A

Absorption Rate

The rate at which a soil will accept water (= percolation rate)

Application Depth

The depth of irrigation water applied during one irrigation event or cycle.

Application Depth (net)

The depth of water applied after losses due to application efficiency are subtracted from the water that is pumped.

Application Rate

Rate at which water is applied by an irrigation equipment in a certain pattern. It is usually measured in mm/hr or mm/day.

Area Irrigated

The surface area to be irrigated

Atmospheric Pressure

Absolute pressure measured at any location. Standard atmospheric pressure at sea level is defined as 14.7 psi or 10 m of water head or 1 bar.

Automatic Control Valve

An electric or hydraulic remote control valve which is activated by an automatic controller. Also called a section valve, zone valve, remote control valve.

Available Soil Moisture

Difference at any given time between the actual soil moisture content in the root zone, soil and the wilting point.

Available Water

Amount of water in a soil that can be readily absorbed by plant roots. It is the amount of water released between field capacity and the permanent wilting point.

Average Annual Precipitation

Long term historic arithmetic mean of precipitation received by an area expressed in mm.

B

Back Pressure

Increase of pressure in the downstream piping system above the supply pressure at the point of consideration which would cause or tend to cause a reversal of the normal direction of flow.

Backwashing

Cleaning filters by reversing the flow of water or discharging water over the screen to wash away contaminants.

Ball Valve

Valve with a single arm or lever that requires a quarter turn to turn on or off.

Basin Irrigation

A surface irrigation method in which crops are surrounded by a border to form a submersion check called basin of round, square or any other form. Irrigation water generally comes directly from the supply ditch/canal or from other basin.

Best Management Practice

An irrigation best management practice is a voluntary irrigation practice that is both economical and practical and is designed to reduce water consumption and protect water quality while maintaining a healthy environment.

Boombacks

Structures used to suspend the sprinklers at a distance of 3-6m behind the machine towers to reduce wheel rutting and bogging

Booster Pump

A pump which is installed in the water supply line, where some pressure already exists, and is designed to raise/boost the pressure in the irrigation system.

Border Ditch

Small excavation used as a border of an irrigated strip or plot with water being spread from one or both sides.

Border Irrigation

A subsystem of controlled flood irrigation in which the land is divided into parallel border strips separated from one another by earth ridges. Water is successively delivered into each strip from a head or field ditch at its upper end.

Branches (canal)

The off-taking canals from main canal

Bubbler

Water emission device that tends to bubble water directly to the ground or throw water a short distance before water contacts the ground surface.

Butterfly Valve

This type of valve uses a rotating disk to control the water flow.

C

Cable-Tow Traveller

A gun sprinkler mounted on a wheel cart to which a soft hose is connected. A cable anchored at the end of the traveller run winds on a car mounted winch.

Canal Evaporation Losses

Losses due to evaporation from the water surfaces of canals

Capillary Action

The means by which liquid moves through the porous spaces in a solid, such as soil, plant roots. Capillary action is essential in carrying nutrients to the plants.

Capillary Moisture

Is the water held in pore spaces by the surface tension between the water and the soil particles. Capillary moisture is the primary source of water for plants.

Capillary Movement

Describes the slow movement of water which continues after drainage seizes.

Capillary Radius

Additional wetted radius in soil profile beyond surface wetted radius for point source emitters.

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.

Capital Cost

The total expenditure incurred on a work since the beginning of its construction, excluding cost of operation, maintenance and repairs.

Catchment

The area from which a stream or waterway and reservoir receives surface flow which originates as precipitation.

Cavitation

Process where pressure in the suction line falls below the vapour pressure of the liquid, is formed and moves with the liquid flow.  These vapour bubbles or "cavities" collapse when they reach regions of higher pressure on their way through pumps. The formation and collapse of low pressure vapour cavities in a flowing liquid, often resulting in serious damage to pumps, impellers, etc.

Centre Pivot

A self propelled system consisting of a lateral mounted on frame towers that rotates around a centre pivot point. Sprinklers are mounted along the lateral.

Certified Irrigation Contractor (CIC)

The Certified Irrigation Contractor is an irrigation professional whose principle business is 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 contact.

Certified Irrigation Designer (CID)

The 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.

Chemigation

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

Christiansen's Uniformity Coefficient

see uniformity coefficient

Class, Soil

Group of soils defined as having a specific range in one or more particular properties such as acidity, degree of slope, texture, structure, land- use capability, degree of erosion, or drainage.

Clay Loam

Soil textural class. See also texture, soil.

Climate

arid climate - Climate by low rainfall and high evaporation potential. A region is usually considered as arid when precipitation averages less than 10 inches per year.

humid climate - Climate characterised by high rainfall and low evaporation potential. A region generally is considered as humid when precipitation averages more than 40 inches per year.

semiarid climate - Climate characterised as neither entirely arid nor humid, but intermediate between the two conditions.  A region is usually considered as semiarid when precipitation averages between 10 and 20  inches per year.

subhumid climate - Climate characterised by moderate rainfall and moderate to high evaporation potential. A region is usually considered subhumid when precipitation averages more than 20 inches per year, but less than 40 inches per year.

Coarse Sand

Soil textural class.

Coarse Sandy Loam

Soil textural class.

Crop Coefficient

The proportion of water used by the crop in relation to evapotranspiration from a reference grass crop.

D

Daily Water Use

The amount of water used by the plant in a 24 hour period

Deep Percolation

Irrigation water percolating below the root zone where it is lost to crop production.

Deep Well Turbine Pump

A pump having one or more stages, each consisting of an impeller on a vertical shaft, surrounded by stationary and usually symmetrical guide vanes in a pump bowl assembly. Power is delivered to the impeller by a shaft and a column carries the water upward.

Deficit Irrigation

Irrigation management with a supply of water less then the seasonal ET requirements of the crop. Relies on stored soil moisture in the root zone to provide the difference and requires feeling the root zone soil profile to field capacity before or early in the growing season.

Delivery Structures

All the structures (canals or pipes and their appurtenant works, such as intakes, distributors, drops and discharge structures) which ensure delivery of water to the irrigators of an irrigated area from the main canal.

Desalinisation

The removal of salts from saline water to provide fresh water.

Design Evapotranspiration Rate

The average daily peak evapotranspiration rate for the proposed crop for seven days.

Design Pressure

Is the total pressure available to operate the irrigation system.

Design System Capacity

The volume of water that the irrigation system could deliver in a day (if operating continuously) divided by the irrigated area, normally reported in mm/day

Diameter Coverage

The diameter of the circular area on the ground covered by a sprinkler. It is measured in meters.

Direct Coupled Pump

A common pump setup where pump and motor are coupled by a shaft instead of a belt. Pump revolutions are fixed at 1450 or 2900 revs per minute.

Discharge Rate

The rate at which water is discharged from sprinklers, emitters, pumps, pipes etc, expressed in L/s or L/hr or cubic meters per hour (= flow)

Distribution Channel

Channel to deliver water from main channels to individual farms

Distribution Curve (of a sprinkler head)

A curve showing the rate of water application by a sprinkler at various points along the radius in mm/hr.

Distribution Pipelines

Pipes which deliver water from main channels or pipelines to individual farms.

Distribution Uniformity (DU)

Refer to Emission Uniformity.

Drain Valve

An automatic or manual valve used to drain water from a line.

Drainage Channel

An open channel to take drainage water or an improved natural waterway designed to remove access water from rural lands.

Drawdown

A lowering of the ground water surface caused by pumping.

Drip Irrigation

Any type of irrigation system that applies water to the soil very slowly through tubes/tapes either above or below the soil surface (= trickle irrigation)

Drip System

An irrigation system that uses drip irrigation.

E

Effective Rainfall

In irrigation practise that portion of the total precipitation which is retained by the soil so that it is available for use for crop production.

Effective Rooting Depth

Soil depth from which the crop extracts most of the water needed for evapotranspiration.

Effective Water Holding Capacity

The amount of water held in the soil after the access gravitational water has drained away and after the rate of downward movement of water has materially decreased, preferably given as a percentage by volume and not by weight (= field capacity)

Efficiency

Refer to Irrigation Efficiency

Emission Uniformity

A measure of how uniformly water is applied over a field, calculated as a minimum depth of applied water, divided by the average discharge of all emitters measured multiplied by 100.

Emitter Discharge Coefficient

The relationship between the dimensions and configurations of low passages and consequent pressure loss through the emitter.

Emitter Discharge Exponent.

The relative ability of an emitter to compensate for variations in pressure. The smaller the exponent, the less sensitive the emitter discharge rate to pressure variation.

Emitters

A collective name used to describe drippers, micro jets and mini sprinklers.

Evaporation

The process where liquid water is converted into a gas. In irrigation the water evaporated from the soil or plant surface

Evaporemeter

An instrument used to measure evaporation. Usually a US Class A pan

Evapotranspiration (ET)

The combination of water transpired from the plant and evaporated from the soil and plant surfaces.

F

Farm Irrigation Efficiency

The ratio or percentage of the irrigation water consumed by crops of an irrigated farm to the water diverted from the source of supply, measured at the farm headgate (= farm delivery efficiency)

Fertigation

Applying liquid fertiliser through an irrigation system.

Field Capacity

The amount of water remaining in a soil when the downward water flow due to gravity becomes negligible. If a soil is saturated by rainfall or irrigation and then allowed to drain freely for twenty four hours, the soil is usually at field capacity. For most crops the field capacity is the ideal moisture level.

Filter Backwash

Refer to Backwashing

Filtering Area

The surface area of a sand or mash filter available for filtration.

Filtration

The removal of suspended solids from irrigation water.

Fittings

The generic name for the various parts that attach the pipes together

Flood Irrigation

All types of irrigation which make use of rising water from flood for inundating areas without major structural works.

Flow Control Valve

A valve that can be mechanically adjusted to restrict flow and thus discharge pressure.

Flow Meter

Device for measuring the flow rate of an irrigation system.

Flow Rate

The quantity of water available and/or needed per second, per minute, per hour or per day

Flow Restrictions

Physical restrictions in the piping system that effect the flow of water causing a pressure loss.

Friction Head

The energy required to overcome friction caused by fluid movement through pipes, fittings and valves, around corners or by pipe-size changes

Friction Loss

A loss of pressure caused by friction as water moves through the irrigation system.

Fully Automatic Irrigation System

An irrigation system or network on a farm, where by the water requirements of the plants are met automatically. It makes use of devices which measure soil moisture, or other indicators of irrigation need and trigger a series of operations to convey the necessary water through the network at the right time.

Furrow Irrigation

A method similar to corrugation irrigation used in permeable soils. It consists in feeding narrow furrows very close to one another with small discharges so as to wet more easily all the soil situated between two rows of crops.

Gate Valve

It is a sliding gate which moves up or down to block the flow. Often used as isolation valves. Never used as control valves.

Geographic Information System (GIS)

All information system concerning a point or a group of points geo-referenced on the Earth's surface, such as maps or satellite images, digitally stored, processed and manipulated by a computer program.

Gravitational Water

Is the free water in the soil which moves into, through, or out of the soil under the influence of gravity.

Gravity Flow

A water system that relies on gravity to provide the pressure required to deliver the water.

Gravity Irrigation

Method of operating a system or part of a system using gravity alone, water being available at a sufficient level (or pressure) to ensure its conveyance or delivery to the fields or its distribution in the fields.

Ground Water

That portion of water below the surface of the ground at a pressure equal to or greater then atmospheric (= watertable)

Gypsum Block

Refer to Resistance Block

Hand Moved System

An irrigation system designed to be moved manually.

Hard Hose Traveller

A gun sprinkler mounted on wheel cart to a hard hose connected to a large stationary hose reel. The hose pulls the sprinkler through the field.

Head

A measure of water pressure in m or bar or psi or Kpa.

Head to Head

Refers to the situation where sprinklers are spaces so that the water from one sprinkler throws all the way to the next sprinkler.

Head Works

A collective term for all works required at intakes of main or principle canals to divert and control the river flows and to regulate water supplies into the main canal or canals.

Heavy Soil

Soils in which clay particles predominates. Heavy soil drains poorly.

Hydraulic Conductivity

The rate of flow of the water through the unit cross section of a soil under a unit hydraulic gradient (= soil permeability)

Hydraulically Controlled

A system which uses water pressure through tubing to operate remote control valves.

Hydrograph

A graph showing the discharge with respect to time.

Hydrology

Science dealing with waters of the earth in rivers, streams, lakes, in or below the surface.

Hygroscopic Water

Water tightly held by soil particles. It does not move under the influence of capillary action or gravity and it is normally unavailable to plants.

Impeller

The rotating component of the pump that moves water through the pump.

Infiltration Rate

The rate at which water penetrates the surface of a soil measured in mm/hr or mm/day.

In-Line Emitters

Drip emitters installed inside the drip tubing as part of the tubing flow path.

Intake

A structure placed in the surface water source to permit water withdrawal.

Irrigation

Became from two Latin words 'in' and 'rigare' which means 'to water'. In other terms irrigation is the artificial watering of the land for the purpose of growing crops.

Irrigation Cycle

Successive deliveries of water on all the units of a network in such as way as to achieve a given irrigation on the entire field concerned.

Irrigation Efficiency

A measure of the amount of irrigation water beneficially used, divided by the amount of water applied.

Irrigation Method

The way the irrigation water is applied on the ground.

Irrigation Period

Number of days over which an irrigation cycle must be completed.

Irrigation Requirements

The quantity of water exclusive of precipitation, required for normal crop production. It includes soil evaporation and some unavoidable losses under the given conditions.

Irrigation System Capacity

The rate at which an irrigation system can apply water to a given area.

Isolation Valves

A valve used for isolating all or part of the irrigation system for repairs and maintenance. Common types of isolation valves are the ball valves, butterfly valve and gate valve.

Land Survey

Surveys relating to the establishment of land boundaries and subdivisions made to create or define limitations of titles.

Lateral Line

The water delivery pipeline or polyethylene hose that supplies water to the emitters from the mainlines or submains.

Lateral Move Irrigation Machine

A sprinkler method using an automatic irrigation machine, consisting of a nozzle line fitted with rotating sprinklers or fixed diffusers, and divided into sections by self propelled towels with an electric motor. It irrigates a rectangular field. It is supplied with water at some point either by directly pumping from a ditch, parallel to its movement or by successively connecting a flexible pipe to outlets fed by a pipeline under pressure (= Linear Move Traveller).

Leaching

Applying irrigation water in excess of the soil moisture depletion level to remove salts from the root zone.

Leaching Requirement

The fraction of water entering the soil that must pass through the root zone, in order to prevent soil salinity from exceeding a specified value.

LEPA

Low Energy Precision Application system is a Centre Pivot or a Lateral move irrigator with low energy requirements using either spray, bubbler or sock emitters.

Line Source

Drip tape or tubing with emission points with close regular intervals

Loam Soil

A soil that contains about 50% sand, 30% silt (particles between 0.002 and 0.02mm diameter) and 20% clay. Loam soils feel smooth and spongy when rolled into a ball

Main Channel

Channel which convey bulk water from head works, storage or river diversion point into the distribution system.

Main Pipelines

Pipes which convey water from the pump to the irrigated areas. Purpose is to deliver water from storage or river into the distribution system

Manual System

A system where control valves are operated manually.

Master Valve

An automatic or manual valve installed at the supply point which controls water flow into the main piping system.

Maximum Practical Suction Lift (MPSL)

An estimate of the lift required to move water on the suction side of the pump.

Media Filter

A filter consisting of a tank filled with filtering media such as, silica sand or crushed granite that removes suspended solids from irrigation water by passing the water through the filtering media. (= sand filter).

MegaLitre (ML)

Measurement of volume equal to one million litres.

Micro Jets

Generally spray outlets with no moving parts where the shape of the micro jet is used to spread water from central orifice.

Micro Sprinkler

Mini sprinklers with small orifices that allow for discharge rates less than 300 L/hr.

Moisture Holding Capacity

The amount of water required to fill all the pore spaces between the soil particles.

Net Irrigation Amount

The amount of water used by the crop since the last irrigation

Net Irrigation Requirement

Is the crops irrigation need (without including any losses of any kind) expressed as a layer of water in mm/day, month.

Net Positive Suction Head (NPSH)

The pump manufacturer's specified suction head at sea level, in meters.

Neutron Probe

An instrument that measures soil water content, by neutron emission from saturation to complete dryness.

Nominal Discharge of a Dripper

Discharge in litres per hour at nominal pressure indicated by the manufacturer.

Nominated Head

The average pressure in meters or bars of head at which an irrigation system is to be operated at.

Nozzle

The part of a sprinkler that the water comes out of.

Nozzle Diameter

Diameter of the nozzle hole. It is measured in inch or mm.

Operating Pressure

The pressure at which a device or irrigation system is designed to operate.

Over Irrigation

Excessive irrigation with regard to the actual requirements due to excessive doses of watering an insufficient irrigation interval or an overestimation of the requirements. It causes either leaching or water logging of the soil.

Overhead Irrigation

Irrigation by which water is ejected into the air to fall onto the soil surface as spray (= sprinkler irrigation)

Peak Crop Water Requirement

For a given crop the peak water requirement during the month.

Pan Evaporation

Rate of water lost by evaporation from an open water surface of pan (usually class A pan).

Percolation Rate

The maximum rate at which water will flow into the subsoil from the top soil under specific conditions expressed in mm/hour or mm/day.

Permanent Wilting Point

The moisture content of the soil, expressed as a percentage of the soil volume or as a percentage of dry weight, at the time when the plant will be under stress as a result of the deficiency in the soil moisture.

pH

The reciprocal logarithmic concentration of hydrogen ions in water. A measure of the acidity or alkalinity of a liquid. A pH of 7.0 is neutral; a pH less then 7.0 is acidic; and a pH more then 7.0 is alkaline.

Piezometer

Vertical tube which is lower and connected to an aquifer, and its upper end located at or above the ground level used to determine the hydraulic head of that aquifer.

Piezometric Head

Combined elevation and pressure head as measured from reference plan.

Planting Area

A term used to define the area of land a tree/vine is planted on, and is obtained by multiplying the row spacing by the tree/vine spacing along the tree line.

Polyethylene Pipe (PE)

A black elastic pipe that is often used in irrigation systems

Positive Displacement Pump

Piston or diaphragm pumps, powered by electricity, water or fuel for injecting chemicals through an irrigation system at precise rates.

PRD

Partial Root Zone Drying-

Precipitation

Water from the atmosphere that falls to the ground in the form of rain, snow or hail

Precipitation Rate

A measurement of water application which is given in the depth of water applied to the soil. Measured in mm/hour.

Pressure Compensating

A valve feature which maintains a constant discharge flow regardless of inlet pressure.

Pressure Differential

The pressure difference between two points (for example, the pressure difference between the inlet and the outlet of a filter)

Pressure Gauge

A device used to measure water pressure.

Pressure Head

The pressure energy necessary at the distribution water system entrance to overcome losses and operate various irrigation equipment/emitters at the designed pressure.

Pressure Loss

The loss of pressure under flow conditions caused by friction or elevation.

Pressure Rating

Refer to Class Pipe.

Pressure Relieve Valve

A valve which will open when the inlet pressure exceeds a preset pressure.

Propeller Pump

A pump having one or more stages, each consisting of an impeller on vertical shaft. The impeller develops head by the propelling or lifting action on the water. Power is delivered to the impeller by a shaft.

Pump

A device which increases the water pressure or moves water.

Pump Duty

The maximum discharge and pressure required at the pump to allow for efficient irrigation

Pumping Lift

The sum of the static lift and the draw down.

Pump Performance Curve

Curve that shows the relationship of pump discharge to pressure for a particular size and make of pump

PVC Pipe

Abbreviation for Un-plasticised Poly Vinyl Chloride Pipe.

Radius

How far out from the sprinkler the water sprays.

Readily Available Water (RAW)

Soil water to which the plant has easy access. This is often estimated to be half the total available water.

Reducer

A fitting used to change from one size pump or pipe to an other.

Refill Point

Is the volumetric soil moisture content at which the plant can no longer freely extract its daily water use requirements.

Regulated Deficit Irrigation (RDI)

An irrigation strategy to manipulated yield, quality and vegetative growth with water stress.

Resistance Block

A device usually made gypsum, that measures the conductivity of current passing between two electrodes to indirectly measure soil moisture.

Riser

The connection between a sprinkler or other irrigation device and a pipe that supplies the water to it.

Rotors

Sprinklers that discharge a steady flow of water to irrigation areas.

Runoff

Water that drains or flows off the surface of the land, when the precipitatio9n rate it is higher than the soil infiltration rate or when the soil profile is saturated.

Salinity

Soil condition in which the salt concentration in the crop root zone is too high for optimum plant growth

Salinity Control

Prevention of salt water contamination of agricultural water supplies or reducing alkaline salts and preventing deterioration of cultivable lands.

Sand Separator

Filter used to remove large, heavy particles from water.

Sandy Soil

A soil in which sand particles (particles greater than 0.02 m in diameter) constitute more then 75% of the mass. Sandy soils never feel sticky when wet and cannot be rolled into a stable ball.

Saturated Zone

Area below the land surface where all the pores are filled with water.

SDI

Subsurface Drip Irrigation

Seasonal Irrigation

An irrigation is termed seasonal when the lands of the area are irrigated only during a part of the year called watering/irrigation season.

Seepage

The slow movement of water to small cracks, pores etc in the surface of unsaturated material into or out of a body of surface or subsurface water.

Side-Roll Move Sprinkler Lateral System

A sprinkler method in which the nozzle line, which carries medium pressure sprinklers, is used as an axel to the wheels which support it at regular intervals.

Siphon Tube

Small flexible pipe used to discharge water from a farm channel onto land. using siphonic pressure

Soil Horizons

A term used to describe the different layers of soil across a vertical soil profile.

Soil Moisture Deficit

The amount of water that must be applied to the soil.

Soil Moisture Tension

The equivalent negative pressure or suction in the soil moisture expressed in bar or kilopascal.

Soil Profile

Various layers of different textures and shades in a vertical soil profile. The top layer called the A horizon, is the one where most roots are, where most biological activity occurs and where organic matter accumulates. The next layer called the B horizon, where clay particles and soluble substances are washed down. Below that is the C horizon or parent rock.

Soil Texture

Refers to the amount of clay, silt and sand in the soil.

Soil Water Content

A volumetric measure of how much water is in the soil. Usually expressed as a percentage of the soil volume. For example 8% is equivalent to 80 litres of water per cubic meter of soil.

Solid Set System

A complete, above ground aluminium or buried pipe system that is placed in the field to be irrigated prior to the start of the growing season and left in place throughout the growing season.

Specific Discharge Rate (SDR)

Is the required discharge rate of the emitter, divided by the distance between emitters, expressed as L/hr/m.

Spray Heads

Sprinkler heads with interchangeable nozzles that spray water in specific circular patterns.

Sprinkler

Sprinkler heads are devices/emitters which distribute water over a given area for irrigation.

Sprinkler Irrigation

A method of irrigation under pressure in which water is sprinkled in the form of artificial rain.

Sprinkler Spacing

The sights of the rectangle or square formed by the sprinklers. Composed of the distance between the sprinklers on the line and the distance between the lines.

Square Spacing

The term given to a sprinkler head layer pattern where the sprinklers, when viewed from above, appear as more or less a square with one sprinkler in each corner.

Static Pressure

The pressure of water when it is not moving

Station

Each zone of the irrigation area that is controlled by a separate valve.

Submains

Pipes that convey water from the mainline to numerous laterals.

Submersible Pump

A turbine pump with a submersible electric motor that is located below the water level in the well.

Subsoil

Soil below the root zone

Subsurface Drainage System

Any drainage system that is designed to control the ground water table.

Supply Channel

Open channel flume designed to convey water from upstream source to farms (= canal)

Supply Point

Point of delivery from an irrigation authority supply system to an individual farm (farm off take)

Surface Drainage System

System of open drainage systems, pipelines and improved natural waterways designed to collect drainage from rainfall and irrigation runoff on rural lands and convey it to disposal.

Surface Irrigation

A method of irrigation in which water is applied to the land by allowing it to flow by simple gravity, before infiltrating.

Surface Runoff

Water flowing off the lower end of the field.

Surface Water

Water in rivers, dams and lakes.

Surge

An energy wave in pipelines caused by sudden opening or closing of valves (= water hammer).

Surveying and Mapping

The measuring of ground surface, layout and structures, and the preparation of maps, profiles, cross sections and alignments.

Tail Water

Flow of surface water from a given area resulting from the effects of applied irrigation water in excess of crop water requirement and leaching.

Tensiometer

An instrument for measuring the suction that plant roots have to exert in order to extract moisture from the soil. Measures soil moisture tension in the range 0 to about 70 kPa.

Tile Drain

Buried horizontal pipeline containing openings (or slots) to allow gravity entry of excess ground water which is then lead to a suitable point of discharge or pit.

Total Available Soil Moisture

Amount of soil moisture available in the root zone to the crop which is the difference between water content at field capacity and at wilting point.

Total Available Water

The portion of water in a soil that can be absorbed by plant roots.

Total Dynamic Head

Refer to Total Head

Total Head

The energy required to pump water from its source to the point of discharge; equal to the total static head, plus pressure head, plus friction head, plus the velocity head. Also commonly called Total Operating Head or Total Dynamic Head.

Total Operating Head

Refer to Total Head

Total Pressure Head

The sum of all factors which increase or decrease the available water pressure.

Total Static Head

The potential energy due to the vertical distance between the pumping water level and the entrance to the distribution system.

Transpiration

The biological process of plants by which water is converted from the liquid state at the leaf surface to a gas, generally considered to govern the energy balance of the leaf surface.

Triangle Spacing

The term given to a sprinkler head layout pattern where the sprinklers, when viewed from above, appear as a more or less equilateral triangle with one sprinkler in each corner. Triangular spacing results in the most uniform and efficient water application using sprinklers.

Trickle Irrigation

Another name for drip irrigation.

Unconfined Aquifers

An aquifer in which the groundwater table is free to rise and fall according to hydraulic gradients.

Underground Drainage

Drainage, either natural or artificial, beneath the surface of the earth.

Uniformity of Application

A general term designating how uniform the application of water is.

Unsaturated Zone

Area immediately below the land surface where pores or fractures contain both air and water.

Valve

A device used to control the flow of water. Isolation valves are used to shut off water for repairs. Control valves turn the water on and off to the individual circuits of sprinklers or drip emitters. Check valves allow the water to flow in only one direction. Master valves are located at the water source and turn on and off the water for the entire irrigation system when not in use.

Velocity

The speed at which water moves through a pipe, expressed as meters per sec.

Velocity Head

The energy required to put water in motion.

Venturi Device

It is a device for injecting chemicals through an irrigation system. The device consists of a constriction in the pipe flow area resulting in a negative pressure or suction at the throat of the constriction.

Water Application Efficiency

The ratio of the average depth of irrigation water stored in soil during irrigation to the average depth of irrigation water applied.

Water Balance

Mathematical calculations for in and out flow of water components for a given area or soil profile.

Water Deficit

Is an amount of water held within the soil between the refill point and field capacity of a plant's root zone. This water is readily available to the plant and indicates the amount of water that is required to be added to the soil profile.

Water Hammer

The sudden rise in pressure that occurs when a valve is closed and or power is shut and a column of moving liquid is suddenly halted.

Water Meter

A device used to measure the quantity of water that flows through a pipe.

Water Stress

Physiological response of plants to a limitation in the supply of water.

Water Table

The upper surface of ground water or that level in the ground where the water is at atmospheric pressure.

Waterlogging

Process of soil becoming saturated with water.

Well

A ground water source, usually a hole dug in the ground down to the water table.

Zone

It is an area to be watered by one sprinkler valve.