Glossary/water dictionary

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rainfall intensity

The rate at which rainfall occurs expressed in depth units per unit of time. It is the ratio of the total amount of rain to the length of the period in which the rain falls.^

rating curve

A drawn curve showing the relation between gage height and discharge of a stream at a given gaging station.^


Water added to an aquifer; for instance, rainfall that seeps into the ground.^

reclaimed wastewater

Wastewater treatment plant effluent that has been diverted for beneficial uses such as irrigation, industry, or thermoelectric cooling instead of being released to a natural waterway or aquifer.^


Act or process of reclaiming swampy, marshy, deteriorated, desert and virgin lands and making them suitable for cultivation or habitation; also, conversion of foreshores into properly drained land for any purpose, either by enclosure and drainage, or by deposition of material thereon.^

recycled water

Water that is used more than once before it passes back into the natural hydrologic system.^

renewable resource

A resource capable of being continuously renewed or replaced through such processes as organic reproduction (biomass), groundwater recharge (water) or weathering of parent material (soil).^


A pond, lake, or basin, either natural or artificial, for the storage, regulation and control of water.^

resource management

The introduction and enforcement of restraints, including specific technical practices, to safeguard the future of renewable resources and uphold the principle of sustained yield.^

return flow

(1) That part of a diverted flow that is not consumptively used and returned to its original source or another body of water. (2) (Irrigation) Drainage water from irrigated farmlands that re-enters the water system to be used further downstream.^

return flow (irrigation)

Irrigation water that is applied to an area and which is not consumed in evaporation or transpiration and returns to a surface stream or aquifer.^

reverse osmosis

(1) (Desalination) The process of removing salts from water using a membrane. With reverse osmosis, the product water passes through a fine membrane that the salts are unable to pass through, while the salt waste (brine) is removed and disposed. This process differs from electrodialysis, where the salts are extracted from the feedwater by using a membrane with an electrical current to separate the ions. The positive ions go through one membrane, while the negative ions flow through a different membrane, leaving the end product of freshwater. (2) (Water Quality) An advanced method of water or wastewater treatment that relies on a semi-permeable membrane to separate waters from pollutants. An external force is used to reverse the normal osmotic process resulting in the solvent moving from a solution of higher concentration to one of lower concentration.^

riparian water rights

The rights of an owner whose land abuts water. They differ from state to state (US) and often depend on whether the water is a river, lake, or ocean. The doctrine of riparian rights is an old one, having its origins in English common law. Specifically, persons who own land adjacent to a stream have the right to make reasonable use of the stream. Riparian users of a stream share the streamflow among themselves, and the concept of priority of use (prior appropriation doctrine) is not applicable. Riparian rights cannot be sold or transferred for use on non-riparian land.^


A natural stream of water of considerable volume, larger than a brook or creek.^


(1) That part of the precipitation, snow melt, or irrigation water that appears in uncontrolled surface streams, rivers, drains or sewers. Runoff may be classified according to speed of appearance after rainfall or melting snow as direct runoff or base runoff, and according to source as surface runoff, storm interflow, or groundwater runoff. (2) The total discharge described in (1), above, during a specified period of time. (3) Also defined as the depth to which a drainage area would be covered if all of the runoff for a given period of time were uniformly distributed over it.^