Water Glossary

Aquifer: a sand, gravel or rock formation capable of storing or conveying water below the surface of the land.

Blue ribbon stream: one of 12 high quality trout streams in Montana designated by a Murphy instream flow designation.

Coliform bacteria: a group of bacteria predominantly inhabiting the intestines of man or animal but also found in soil. Coliform bacteria are commonly used as indicators of the possible presence of pathogenic organisms.

Cubic feet per second (cfs): a unit expressing rate of discharge, typically used in measuring stream flow. One cfs is equal to the discharge in a stream of a cross-section one foot wide and one foot deep, flowing with an average velocity of one foot per second.

Dewatered: natural flow of streams reduced due to withdrawals.

Erosivity: the capacity of a soil or land surface to be worn down or washed away by the action of water, ice or wind.

Floodplain: any normally dry land area that is susceptible to being inundated by water from any natural source.

Floodway: the channel of a river or stream and those parts of the adjacent floodplain adjoining the channel that are required to carry and discharge the base flood.

Groundwater: water in porous materials beneath the ground surface.

Hydric soil: a soil that, in its undrained condition, is saturated, flooded, or ponded long enough during the growing season to develop anaerobic conditions that favor the growth of water-loving plants.

Hydrograph: a record showing the changes in flow of a river over time.

Instream flow: the water left in a stream to maintain the existing aquatic resources and associated wildlife and riparian habitat.

Irrigation return flow: irrigation water not consumed and returned to a surface or groundwater supply.

Murphy Right: special instream flow water rights recognized in 1969 when an instream flow protection bill was passed by the Montana legislature to protect the unappropriated waters of 12 high-priority trout streams.

Nonpoint source: entry of a pollutant into a water body from widespread or diffuse sources with no definite point of entry. The source is not a readily discernible point like a discharge pipe.

Ordinary high-water mark: the line that water impresses on land by covering it for sufficient periods to cause physical characteristics that distinguish the area below the line from the area above it.

Permeable: the capacity of porous rock, sediment or soil to transmit water.

Riparian areas: land areas adjacent to water that are identified by the presence of vegetation requiring large amounts of water, normally available from a high water table. Common riparian vegetation includes sedges, willows, alders and/or cottonwoods.

Siltation: particles of soil smaller than sand but larger than clay particles that are washed into streams and may impair biological and physical processes.

Snowpack: the winter accumulation of snow.

Transmissivity: the rate at which water passes through an aquifer.

Tributary: a stream that contributes its water to another stream or body of water.

Water budget: the accounting of the inflows and outflows of water to and from a system.

Water table: the upper level of a saturated zone in an aquifer below the soil surface.

Withdrawals: removing water from surface or groundwater sources in order to use it elsewhere.

< Back to The Gallatin Watershed Sourcebook Table of Contents