can be either sharp-crested or broad-crested. Flow opening may be rectangular, triangular, trapezoidal (cipolletti), or specially shaped to make the discharge linear with flow depth (sutro weir). Calibration is based on laboratory ratings.

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