GLOSSARY
Abandonment – The intentional, prolonged, non-use of a water right, resulting in the loss of the right.
Alluvial – Characterized by loose, unconsolidated soil or sediment deposited by water.
Application efficiency – The ratio of the amount of water consumed by crops to the amount of water applied to a field for irrigation, often expressed as a percentage.
Aquifer – A geological formation or structure that stores and/or transmits water, such as to wells and springs. Use of the term is usually restricted to those water-bearing formations capable of yielding water in sufficient quantity to constitute a usable supply for people’s uses.
Base flow – Sustained flow of a stream in the absence of direct surface runoff. It includes natural and human-induced streamflows. Natural base flow is sustained largely by groundwater discharge.
Beneficial use – Defined in Montana as the use of water for the benefit of the appropriator, other persons, or the public, including but not limited to agricultural (including stock water), domestic, fish and wildlife, industrial, irrigation, mining, municipal, power, and recreational uses. A beneficial use also includes the use of water for leasing under special provisions of Montana Codes Annotated 85-2-141.
Closed basin – A term used when no more water rights are being granted in the basin in accordance with citizen petition or by legislation mandate.
Conjunctive use – Planned management of surface water and groundwater resources as an interrelated system.
Consumed fraction – The proportion of diverted or applied irrigation water that is consumed (for intended or unintended purposes) or unable to be recovered for reuse within the hydrologic system of use.
Consumptive use – Water removed from the hydrologic system of interest through evaporation or plant transpiration.
Conveyance – Transfer of water from point of withdrawal/diversion to place of use, often in ditches, canals or pipes.
Conveyance efficiency – The ratio of the amount of water applied to the field to the amount of water diverted for irrigation, often expressed as a percentage.
Diversion – The transfer of water from a stream, lake, aquifer, or other source of water to another watercourse or to the land, as in the case of an irrigation sys
Period of use – The time period during each year that the holder of a valid water right is allowed to use water. Place of use – The location where water is used by a water right holder.
Prior Appropriation Doctrine – A legal theory of water law and a system of water rights management which allocates water between users based upon a priority of water use. It is often defined as a water system where “first in time” is “first in right”. During dry years, the person with the first right has the first chance to use the available water. The holder of the second right (a junior right) would have the second chance, and so on.
Priority date – The date a water right was first established. The priority date is used to disperse water according to seniority.
Return flow – Defined in Montana as that part of a diverted flow which is applied to irrigated land and is not consumed and returns underground to its original source or another source of water, and to which other water users are entitled to a continuation of, as part of their water right. Return flow results from use and not from water carried on the surface in ditches and returned to the stream.
Reusable fraction – The proportion of diverted or applied irrigation water that is not consumed and that becomes available for reuse within the hydrologic system in question.
Runoff – The flow of water over the land surface and eventually in stream channels typically as a function of precipitation, snowmelt, spring discharge, or excess irrigation water.
Seepage – Water that moves from the surface to groundwater through porous soils.
Senior water right – Between two or more water rights on a source, the water right with the earliest priority date.
Surface water – Water above the surface of the land including, but not limited to: lakes, rivers, streams, wetlands, wastewater, flood water, and ponds.
Unintended consumption – Water evaporated or transpired for unintended purposes – for example evaporation from fields or water surfaces, weeds, ditch vegetation, etc.
Water budget – An accounting of the inflows, storage, and outflows of water to and from a system.
Water right (or appropriation right) The right to put water to a beneficial use.
Water table – The top of the water surface in the saturated part of an aquifer.
Easement – A legal instrument enabling the giving, selling, taking, or use of certain property rights such as land use, without transfer of title, such as for the passage of utility lines.
Evapotranspiration (ET) – Loss of water from soil evaporation and transpiration of plants. i.e. plant use
Groundwater – Any water beneath the land surface or beneath the bed of a stream, lake, or reservoir, and which is not a part of the surface water. The upper surface of the saturated zone is called the water table.
Groundwater recharge – Movement of surface water to groundwater.
Groundwater discharge – Movement of groundwater to a surface water body.
Headgate – A structure installed at the point of diversion to regulate flow.
Instream flows – Water in streams and rivers that maintains the existing water quality or aquatic resources and associated wildlife and riparian habitat.
Intended consumption – Water evaporated or transpired for the intended purpose, such as crop growth.
Irrigation district – A quasi-public governmental organization created by petition and court decree to operate an irrigation system in a defined area that includes the operation of works, delivery of water, and administration of the organization. It is overseen by a board that is elected by the members of the district.
Irrigation efficiency – The ratio of the amount of water consumed by crops to the amount of water diverted for irrigation, often expressed as a percentage.
Junior water right – Between two or more water rights on a source, a water right that is secondary to an earlier (more senior) water right.
Managed (artificial) recharge – A process through which water is put back into groundwater storage through activities such as irrigation and engineered or natural infiltration galleries.
Non-recoverable seepage – Seepage from fields or conveyance structures that does not make it to the aquifer or back to surface water or may become too saline or contaminated to be considered viable for reuse.
Non-reusable fraction – The proportion of diverted or applied irrigation water that is not consumed by evapotranspiration, but does not make it to the aquifer or back to surface water or may become too saline or contaminated to be considered viable for reuse.
Table of Contents | Key Messages | Water and Irrigated Agriculture | Irrigated Agriculture in Montana | The Paradox of Irrigation Efficiency | Hydrology of Irrigated Agriculture | Assessing Consequences of Changing Irrigation Methods | Water Policy and Irrigated Agriculture | Adapting to Change | Conclusion | List of Contributors | Glossary | Footnotes | References