Glossary/water dictionary

Alphabetical     Full list     References

calibrated orifices

A water control structure whose orifice, perforated with great accuracy in a thin wall, allows the passage of relatively large discharges of 50-150 litres, meant to be temporarily stored in a basin or furrow.^

canal evaporation Losses

Losses due to evaporation from the water surfaces of canals. They are generally accounted for as part of the total losses occurring in an irrigation system.^

capillary action

The means by which liquid moves through the porous spaces in a solid, such as soil, plant roots and the capillary blood vessels in our bodies due to the forces of adhesion, cohesion and surface tension. Capillary action is essential in carrying substances and nutrients from one place to another in plants and animals.^

capital cost

The total expenditure incurred on a work since the beginning of its construction, excluding cost of operation, maintenance and repairs, but including cost of investigations and of all extensions and improvements.^

case study

(General) A record of the history of a specific study or project performed. (Specific) A written account of an event or situation to which participants are to react, with an emphasis is on decision making. A case study can be used to start a general session, or as part of a small group session.^


(1) The catching or collecting of water, especially rainfall. (2) A reservoir or other basin for catching water. (3) The water thus caught. ^

catchment area

(1) The intake area of an aquifer and all areas that contribute surface water to the intake area. (2) The areas tributary to a lake, stream, sewer, or drain. (3) A reservoir or basin developed for flood control or water management for livestock and/or wildlife. (4) The area from which a lake, a reservoir or a chosen crosssection of a stream or waterway receives water. ^

catchment area (basin)

The area draining into a river, reservoir, or other body of water.^

centre pivot sprinkler

A sprinkler system in which the water source is in the centre, and a system of pipes and sprinkler heads rotates or pivots about the central point to water a given circular area.^


An underground catch basin for combined liquid and solid waste, such as household sewage, so designed as to retain the organic matter and solids but permitting the liquids to seep through the bottom and sides.^


(1) (Watercourse) A natural stream that conveys water; a natural or artificial watercourse with definite bed and banks to confine and conduct flowing water; a ditch or channel excavated for the flow of water. River, creek, run, branch, anabranch and tributary are some of the terms used to describe natural channels, which may be single or braided. Canal, aqueduct, and floodway are some of the terms used to describe artificial (man-made) channels. (2) (Landform) The bed of a single or braided watercourse that commonly is barren of vegetation and is formed of modern alluvium. Channels may be enclosed by banks or splayed across and slightly mounded above a fan surface and include bars and dumps of cobbles and stones. Channels, excepting floodplain playas, are landform elements.^

chemical oxygen demand (COD)

(Water quality) (1) A measure of the chemically oxidizable material in the water which provides an approximation of the amount of organic and reducing material present. The determined value may correlate with biochemical oxygen demand (BOD) or with carbonaceous organic pollution from sewage or industrial wastes. (2) A chemical measure of the amount of organic substances in water or wastewater. A strong oxidizing agent together with acid and heat are used to oxidize all carbon compounds in a water sample. Non-biodegradable and recalcitrant (slowly degrading) compounds, which are not detected by the test for BOD, are included in the analysis. The actual measurement involves a determination of the amount of oxidizing agent (typically, potassium dichromate) that is reduced during the reaction. ^


The sum total of the meteorological elements that characterise the average and extreme conditions of the atmosphere over a long period of time at any one place or region of the earth’s surface. The collective state of the atmosphere at a given place or over a given area within a specified period of time. ^

climatic cycle (1)

Actual or supposed cyclic recurrences of such weather phenomena as wet and dry years, hot and cold years, at more or less regular intervals in response to long-range terrestrial and solar influences, such as volcanic dust and sunspots.^

climatic cycle (2)

The periodic changes of climate, including a series of dry years following a series of years with heavy rainfall.^

climatic year

A period used in meteorological measurements. A continuous 12-month period during which a complete annual cycle occurs, arbitrarily selected for the presentation of data relative to hydrologic or meteorologic phenomena. The climatic year in the United States begins on October 1st and runs through September 30th. ^

climatology, climatological

The science and study dealing with climate and climatic phenomena as exhibited by temperature, winds and precipitation.^

cluster sampling

Where clusters of observation are formed on a basis that reduces cost (e.g. within a limited area). Care is taken to ensure heterogeneity and to avoid redundancy of information.^

commercial water use

Water used for motels, hotels, restaurants, office buildings, other commercial facilities, and institutions. Water for commercial uses comes both from public-supplied sources, such as a county water department, and self-supplied sources, such as local wells.^


The process of water vapour in the air turning into liquid water. Water drops on the outside of a cold glass of water are condensed water. Condensation is the opposite process of evaporation.^

conjunctive irrigation planning

Planning an irrigation project in a given area having groundwater resources and surface water, so that both the surface and groundwater resources yield the most economical and suitable combination of the use of water from the two sources.^

consumptive use

That part of water withdrawn that is evaporated, transpired by plants, incorporated into products or crops, consumed by humans or livestock, or otherwise removed from the immediate water environment. ^

consumptive water use

The quantity of water used by the vegetative growth of a given area in transpiration or building of plant tissue and that evaporated from the soil or from intercepted precipitation on the area in any specific time. It is expressed in water depth per unit of time. ^

continuous flow irrigation system

A system in which individual irrigators receive the quantity of water to which they are entitled in the form of a continuous flow.^

continuous supply

Continuous and constant discharge to inlets of the individual farms or fields.^

contour ditch irrigation

A sub-system of controlled irrigation in which water flows through openings in ditches (which more or less follow the contours) or over the ditch banks as sheet flow across the fields. The delivery is controlled by the spacing between ditches and by the size and site of the openings of each ditch.^

control structure

A stage-discharge regulating device of a spillway. It may be of any form, viz. weir, side channel, glory spillway, orifice, tube, pipe or channel.^

controlled flooding

Water is diverted to levelled lands and in a sequential manner in such a way as to deliver the desired dose to all points; it includes flooding from ditches, border irrigation and corrugation irrigation.^

conventional technology

Technology based on a long history of experience without making use of later developments. Losses of water in transit from the source of supply to the point of service, whether in natural channels or in artificial ones, such as canals, distributaries, ditches or watercourses.^

conveyance loss (1)

Water that is lost in transit from a pipe, canal or ditch by leakage or evaporation. Generally, the water is not available for further use; however, leakage from an irrigation ditch may percolate to a groundwater source and be available for further use.^

conveyance loss (2)

Comprises evaporation from the water surface, seepage and incidental transpiration by vegetation growing in the water or along the banks of natural channels, canals or watercourses.^

conveyance structures

Structures built to help provide general control and conveyance of the flow from the intake structures to the area to be irrigated.^


Democratic organisation for service provision controlled by its members, who contribute equitably to the capital of the cooperative.^

corrugation irrigation

A sub-system of controlled flood irrigation. Corrugations between crop rows are fed at the head by flows from a furrow long enough to wet laterally the ridges situated between the corrugations. In soils with a large natural slope, corrugations with a small longitudinal slope appear to be parallel to the contours.^

cost-benefit analysis

Quantitative and qualitative evaluation of the positive and negative impacts of a project.^

crop irrigation requirement

Consumptive use minus effective precipitation.^

crop water requirement

The total water needed for evapotranspiration from planting to harvest for a given crop in a specific climatic regime when adequate soil water is maintained by rainfall and/or irrigation so that it does not limit plant growth and crop yield.^

cross-irrigable area

The total area within the extreme limits set for irrigation by a project, supply system or canal, minus areas excluded because of their unsuitability for irrigation. ^

cut-off drainage system

A drainage system for draining seepy hillsides. Tiles are placed along the hillside to intercept the seep water and prevent it from reaching the bottom land, or an open channel is dug along the hillside to achieve the same effect.^