Glossary/water dictionary

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data transmission

The sending of data from one place to another, or from one part of the system to another, utilising different transmission facilities, such as telephone or telegraph lines, direct radio links, or satellite transmission systems.^

decision support system

Systems for helping planners make decisions using models to select the most favourable solution from among alternatives that are available according to established criteria.^

delivery structures

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

demand management

A programme adopted to achieve effective management of the use of water resources in order to meet the general objectives of: economic efficiency, environmental conservation, and community and consumer satisfaction.^

depreciation and renewal funds

The provision for interventions necessitated by the changing of spare parts is covered by a renewal fund that capitalises the depreciation stocks normally constituted for this purpose. However, it is possible to practise a less expensive policy by capitalising only lesser amounts based on the technical depreciation periods of equipment, which always exceed those for legal or fiscal depreciation.^

depth integrating sediment sampler

A device to take a sample of suspended sediment in a stream. It is lowered from the stream surface to the bed and raised to the surface again at a constant rate. The sample of sediment laden water is drawn in continuously, thus obtaining a composite sample which is integrated over the depth of the stream.^

derived data

Records of observations and measurements of physical facts, occurrences and conditions that have been developed from basic data by means of standard methods of computation and estimation.^

desalinationt

he removal of salts from saline water to provide freshwater. This method is becoming a more popular way of providing freshwater to populations.^

discharge

The volume of water that passes a given location within a given period of time. Usually expressed in cubic feet per second.^

discharge rating curve

A curve that expresses graphically the relation between the discharge and its corresponding stage (or elevation of water surface) in a stream or conduit at a given point.^

domestic water use

Water used for household purposes, such as drinking, food preparation, bathing, washing clothes, dishes, and dogs, flushing toilets, and watering lawns and gardens. About 85% of domestic water (in the US) is delivered to homes by a public-supply facility, such as a county water department; about 15% of the US population supply their own water, mainly from wells.^

drainage basin

Land area where precipitation runs off into streams, rivers, lakes and reservoirs. It is a land feature that can be identified by tracing a line along the highest elevations between two areas on a map, often a ridge. Large drainage basins, like the area that drains into the Mississippi River, contain thousands of smaller drainage basins. Also called a 'watershed'.^

drawdown

A lowering of the groundwater surface caused by pumping.^

drip irrigation

A common irrigation method where pipes or tubes filled with water slowly drip onto crops. Drip irrigation is a low-pressure method of irrigation and less water is lost to evaporation than with high-pressure spray irrigation.^

drop structure

A structure designed to secure the lowering of the water surface in a channel in a short distance, and the safe destruction of the liberated surplus energy. ^

dry spell

A sustained period of time with insufficient precipitation.^

duty of water

The relation between the area irrigated, or to be irrigated, and the quantity of water used, or required, to irrigate it for the purpose of maturing its crop. Duty is stated with reference to a base period and the place of its reckoning or measurement. It is usually expressed in volume of water or rate of flow per unit area (litres per hectare).^