Irrigation Terms and Definitions

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

Access Areas

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

Active Storage

• The volume of water stored in a reservoir is measured between the minimum and normal water levels.

Key Evapotranspiration Factors

• Actual crop evapotranspiration involves how the rate of evapotranspiration is affected by soil water, salinity and field size.

Afflux Elevation

• Rise in maximum flood level occurs from introducing a flow obstruction like a dam.

Algal Bloom

• It is the overgrowth of algae in water, producing dangerous toxins.
• It can occur in both fresh and marine water.

Application Efficiency

• The efficiency is the ratio of average depth of infiltrated water stored to average depth applied.

Aquifer

• Geologic formation contains and transmits water sufficiently for economic pumping.

Area Measurement

• Cross-sectional area of flow is measured perpendicular to the flow direction.

Basin Characteristics

• Level field in all directions, with a dike to prevent runoff, which provides undirected water flow.

Basin Irrigation

• Water is applied through a gap in the perimeter dike or adjacent ditch.
• Water is retained until it infiltrates or the excess is drained off.

Bearing Capacity

• Maximum average contact pressure should not produce shear failure in the soil under the foundation.

Border Irrigation

• Parallel border strips are used, where water flows down the slope at a nearly uniform depth.

Border Strip

• An area of land is bound by two border ridges or dikes, which guide the irrigation stream.
• It flows from the inlet point to the ends of the strip.

Channel Bed Slope

• It refers to the inclination or elevation drop per unit length of the channel bottom.

Confined Aquifer

• Groundwater is confined by a relatively impermeable layer.

Contamination

• This is the introduction of substances not naturally found in water, which makes it less desirable or unfit.

Conveyance Efficiency

• it is a ratio between water received at the inlet for a block of fields to water released at the project’s headwork.

Conveyance Loss

• Loss of water from a channel is due to seepage and percolation during transport.

Critical Depth

• Water flow's depth where the energy content is at a minimum, with no backwater forces involved.

Crop Coefficient

• The coefficient is the ratio of actual crop evapotranspiration to its potential.

Crop Evapotranspiration Factors

• It includes water loss through vegetation transpiration and vaporation from the soil.
• Optimal soil conditions, sufficient water/fertilizer for disease-free crop growth is needed.
• It is needed in a large field (one or more ha) to achieve full production potential.

Cropping Pattern

• Sequence of different crops are grown in regular order on a particular field or fields.

Crop Water Requirements

• The amount of water that is used in producing crops is the sum of evapotranspiration or consumptive use, seepage, and percolation losses.

Dam Construction

• A dam is a constructed barrier for water storage.

Dam Height

• Measurement from the lowest point of the ground line to the dam crest.

Dead Storage

• Volume is below the intake structure.
• Sediment volume is based on 25 years of reservoir accumulation.

Designed Height

• Actual height of the embankment after settlement.

Design Irrigable Area

• Maximum area is based on arable lands extent and available water supply for irrigation projects.

Distribution Uniformity

• Numerical value measures uniformity of application for agricultural irrigation systems.

Diversion Dam

• A weir or structure that raises water level in a river or creek.
• It diverts water into the main canal for gravity irrigation.

Diversion Water Requirement

• Total water quantity is diverted from a stream, lake, reservoir, or removed from the ground for crop irrigation.

Drip Irrigation Specs

• Involves dripping water onto the soil at very low rates (2-20 litres/hour) from the emitters.
• Trickle irrigation is used, where water is applied close to plants, wetting only part of the soil.

Drop Structure

• It is an in-line canal structure designed to convey canal water from a higher to lower level.
• It dissipates the excess energy resulting from the drop in elevation.

Effective Rainfall

• Rainwater is used by the crop for growth and development.
• This amount excludes deep percolation, surface runoff, and interception.

Effective Rooting Depth

• Soil depth is where the bulk of the roots extracts most of the water needed for evapotranspiration.

Effective Size

• Particle diameter corresponding to a 10% sieve passing.

Effluent

• It is the discharge from known sources into the water or land.
• Wastewater flows out of manufacturing/industrial plants, including domestic, commercial, and recreational facilities.

Effluent Standard

• Any legal restriction/limitation on effluent parameters is allowed to be delivered into a body of water or land.
• It includes quantities, rates, concentrations, or combinations of physical, chemical, or biological characteristics.

Elevated Flume

• A water-conveying conduit or trough is supported by piers on abutments.

Emitter Spacing

• It refers to the spacing between emitters or emission points along a lateral line.

Emitters

• An applicator in drip, subsurface, or bubbler irrigation dissipates pressure.
• It discharges a small uniform flow or trickle of water at a constant rate, despite pressure differences.

Energy Grade Line

• The specific energy line.
• Vertical Water Surface Profile plus velocity head

Equipment Crossing

• Provision for the passing of equipment and small machinery.

Evapotranspiration Defined

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

Farm Ditch Defined

• Channel conveys irrigation water from the turnout to the paddy field.

Filter Drain

• Prevents migration of small particles and screens off fine materials flowing with seepage water to prevent piping.

Finished Height

• Height of the embankment to be attained during construction.

Farm Water Requirement

• Amount of water needed to replenish the crop water requirement and losses, minus the effective rainfall.

Freeboard

• Extra dam height ensures safety to prevent overtopping from wave action/causes.

Furrows

• Small parallel channels are created to carry water and irrigate crops.

Furrow Irrigation

• Method of irrigation where water runs through small, parallel channels as it moves down the field.

Head Ditch

• Aka supply ditch.
• A small channel is placed along a field to distribute water in surface irrigation.

Homogeneous Embankment

• Dam composed of a single kind of embankment material exclusive for slope protection.

Hydraulic Depth

• Is the ratio of the flow area to the wetted top width.

Hydraulic Grade Line

• Aka hydraulic gradient.
• Profile of the free water surface

Hydraulic Jump

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

Hydraulic Radius

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

Hydrologic Frequency Analysis

• Estimation of the chance of a given event by determining frequency curves of hydrologic data samples.

Inside Slope

• Slope of the upstream face of the embankment.

Invert

• The inside bottom or sill of a conduit.

Inverted Siphon Function

• A closed conduit conveys canal water under pressure.
• It runs to convey canal water by gravity under roadways, railways, drainage channels, and local depressions.

Irrigation Period

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

Karst Topography

• Geological formation reveals dissolution shaped bedrock, often carbonate rocks like limestone or dolomite.

Land Preparation Water Requirement

• Required water in lowland rice production includes evaporation, seepage, percolation, and land soaking losses.

Land Soaking Water Requirement

• Amount of water required in lowland rice production relies on initial soil moisture and physical properties.

Lateral Spacing

• Spacing between irrigation laterals.

Leaching

• Deep percolation of water beyond plant roots leads to loss of salts or nutrients.

Lined Channel

• Impermeable material (usually concrete) are used for channel stabilization and/or reduced seepage in canals.

Loading Limit

• Allowable pollutant-loading limit per unit of time is permitted from the wastewater generator into any receiving water or land.

Manifold

• Pipe network portion is between the mainline and the laterals.

Manufacturer's Coefficient of Variation

• The uniformity/discharge variability is tested.
• It is tested for a specific emitter model, size, and before any field operations.
• A discharge test of 50 emitters is done under set pressure at 200°C.

Natural Spillway

• A spillway is not excavated like a natural draw, saddle or drainage way.

Normal Depth

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

Normal Storage Elevation

• Maximum water surface elevation is attainable by the dam or reservoir without flow in the spillway.

Open Channel Flow

• Water flow is conveyed exposed to the atmosphere.
• This includes canals, ditches, drainage channels, culverts, and pipes under partially full flow conditions.

Optimal Emitter Spacing

• Drip emitter spacing is 80% of the wetted diameter, estimated from field tests.

Outside Slope

• Slope is at the downstream face of the embankment.

Pan Coefficient

• Ratio is between reference evapotranspiration and water loss by evaporation from an open water surface of a pan.

Pan Evaporation

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

Percolation

• Vertical water flow that moves below the root zone.
• It is affected by soil structure, texture, bulk density, mineralogy, organic matter content, salt type, and concentration.

Permeability Test

• Methodology to find the flow rate under laminar conditions with soil cross section and hydraulic gradient.

Pollutant Definition

• Any substance (solid, liquid, gas, radioactive) directly/indirectly alters the water quality or land.
• It affects beneficial uses, is hazardous, or exceeds allowable limits.

Pond Defined

• Sealed section is formed between earth embankments.
• Combined seepage and percolation will be measured.

Potential Irrigable Area

• Area is capable of being irrigated with water availability, suitable soils, and topography.

Reference Crop Evapotranspiration Calculations

• Reference Crop height = 0.2 m.
• Fixed surface resistance = 70 s/m.
• Albedo = 0.23.

Reservoir

• The component of the system that impounds runoff.

Residual Moisture Content

• Moisture is left in the soil before 1st irrigation, which is a description of water depletion when the water supply is cut off.

Reuse Definition

• Process involves taking wastewater, treating it, and using it in another industry like irrigation, liquid fertilizer, or aquaculture.

Road Crossing Defined

• Conveys canal water under roads or railroads.

Shallow Tubewell Specs

• Tube/shaft is vertically set at less than 15 m.
• Lifts groundwater to the surface and pumps are above water.

Seismicity

• Occurrence or frequency of earthquakes in a region.

Seepage

• Water escapes from conveyance facilities, such as ditches, canals, natural channels, and waterways.

Seepage Line

• Aka phreatic line.
• Line with no filter arrangements is where seepage occurs.

Setback Distance

• Distance from irrigation area to a community sensitive to contamination.

Side Slope

• Ratio measures horizontal to vertical dimension of the channel wall.

Slope of the Energy Grade Line

• It is the velocity head in an open channel along slope of water surface profile

Slope of the Hydraulic Grade Line

• Slope of the free water surface.

Spillway

• A channel that releases surplus or flood water that cannot be contained in the active storage of a reservoir.

Sprinkler Irrigation

• Using a system where water is distributed similarly to natural rainfall, pumped via pipes, and sprayed.

Sprinkler Spacing

• Distance between two sprinkler heads along the lateral.

Storage Capacity

• Total capacity at normal water surface elevation.

Storage Ratio

• Ratio of storage capacity to total earth volume is required for embankment construction, which shows relative cost of reservoir types.

Structural Height

• It is the vertical distance measured from the top of the dam down to the bedrock.

Surface Irrigation System

• Water application uses gravity flow.
• Can be a flooded field (basin irrigation), small channels (furrows), or strips of land (borders).

Top Width

• Width measures the channel cross-section at the free surface.

Unconfined Aquifer

• An aquifer with a water table serves as the upper surface of a saturated zone.

Uniformity Coefficient

• Ratio of the particle size at 60% passing divided by that at 10% passing.

Uniform Flow

• Constant water area, depth, discharge, and average velocity along a reach of channel is required.

Unimodal Rainfall Pattern

• Five wet months of more than 200 mm/month, five dry months of less than 100 mm/month, and twotransition months of 100-200 mm/month.
• Total annual rainfall is above 1500 mm.

Unlined Channels

• Unlined canal cut through the soil.
• Soil is excavated from the bed and used to form the embankment.

Upstream Face

• Side of the embankment is wetted by the impounded water.

Waste Material Examples

• Solid, liquid, semi-solid, or contained gas.
• Waste material comes from industrial, commercial, mining, agricultural, community, or household activities.

Wastewater Definition

• Waste in liquid state, containing pollutants.

Water Balance

• It involves inflows (irrigation, rainfall) and outflows (evaporation, seepage, percolation).

Watershed

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

Water Right

• Government-granted privilege to use and appropriate water.

Well Log

• Record shows formation stratification of an aquifer showing depth, thickness, consolidation degree, and other aquifer characteristics.

Well-Protected Reservoir

• Reservoir has high mountain barriers which shields from basin.

Wetted Diameter

• Diameter of the circular area wetted by the sprinkler with a given pressure and no wind.

Wetted Perimeter

• The portion of the perimeter of the canal that is in contact with the flowing water.

Wetted Widths

• Width of the strip would be wetted by a row of emitters at optimal spacing on a lateral line.

Zoned Embankment

• Dam is constructed with a central impervious core and flanked by zones of pervious materials.