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Definitions are from Instream Flows for Riverine Resource Stewardship; Instream Flow Council (Annear, et. al) unless otherwise noted.


Abiotic - The nonliving material components of the environment such as water, sediment, and temperature.

Accretion – 1. Addition of flows to the total discharge of the stream channel, which may come from tributaries, springs, or seeps. 2. Increase of material such as silt, sand, gravel, water.

Adaptive management - A process whereby management decisions can be changed or adjusted based on additional biological, physical or socioeconomic information.

Aggradation - 1. Geologic process in which inorganic materials carried downstream are deposited in streambeds, floodplains, and other water bodies resulting in a rise in elevation in the bottom of the water body. 2. A state of channel disequilibrium, whereby the supply of sediment exceeds the transport capacity of the stream, resulting in deposition and storage of sediment in the active channel.

Alluvial stream - A stream with a bed and banks of unconsolidated sedimentary material subject to erosion, transportation, and deposition by the river.

Anadromous - Fish that mature in seawater but migrate to fresh water to spawn.

Annual flow - The total volume of water passing a given point in one year. Usually expressed as a volume (such as acre-feet) but may be expressed as an equivalent constant discharge over the year, such as cubic feet per second.

Appropriation - A specified amount of water set aside by Congress, other legislative body or state or provincial water regulatory authority to be used for a specified purpose at a specified place, if available.

Aquatic habitat - A specific type of area and its associated environmental (i.e.,
biological, chemical, or physical) characteristics used by an aquatic organism, population, or community.

Aquatic life - All organisms living in or on the water. This includes plants from the smallest phyroplankton through algae, pheriton, and emergent vegetation as well as animal life from zooplankton through benthic invertebrates, fishes, and amphibians, reptiles, birds, and mammals.

Aquifer - An underground formation that contains sufficient saturated permeable material to yield significant quantities of water to wells and springs.

Armoring - 1. The formation of an erosion-resistant layer of relatively large particles on the surface of a streambed or stream bank that results from removal of finer particles by erosion, and which resists degradation by water currents. 2. The application of materials to reduce erosion. 3. The process of continually winnowing away smaller substrate materials and leaving a veneer of larger ones.

Average daily flow – The long-term average annual flow divided by the number of days in the year usually expressed as an equivalent constant discharge such as cubic feet per second. In some settings, the value can be used to represent only the portion of the daily flow values in a defined period such as those that occur within a calendar month.

Average velocity – In a channel, it is equal to the discharge divided by the cross-sectional area of the cross section. For any point along the cross section, a measurement of 60% of the depth, measured from the surface, closely approximates the average velocity for the water column. In water greater than 76 cm (2.5 ft) deep, the average of measurements made at 20% and 80% of the depth approximates the mean column velocity.


Backwater - 1. A pool surface created in an upstream direction that results from damming a vertical or horizontal channel that impedes the free flow of water. 2. In general, an off-shoot from the main channel with little flow and where the water surface elevation is maintained by conditions in the main channel acting on the downstream end of the backwater.

Bankfull discharge - The discharge corresponding to the stage at which the floodplain begins to be inundated, usually provided by natural peak flow every 1-2 years. The maximum discharge that the channel can convey without overflowing onto the floodplain. Calculating the bankfull discharge is one deterministic method of calculating the channel forming discharge.

Base flow - Streamflow contributed solely from shallow groundwater in the absence of significant precipitation, runoff events or supplemental release from storage above the natural flow.

Baseline - The conditions occurring during the reference timeframe, usually referring to water supply habitat values, or population status. Baseline is often some actual recent historical period but may also represent the same climatological-meteorological conditions but with present water development activities on line; the same climatological-meteorological conditions but with both current and proposed future development on line; or virgin or predevelopment conditions. The definition of baseline is dependent on the objectives of the study. Quite often, two or more baseline conditions may be necessary to evaluate a specific project.

Bedload - Material moving on or near the streambed and frequently in contact with it.

Bedload discharge - The quantity of bedload passing a transect in a unit of time.

Bed material - Mixture of substances composing the stream’s bed.

Benthic - Associated with the bottom of a body of water.

Bioaccumulation - The accumulation of a substance (e.g. toxic chemicals such as methylmercury or PCBs) in an organism or part of an organism.

Biomagnification - The bioaccumulation of a substance up the food chain, which results in higher concentrations at the higher trophic levels.

Biological diversity - The variety and variability among living organisms and the ecological complexes in which they occur. Diversity can be defined as the number of different items and their relative frequency. For biological diversity, these items are organized at many levels, ranging from complete ecosystems to the chemical structures that are the molecular basis of heredity. Thus, the term encompasses different ecosystems, species, genes, and their relative abundance.

Biotic - Of or pertaining to the living components of an ecosystem.

Braided - Pattern of two or more interconnected channels typical of alluvial streams.

Bypass - 1. A channel or conduit in or near a dam that provides a route for fish to move through or around the dam without going into the turbines.
2. That stream reach below a dam that is essentially skirted by the flow used to generate electricity.


Catchment - The total land area that drains water to a river, stream or lake. Also called a watershed, drainage area, and basin.

CFS - Cubic feet per second (measure of streamflow or discharge).

Channel - That cross section containing the stream that is distinct from the
surrounding area due to breaks in the general slope of the land, lack of terrestrial vegetation, and changes in the composition of the substrate materials.

Channel-forming flow - A theoretical discharge that, if maintained indefinitely, would produce the same channel geometry as the natural long-term hydrograph. Generally applicable only to stable, alluvial streams that have the ability to change their shape and are neither aggrading nor degrading. Often referred to as the bankfull flow, dominant flow, effective flow, or a flow of a specified recurrence interval, typically between the mean annual and 5-year peak flow.

Channelization - The mechanical alteration of a natural stream by dredging, straightening, lining, or other means of accelerating the flow of water.

Channel-maintenance flow – 1. A range of flows making up a portion of the rising and falling limbs of the annual hydrograph that is capable of keeping the stream in a condition of sediment equilibrium over time (years) by moving all sizes and amounts of bedload sediment, scouring vegetation, and maintaining riparian vegetation. The range of flows required begins at a flow that mobilizes hydraulically limited gravels and extends up to the instantaneous 25-year flow. 2. A range of flows that transports bedload sediment through the channel network, prevents constriction of the channel by sediment and vegetation, and sustains channel bank and floodplain vegetation.

CMS - Cubic meters per second (measure of streamflow or discharge). Also, expressed as m3/s.

Colluvial - Pertaining to material or processes associated with transportation and/or deposition by mass movement (direct gravitational action) and local, unconcentrated runoff on side slopes and/or at the base of slopes.

Connectivity - Maintenance of lateral, longitudinal, and vertical pathways for biological, hydrological, and physical processes.

Consumptive use - Represents the difference between the amount of water diverted and the amount of the return flow to the system (e.g., surface stream or underground basin). It is that amount by which the total resource is depleted.

Cover - Structural features (e.g., boulders, log jams) or hydraulic characteristics (e.g., turbulence, depth) that provide shelter from currents, energetically efficient feeding stations, and/or visual isolation from competitors or predators.

Cross section - A plane across a stream channel perpendicular to the direction of water flow.

Cross-sectional area - The area of the stream’s vertical cross section, perpendicular to flow.

Cubic feet per second (ft3/s, cfs) - The rate of discharge representing a volume of 1 cubic foot passing a given point during 1 second and equivalent to 7.48 gallons per second or 448.8 gallons per minute.


Degradation -1. A decline in the viability of ecosystem functions and processes. 2. Geologic process by which streambeds and floodplains are lowered in elevation by the removal of material (also see Down cutting).

Density - Number of individuals per unit area.

Deposition - The settlement or accumulation of material out of the water column and onto the streambed.

Detritus - Nondissolved organic debris such as leaves and twigs.

Dewatered - A length of stream without water (due to human removal).

Diadromous - Fishes that move between marine and fresh waters for purposes of spawning (i.e., anadromous and catadromous).

Discharge -The rate of streamflow or the volume of water flowing at a location within a specified time interval. Usually expressed as cubic meters per second (cms) or cubic feet per second (cfs).

Diversion - A withdrawal from a body of water by means of a ditch, dam, pump or other man-made contrivance.

Diversity - That attribute of a biotic (or abiotic) system describing the richness of plant or animal species or complexity of habitat.

Domestic use - Water used for normal household purposes, such as drinking, food preparation, bathing, washing clothes and dishes, flushing toilets, and watering lawns and gardens. Also called residential water use or domestic water use. The water may be obtained from a public supply or may be self-supplied.

Down cutting (degradation) - Geologic process by which streambeds and floodplains are lowered in elevation by the removal of bed material.

Drainage area -The total land area draining to any point in a stream. Also called catchment area, watershed, and basin.

Drought - A prolonged period of less-than-average water availability.

Dry year - A time period with a given probability of representing dry conditions; for example, a given year may be as dry or drier than 80% of all other similar periods.

Dynamic equilibrium - A quasi steady-state condition attained in an alluvial channel, whereby sediment supplies are just balanced by sediment transport capacity, resulting in no net change in average streambed elevation over time.


Ecological integrity -The ability to support and maintain a balanced, integrated, adaptive community of organisms having a species composition, diversity, and functional organization comparable to that of the natural habitat of the region.

Ecosystem - Any complex of living organisms interacting with nonliving chemical and physical components that form and function as a natural environmental unit.

Effective discharge - The flow that transports the largest fraction of the average annual bed material load. Calculating the effective discharge is one deterministic method of calculating the channel forming discharge.

Effective habitat - 1. That portion of available physical habitat occupied by a life stage due to mortality (or other constraint) of previous life stages. Effective habitat analysis implies following cohorts of habitat use through time, as a population-limiting habitat event may not manifest itself until some later date. 2. Habitat effectively available due to hydropeaking or other flow fluctuations reducing the habitat for a single life stage.

Embeddedness - The degree that larger particles (boulders, rubble, or gravel) are surrounded or covered by fine sediment. Usually measured in classes according to percent of coverage.

Energy slope - The difference in total energy (potential plus kinetic) of a fluid between two points divided by the linear distance between the two points.

Estuary - The zone between the fresh water of a coastal stream and the seawater of an ocean influenced by the tide.

Eutrophication - The process whereby water bodies, such as lakes, estuaries, or slow-moving streams receive excess nutrients that stimulate excessive plant growth (algae, periphyton attached algae, and nuisance plants weeds). This enhanced plant growth, often called an algal bloom, reduces dissolved oxygen in the water when dead plant material decomposes and can cause other organisms to die. Nutrients can come from many sources, such as fertilizers applied to agricultural fields, golf courses, and suburban lawns; deposition of nitrogen from the atmosphere; erosion of soil containing nutrients; and sewage treatment plant discharges.

Evapotranspiration - The combined loss of water from open-surface evaporation and the transpiration of water from leaf and stem tissues of growing vegetation.

Exceedence - That probability of an event exceeding others in a similar class. Note that this may be “equal or exceed” or “exceed only.” Probabilities may also be expressed as nonexceedence; that is, the probability of being “less than or equal” or just “less than.”

Exotic - Introduced species not native to a given area.


Feeding station - 1. A microhabitat type that provides conditions for obtaining large amounts of food with minimal expenditure of energy. 2. Microhabitat that simultaneously maximizes feeding efficiency and minimizes predation risk.

Fill - The localized deposition of material that is eroded and transported from other areas, resulting in a change in bed elevation. This is the opposite of scour.

Fishery - 1. The interaction of aquatic organisms and aquatic environments and their human users to produce sustained benefits for people; (2) a dynamic product of physical, biological, and chemical processes. Each component (process) is important, affects the other, and presents opportunities for impacting or enhancing the nature or character of fisheries resources. Fish populations are merely one attribute of a fishery.

Flood - Any flow that exceeds the bankfull capacity of a stream or channel and flows out on the floodplain.

Floodplain - 1. The area along waterways that is subject to periodic inundation by out-of-bank flows. 2. The area adjoining a water body that becomes inundated during periods of over-bank flooding and that is given rigorous legal definition in regulatory programs. 3. Land beyond a stream channel that forms the perimeter for the maximum probability flood. 4. A relatively flat strip of land bordering a stream that is formed by sediment deposition. 5. A deposit of alluvium that covers a valley flat from lateral erosion of meandering streams and rivers.

Flow - 1. The movement of a stream of water or other mobile substance from place to place. 2. Discharge. 3. Total quantity carried by a stream.
Flow regime - The distribution of annual surface runoff from a watershed over time such as hours, days, or months (See also Hydrologic regime).

Flushing flow - A stream discharge with sufficient power to remove silt and sand from a gravel/cobble substrate but not enough power to remove gravels.

Fluvial - Pertaining to streams or produced by river action.

Frazil ice - Fine spicules of ice formed in water (i.e., slush) that are the first stage of ice formation. They may accumulate to form cap ice or anchor ice in settings that have high turbulence.

Free-flowing - A stream or stream reach that flows unconfined and naturally without impoundment, diversion, straightening, rip-rapping, or other modification of the waterway.


Gradient -The rate of change of any characteristic, expressed per unit of length. (See Slope.) May also apply to longitudinal succession of biological communities.

Groundwater - In general, all subsurface water that is distinct from surface water; specifically, that part which is in the saturated zone of a defined aquifer. Sometimes called underflow.


Habitat -The physical, chemical, and biological surroundings in which an organism or population (living and nonliving) lives; includes life requirements such as food and shelter (See Physical habitat).

Habitat bottleneck - The cumulative constraint on species abundance caused solely by repeated reductions in habitat capacity through time due to microhabitat or macrohabitat limitations.

Habitat guild - Groups of species that share common characteristics of microhabitat use and selection at various stages in their life histories.

Habitat suitability curves - Collectively refers to category one to four suitability index (SI) curves.

Head cutting - Upstream migration or deepening of a stream channel that results from erosion of the stream channel due to high water velocities.

Headwater - The source for a stream in the upper tributaries of a drainage basin.

Hydraulic control - A horizontal or vertical constriction in the channel, such as the crest of a riffle, which creates a backwater effect.

Hydrograph - A graph showing the variation in discharge over time.

Hydrologic regime -The distribution over time of water in a watershed, among precipitation, evaporation, soil moisture, groundwater storage, surface storage, and runoff.

Hydropeaking - The practice of abruptly alternating between a low base and a high peak flow, for electrical power generation during periods of high demand. Compare with hydropulsing in which flows may also range from low to high, but are gradually varied over a longer period.

Hyporheic zone - 1. The layer of stream channel substrate that extends as deep and wide as interstitial flow. 2. The interface between the stream bed and shallow groundwater.


Impervious - A term applied to a material through which water cannot pass or passes with great difficulty; impermeable.

Index of biotic integrity (IBI) - A numerical gauge of the biological health of stream fish communities based on various attributes of species richness, species composition, trophic relations, and fish abundance and condition.

Indigenous - A fish or other aquatic organism native to a particular water body, basin, or region.

Instantaneous flow - 1. Discharge that is measured at any instance in time. 2. Flow that is measured instantaneously and not averaged over longer time such as day or month. (Instream flow references are generally related in cubic feet per second (cfs) but regardless of unit of measure are not accomplished through averaging discharge volume over time.)

Instream cover - Any material located within the water column of a stream that provides protection from predators or competitors, or mitigates the imports of other stream conditions for fish wildlife and aquatic animals.

Instream flow – Any quantity of water flowing in a natural stream channel at any time of year. The quantity may or may not be adequate to sustain natural ecological processes and may or may not be protected or administered under a permit, water right, or other legally recognized means.
Instream flow requirement - 1. That amount of water flowing through a natural stream course that is needed to sustain, rehabilitate, or restore the ecological functions of a stream in terms of hydrology, biology, geomorphology, water quality, and connectivity at a particular level.
2. That amount of water flowing through a natural stream course needed to sustain instream values at an acceptable level based on appropriate study. Instream values and uses include protection of fish and wildlife habitat, migration, and propagation; outdoor recreation activities; navigation; hydropower generation; waste assimilation (water quality); and ecosystem maintenance, which includes recruitment of fresh water to the estuaries, riparian vegetation, floodplain wetlands, and maintenance of channel geomorphology. Water requirements sufficient to maintain all of these uses at an acceptable level are the instream flow requirements.

Instream flow reservation - A specified streamflow or water level below which further diversion is not allowed. Instream flow reservations are typically recognized and administered under the authority of some type of legal means such as a water right, permit, or operating agreement.

Instream flow rights - A legal property right to maintain or protect a designated streamflow for in-channel purposes. Such rights are limited to a specified amount of water within its natural course.

Instream use - Any use of water that does not require diversion or withdrawal from the natural watercourse, including in-place uses such as navigation and recreation.

Invertebrate - All animals without a vertebral column; for example, aquatic insects.


Landscape Connectivity - The degree to which the landscape facilitates or impedes movement among resource patches (Taylor et al, 1993).

Large woody debris - Any large piece of woody material that intrudes into the stream channel; often defined as having a diameter greater than 10cm and a length greater than 1 m. Synonyms: Large organic debris, woody debris, log.

Larva - An immature form that must pass through one or more metamorphic changes before becoming an adult.

Lentic - Standing water such as lakes, reservoirs, ponds, and marshes.

Longitudinal succession - Gradation in the composition of communities along a spatial gradient.


Macrohabitat - Abiotic habitat conditions in a segment of river controlling longitudinal distribution of aquatic organisms, usually describing channel morphology, flow, or chemical properties or characteristics with respect to suitability for use by organisms.

Macroinvertebrate - An invertebrate animal without a backbone that can be seen without magnification.

Main stem - The main channel of a river, as opposed to tributary streams and smaller rivers that feed into it.

Mean column velocity - The average velocity of the water measured on an imaginary vertical line at any point in a stream. A measurement of 60% of the depth, measured from the surface, closely approximates the average velocity for the water column. In water greater than 76 cm (2.5 ft) in depth, the average of measurements made at 20% and 80% of the depth approximates the mean column velocity.

Meander -The winding of a stream channel.

Mean monthly flow – The average flow for one month that is computed from several years’ worth of data for that month, which is usually expressed as cfs or cms.

Mesohabitat - A discrete area of stream exhibiting relatively similar characteristics of depth, velocity, slope, substrate, and cover, and variances thereof (e.g., pools with maximum depth <5 ft, high gradient riffles, side channel backwaters).

Metapopulation - A group of spatially separated populations of the same species which interact at some level (Richard Levins in 1969 – Wikipedia)

Microhabitat - Small localized areas within a broader habitat type used by organisms for specific purposes or events, typically described by a combination of depth, velocity, substrate, or cover.

Minimum flow – 1. Traditionally thought of as the lowest streamflow required to protect some specified aquatic function as established by agreement, rule, or permit. In the absence of higher flows at other times of year, aquatic habitat may change, which leads to significant changes in aquatic community structure, which can lead to a subsequent conclusion that a lower minimum flow will maintain aquatic function. 2. The lowest discharge recorded over a specified period of time.

Mitigation - An action taken to avoid, alleviate, or compensate for potentially adverse effects to aquatic habitat that have been modified through human actions.


Natural flow - The flow regime of a stream as it would occur under completely unregulated conditions; that is, not subjected to regulation by reservoirs, diversions, or other human works. Also referred to as the virgin flow.

Natural hydrograph - A graph showing the variation in discharge (or river stage) that would exist in the absence of any human alteration, over a specific time period.

Naturalized flow - Measured flows that are adjusted for upstream water licenses or uses to approximate the flows that would occur in the absence of regulation and extraction.

Nose velocity - The velocity at the approximate point vertically in the channel where a fish is located.


Open channel hydraulics - The analysis of water flow and associated materials in an open channel with a free water surface, as opposed to a tunnel or pipeline.

Overhead cover - Material (organic or inorganic, including surface ice) that provides protection to fish, wildlife, or other aquatic animals from above.


Period of record - The length of time for which data for an environmental variable have been collected on a regular and continuous basis.

Phenology - The periodic natural patterns of maturation, timing, or distribution in the life history of an organism.

Physical habitat -Those abiotic factors such as depth, velocity, substrate, cover, temperature, water quality that make up some of an organism’s living space.

Pool - Part of a stream with reduced velocity, often with water deeper than the surrounding areas, which is usable by fish for resting and cover.


Q710-The lowest continuous 7-day flow with a 10-year recurrence interval. Sometimes called 7Q10.


Ramping rate -The rate of change in discharge from base flow to generation flow below a peaking hydroelectric facility.

Rapids - A part of a stream with considerable turbulence where the current is moving with much greater velocity than usual and where the water surface is broken by obstructions, but without a sufficient break in slope to form a cascade.

Reach - A comparatively short length of a stream, channel, or shore. One or more reaches compose a segment. The actual length is defined by the purpose of the study but is usually no greater than 5-7 times the channel width.

Recharge - Process by which water is added to the zone of saturation, as recharge of an aquifer.

Recurrence interval - The average time interval between events equaling or exceeding a given magnitude in a time series.

Regime - The general pattern (magnitude and frequency) of flow or temperature events through time at a particular location (such as snowmelt regime, rainfall regime).

Regulated flow – Artificial modification of the natural flow of a stream by reservoirs, diversions, or other works of humans to achieve a specified purpose or objective.

Rehabilitate - To bring about changes in management that allow the physical and biological processes of a stream, river, or lake to function in a more natural way in order to achieve or more closely approximate a condition of dynamic equilibrium or balance. Rehabilitation does not necessarily mean restoring a riverine resource to predevelopment conditions.

Restoration – To return a stream, river, or lake to its natural, predevelopment form and function. Restoration typically eliminates the human influences that degraded or destroyed riverine processes and characteristics.

Riffle - A relatively shallow reach of stream in which the water flows swiftly and the water surface is broken into waves by obstructions that are completely or partially submerged.

Riparian - Pertaining to anything connected with or adjacent to the bank of a stream or other body of water.

Riparian right - The right—as to fishing or the use of water—of one who owns land situated along the bank of a stream or other body of water.

Riparian vegetation - Vegetation that is dependent upon an excess of moisture during a portion of the growing season on a site that is perceptively more moist than the surrounding area.

Riparian zone - The transitional zone or area between a body of water and the adjacent upland identified by soil characteristics and distinctive vegetation that requires an excess of water. It includes wetlands and those portions of floodplains that support riparian vegetation.

River - A large stream that serves as the natural drainage channel for a relatively large catchment or drainage basin.

River Continuum Concept - A framework for integrating predictable and observable biological features of lotic systems based on consideration of the gradient of physical factors formed by the drainage network.

Run - A portion of a stream with low surface turbulence that approximates uniform flow, and in which the slope of the water surface is roughly parallel to the overall gradient of a stream reach.


Scour - The localized removal of material from the streambed by flowing water. This is the opposite of fill.

Sediment - Solid material, both mineral and organic, that is in suspension in the current or deposited on the streambed.

Sediment load - A general term that refers to material in suspension and/or in transport. It is not synonymous with either discharge or concentration. (See Bedload).

Side channel - Lateral channel with an axis of flow roughly parallel to the main stem, which is fed by water from the main stem; a braid of a river with flow appreciably lower than the main channel. Side channel habitat may exist either in well-defined secondary (overflow) channels, or in poorly-defined watercourses flowing through partially submerged gravel bars and islands along the margins of the main stem.

Sinuosity - The ratio of channel length between two points on a channel to the straight-line distance between the same two points.

Slope - The inclination or gradient from the horizontal of a line or surface. The degree of inclination can be expressed as a ratio, such as 1:25, indicating one unit rise in 25 units of horizontal distance or as 0.04 height per length. Often expressed as a percentage and sometimes also expressed as feet (or inches) per mile.

Stage - The distance of the water surface in a river above a known datum.

Standing crop - Quantity of living organisms present in the environment at a given time.

Stochastic - Allowing for randomness or variability in processes. Literally, making a best guess.

Storage - Water artificially impounded in surface or underground reservoirs for future use. Water naturally detained in a drainage basin, such as ground- water, channel storage, and depression storage.

Stream - A natural watercourse of any size containing flowing water, at least part of the year, supporting a community of plants and animals within the stream channel and the riparian vegetative zone.

Streambed - The bottom of the stream channel; may be wet or dry.

Stream classification - Various systems of grouping or identifying streams possessing similar features according to hydrogeomorphic structure (e.g., gradient), water source (e.g., spring creek), associated biota (e.g., fish species), or other characteristics.

Stream competency -The maximum size particle that a stream can carry, dependent upon water velocity and gradient.

Stream corridor - A perennial, intermittent, or ephemeral stream and adjacent vegetative fringe. The corridor is the area occupied during high water and the land immediately adjacent, including riparian vegetation that shades the stream, provides input of organic debris, and protects banks from excessive erosion.

Stream order -  Strahler's (1952) stream order system is a simple method of classifying stream segments based on the number of tributaries upstream. A stream with no tributaries (headwater stream) is considered a first order stream. A segment downstream of the confluence of two first order streams is a second order stream. Thus, a nth order stream is always located downstream of the confluence of two (n-1)th order streams. DNR Fisheries Stream Survey Manual, 2006

Substrate - The material on the bottom of the stream channel, such as rocks or vegetation.

Suspended sediment - Particles having such a density or grain size as to permit suspension in the moving water column for long distances downstream. Much of this material settles out when water movement slows or ceases.

Sustainability - A state in which all humans, present and future, can live at a prescribed level within the limits of what nature can provide to our species and withstand from it in continuity and at no undue harm to other forms of life.


Temporal variability - Pertaining to, or involving the nature of time, occurrence in time, and variability in occurrence over some increment in time (e.g., diurnally, daily, monthly, annually).

Terrace - An alluvial feature of streams that is formed by down-cutting and subsequent abandonment of a former floodplain, with the development of a new floodplain within the walls of the escarpment.

Thalweg - A longitudinal profile of the lowest elevations of a sequential series of cross sections.

Time-series analysis - Analysis of the pattern (frequency, duration, magnitude, and time) of time-varying events. These events may be discharge, habitat areas, stream temperature, population factors, economic indicators, power generation, and so forth.

Time step - The interval over which elements in a time series are averaged.

Transpiration - (Botany) A process by which water vapor escapes through the plant via its stomata and lenticels into the atmosphere and enables mass flow of nutrients and water from roots to shoots. (

Trophic level - Any of the sequential stages in a food chain, occupied by producers at the bottom and in turn by primary, secondary, and tertiary consumers. The American Heritage Science Dictionary. Retrieved October 25, 2007, from website: level

Tributary - A stream feeding, joining, or flowing into a larger stream (at any point along its course or into a lake). Synonyms: feeder stream, side stream.

Turbidity - A measure of the extent to which light passing through water is reduced due to suspended materials.

Turbulent flow - Type of flow in which any particle of water may move in any
direction with respect to any other particle. Flow in which the velocity at any point varies erratically.


Velocity -The distance traveled by water in a stream channel divided by the time required to travel that distance.


Water allocation - Determining the quantity of water from a given source that can or should be ascribed to various instream or out-of-stream uses. May be referred to as water reservation in some settings.

Water body - Any natural or artificial pond, lake, stream, river, estuary, or ocean that contains permanent, semi-permanent, or intermittent standing or flowing water.

Water budget - 1.The balance of all water moving in and out of a specified area in a specified period. 2. An administratively segregated volume of water reserved for a specific use.

Water yield (water crop or runout) - The runoff from the drainage basin, including ground-water outflow that appears in the stream plus ground-water outflow that bypasses the gaging station and leaves the basin underground. Water yield is the precipitation minus the evapotranspiration. (USGS Langbein)

Water management - Application of practices to obtain added benefits from precipitation, water, or water flow in any of a number of areas, such as irrigation, drainage, wildlife and recreation, water supply, watershed management, and water storage in soil for crop production. Includes irrigation water management and watershed management.

Water quality standard - 1. A plan for water quality management specifying the use of the water (e.g., recreation, fish and wildlife, propagation, drinking water, industrial, or agriculture). 2. Criteria to measure and protect these uses; implementation and enforcement plans. 3. Antidegration statement to protect existing water quality.

Water resources -The supply of groundwater and surface water in a given area.

Water right - A legally protected right to use surface or groundwater for a specified purpose (such as crop irrigation or water supply), in a given manner (such as diversion or storage), and usually within limits of a given period of time (such as June through August). While such rights may include the use of a body of water for navigation, fishing, hunting, and other recreational purposes, the term is usually applied to the right to divert or store water for some out-of-stream purpose or use.

Watershed - The total land area that drains water to a river, stream or lake. Also called catchment area, drainage area, and basin.

Weighted usable area (WUA) -The wetted area of a stream weighted by its suitability for use by aquatic organisms or recreational activity. Units: square feet or square meters, usually per specified length of stream.

Wetted perimeter - The length of the wetted contact between a stream of flowing water and the stream bottom in a plane at right angles to the direction of flow.

Wet year - A water year characterized by above average discharge. Exact measure of deviation from some average, or median value depends on the decision setting.

Withdrawal - Water taken from a surface or groundwater source for off-stream use.