Irrigation System Terms

• This standard defines general terms for classification, planning, design, construction, and operation in irrigation.

Access Areas

• Areas open for public entry include golf courses, public and private parks, playgrounds, schoolyards, playing fields, residential and industrial parks.

Active Storage

• Represents the water volume stored in a reservoir between the minimum and normal water levels.

Actual Crop Evapotranspiration

• The rate of evapotranspiration, which is equal to or less than the predicted rate, is influenced by available soil water, salinity levels, field size, or other factors.

Afflux Elevation

• Denotes the rise in maximum flood level due to an obstruction, like a dam, compared to the unobstructed level.

Algal Bloom

• Refers to overgrowths of algae in water that produce harmful toxins in fresh or marine environments.

Application Efficiency

• The ratio of the average depth of irrigation water infiltrated and stored in the root zone to the average depth of water applied.

Aquifer

• A geologic formation that contains water and transmits it at a rate that allows for economical development through pumping.

Area

• The cross-sectional area of flow, measured perpendicularly to the flow's direction.

Basin

• A level field in all directions, surrounded by a dike to prevent runoff, allowing undirected water flow.

Basin Irrigation

• A surface irrigation method where water is applied to a basin through a gap in the perimeter dike or adjacent ditch. Water is retained in the basin until it infiltrates into the soil, or any excess water is drained off.

Bearing Capacity

• The maximum average contact pressure between a foundation and the soil that should not cause shear failure in the soil.

Border Irrigation

• An irrigation method utilizing parallel border strips where water flows down a slope at a nearly uniform depth.

Border Strip

• A land area bounded by two border ridges or dikes that guide the irrigation stream from the entry point to the ends of the strip.

Channel Bed Slope

• The inclination or elevation drop per unit length of the channel bottom.

Confined Aquifer

• Groundwater that is confined by a relatively impermeable layer.

Contamination

• Introduction of substances not naturally found in water, making it less desirable or unfit for its intended use.

Conveyance Efficiency

• Ratio of water received at the inlet for a block of fields relative to that released at the project's headwork.

Conveyance Loss

• Water lost from a channel during transport due to seepage and percolation.

Critical Depth

• The depth of water flow where the energy content is minimal, such that no backwater forces are involved.

Crop Coefficient

• The ratio of actual to potential crop evapotranspiration.

Crop Evapotranspiration

• The rate of evapotranspiration of a disease-free crop growing in a large field under optimal soil conditions, including sufficient water and fertilizer; includes water loss through transpiration and vaporization.

Cropping Pattern

• The sequence of different crops grown in regular order on a particular field or fields.

Crop Water Requirements

• The total water amount used to produce crops, which sums up evapotranspiration or consumptive use, plus seepage and percolation losses.

Dam

• Any kind of barrier constructed to store water.

Dam Height

• Vertical distance from lowest ground point to the dam crest.

Dead Storage

• Volume below the intake structure, based on 25 years of sediment accumulation in the reservoir.

Depth

• Depth of water in the channel cross-section.

Designed Height

• The actual height of the embankment after settlement.

Design Irrigable Area

• The maximum area that an irrigation project can serve, considering arable lands and water supply.

Distribution Uniformity

• A numerical value indicating the uniformity of application for agricultural irrigation systems.

Diversion Dam

• A structure or weir across a river/creek that raises water level and diverts water to facilitate gravity irrigation.

Diversion Water Requirement

• Total water quantity diverted from a stream, lake, or extracted from the ground to irrigate.

Drip Irrigation (Trickle Irrigation)

• Dripping water onto soil at 2-20 liters/hour from emitters, close to plants, wetting only roots.

Drop

• An in-line canal structure designed to convey canal water from a higher level to a lower level, duly dissipating the excess energy resulting from the drop in elevation.

Effective Rainfall

• Amount of rainwater that falls on field, used by crop for growth, excluding deep percolation, runoff, and interception.

Effective Rooting Depth

• Soil depth from which crop roots extract most water needed for evapotranspiration.

Effective Size

• Particle diameter corresponding to 10% sieve passing.

Effluent

• Discharges from known sources into water/land, or wastewater from manufacturing, industrial, domestic, commercial, and recreational facilities.

Effluent Standard

• Legal restrictions on quantities, rates, concentrations, or physical, chemical, or biological parameters of effluent from a source into a body of water or land.

Elevated Flume

• Water-conveying conduit or trough supported on abutments by piers.

Emitter Spacing

• Spacing between emitters or emission points along a lateral line.

Emitters

• Applicators in drip, subsurface, or bubbler irrigation, designed to dissipate pressure and discharge a small, uniform flow/trickle of water at a constant rate, not varied by pressure differences.

Energy Grade Line (Specific Energy Line)

• Grade line of the water surface profile, plus the velocity head in open channels.

Equipment Crossing

• Provision for passing equipment and small machinery.

Evapotranspiration

• Combination of water transpired by vegetation and evaporated from soil, water, and plant surfaces.

Farm Ditch

• A channel conveying irrigation water from the turnout to the paddy field.

Filter Drain

• A dam component that prevents the migration of small particles and screens off fine materials from seepage water, to prevent piping.

Finished Height

• The attained height of the embankment during construction.

Farm Water Requirement

• The amount of water needed to replenish crop water and losses minus effective rainfall.

Freeboard

• Additional dam height as safety factor to prevent overtopping by wave action/causes.

Furrows

• Small parallel channels that carry water to irrigate crops.

Furrow Irrigation

• Method of irrigation where water flows through small, parallel channels down the slope.

Head Ditch (Supply Ditch)

• Small channel along a field part for distributing water in surface irrigation.

Homogeneous Embankment

• A dam made of a single kind of embankment material other than slope protection.

Hydraulic Depth

• The ratio of flow area to wetted top width.

Hydraulic Grade Line (Hydraulic Gradient)

• The Profile of the free water surface.

Hydraulic Jump

• Occurs when a thin sheet of incoming flow at high velocity strikes water of sufficient depth.

Hydraulic Radius

• Cross-sectional area of flow divided by the wetted perimeter.

Hydrologic Frequency Analysis

• Estimation of chance or likelihood for hydrology events using frequency curves fit to data samples.

Inside Slope

• Slope of the upstream face of the embankment.

Invert

• The inside bottom or sill of the conduit.

Inverted Siphon

• A closed conduit designed to convey canal water fully and under pressure, under roadways, railways, drainage channels, and depressions.

Irrigation Period

• The time required to cover an area with one application of water.

Karst Topography

• Geological formation shaped by the dissolution of bedrock, like limestone or dolomite.

Land Preparation Water Requirement

• The amount of water required in lowland rice production, which includes losses through evaporation, seepage, percolation, and soaking.

Land Soaking Water Requirement

• The water required in lowland rice production, based on soil moisture and physical properties.

Lateral Spacing

• Spacing between irrigation laterals.

Leaching

• Deep percolation of water beyond the root zone, resulting in salt and nutrient loss.

Lined Channel (Lined Canal)

• Canals with impermeable material, usually concrete, for channel stabilization and reduced seepage.

Loading Limit

• Allowable pollutant-loading limit per time unit for wastewater discharge into water or land.

Manifold

• The portion of the pipe network between the mainline and the laterals.

Manufacturer's Coefficient of Variation

• Measure of discharge variability, before field operations, determined via discharge testing of 50 emitters at 200°C.

Natural Spillway

• Spillway not excavated, such as natural draw.

Normal Depth

• Constant flow depth along a longitudinal channel section under uniform flow.

Normal Storage Elevation

• Maximum water surface elevation the dam or reservoir can attain without spillway flow.

Open Channel Flow

• Water flow conveyed with the top surface exposed to the atmosphere, such as in canals.

Optimal Emitter Spacing

• Drip emitter spacing at 80% of estimated wetted diameter from field tests.

Outside Slope

• Slope at the downstream face of the embankment.

Pan Coefficient

• Ratio between reference evapotranspiration and water loss from open pan evaporation.

Pan Evaporation

• Rate of water loss by evaporation from open water surface of a pan.

Percolation

• Vertical water flow below the root zone influenced by soil structure, texture, density, and content of minerals.

Permeability Test

• Method to determine the rate of flow under laminar flow conditions through a unit cross sectional area of soil under a unit hydraulic gradient.

Pollutant

• Any substance that alters water/land quality negatively affecting any beneficial use, hazardous to health, objectionable in odor, causing temperature changes, or violating standards/restrictions.

Pond

• Sealed section between Earth embankments used to measure combined seepage and percolation.

Potential Irrigable Area

• The area that can be irrigated, based on water availability, suitable soils, and topography.

Reference Crop Evapotranspiration

• The evapotranspiration rate from a reference surface with assumed crop height of 0.12 m and fixed surface resistance of 70 s/m.

Reservoir

• Part of a system impounding runoff.

Residual Moisture Content

• The soil moisture before irrigation water delivery, reflecting water depletion.

Re-use

• Treating and reusing wastewater from one process in another, like irrigation.

Road Crossing

• Conveys canal water under roads or railroads.

Shallow Tubewell

• Tube/shaft vertically set below 15m to bring groundwater to surface with pumps.

Seismicity

• Occurrence/frequency of earthquakes in a region.

Seepage

• Water escaping from conveyance facilities, such as canals.

Seepage Line (Phreatic Line)

• Line where seepage occurs without filter arrangements.

Setback Distance

• The distance from the edge of irrigation area to community sensitive to contamination.

Side Slope

• The ratio of the horizontal to vertical dimension of channel wall.

Slope of the Energy Grade Line

• The slope of the water surface profile plus the velocity head in open channels.

Slope of the Hydraulic Grade Line

• The slope of the free water surface.

Spillway

• Channel releasing surplus/flood water that the active storage can't contain.

Sprinkler Irrigation

• Applying irrigation water like rainfall, distributed via pipes and sprayed into the air with sprinklers.

Sprinkler Spacing

• Distance between two sprinkler heads along the lateral.

Storage Capacity

• Total capacity at normal water surface elevation.

Storage Ratio

• The ratio of storage capacity to total earth volume indicates reservoir cost.

Structural Height

• Vertical distance from dam top to bedrock.

Surface Irrigation System

• Applying water to field by gravity, flooding entire field or feeding small channels.

Top Width

• Width of the channel cross-section at an free surface.

Unconfined Aquifer

• Aquifer that has water table as upper surface of saturated zone.

Uniformity Coefficient

• Ratio of particle size at 60% passing relative to that at 10% passing.

Uniform Flow

• Flow with consistent water area, depth, discharge, and average velocity through a channel reach.

Unimodal Rainfall Pattern

• Rainfall pattern with five wet months above 200 mm, five dry months below 100 mm and annual rainfall above 1500 mm.

Unlined Channels

• Canals cut through soil, using excavated soil to embankments.

Upstream Face

• The side of the embankment wetted by impounded water.

Waste

• Any material discarded from commercial, industrial, mining, agricultural, community and household operations.

Wastewater

• Waste in a liquid state containing pollutants.

Water Balance

• Accounting of water inflows like irrigation and outflows like evaporation.

Watershed

• The area that contributes runoff or drains water into the reservoir.

Water Right

• Privilege granted by the government to use and appropriate water.

Well Log

• Record of formation stratification showing aquifer depth, thickness and consolidation.

Well-Protected Reservoir

• Reservoir with basin shielded by high mountain barriers.

Wetted Diameter

• Diameter of circular area wetted by the sprinkler when at pressure and without wind.

Wetted Perimeter

• Portion of the canal's perimeter contacting flowing water.

Wetted Widths

• Strip width wetted by emitters spaced at optimal spacing on lateral line.

Zoned Embankment

• Dam consisting of impervious core flanked by more pervious areas.