PNS/BAFS/PAES 216:2017 - General Irrigation Terminologies

volume of water stored in reservoir between the minimum water level and normal water level

active storage

rate of evapotranspiration equal to or smaller than predicted crop evapotranspiration as affected by the level of available soil water, salinity, field size or other causes

actual crop ET

rise in maximum flood level from the original unobstructed flood level which result after an obstruction to the flow such as a dam, has been introduced

afflux elevation

overgrowths of algae in water producing dangerous toxins in fresh or marine water

algal bloom

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

application efficiency

geologic formation which contains water and transmits it at a rate sufficient to be economically developed for pumping artificially developed well

aquifer

cross-sectional area of the flow which is measured perpendicular to the direction of flow

area

field that is level in all directions, encompassed by a dike to prevent runoff, and provides an undirected flow of water onto the field

basin

type of surface irrigation where water is applied to the basin through a gap in the perimeter dike or adjacent ditch; water is retained until it infiltrates into the soil or the excess is drained off

basin irrigation

method of irrigation which makes use of parallel border strips where the water flows down the slope at a nearly uniform depth

border irrigation

area of land bounded by two border ridges or dikes that guide the irrigation stream from the inlet point of application to the ends of the strip

border strip

inclination or elevation drop per unit length of the channel bottom

channel bed slope

groundwater that is confined by relatively impermeable layer

confined aquifer

introduction of substances not found in the natural composition of water that make the water less desirable or unfit for intended use

contamination

ratio between water received at the inlet for a block of fields to that released at the project’s headwork

conveyance efficiency

loss of water from a channel during transport due to seepage and percolation

conveyance loss

depth of water flow where the energy content is at minimum hence, no other backwater forces are involved

critical depth

ratio of the actual crop evapotranspiration to its potential evapotranspiration

crop coefficient

rate of evapotranspiration of a disease-free crop growing in a large field (one or more ha) under optimal soil conditions

crop ET

sequence of different crops grown in regular order on any particular field or fields

cropping pattern

amount of water used in producing crops which is the sum of evapotranspiration or consumptive use plus seepage and percolation losses

crop water requirement

any barrier constructed to store water

dam

vertical distance from lowest point of the ground line to the dam crest

dam height

volume below the intake structure; sediment volume based on 25 years of accumulation in the reservoir

dead storage

depth of water in the channel cross-section

depth

actual height of the embankment after settlement

design height

maximum area which an irrigation project can serve considering the extent of arable lands and the available water supply

design irrigable area

numerical value on the uniformity of application for agricultural irrigation systems

distribution uniformity

structure or weir provided across the river or creek to raise its water level and divert the water into the main canal to facilitate irrigation by gravity

diversion dam

the total quantity of water diverted from a stream, lake, or reservoir, or removed from the ground in order to irrigate a crop

diversion water requirement

involves dripping water onto the soil at very low rates (2-20 litres/hour) from the emitters where water is applied close to plants so that only part of the soil in which the roots grow is wetted

drip irrigation/trickle irrigation

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

drop

amount of rainwater that falls directly on the field and is used by the crop for growth and development excluding deep percolation, surface runoff and interception

effective rainfall

soil depth from which the bulk of the roots of the crop extracts most of the water needed for evapotranspiration

effective rooting depth

particle diameter corresponding to a 10% sieve passing

effectie size

discharges from known sources which is passed into a body of water or land, or wastewater flowing out of a manufacturing plant, industrial plant including domestic, commercial and recreational facilities

effluent

any legal restriction or limitation on quantities, rates, and/or concentrations or any combination thereof, of physical, chemical or biological parameters of effluent which a person or point source is allowed to delivery into a body of water or land

effluent standard

water conveying conduit or trough which is supported on abutments by piers

elevated flumes

spacing between emitters or emission points along a lateral line

emitter spacing

applicator used in drip, subsurface, or bubbler irrigation designed to disspate pressure and to discharge a small uniform flow or trickle of water at a constant rate that does not vary significantly because of minor differences in pressure

emitters

combination of water transpired from vegetation and evaporated from the soil, water, and plant surfaces

ET

channel which conveys irrigation water from the turnout to the paddy field

farm ditch

dam component which prevents migration of small particles and screen off fine materials that flow with seepage water and prevent piping

filter drain

height of the embankment to be attained during construction

finished height

amount of water to replenish the crop water requirement and losses less the effective rainfall

farm water requirement

additional height of the dam provided as a safety factor to prevent overtopping by wave action or other causes

freeboard

small parallel channels, made to carry water in order to irrigate the crop

furrows

method of irrigation where water runs through small parallel channels as it moves down the slope of the field

furrow irrigation

small channel along one part of a field that is used for distributing water in surface irrigation

head/supply ditch

dam composed of a single kind of embankment material exclusive for slope protection

homogenous embankment

ratio of flow area to the wetted top width

hydraulic depth

profile of the free water surface

hyfraulic grade line/hydraulic gradient

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

hydraulic jump

cross-sectional area of flow divided by the wetted perimeter

hydraulic radius

estimation of the chance or likelihood of occurrence of a given event by determining the frequency curves of best fit to samples of hydrologic data

hydrologic frequency analysis

slope of the upstream face of the embankment

inside slope

inside bottom or sill of t the conduit

invert

closed conduit designed to convey canal water in full and under pressure running condition, to convey canal water by gravity under roadways, railways, drainage channels and local depressions

inverted siphon

time required to cover an area with one application of water

irrigation period

geological formation shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rocks such as limestone or dolomite

Karst topography

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

land preparation water requirement

amount of water required in lowland rice production which is a function of the initial soil moisture and the physical properties of the soil

land soaking water requirement

spacing between irrigation laterals

lateral spacing

deep percolation of water beyond the root zone of plants, resulting in loss of salts or nutrients

leaching

canals with impermeable material (usually concrete) for channel stabilization and/or reduced seepage

lined channel or lined canal

allowable pollutant-loading limit per unit of time, which the wastewater generator is permitted to discharge into any receiving body of water or land

loading limit

portion of the pipe network between the mainline and the laterals

manifold

spillway which is not excavated such as natural draw, saddle or drainage way

natural spillway

constant flow depth along a longitudinal section of a channel under a uniform flow condition

normal depth

maximum elevation the water surface which can be attained by the dam or reservoir without flow in the spillway

normal storage elevation

water flow that is conveyed in such a manner that top surface is exposed to the atmosphere such as flow in canals, ditches, drainage channels, culverts, and pipes under partially full flow conditions

open channel flow

drip emitter spacing which is 80% of the wetted diameter estimated from field tests

optimal emitter spacing

slope at the downstream face of the embankment

outside slope

ratio between reference evapotranspiration and water loss by evaporation from an open water surface of a pan

pan coefficient

rate of water loss by evaporation from an open water surface of a pan

pan evaporation

vertical flow of water to below the root zone which is affected by soil structure, texture, bulk density, mineralogy, organic matter content, salt type and concentration

percolation

method to determine the rate of flow under laminar flow conditions through a unit cross sectional are of soil under unit hydraulic gradient

permeability test

any substance, whether solid, liquid, gaseous or radioactive, which directly or indirectly alters the quality of any segment of the receiving water body or land resource so as to affect or tend to affect adversely any beneficial use

pollutant

area capable of being irrigated, principally as regards to availability of water, suitable soils, and topography of land

potential irrigable area

rate of evapotranspiration from a reference surface which is a hypothetical reference crop with an assumed crop height of 0.2 m, a fixed surface resistance of 70 s/m and an albedo of 0.23

reference crop ET

part of the system that impounds the runoff

reservoir

moisture left in the soil before the initial irrigation water delivery which describes the extent of water depletion from the soil when the water supply has been cut-off

residual moisture content

tube or shaft vertically set into the ground at a depth that is usually less than 15 m for the purpose of bringing groundwater into the soil surface whose pumps are set above the water level

shallow tubewell

occurrence or frequency of earthquakes in a region

seismicity

water escaping below or out from water conveyance facilities such as open ditches, canals, natural channels, and waterway

seepage

line with no filter arrangements where seepage occurs

seepage line or phreatic line

ratio of the horizontal to vertical dimension of the channel wall

side slope

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

slope of the energy grade line

slope of the free water surface

slope of the hydraulic grade line

channel which releases surplus or flood water which cannot be contained in the active storage space of the reservoir

spillway

method of applying irrigation water similar to natural rainfall where water is distributed through a system of pipes by pumping and then sprayed into the air through sprinklers so that it breaks up into small water drops which fall to the ground

sprinkler irrigation

distance between two sprinkler heads along the lateral

sprinkler spacing

total capacity at normal water surface elevation

storage capacity

ratio of the storage capacity to the total earth volume required for embankment construction which indicates the relative cost of the different types of reservoir

storage ratio

vertical distance measured from the top of the dam down to the bedrock

structural height

application of water by gravity flow to the surface of the field. Either the entire field is flooded (basin irrigation) or the water is fed into small channels (furrows) or strips of land (borders)

surface irrigation system

width of the channel cross-section at the free surface

top width

aquifer which has water table serving as upper surface of the zone of saturation

unconfined aquifer

ratio of the particle size at 60% pasing to that at 10% passing

uniformity coefficient

occurs when flow has a constant water area, depth, discharge, and average velocity through a reach of channel

uniform flow