Definition of Terms

There is a lot of technical terms on the Rivers and Streams website. This page is designed to help navigate and define these words and phrases. Use the line below to skip to a certain letter.
not derived from living organisms.
The gradual addition of new land to old by the deposition of sediment carried by water.
An increase in the acidity of an ecosystem, caused by natural processed or acid deposition.
A measure of hydrogen ion concentration with a pH less than 7.0. See pH.
Acid rain:
Rain having a pH of less than 7.0 can be considered acidic and if it has a pH low enough can potential threaten the life or well-being of vegetation or aquatic systems.
To enhance the oxygen concentration of water.
Life processes occurring only in the presence of molecular oxygen.
The geological process in which inorganic materials carried downstream are deposited in streambeds, floodplains, and other water bodies resulting in a rise in bottom elevation. Compare with degradation.
A measure of hydrogen ion concentration with a pH more than 7.0. See pH.
Acid-neutralizing capacity of water usually due to carbonates, bicarbonates, and hydroxides.
Related to material deposited by running water.
A life history strategy of fishes that includes migration between fresh- and saltwater. Reproduction occurs in freshwater while growth occurs in the ocean. Compare with catadromous, diadromous, and potamodromous.
Life processes that occur in the absence of molecular oxygen.
A lack of oxygen.
A term to characterizing growing, living in, frequenting, or pertaining to water.
An underground layer of earth that contains water or allows for its passage.
Microscopic organisms growing on the bottom of other substrates
Bank angle:
Angle formed by the slope of the bank, measured in degrees from the horizontal.
Bank erosion:
Erosion of bank material caused by water current, wave action, or surface erosion.
Bank-full depth:
Depth of water measured from the surface to the channel bottom when the water surface is aligned with the top of the stream bank.
Bank-full discharge:
Maximum streamflow that can be held within the channel without overtopping its banks and spreading onto the floodplain.
Bank-full width:
Distance between the tops of the most prominent banks on either side of a stream channel.
Bank sloughing:
Slumping of saturates, cohesive soils near a water body that cannot freely drainage during rapid drops in water level.
A submerged or exposed accumulation of sand, grave, or other alluvial material formed in a water body along the banks. Common types of bars include alternate, braided, channel junction, delta, diagonal, dune, island, and mid-channel.
Base flow:
Water that percolates into the ground and is conveyed to the stream slowly over long periods of time, thereby sustaining streamflow during periods without rainfall.
Bed load:
Substrate moving on or near a streambed and frequently in contact with it.
Solid rock, underlying surficial deposits or exposed.
Bottom-dwelling organism including plants, invertebrates, and vertebrae animals that inhabit the benthic zone of a water body.
Biological indicies:
A measure of the health or condition of a water body based upon values for a specific biological or physical parameter.
Biological based standards used to assess or regulation water body conditions.
Use of biological characteristics of a water body to assess its health or condition.
A substrate particle larger than 25 cm (10 in) in diameter.
A stream that divides into a network of several branching and reuniting channels separated by bars.
Overhead cover or branches and foliages from adjacent vegetation.
A life history strategy that includes migration between fresh- and saltwater. Fish reproduce and spend their early life in saltwater, migrate into freshwater to grow, and return to saltwater as adults.
The land area above a specific point from which water drains towards a water body.
Catchment area:
The total area draining into a given water body.
A natural or artificial waterway that periodically or continuously contains moving water, has a definite bed, and has banks that confine water at low to moderate streamflow.
Channel bottom:
The submerged portion of the channel cross section.
the mechanical alteration of a stream by deepening or straightening an existing channel or creating a new channel to facilitate water movement.
Channel unit:
Relatively similar areas of a channel that different in depth, velocity, and substrate characteristics from other areas, creating different habitats in a stream. Common types of channel units include: cascade, chute, falls, rapids, riffles, run, glide, and pool.
Stream substrate particles between 64 and 128 mm (2.5-5 in) in diameter.
Gently inclined surface at the base of a slow that represents a transition between landforms. Characterized by erosion, transport and sites of deposition.
A measure of the ability of a solution to carry an electrical current. Dependent on the total concentration of dissolved, ionized substances in an solution.
The location where two streams flow together and form one.
A small lotic system that serves as a natural drainage course for a small basin.
A passage, typically a pipe that is beneath a road or railroad to transport water.
Water moving in one direction and the speed at which it is moving.
An obstruction to the flow of water that increase the water elevation upstream of the barrier.
Process by which streambed and floodplains are lowered in elevation by the removal of materials. Compare with aggradation.
Settling of material from the water column and accumulation on the bottom or stream banks.
Measured distance between stream bed and surface of water
Life history strategy that includes movement between fresh- and saltwater. Two migrations to spend various states in life in different ecosystems. Compare with anadromous, catadromous, and potamodrous.
Microscopic algae that occurs as plankton or attached to the bottom with a skeleton made of silicon.
Rate at which a volume of water flows past a point per unit of time. Usually expressed as cubic meters per second or cubic feet per second.
Dissolved oxygen:
Concentration of oxygen dissolved in water, expressed as milligrams per liter or as a percent of saturation.
A watershed that contains all tributary rivers, streams, ponds, and lakes that drain a given area.
Drainage basin:
The total surface land area drained by a stream or river from its headwater to its mouth. See catchment basin and watershed.
Any complex of living organisms interacting with abiotic components that form and function as a natural environmental unit.
Circular current of water, formed where water flows past some obstruction.
A species that is unique to a locality or drainage.
Combination of biotic, biotic, and climatic conditions that influences an organism, population or community.
Process of weathering away of streambanks and adjacent land slopes by water, ice, wind, or other factors.
Process through which excessive organismal growth, typically algae, is induced by excess nutrient input. Also a natural process of maturing in a body of water.
Particulate matter, less than 2 mm in diameter and includes sand, silt, clay, and fine organic material.
Area adjoining a water body that becomes inundated during periods of overbank flooding and that is given rigorous legal definitions in regulatory programs. The land bordering a stream channel that is formed by alluvial deposition.
The movement of water from one location to another. See discharge.
Study of the origin of landforms, the processes that form them, and their material composition, and functional relationships.
A shallow stream reach with a maximum depth that is 5% or less of the average stream width, a water velocity less than 20 cm/sec, and is without surface turbulence.
Slope, or the change in vertical elevation per unit of horizontal distance, of the water surface in a stream.
Substrate particle size between 2 and 64 mm (0.1 and 2.5 in) in diameter.
Specific type of place within an ecosystem occupied by an organism, population or community that contains both living and nonliving components with specific abiotic and biotic characteristics.
Total concentration of calcium and magnesium ions expressed as mg/L.
Head cut:
Upstream migration or deepening of a stream channel that results from cutting of the streambank by high water velocities.
Headwater stream:
Upper reaches of tributaries in a drainage basin.
A graph showing stage, flow, velocity or other characteristics of water with respect to time at a given point on a stream.
Material through which water cannot pass or passes with great difficulty.
Natural or artificial body of water that is confined by a structure such as a dam to retain water.
Index of biotic integrity (IBI):
A measure of the degree to which aquatic resource quality deviates from what would be expected at an undisturbed location. Calculated based on data from biological communities that measure species composition, trophic position, species abundance, and condition.
Indicator organisms:
Organisms that respond predictably to various environmental changes and whose presence, absence, and abundance are used as indicators of environmental conditions.
Intermittent stream:
A stream that does not have a continuous flow of water throughout the year.
An aquatic system with standing or slow flowing water such as a lake, pond, or swamp.
Physical characteristics of a rock or deposit defined by type or distribution of particle sizes.
An aquatic system with rapidly flowing water such as a stream or river.
An invertebrate animal large enough to be seen without magnification and large enough to be retained by a 0.595 mm screen.
A plant that can by seen without magnification.
Sinuous curves of a river having specific geometric dimensions that describe the degree of curvature.
Specific locations where organisms live that contain combinations of habitat characteristics that directly influence the organism.
Physical attributes of a water body and the methods for measuring those attributes
Native species:
Plant and animal species that naturally occur in aquatic and terrestrial habitats.
Non-point source:
Term applied to pollutants entering a water body in a diffuse pattern rather than from a single location. Includes land runoff, atmospheric deposition, or percolation.
Elements or compound essential for growth, development, and life for organisms such as oxygen, nitrogen, and phosphorus.
Any living thing composed of one or more cells
Bend or meander in a stream that becomes detached from the stream channel over time or because of human intervention.
Pebble count:
Method of measuring the composition of streambed material by manual collection while wading in a stream.
Microflora and fauna attached to the bottom or other submerged objects.
Measure of the rate at which water can penetrate and pass through a medium such as soil.
Perennial stream:
A stream that flows continuously throughout the year.
Measure of the acidity and alkalinity of a solution on a scale of 0 (highly acidic) to 14 (highly basic).
Physiographic province:
A region of which all parts are similar in geological structure and climate, while differing from adjacent regions.
Presence of matter or energy, usually of human origin, whose nature, location, or quantity produces an undesired environmental effect.
Small depression with standing water or an areas of slow water in a stream.
Life cycle strategy of a fish that includes migrations, spawning, and feeding entirely in freshwater. Compare with anadromous, catadromous, and diadromous.
Moderately steep stream area (4-8% gradient) with turbulent water movement and intermittent whitewater.
A specified length of stream. A relatively similar stretch of a stream with a repetitive sequence of physical characteristics and habitat types. A portion of a stream that extends downstream from the confluence of two streams to the next confluence.
A natural or artificial impoundment where water is collected, stored, regulated, and released for human use.
Actions taken to return a habitat, ecosystem, or community to its original condition after damage resulting from a natural or human disturbance.
Shallow reaches with low flow (1-4% gradient) in channels of finer particles, characterized by small hydraulic jumps over rough substrate causing ripples and waves without breaking the surface tension.
Riparian vegetation:
Vegetation growing on or near the banks of a stream or other water body.
Large, natural stream or modified channel that flows in a defined course.
Root wad:
Root mass from a tree.
Irregularity of a substrate surface.
Stream substrate particles between 128 and 256 mm (5-10 in) in diameter. Synonymous with small boulders.
Swiftly flowing stream reach with a gradient less than 4%, little to no surface agitation or turbulence, and approximately uniform flow.
Natural drainage of water away from an area. Precipitation that flows overland before entering a stream channel.
substrate particles between 0.062 and 2 mm (0.00003-0.01 in) in diameter.
Fragmented inorganic and organic material that is suspended in, transported, and deposited by water or air.
Action of forming and depositing sediments.
Fine soil that is between 0.004 and 0.062 mm (0.00002-0.0003 in) in diameter.
Settling of fine suspended sediments in water where velocity is reduced.
Ratio of channel length between two points in a channel to the straight line distance between the same two points.
Elevation of a water surface above or below an established reference point.
Natural water course containing flowing water, at least part of the year, that supports living communities within the channel and riparian area.
Stream order:
Hierarchical ordering of streams based on the degree of branching. For example, a first-order stream is an un-forked stream. Two first-order streams flow together to form a second-order stream, etc.
Stream power:
Stream power is the amount of work performed by the stream flow per unit time, which can be expressed relative to a unit of stream bed area or length of channel. Power is traditionally expressed in watts, which ultimately can be expressed as ML2/T3 , where the dimensions include: M = mass, L = length, T = time.


  1. Stream power per unit area [? a (M /T3 -or- watts/L2)] can be defined as a product of the shear stress [t (M/LT2)] and average velocity [V (L/T)]. That is, ? a = t V.
  2. Stream power per unit length of channel [? l (ML / T3 -or- watts/m)] can be defined as a product of the water density[? (M/L3)], acceleration of gravity [g (L/T2)], discharge [Q (L3/T)], and water surface slope [S(L/L)]. That is, ? l = ? g Q S.
Suspended solids:
particles of unfiltered, undissovled solid matter such as soil that are present in water.
A relatively level bench or step-like surface breaking the continuity of a slope.
Path of a stream that follows the deepest part of the channel.
Capability of an organism to endure to unfavorable environmental conditions.
Stream that flows into or joins a large stream.
Related to the process of energy and nutrient transfer from one level of organisms to another in an ecosystem.
The relative clarity of a water body measured to the extent to which light penetrations in water is reduced by suspended materials.
Speed at which water travels downstream over a given period of time.
Water body:
Any natural or artificial pond, lake, stream, or river that contains permanent, intermittent, standing, or flowing water.
Water quality:
Term used to describe biological, chemical, and physical characteristics of an aquatic environment.
Region or area drained by surface and groundwater flow in rivers, streams, or other channels. Synonymous with drainage basin and catchment.
Term used to describe areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions, including swamps, marshes, bogs, and other similar areas.
Woody debris:
Collection of materials in the water or substrate on the bank or shoreline that is primarily composed of wood.