Glossary/water dictionary

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salinity control

Abatement or prevention of saltwater contamination of agricultural, industrial and municipal water supplies, or reducing alkaline salts and preventing deterioration of cultivable lands.^

seasonal irrigation

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

secondary wastewater treatment

Treatment (following primary wastewater treatment) involving the biological process of reducing suspended, colloidal and dissolved organic matter in effluent from primary treatment systems and which generally removes 80% to 95% of the biochemical oxygen demand (BOD) and suspended matter. Secondary wastewater treatment may be accomplished by biological or chemical-physical methods. Activated sludge and trickling filters are two of the most common means of secondary treatment. It is accomplished by bringing together waste, bacteria, and oxygen in trickling filters or in the activated sludge process. This treatment removes floating and settleable solids and about 90% of the oxygen-demanding substances and suspended solids. Disinfection is the final stage of secondary treatment.^


Usually applied to material in suspension in water or recently deposited from suspension. In the plural the word is applied to all kinds of deposits from the waters of streams, lakes, or seas.^

sediment yield

The total sediment outflow from a watershed or past a given location in a specified period of time. It includes bedload as well as suspended load including dissolved solids. Usually expressed as load per unit of time (e.g. tonnes per year or kilograms per second).^

sedimentary rock

Rock formed of sediment, and specifically: (1) sandstone and shale, formed of fragments of other rock transported from their sources and deposited in water; and (2) rocks formed by or from secretions of organisms, such as most limestone. Many sedimentary rocks show distinct layering, which is the result of different types of sediment being deposited in succession.^

sedimentation tanks

Wastewater tanks in which floating wastes are skimmed off and settled solids are removed for disposal.^


(1) The slow movement of water through small cracks, pores, interstices etc. of a material into or out of a body of surface or subsurface water. (2) The loss of water by infiltration into the soil from a canal, ditches, laterals, watercourse, reservoir, storage facilities, or other body of water, or from a field.^

self-supplied water

Water withdrawn from a surface water or groundwater source by a user rather than being obtained from a public supply. An example would be homeowners getting their water from their own well.^

septic tank

A tank used to detain domestic wastes to allow the settling of solids prior to distribution to a leach field for soil absorption. Septic tanks are used when a sewer line is not available to carry them to a treatment plant. A settling tank in which settled sludge is in immediate contact with sewage flowing through the tank, and wherein solids are decomposed by anaerobic bacterial action.^

settling pond (water quality)

An open lagoon into which wastewater contaminated with solid pollutants is placed and allowed to stand. The solid pollutants suspended in the water sink to the bottom of the lagoon and the liquid is allowed to overflow out of the enclosure.^

sewage treatment plant

A facility designed to receive the wastewater from domestic sources and to remove materials that damage water quality and threaten public health and safety when discharged into receiving streams or bodies of water.  ^


A system of underground pipes that collect and deliver wastewater to treatment facilities or streams.^


A depression in the Earth's surface caused by dissolving of underlying limestone, salt or gypsum. Drainage is provided through underground channels that may be enlarged by the collapse of a cavern roof.^

social benefits

Benefits as a result of the project, during and after construction, consisting mainly of opportunities for: (i) employment of labour; and (ii) employment of capital.^

sodium adsorption rate (SAR)

A ratio for soil extracts and irrigation waters used to express the relative activity of sodium ions in exchange reactions with soil: SAR = Na+ x [(Ca++ + Mg++)/2] -0.5 where the ionic concentrations are expressed in meq/litre.^

soil classification systems

System of classification of soils based on recognition of the type and predominance of the constituents of soil considering grain size, gradation, plasticity and compressibility. Among the widely used soil classification systems are the US Soil Taxonomy and the FAO Soil Classification System.^

soil moisture deficit

The amount of water that must be applied to the soil to cause thorough drainage.^

soil moisture tension

The equivalent negative pressure or suction in the soil moisture; expressed in pressure units (bar or pascal).^


A substance that is dissolved in another substance, thus forming a solution.^


A mixture of a solvent and a solute. In some solutions, such as sugar water, the substances mix so thoroughly that the solute cannot be seen. But in other solutions, such as water mixed with dye, the solution is visibly changed.^


A substance that dissolves other substances, thus forming a solution. Water dissolves more substances than any other, and is known as the 'universal solvent'.^

specific conductance

A measure of the ability of water to conduct an electrical current as measured using a 1cm cell and expressed in units of electrical conductance, i.e., Siemens per centimeter at 25 degrees Celsius. Specific conductance can be used for approximating the total dissolved solids content of water by testing its capacity to carry an electrical current. In water quality, specific conductance is used in groundwater monitoring as an indication of the presence of ions of chemical substances that may have been released by a leaking landfill or other waste storage or disposal facility. A higher specific conductance in water drawn from downgradient wells when compared to upgradient wells indicates possible contamination from the facility.^

spray irrigation

An common irrigation method where water is shot from high-pressure sprayers onto crops. Because water is shot high into the air onto crops, some water is lost to evaporation.^


A water body formed when the side of a hill, a valley bottom or other excavation intersects a flowing body of groundwater at or below the local water table, below which the subsurface material is saturated with water.^

sprinkler irrigation

A method of irrigation under pressure in which water is sprinkled in the form of artificial rain through lines carrying distribution components: rotary sprinklers, diffusers with permanent water streams, perforated pipes. In comparison with surface and drip irrigation, the length of the path of travel by the water drops through the air causes: (1) great sensitivity to wind, which reduces the uniformity of distribution; or (2) ‘air conditioning’ effects on the crops if used in antifrost sprinkling or spraying.^

storm sewer

A sewer that carries only surface runoff, street wash and snow melt from the land. In a separate sewer system, storm sewers are completely separate from those that carry domestic and commercial wastewater (sanitary sewers).^


A general term for a body of flowing water; natural water course containing water at least part of the year. In hydrology, it is generally applied to the water flowing in a natural channel as distinct from a canal.^


The water discharge that occurs in a natural channel. A more general term than runoff, streamflow may be applied to discharge whether or not it is affected by diversion or regulation.^


A dropping of the land surface as a result of groundwater being pumped. Cracks and fissures can appear in the land. Subsidence is virtually an irreversible process.^

subsurface drainage system

Any drainage system (drainage wells, open ditches or drain pipes) that is designed to control the groundwater table.^

surface drainage system

Shallow ditches or open drains that serve to receive surface flow or drainage water.^

surface irrigation

A method of irrigation in which water is applied to the land by allowing it to flow by simple gravity, before infiltrating. It includes various systems depending upon the relative magnitude of the surface flooding phase and infiltration phase after accumulation (submersion).^

surface water

Water that is on the Earth's surface, such as in a stream, river, lake or reservoir.^

suspended sediment

Very fine soil particles that remain in suspension in water for a considerable period of time without contact with the bottom. Such material remains in suspension due to the upward components of turbulence and currents and/or by suspension.^

suspended solids

Solids that are not in true solution and that can be removed by filtration. Such suspended solids usually contribute directly to turbidity. Defined in waste management, these are small particles of solid pollutants that resist separation by conventional methods.^

suspended-sediment concentration

The ratio of the mass of dry sediment in a water-sediment mixture to the mass of the water-sediment mixture. Typically expressed in milligrams of dry sediment per liter of water-sediment mixture.^

suspended-sediment discharge

The quantity of suspended sediment passing a point in a stream over a specified period of time. When expressed in tonnes per day, it is computed by multiplying water discharge (in cubic feet per second) by the suspended-sediment concentration (in milligrams per liter) and by the factor 0.0027.^

system modernisation

This operation consists in replacing certain structures by using a new or improved technology, e.g. replacing channels and ditches by underground pipes.^