Knowledge Base

ICE — A solid form of water. Water frozen, or reduced to the solid state by cold. Ice is a transparent, nearly colorless, crystalline, and brittle substance. Water in freezing expands about one eleventh of its volume, the specific gravity of ice being 0.9166, that of water at 4C (39.2F) being 1.0. Pure water freezes at 0C (32F), and ice melts at the same temperature.

ICEBERG — A massive piece of ice that breaks off and floats away from a Glacier. Icebergs occur as huge blocks, or in peaked forms of great variety and beauty. About one ninth of the bulk of an iceberg projects above sea level.

ICE WATER — Chilled or iced water, especially served as a beverage.

IMHOFF CONE — A clear, cone-shaped container used to measure the volume of settleable solids in a specific volume of water.

IMPACT ZONE — The spot on a wave where the water is just about to collapse and explode, the spot of greatest danger to and opportunity for a surfer.

IMPERMEABILITY — Characteristic of geologic materials that limit their ability to transmit significant quantities of water under the pressure differences normally found in the subsurface environment.

IMPERMEABLE — Unable to transmit water; not easily penetrated. The property of a material or soil that does not allow, or allows only with great difficulty, the movement or passage of water. Not the same as Nonporous.

IMPERVIOUS — A term denoting the resistance to penetration by water or plant roots; incapable of being penetrated by water; non-porous.

IMPERVIOUSNESS — The portion of a subbasin, subwatershed, or watershed, expressed as a percentage, that is covered by surfaces such as roof tops, parking lots, sidewalks, driveways, streets, and highways. Impervious surfaces are important because they will not absorb rainfall and, therefore, cause almost all of the rainfall to appear as surface runoff.

IMPORT (Water) — Water piped or channeled into an area.

IMPORTATION (of Water) — The act or process whereby water is brought into an area or region which would not naturally receive such waters. Typically, it refers to the artificial transport of water through aqueducts, canals, or pipelines from one water basin, drainage area, or Hydrographic Area to another, thereby affecting the natural surface and groundwater drainage and flow patterns in both the water exporting and importing areas. In terms of a Water Banking or Water Marketing concept, such actions to move water from areas of low use to areas of high use place a more realistic monetary value on water as a scarce economic commodity and result in enhanced economic efficiency by putting existing water resources, wherever located, to more productive economic use. However, considerable public concern and controversy surround this practice. These concerns deal primarily with issues relating to altering the natural flows of both surface and ground waters, adverse environmental and habitat impacts on water exporting areas, the limitations placed on the long-term growth and development of the water exporting region or hydrographic area, the potentially adverse hydrologic effects on groundwater (water table and aquifer) conditions in the exporting area as well as the generally unknown effects on surrounding hydrographic areas and aquifer conditions, and the dependency acquired by the water importing area to continued diversions and water importations. The concept of a public policy limiting an area's development to its natural ability to support population growth only through existing and readily available natural resources, particularly water, is referred to as an Antediluvian Policy.

IMPOUND — To accumulate and store water as in a reservoir.

IMPOUNDMENT — (1) A body of water such as a pond, confined by a dam, dike, floodgate or other barrier. It is used to collect and store water for future use. (2) (Water Quality) Generally an artificial collection and storage area for water or wastewater confined by a dam, dike, floodgate, or other barrier.

IMPROVED IRRIGATED ACREAGE — Refers to farm acreage which has been leveled, planed and serviced by improved conveyance and control structures.

INCH — A fall, as of rain or snow, sufficient to cover the surface to the depth of one inch (2.54 centimeters).

INCH-DEGREES — The product of inches of rainfall times temperature in degrees above freezing (Fahrenheit), used as a measure of the snowmelting capacity of rainfall.

IN-CHANNEL STORAGE — Water storage volume in a canal above the minimum water level required for conveyance.

INCHOATE WATER RIGHT — An unperfected water right.

INCIDENTAL RECHARGE — 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). Also see Artificial (or Induced) Recharge, Natural Recharge, and Perennial Yield.

INCIDENTAL WASTE WATER RECLAMATION — Treated waste water returned to fresh-water streams or other water bodies. Additional use made of this treated waste water is only incidental to waste water treatment and disposal.

INCINERATION — (Water Quality) A treatment technology involving the destruction of waste by controlled burning at high temperatures, e.g., burning sludge to remove the water and reduce the remaining residues to a safe, non-burnable ash that can be disposed of safely on land, in some waters, or in underground locations.

INCISED RIVER — A river which cuts its channel through the bed of the valley floor, as opposed to one flowing on a floodplain; its channel formed by the process of degradation.

INDEX MODEL — A hydrologic computer model based on empirical, statistical relationships.

INDEX OF WETNESS — The precipitation for a given year expressed as a ratio to the mean annual precipitation.

INDIRECT DISCHARGE — The introduction of pollutants from a non-domestic source into a publicly owned waste-treatment system. Indirect dischargers can be commercial or industrial facilities whose wastes enter local sewers.

INDUSTRIAL WASTE — Unwanted materials from an industrial operation; may be liquid, sludge, or hazardous waste.

INDICATOR (ORGANISM) — (Water Quality) An organism, species, or community that shows the presence of certain environmental conditions.

INDICATOR BACTERIA — (Water Quality) Nonpathogenic bacteria whose presence in water indicate the possibility of pathogenic species in the water.

INDICATOR GAGE — A gage that shows by means of an index, pointer, dial, etc., the instantaneous value of such characteristics as depth, pressure, velocity, stage, discharge, or the movements or positions of water-controlling devices.

INDICATOR SPECIES — (Environmental) Any organism that by its presence or absence, its frequency, or its vigor indicates a particular property of its surrounding environment. A species whose presence is a sign that certain environmental conditions exist.

INDICATOR TESTS — (Water Quality) Tests for a specific contaminant, group of contaminants, or constituent which signals the presence of something else. For example, the presence of non-pathogenic coliforms indicate the presence of pathogenic bacteria.

INDIGENOUS — Existing, growing, or produced naturally in a region.

INDIRECT WATER USES — Uses of water that are not immediately apparent to the consumer. For example, a person indirectly uses water when driving a car because water was used in the production process of steel and other automotive components.

INDUCED RECHARGE — 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.

INDUSTRIAL, SELF-SUPPLIED WATER — Water withdrawn from privately developed sources and delivered through water systems established entirely or primarily for commercial and industrial use. Includes water used by mining, manufacturing, military establishments, educational and penal institutions, golf courses, hotels, motels, restaurants, casinos and other small businesses.

INDUSTRIAL WASTEWATER FACILITY — Refers to those facilities that produce, treat or dispose of wastewater not otherwise defined as a domestic wastewater. May include the runoff and leachate from areas that receive pollutants associated with industrial or commercial storage, handling, or processing.

INDUSTRIAL WATER USE — Water used for industrial purposes such as fabricating, manufacturing, processing, washing, and cooling, and includes such industries as steel, chemical and allied products, paper and allied products, mining, and petroleum refining. The water can be obtained from a Public Water Supply System of may be self-supplied.

INFILTRATE, also Infiltration — (1) The flow of a fluid into a substance through pores or small openings; to cause a liquid to permeate a substance by passing through its interstices or pores. It connotes flow into a substance in contradistinction to the word Percolation, which connotes flow through a porous substance. Also the process whereby water passes through an interface, such as from air to soil or between two soil horizons. (2) The technique of applying large volumes of waste water to land to penetrate the surface and percolate through the underlying soil.

INFILTRATION AND INFLOW — (Water Quality) The entrance of groundwater (infiltration) or of surface water (inflow) into sewer pipes. Groundwater can seep through defective pipe joints or cracked pipe sections; roof or basement drains are sources of surface water inflow. Excessive infiltration and inflow can cause sewers to back up or can overload sewage treatment plants, causing a reduction in treatment time or a complete bypass of the treatment process during periods of significant rainfall.

INFILTRATION CAPACITY — The maximum rate at which the soil, when in a given condition, can absorb falling rain or melting snow.

INFILTRATION CAPACITY CURVE — A graph showing the time variation of infiltration capacity. A standard infiltration capacity curve shows the time variation of the infiltration rate which would occur if the supply were continually in excess of infiltration capacity.

INFILTRATION CAPACITY, ULTIMATE — The relatively steady, slow, infiltration capacity which exists after a sufficiently long period of infiltration at capacity rate.

INFILTRATION GALLERY — A sub-surface groundwater collection system, typically shallow in depth, constructed with open-jointed or perforated pipes that discharge collected water into a watertight chamber from which the water is pumped to treatment facilities and into the distribution system. Usually located close to streams or ponds.

INFILTRATION INDEX — The average rate of infiltration, in inches per hour, derived from a time intensity graph of rainfall, so that the volume of rainfall in excess of this rate equals the total direct runoff. Also referred to as a "o" (Phi) or "W" index.

INFILTRATION RATE — Rate of downward movement or flow of water from the surface into the soil. (1) The rate at which infiltration takes place, expressed in depth of water per unit time, usually in inches per hour. (2) The rate, usually expressed in cubic feet per second, or million gallons per day per mile of waterway, at which ground water enters an infiltration ditch or gallery, drain, sewer, or other underground conduit.

INFILTROMETER — An instrument which determines the rate and amount of water percolating into the soil by measuring the difference between the amount of water applied and that which runs off. Essentially, the infiltrometer consists of a sprinkling mechanism (rain simulator) which provides a rather uniform sprinkling of water to a prescribed area at prescribed rates and size drops (impact), a rain gage (either total or intensity), and a catchment basin or receptacles in which either the rate or total flow of surface runoff is measured. Infiltration or amount absorbed by the soil is usually expressed in inches (of water) per standard interval of time.

INFLOW — (1) The act or process of flowing in or into. (2) Something that flows in or into. (3) (Water Quality) Water, other than wastewater, that enters a sanitary sewer system (including sewer service connections) from sources such as roof leaders, cellar drains, yard drains, area drains, foundation drains, drains from springs and swampy areas, manhole covers, cross connections between storm sewers and sanitary sewers, catch basins, cooling towers, surface runoff, street wash waters, or drainage. Inflow does not include, and is distinguished from, Infiltration.

INFLOW DESIGN FLOOD — The maximum probable flood defined as the largest flood that can be expected to occur on a given stream at a selected point. This flood is used for design to prevent failure of the dam.

INFLUENT — Water, wastewater, or other liquid flowing into a reservoir, basin, or treatment plant.

INFLUENT SEEPAGE — The movement of gravity water in the Zone of Aeration from the ground surface toward the water table.

INFLUENT STREAM — A stream that contributes water to the Zone of Saturation and to Bank Storage. This term has generally been replaced by the term Losing Stream. Also see Stream.

INFLUENT WATER — Water that flows into sink holes, open cavities, and porous materials and disappears into the ground.

INFORMATION — (Data Analysis) The synthesis and manipulation of Data through various analytical, tabular, graphical, presentation, or other techniques into a format that readily lends itself to hypothesis testing, planning, and decision making. The fundamental distinction between the data and the information is that the data represents the original observations of an event, characteristic, or phenomenon whereas information represents the transformation of that data, possibly along with the combination of other relevant data and/or other information, into formats that may be used for decision-making purposes.

INFORMATION MANAGEMENT — (Data Analysis) The manipulation, re-organization, analysis, graphing, charting, and presentation of data for specific management and decision-making purposes. Typically, a fundamental distinction is made between information and data, which constitutes the raw numbers (or descriptions, in the case of qualitative data).

INFRASTRUCTURE — (1) An underlying base or foundation, especially for an organization or a system. (2) The basic facilities, services, and installations needed for the functioning of a community or society, such as transportation and communications systems, water and power lines, and public institutions including schools, post offices, and prisons.

INFUSE — To steep in liquid (as water) without boiling so as to extract the soluble constituents or principles.

INITIAL DETENTION — The volume of water on the ground, either in depressions or in transit, at the time active runoff begins. It is that part of precipitation that does not appear either as infiltration or runoff at the time active runoff begins. It includes interception by vegetal cover, depression storage, and evaporation during precipitation, but does not include surface detention.

INITIAL LOSS — Rainfall which precedes the beginning of surface runoff. It includes interception, surface wetting, and infiltration, unless otherwise specified.

INITIAL STORAGE — That portion of precipitation required to satisfy interception by vegetation, the wetting of the soil surface, and Depression Storage.

INITIAL WATER DEFICIENCY — The quantity, usually expressed in depth of water in inches on a unit area, by which the actual water content of a given soil zone (usually the Root Zone) is exceeded by the field capacity of that zone at the beginning of the rainy season.

INJECTION — Generally refers to a system of artificially introducing surface water into the ground water system as a means of storage or recharge. Most typically, this includes the use of Recharge Wells which work directly opposite of pumping wells to inject surface water into underlying formations. Depending on the water-bearing formation, these methods may have limited usefulness and are generally better used for pumping water into deep, confined aquifers. (Water Quality) Refers to a system of subsurface disposal of brine effluent into an acceptable formation.

INJECTION WELL — Refers to a well constructed for the purpose of injection treated wastewater directly into the ground. Wastewater is generally forced (pumped) into the well for dispersal or storage into a designated aquifer. Injection wells are generally drilled into nonpotable aquifers, unused aquifers, or below freshwater levels.

INJECTION ZONE — A geological formation receiving fluids trough a well.

INLAND FRESHWATER WETLANDS — Swamps, marshes, and bogs found inland beyond the coastal saltwater wetlands.

INLET — A recess, such as a bay or cove, along a coast. A stream or bay leading inland, as from the ocean; an estuary. Also, a narrow passage of water, as between tow islands. A drainage passage, as to a culvert.

IN-LINE FILTRATION — A pre-treatment method in which chemicals are mixed by the flowing water; commonly used in pressure filtration installations. Eliminates need for Flocculation and Sedimentation.

INLINE RESERVOIR — A reservoir constructed in line with the canal used to regulate flow for a balanced operation.

INSET — An inflow, as of water; a channel.

INSTREAM AERATION — The addition of air to a flowing stream to maintain the dissolved oxygen content of the water at an acceptable level.

INSTREAM FLOW — Nonconsumptive water requirements which do not reduce the water supply; water flows for uses within a defined stream channel. Examples of instream flows include:
[1] Aesthetics — Water required for maintaining flowing steams, lakes, and bodies of water for visual enjoyment;
[2] Fish and Wildlife — Water required for fish and wildlife;
[3] Navigation — Water required to maintain minimum flow for waterborne commerce;
[4] Quality Dilution — Water required for diluting salt and pollution loading to acceptable concentrations; and
[5] Recreation — Water required for outdoor water recreation such as fishing, boating, water skiing, and swimming.

INSTREAM FLOW NEEDS — Those habitat requirements within the running water Ecosystem related to current velocity and depth which present the optimum conditions of density (or diversity) or physiological stability to the aquatic organisms being examined at various life cycle stages.

INSTREAM USE — Typically non-consumptive uses of water that do not require diversion from its natural watercourse (e.g., fish and other aquatic life, recreation, navigation, esthetics, and scenic enjoyment). Hydroelectric power production water use is also considered a non-consumptive, but may require temporary diversion from the natural stream flow. Also referred to as In-Channel Use, Nonwithdrawal Use, or Instream Flow.

INSULATED STREAMS — Streams or a reach of a stream that neither contribute water to the zone of saturation nor receive water from it. Such streams are separated from the zones of saturation by an impermeable bed. Also see Stream.

INTANGIBLE FLOOD DAMAGE — Estimated damage done by disruption of business, danger to public health, shock, loss of life, and other factors not directly measurable.

INTEGRATED (WATER) RESOURCE PLANNING (IRP) — A comprehensive, interdisciplinary approach to water resource planning that encompasses water resource assessment, demand considerations, analysis of alternatives, risk management, resource diversity, environmental considerations, least-cost analysis, multidimensional modeling, and participatory decision making and public input, among other factors. Integrated Resource Planning begins with specific policy objectives that are applied to extensive lists of options for water supply sources, distribution systems, or other operational requirements. The options are then narrowed after evaluating demand requirements, environmental impacts, conservation options, costs, risks, and other aspects of a project. IRP involves a dynamic process of assessing demand and supply conditions and creatively integrating alternatives and new technologies. While the concepts of IRP are relatively new to the process of water planning, it has been used extensively in the energy industry. As a planning process it helps decision makers select the best mix of water resources, facilities, and conservation measures to meet water demands. In addition to traditional planning techniques, IRP also
[1] Includes extensive public involvement;
[2] Considers both supply-side (resources and facilities) and demand-side (conservation) alternatives as ways of meeting demands;
[3] Considers goals and objectives in addition to dollar costs (e.g., environmental concerns, public acceptability, etc.);
[4] Considers uncertainty in demand forecasts, regulations, etc.; and
[5] Considers the effect of water rates on water demands.

INTENSIVE CROPS — Crops generally grown under irrigation in the Western United States requiring large inputs of labor and capital. Examples include potatoes, sugar beets, fruit, and corn.

INTER-BASIN TRANSFER (of Water) — A transfer or diversion of water (either groundwater or surface water) from one Drainage or Hydrographic Basin to another.

INTERCEPTING DRAIN — A drain constructed at the upper end of an area to intercept and carry away surface or ground water flowing toward the area from higher ground.

INTERCEPTION (HYDROLOGY) — The process of storing rain or snow on leaves and branches which eventually evaporates back to the air. Interception equals the precipitation on the vegetation minus streamflow and throughfall.

INTERCEPTOR SEWERS — Large sewer lines that, in a combined system, control the flow of sewage to the treatment plant. In a storm, they allow some of the sewage to flow directly into a receiving stream, thus keeping it from overflowing onto the streets. Also used in separate systems to collect the flows from main and trunk sewers and carry them to treatment points.

INTERFERENCE (WELLS) — A change in the water level of one well caused by the pumping at another well. The condition occurring when the area of influence of a water well comes into contact with or overlaps that of a neighboring well, as when two wells are pumping from the same aquifer or are located near each other.

INTERFLOW — (1) That movement of water of a given density in a reservoir or lake between layers of water of different density, usually caused by the inflow of water either at a different temperature, or with different silt or salt contents. (2) Runoff due to that part of the precipitation which infiltrates the surface soil (but not to the water table) and moves laterally through the upper soil horizons toward the stream channels. The interflow is included in direct runoff and is part of the Flood Hydrograph.

INTERMEDIATE ZONE — The subsurface water zone below the Root Zone and above the Capillary Fringe.

INTERMITTENT — Alternately containing and empty of water as an intermittent lake.

INTERMITTENT STREAM — A stream that carries water only part of the time, generally in response to periods of heavy runoff either from snowmelt or storms. Flow generally occurs for several weeks or months in response to seasonal precipitation, due to ground water discharge, in contrast to the Ephemeral Stream that flows but a few hours or days following a single storm.

INTERMITTENTLY EXPOSED — A water regime in wetland classification in which surface water is present throughout the year except in years of extreme drought.

INTERMITTENTLY FLOODED — A water regime in wetland classification in which the substrate is usually exposed, but surface water is present for variable periods without detectable seasonal periodicity.

INTERNAL DRAINAGE — (1) Movement of water down through soil to porous aquifers or to surface outlets at lower elevations. (2) Drainage within a basin that has no outlet.

INTERNAL EROSION (of a Dam) — The progressive development of erosion by seepage, appearing downstream of the dam as a hole or seam discharging water that contains soil particles. Also referred to as Piping.

INTERNAL SOIL DRAINAGE — The downward movement of water through the soil profile. The rate of movement is determined by the texture, structure, and other characteristics of the soil profile and underlying layers and by the height of the water table, either permanent or perched. Relative terms for expressing internal drainage are none, very slow, medium, rapid, and very rapid.

INTERSTATE WATERS — According to law, interstate waters are defined as: (1) rivers, lakes and other waters that flow across or form a part of state or international boundaries; (2) waters of the Great Lakes; and (3) coastal waters whose scope has been defined to include ocean waters seaward to the territorial limits and waters along the coastline (including inland steams) influenced by the tide.

INTERSTITIAL — Referring to the Interstices or pore spaces in rock, soil, or other material subject to filling by water.

INTERSTITIAL MONITORING — The continuous surveillance of the space between the walls of an underground storage tank.

INTERSTITIAL PRESSURE — (Hydraulics) The upward pressure of water in the pores or Interstices of a material.

INTERSTITIAL WATER — Water in the pore spaces of soil or rock.

INTRABASIN TRANSFER — The diversion of water within a drainage basin.

INUNDATE — (1) To cover with water, especially floodwaters. (2) To overwhelm as if with a flood; swamp.

INUNDATION — The covering by water of lands not normally so covered.

INUNDATION MAP — A map delineating the area that would be inundated in the event of a dam failure.

INVASIVE PLANT — A plant that moves in and takes over an Ecosystem to the detriment of other species; often the result of Environmental Manipulation.

INVENTORY — A scientific survey of natural resources, e.g., plants, animals, water, timber, etc.

INVERTED SIPHON — A closed pipeline with its end sections above the middle section, used for crossing under drainage channels, roadways, depressions, or other structures. The term is common but misleading as there is no siphon action involved.

ION — (1) An atom or molecule that carries a net charge (either positive or negative) because of an imbalance between the number of protons and the number of electrons present. If the ion has more electrons than protons, it has a negative charge and is called an anion; if it has more protons than electrons it has a positive charge and is called a cation. (2) (Water Quality) An electrically charged atom that can be drawn from waste water during electrodialysis.

ION EXCHANGE — The substitution of one Ion for another in certain substances. Either Anion Exchange or Cation Exchange is possible. The most common cation exchange involves the conversion of Hard Water to Soft Water by means of a Water Softening process. Hard water contains the divalent ions of calcium (Ca+2) and magnesium (Mg+2), which cause soap and detergents to form precipitates in water. A Water Softener consists of a resin that is saturated with sodium ions (Na+). As hard water percolates through the resin, the ions of calcium or magnesium are removed as they attach to the resin, thus releasing (being exchanged for) sodium ions.

ION EXCHANGE TREATMENT — A common water-softening technique often found on a large scale at water purification plants that remove some organics and radium by adding calcium oxide or calcium hydroxide to increase the pH to a level where the metals will precipitate out.

IRRECOVERABLE LOSSES — Water lost to a salt sink or lost by evaporation or evapotranspiration from a conveyance facility, drainage canal, or in fringe areas.

IRREGULARLY EXPOSED — A water regime in wetland classification in which the land surface is exposed by tides less often than daily.

IRREGULARLY FLOODED — A water regime in wetland classification in which tidal water alternately floods and exposes the land surface less often than daily.

IRRIGABLE LAND — (1) Land capable of being irrigated by any method. (2) (USBR) Arable land under a specific project plan for which irrigation water is, can be, or is planned to be provided and for which facilities necessary for sustained irrigation are provided or are planned to be provided. For the purpose of determining the areas to which acreage limitations are applicable, it is that acreage possessing permanent irrigated crop production potential, after excluding areas occupied by and currently used for homesites, farmstead buildings, and related permanent structures such as feed lots, equipment storage yards, permanent roads, permanent ponds, and similar facilities, together with roads open for unrestricted use by the public. Areas used for field roads, farm ditches and drains, tailwater ponds, temporary equipment storage, and other improvements subject to change at will by the landowner are included in the irrigable acres.

IRRIGATE — (1) To supply (dry land) with water by means of ditches, pipes, or streams; to water artificially. (2) To wash out (a body cavity or wound) with water or a medicated fluid. (3) To make fertile or vital as if by watering.

IRRIGATED ACREAGE — The land area that is irrigated, which is equivalent to total irrigated crop acreage minus the amount of acreage that was double cropped.

IRRIGATED AREA — The area upon which water is artificially applied. This excludes farm roads, irrigation ditches, and farmsteads.

IRRIGATED CROP ACREAGE — The total amount of land area that is irrigated, including acreage that is double cropped.

IRRIGATED CROPLAND — All lands being supplied water by artificial means, excluding waterfowl refuges, that are being used for the production of orchard, field, grain crops and pasture.

IRRIGATED LAND — Land receiving water by controlled artificial means for agricultural purposes from surface or subsurface sources.

IRRIGATION — The controlled application of water for agricultural purposes through man-made systems to supply water requirements not satisfied by rainfall. A listing of the types of irrigation systems includes:
[1] Center-Pivot — Automated sprinkler irrigation achieved by automatically rotating the sprinkler pipe or boom, supplying water to the sprinkler heads or nozzles, as a radius from the center of the field to be irrigated. Water is delivered to the center or pivot point of the system. The pipe is supported above the crop by towers at fixed spacings and propelled by pneumatic, mechanical, hydraulic, or electric power on wheels or skids in fixed circular paths at uniform angular speeds. Water is applied at a uniform rate by progressive increase of nozzle size from the pivot to the end of the line. The depth of water applied is determined by the rate of travel of the system. Single units are ordinarily about 1,250 to 1,300 feet long and irrigate about a 130-acre circular area;
[2] Drip — A planned irrigation system in which water is applied directly to the Root Zone of plants by means of applicators (orifices, emitters, porous tubing, perforated pipe, etc.) operated under low pressure with the applicators being placed either on or below the surface of the ground;
[3] Flood — The application of irrigation water where the entire surface of the soil is covered by ponded water;
[4] Furrow — A partial surface flooding method of irrigation normally used with clean-tilled crops where water is applied in furrows or rows of sufficient capacity to contain the designed irrigation system;
[5] Gravity — Irrigation in which the water is not pumped but flows and is distributed by gravity;
[6] Rotation — A system by which irrigators receive an allotted quantity of water, not a continuous rate, but at stated intervals;
[7] Sprinkler — A planned irrigation system in which water is applied by means of perforated pipes or nozzles operated under pressure so as to form a spray pattern;
[8] Subirrigation — Applying irrigation water below the ground surface either by raising the water table within or near the root zone or by using a buried perforated or porous pipe system that discharges directly into the root zone;
[9] Traveling Gun — Sprinkler irrigation system consisting of a single large nozzle that rotates and is self-propelled. The name refers to the fact that the base is on wheels and can be moved by the irrigator or affixed to a guide wire;
[10] Supplemental — Irrigation to insure increased crop production in areas where rainfall normally supplies most of the moisture needed;
[11] Surface — Irrigation where the soil surface is used as a conduit, as in furrow and border irrigation as opposed to sprinkler irrigation or subirrigation.

IRRIGATION CANAL — A permanent irrigation conduit constructed to convey water from the source of supply to one or more farms.

IRRIGATION CONVEYANCE LOSS AND WASTE — The loss of water in transit from a reservoir, point of diversion, or ground water pump (if not on farm) to the point of use, whether in natural channels or in artificial ones, such as canals, ditches, and laterals.

IRRIGATION DELIVERY REQUIREMENT, FARM — The amount of water in acre-feet per acre required to serve the irrigated area. It is the crop irrigation requirement plus farm waste and deep percolation.

IRRIGATION DEPLETION — The amount of diverted water consumptively used, beneficially and nonbeneficially, in serving a cropped area. It is the gross diversion minus return flow and includes losses due to deep percolation.

IRRIGATION EFFICIENCY (I.E.) — Basically, the efficiency associated with water application. Generally, the loss of water in transit from a reservoir, point of diversion, or ground water pump to the point of use, whether in natural channels or in artificial ones, such as canals, ditches, and laterals. More specifically, the percentage of water applied, and which can be accounted for, in the soil-moisture increase for Crop Consumptive Use, i.e., the Crop Requirement. It is defined as the ratio of the volume of water required for a specific Beneficial Use as compared to the volume of water delivered, or applied, for this purpose. It is commonly interpreted as the volume of water stored in the soil for Evapotranspiration compared to the volume of water delivered for this purpose, but may be defined and used in different ways. The Distribution Uniformity (DU) of a field's irrigation system is one of the limiting factors of a system's irrigation efficiency.

IRRIGATION FREQUENCY — Time interval between irrigations.

IRRIGATION LATERAL — A branch of a main canal conveying water to a farm ditch; sometimes used in reference to farm ditches.

IRRIGATION LEACHING REQUIREMENT — The amount of water required to move residual salts out of the root zone and maintain an adequate soil-salt balance for crop production.

IRRIGATION PERIOD — The number of hours or days that it takes to apply one irrigation to a given design area during the peak consumptive-use period of the crop being irrigated.

IRRIGATION PIT — A small storage reservoir constructed to regulate or store the supply of water available to the irrigator.

IRRIGATION RELEASES — Refers to those waters released from storage primarily for irrigation. Does not include Precautionary Drawdowns.

IRRIGATION REQUIREMENT, CROP — The amount of irrigation water in acre-feet per acre required by the crop; the quantity of water, exclusive of precipitation, that is required for production of a specific 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.

IRRIGATION RETURN FLOW — Applied water which is not consumptively used, that is, water that is not transpired, evaporated, or deep percolated into a ground water basin, and returns to a surface or ground water supply. In cases of water rights litigation, the definition may be restricted to measurable water returning to the stream from which it was diverted, thereby excluding waters used for deep percolation and salt leaching.

IRRIGATION STRUCTURE — Any structure or device necessary for the proper conveyance, control, measurement, or application of irrigation water.

IRRIGATION, SUPPLEMENTAL — An additional irrigation water supply which supplements the initial, or primary supply.

IRRIGATION SYSTEMS TAILWATER RECOVERY — A water runoff collection and storage system to provide a constant quantity of water back to the initial system or to another field.

IRRIGATION WATER — Water diverted or pumped for irrigation of crops or pasture. It does not include undiverted water which naturally floods unimproved pastures by overflow during high-runoff years, and water which may beneficially subirrigate land for which no other source of water is diverted.

IRRIGATION WATER MANAGEMENT — The use and management of irrigation water where the quantity of water used for each irrigation is determined by the water-holding capacity of the soil and the need for the crop, and where the water is applied at a rate and in such a manner that the crop can use it efficiently and significant erosion does not occur.

IRRIGATION WATER REQUIREMENT — The total quantity of water, exclusive of effective precipitation, that is required for crop production, to include crop consumptive use, leaching requirements, and on-farm conveyance losses.

IRRIGATION WATER USE — Artificial application of water on lands to assist in the growing of crops and pastures or to maintain vegetative growth on recreational lands, such as parks and golf courses.