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Irrigation Glossary



ID Abbreviation for inside diameter (usually of a pipe).

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.

Impact power

  • Rate at which drops deliver kinetic energy to the soil.
  • Kinetic energy of impact on soil per unit volume.

Impact rate

  • Impact power per unit area.
  • Impact power per square foot.

Infiltration See also intake rate.

  • Process of water movement through the soil surface into the soil matrix.
  • The act of water entering the soil profile.

Infiltration rate (Preferred term is intake rate.)

  • Downward flow of water into the soil at the air-soil interface. 
  • Volume of water infiltrating through a horizontal unit area of soil surface at any instant.
  • How quickly water moves into the soil.

Infiltrometer  Device used to measure the infiltration rate / intake rate of water into soil.

  • ring infiltrometer Consists of metal rings that are inserted (driven) into the soil surface and filled with water.  The rate at which water enters the soil is observed.
  • sprinkler 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.
  • flowing infiltrometer Consists of an inlet device to apply a specific flow rate to a furrow and a collection sump with a pump to return tail water to the inlet device.  Water infiltrated by the soil in the test section (typically 10 meters) is replaced with water from a reservoir to keep the flow rate constant.  The rate of water infiltrated verses time is also plotted.  An equation (typically for a curvilinear line) then represents the intake characteristics for that particular soil condition.

Inrush current Current necessary to initially open the solenoid valve.

Intake family Grouping of intake characteristics into families based on field infiltrometer tests on many soils.  

Intake, initial Depth (rate) of water absorbed by a soil during the period of rapid or comparatively rapid intake following initial application.

Intake rate (of soil) Rate that (irrigation) water enters the soil at the surface.

Intake rate (basic) Rate at which water percolates into the soil after infiltration has decreased to a low and nearly constant value.

Interception Part of precipitation or sprinkler irrigation system applied water caught on the vegetation and prevented from reaching the soil surface.

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.

Inverted siphon Closed conduit (for conveying water) with end sections above the middle section; used for crossing under a depression, under a highway or other obstruction.  Sometimes called a sag pipe.

Iron pipe size One of several systems which specify pipe dimensions.

Irrecoverable water loss Water loss that becomes unavailable for reuse through evaporation, phreatophytic transpiration, or ground-water recharge that is not economically recoverable.

Irrigable area Area capable of being irrigated, principally based on availability of water, suitable soils, and topography of land.


  • Intentional application of water to the soil, usually for the purpose of crop production (reclaiming soils, temperature modification, improving crop quality).
  • Intentional application of water for purposes of sustained plant growth and/or optimized production.

Irrigation audit Procedure to collect and present information concerning the uniformity of application, precipitation rate, and general condition of an irrigation system and its components.

Irrigation design Plan of an irrigation system with pipe sizing, head layout and valve location. 

Irrigation district Cooperative, self-governing, semipublic organization set up as a subdivision of a state or local government to provide irrigation water.

Irrigation frequency Measure of the number of irrigations per unit time.


  • gross Water actually applied, which may or may not be total irrigation water requirement; i.e. leaving storage in the soil for anticipated rainfall, harvest.
  • net Actual amount of applied irrigation water stored in the soil for plant use or moved through the soil for leaching salts.  Also includes water applied for crop quality and temperature modification; i.e. frost control, cooling plant foliage and fruit.  Application losses, such as evaporation, runoff, and deep percolation, are not included. See also, irrigation requirement, net.

Irrigation interval

  • Average time interval between the commencement of successive irrigations for a given field (or area).
  • Time between irrigation events.  Usually considered the maximum allowable time between irrigations during the peak ET period.

Irrigation period Time that it takes to apply one irrigation to a given design area during the peak consumptive-use period of the crop being irrigated.

Irrigation (water) requirement

  • net irrigation requirement
    • Depth of water, exclusive of effective precipitation, stored soil moisture, or ground water, that is required for meeting crop evapotranspiration for crop production and other related uses.  Such uses may include water required for leaching, frost protection, cooling and chemigation.
    • Difference between  evapotranspiration and effective precipitation.
    • Quantity of water needed by the landscape to satisfy the evaporation, transpiration and other uses of the water in the soil.
  • gross irrigation requirement
    • Total amount of water applied (or desired). See also irrigation water requirement.
    • Total irrigation requirement including net crop requirement plus any losses  incurred in distributing and applying and in operating the system.
  • irrigation water requirement
    • Calculated amount of water needed to replace soil water used by the crop (soil water deficit), for leaching undesirable elements through and below the plant root zone, plus other needs; after considerations are made for effective precipitation.
    • Plant water requirement adjusted for application uniformity (and efficiency).(Same as gross irrigation requirement.)

Irrigation sagacity Ratio of volume of irrigation water beneficially or reasonably used to the total volume of irrigation water that has left the region, both in a specified period of time.

Irrigation schedule

  • Procedure of establishing and implementing the time and amount of irrigation water to apply.
  • Determining when to irrigate and how much water to apply, based upon measurements or estimates of soil moisture or crop water used by a plant.
  • Set of specifications identifying times to turn on and off water to various zones of an irrigation system.

Irrigation set Area irrigated at one time within a field.

Irrigation slope Elevation difference along the direction of irrigation. Sometimes called irrigation grade.

Irrigation system

  • Physical components (pumps, pipelines, valves, nozzles, ditches, gates, siphon tubes, turnout structures) and management used to apply irrigation water by an irrigation method. 
  • Set of components which includes (may include) the water source, water distribution network, control components and possibly other general irrigation equipment.
  • drip/trickle/micro 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.
  • bubbler irrigation  Application of water to flood the soil surface using a small stream or fountain.  The discharge rates for point-source bubbler emitters are greater than for drip or subsurface emitters but generally less than 1 gpm.  A small basin is usually required to contain or control the water.
  • surface
    • Type of irrigation where water is distributed to the plant material by a ground surface distribution network possibly including rows or dikes.
    • Broad class of irrigation methods in which water is distributed over the soil surface by gravity flow.
    • basin irrigation Irrigation by flooding areas of level land surrounded by dikes. Used interchangeably with level border irrigation, but usually refers to smaller areas.
    • 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.
    • flood irrigation Method of irrigation where water is applied to the soil surface without flow controls, such as furrows, borders or corrugations.
    • furrow irrigation Method of surface irrigation where the water is supplied to small ditches or furrows for guiding across the field.
      • alternate set irrigation Method of managing irrigation whereby, at every other irrigation, alternate furrows are irrigated, or sprinklers are placed midway between their locations during the previous irrigation.
      • alternate side irrigation   Practice of furrow irrigating one side of a crop row (for row crops or orchards) and then, at about half the irrigation time, irrigating the other side.
      • cutback irrigation Reduction of the furrow or border inflow stream after water has advanced partially or completely through the field in order to reduce runoff.
      • surge   Surface irrigation technique wherein flow is applied to furrows (or less commonly, borders) intermittently during a single irrigation set.
    • wild flooding Surface irrigation system where water is applied to the soil surface without flow controls, such as furrows, borders (including dikes), or corrugations.
  • sprinkler   Type of irrigation using mechanical devices with nozzles (sprinklers) to distribute the water by converting water pressure to a high velocity discharge stream or streams.
    • continuous/self-move system
      • Lateral, sprinkler (traveler), or boom that is continuous or self moving while water is being applied.  Power for moving the facility is typically provide by electric or hydraulic (water) motors or small diesel engines. 
      • boom   Elevated, cantilevered boom with sprinklers mounted on a central stand.  The sprinkler-nozzle trajectory back pressure rotates the boom about a central pivot which is towed across the field by a cable attached to a winch or tractor.  Can also be a periodic-move system.
      • center pivot   Automated irrigation system consisting of a sprinkler lateral rotating about a pivot point and supported by a number of self-propelled towers.  Water is supplied at the pivot point and flows outward through the pipeline supplying the individual sprinklers or spray heads.
      • corner pivot   Additional span or other equipment attached to the end of a center pivot irrigation system that allows the overall radius to increase or decrease in relation to field boundaries.
      • lateral (linear) move   Automated irrigation machine consisting of a sprinkler line supported by a number of self-propelled towers.  The entire unit moves in a generally straight path perpendicular to the lateral and irrigates a basically rectangular area.
      • traveler (traveling gun) irrigation
        • Large rotating sprinkler(s) mounted on a trailer to deliver water in a circle.  The sprinkler and associated trailer are towed through the field by any of several means.
        • Travelers are also called cable-tow, hard hose and hose drag. 
    • periodic-move system   System of laterals, sprinklers heads (gun types), or booms that are moved between irrigation settings.  They remain stationary wh ile applying water.
      • gun type   Single sprinkler head with large diameter nozzles, supported on skids or wheels.  Periodically moved by hand or mechanically with a tractor, cable, or water supple hose. ... 
      • portable (hand move) irrigation   Sprinkler system which is moved by uncoupling and picking up the pipes manually, requiring no special tools.
      • side move   Sprinkler system with the supply pipe supported on carriages and towing small diameter trailing pipelines each fitted with several sprinkler heads.
      • side role (wheel line)   Supply pipe is usually mounted on wheels with the pipe as the axle and where the system is moved across the field by rotating the pipeline by engine power.
      • towed sprinkler   System where lateral lines are mounted on wheels, sleds, or skids and are pulled or towed in a direction approximately parallel to the lateral.  Rollers or wheels are secured in the ground near the main water supply line to force an offset in the tow path equal to half the distance the lateral would have been moved by hand.
    • solid set/fixed  System of portable surface or permanently buried laterals totally covering the irrigated area or field.  Typically several adjacent laterals or heads are operated at one time.  Portable laterals are typically removed from the field at end of germination, plant establishment, or the irrigation season and are replaced the next irrigation system.

Isolation vale Any mechanical valve used to isolate a section of a piping system

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