Useful Links & Glossary of terms

Glossary of Agricultural Irrigation Terms


intentional, prolonged nonuse of a water right, resulting in its loss.

acre-foot (acre-ft)

the volume of water required to cover 1 acre of land (43,560 square feet) to a depth of 1 foot. Equal to 325,851 gallons or 1,233 cubic meters.


a judicial procedure decreeing the quantity and priority date of all existing water rights in a basin

Administrative Rules of Montana (ARM)

a collection of state agency rules used in the implementation of federal and state codes.


to capture, impound, or divert water from its natural course and apply toward a beneficial use.


a geologic formation(s) that is water bearing. 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.

artificial recharge

a process where water is put back into ground-water storage from surface-water supplies such as irrigation, or induced infiltration from streams or wells.


the area drained by a river and its tributaries: a watershed.

change of water right

any change in a way a water right is used. Can be changed in type, place, time of use, point of diversion, adding points of diversion, etc. Changes of water rights must be approved by the Department of Natural Resources (DNRC) to assure that no injury occurs to other water rights.

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that part of water withdrawn that is evaporated, transpired by plants, incorporated into products or crops, consumed by humans or livestock, or otherwise removed from the immediate water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. Also referred to as water consumed.

cubic feet per second (cfs)

a rate of the flow, in streams and rivers, for example. It is equal to a volume of water one foot high and one foot wide flowing a distance of one foot in one second. One “cfs” is equal to 7.48 gallons of water flowing each second. As an example, if your car’s gas tank is 2 feet by 1 foot by 1 foot (2 cubic feet), then gas flowing at a rate of 1 cubic foot/second would fill the tank in two seconds.

decreed water right

a water right issued by the court upon adjudication of a stream


an open, physical alteration of a stream’s flow away from its natural course.


Department of Natural Resources and Conservation. Montana’s DNRC was established through the Executive Reorganization Act of 1971. It administers the portions of the Montana Water Use Act that relates to water uses after June 30, 1973.

existing right

a Montana water right originating on or before July 1, 1973: subject to adjudication.

gaging station

a site on a stream, lake, reservoir or other body of water where observations and hydrologic data are obtained. The U.S. Geological Survey measures stream discharge at gaging stations.

ground water

(1) water that flows or seeps downward and saturates soil or rock, supplying springs and wells. The upper surface of the saturate zone is called the water table. (2) Water stored underground in rock crevices and in the pores of geologic materials that make up the Earth’s crust.

ground-water recharge 

inflow of water to a ground-water reservoir from the surface. Infiltration of precipitation and its movement to the water table is one form of natural recharge. Also, the volume of water added by this process.

Head gate

The gate that controls water flow into irrigation canals and ditches. A watermaster regulates the head gates during water distribution and posts head gate notices declaring official regulations.

in-stream flow 

Non-consumptive water requirements that do not reduce the water supply, such as water required for maintaining flowing streams for fish or for recreational boating.


a court order prohibiting a specific act or commanding the undoing of some wrong or injury


the controlled application of water for agricultural purposes through manmade systems to supply water requirements not satisfied by rainfall.

junior appropriator

a secondary user on a watercourse, holding a water right inferior to previous (senior) users.

miner’s inch

by Montana law, 1 cubic foot per sec (cfs) is approximately equal to 40 miner’s inches.

priority date

the official date of an appropriation, generally the date of established intent: used in determining seniority among water users.

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.

returnflow (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.

senior appropriator 

an original user on a watercourse, holding a water right superior to all subsequent (junior) users.

surface water

water that is on the Earth’s surface, such as in a stream, river, lake, or reservoir.


process by which water that is absorbed by plants, usually through the roots, is evaporated into the atmosphere from the plant surface, such as leaf pores.

water commissioner

District court appointed official who admeasures and distributes water to parties owning water rights in a source affected by decreed waters.

Water Court

The 1979 Legislature created the Montana Water Court to expedite and facilitate the statewide adjudication of over 219,000 state law-based water rights (generally rights with a pre-July 1973 priority date) and Indian and Federal reserved water rights claims. The Water Court has exclusive jurisdiction over the adjudication of water rights claims.

water master

an attorney versed in water law who serves at the discretion of the Water Court.

water diversion

changing the natural flow of water to another location by using dams, canals, or pipelines.


water that has been used in homes, industries, and businesses that is not for reuse unless it is treated.


the land area that drains water to a particular stream, river, or lake. 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 watersheds, like the Mississippi River basin contain thousands of smaller watersheds.

water table

the upper level of ground water; the level below which soil and rock are saturated with water.