GLOSSARY / KEY TERMS

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U
V | W | X | Y | Z

Glossary Sources



A


Active Floodplain - The level area adjacent to a stream channel that is subject to frequent overflow.

Adaptive Management of Streams - Adjusting restoration goals, design details, and management of the implementation process as new information becomes available. Adaptive management is an ongoing process of evaluating, planning, implementing, and monitoring. Contrast to boilerplate, cookie-cutter design and management approaches.

Aggradation - The process by which streams and other water bodies are raised in elevation by the deposition of material eroded and transported from other areas. The opposite of Degradation.

Allochthonous Material - Organic material that falls into a stream from the surrounding land.

Alluvial Channel - A channel developed in sediment transported and deposited by the stream.

Alluvium - Sediment transported and deposited by streams.

Angle of Repose - The maximum slope at which unconsolidated material remains stable.

Aquatic Life Use Designation (Source: OEPA) - A designation (classification) assigned to a waterbody based on the potential aquatic community that can realistically be sustained given the regional reference condition and the level of protection afforded by the applicable Biological Criteria. A waterbody that meets all applicable criteria is said to be in Attainment whereas one that does not meet any of the governing criteria is said to be in Non-attainment. The State of Ohio applies a Partial Attainment designation to a waterbody that meets some but not all of the applicable criteria.

Armoring - Natural armoring is the formation of a resistant layer of relatively large particles resulting from removal of finer particles by erosion. Also, this term is used for placement of large rock (i.e., riprap) to protect a stream bank from erosion.

Assimilation - The incorporation (or conversion) of nutrients and contaminants into the ecosystem.

Attainment - Meeting the Biocriteria standards for the designated aquatic life use.

Autochthonoous Material - Organic material produced in the stream usually through primary production.

Avulsion - A rapid change in channel direction when a stream suddenly breaks through its banks, typically bisecting an overextended meander arc (oxbow cutoff).



B


Backwater - Condition in which the water surface elevation is raised by downstream flow impediments.

Backwater Curve - Longitudinal profile of the water surface in a stream where the water surface is raised above its normal level by a natural or artificial obstruction.

Bank - The rising ground bordering a lake or river, or forming the edge of a cut or hollow.

Bankfull (Bankfull Stage/Bankfull Discharge) - A field estimate of the channel-forming flow. This discharge occurs when water just begins to leave the channel and spread onto the floodplain (FIWG, 1998).

Base Flow - The sustained low flow of a stream, usually resulting from groundwater inflow to the stream channel rather than surface water run-off.

Baseline Monitoring - Development of a system for continuous or periodic assessment, and recording of existing conditions that will be compared to future observations.

Basin - See Drainage Basin.

Bed - See Streambed.

Bedload - The amount and size of stream bed material or substrate that is mobilized by tractive and erosive forces, measured or calculated at a specified discharge and is transported by jumping, rolling or sliding on the bed layer of the stream. Contrast to Suspended Load.

Bed Material - The composite mixture of substrate of which a streambed is composed.

Bed Roughness - A measure of the irregularity of the streambed as it contributes to flow resistance. Commonly expressed as a Manning's "n" value.

Bedrock - the solid rock or geologic surface underlying unconsolidated surface materials (e.g., water, soil, alluvium).

Benthic - Of, or associated with, the bottom of a water body.

Benthic Macroinvertebrate - Backboneless aquatic animals that dwell on or in the bottom sediments of a stream channel that are large enough to be seem by the unaided eye.

Benthos (or Benthic Organism) - All plants and animals living on or closely associated with the bottom of a stream channel.

Bioaccumulation - Process in which the level of toxic substances in an organism increase over time due to continued exposure.

Biocriteria (or Biological Criteria) - Water quality criteria based on measurable characteristics or narrative descriptions of aquatic communities.

Bioengineering - The use of living plants to stabilize soil. Restoration and stabilization techniques that use plants to prevent erosion, stabilize slopes or streambanks, or to mimic other natural functions and benefits. Preferably native species.

Biological Diversity - The variety of and variability among living organisms and the ecological systems of which they are part, including diversity among species, the variation within species, and the variety of ecosystem functions they provide.

Biological Integrity (Source: OEPA) - The ability of an aquatic community to support and maintain a structural and functional performance comparable to the natural habits of a region.

Biological Monitoring - Sampling the biota of a place (e.g., stream) repetitively to monitor change over time.

Biological Oxygen Demand (BOD) - The amount of oxygen, typically measured in mg/l, removed from an aquatic environment by the life processes of organisms.

Biomass - The amount of living matter, usually given in weight per unit area of habitat.

Biota - The flora/plants and fauna/animals of an area.

Boundary Layer - The thin layer of the water column immediately above the stream bed where friction virtually stops the current.

Braided Channel - A stream characterized by flow within multiple channels. Braiding often occurs when sediment loading is too large to be carried by a single channel. Also known as an anasmotosed channel.

Bridge Scour - Excessive erosion of the stream banks and bottom below a bridge as a result of the concentration and direction of streamflow.

Bridge Scour Depth - The calculated depth at which the streambed and substrate will mobilize and be transported during channel forming flows. Used to determine the safe depth at which to place footings and stable keyways in streambeds that will not erode or be undermined.

Buffer Zone/Buffer Strip - An area of permanent vegetation between waterways and adjoining land uses designed to intercept and filter out pollution before it reaches the surface water resource. Typically, activities such as agriculture or construction are restricted in these areas to protect water quality.



C


Catchment - Another term for Watershed commonly used in Canada and Europe.

Channel - An area containing continuously or periodically flowing water that is confined by banks and a streambed.

Channel Cross-section - The physical measurements (width and depth) across the channel and floodplain.

Channel Dimension - See Channel Cross-section.

Channel Forming Flow - See Dominant Discharge

Channel Migration - Lateral or longitudinal (down-valley) migration of the stream channel within the valley by the process of erosion and deposition.

Channel Pattern - The meander geometry of the channel within its active floodplain, readily visible from a top-down view of the channel.

Channel Profile (or longitudinal profile) - The plot of the stream bottom elevation (and often the water surface, bankfull and valley elevations) longitudinally along the stream. The change in bottom elevation over distance is called Channel Gradient.

Channel Scour - The erosive action of water and sediment that removes and carries away bed and bank material.

Channel Slope (or Channel Gradient) - The inclination of the channel bottom, measured as the elevation drop per unit length of channel.

Channel Storage - Simply water storage within the banks of the channel.

Channelization - The process of modifying - usually through straightening or deepening - the natural course of a waterway to accelerate conveyance or increase drainage of wet areas. Often referred to as hydromodification.

Clarity - The observed clearness of the water.

Combined Sewer Overflow - An outlet for stormwater and untreated sewage during large rainfall or runoff events.

Community - All the living organisms present in an ecosystem. All the groups of organisms living together in the same area, usually interacting or depending on each other for existence.

Conductivity - A measure of the amount of salts dissolved in water.

Confluence - The meeting or junction of two or more streams.

Contaminant - An undesirable substance not normally present or an unusually high concentration of a naturally occurring substance. Any physical, chemical, biological or radiological substance that has an adverse impact on the air, water or soil.

Conveyance - Continuous transport of water.

Critical Flow - The flow regime at a given discharge for which the specific energy (i.e., combination of velocity energy and depth) are a minimum (Froude number = 1). At depths greater than the critical flow depth, the flow is considered to be tranquil or subcritical. At depths less than the critical flow depth, flow is considered to be rapid or supercritical.

Critical Habitat - Areas containing physical and biological features essential to the conservation of a species, and that may require special management considerations or protections.

Critical Shear Stress - The minimum amount of shear stress required to initiate substrate particle motion along the stream bed or banks.

Cross-sectional Area - The area of cross-section below the water surface perpendicular to the direction of flow.

Cumulative Impact - The collective impact on the environment of all past, present and future human activities including farming, development, recreation, water diversions, point source and non-point source discharges. Oftentimes, impacts that are individually minor are significant when viewed collectively.

Cut Bank - The outside, often eroding, bank on a channel bend. Typically opposite a Point Bar.



D


Degradation - The process by which streambeds and floodplains are lowered in elevation by the erosion of material. The opposite of Aggradation. Often an indicator that the stream's discharge or sediment load is changing. Also referred to as downcutting.

Deposition - Accumulation of sediment on the channel bed or banks.

Depth of Flow - The height of the water surface above the streambed.

Designated Use - Classification designated in water quality standards for each water body or segment that defines the optimal purpose for that water body.

Detention - Water management practice or system that delays the downstream progress of stormwater by the use of temporary storage or metered outlets.

Detritus - Decaying organic matter found on the bottom of a stream or lake, or in the top soil layer.

Discharge - Volume of water flowing past a given point in a stream per unit time, typically reported in cubic feet per second.

Dissolved Oxygen (DO) - The amount of free oxygen (i.e., not chemically combined) in water or wastewater, typically expressed in milligrams per liter, ppm, or percent saturation. Dissolved oxygen is necessary for aquatic life and oxidation of organic materials.

Dominant Discharge - A channel forming discharge that, if maintained indefinitely, would produce the same channel geometry as the natural long-term hydrograph. The dominant discharge concept is applicable to stable, alluvial streams (i.e., streams that have the ability to change their shape but are neither aggrading nor degrading).

Drainage Area - The total surface area that drains to a point of interest, typically reported in acres (small watersheds) or square miles.

Drainage Basin - The area drained by a river and its tributaries. Also, an area that drains to a common outlet. Can be from a few square feet to thousands of square miles. Drainage Basin is equivalent to Watershed.

Dynamic Equilibrium - The state at which the channel exhibits patterns of erosion and deposition but there is not net change in the input and output of materials. Considered stable, but over time the features and location of the channel within the valley will change.



E


Ecological Indicator - An attribute of an ecosystem whose presence or absence, quantity, level, pattern, or etc. is used to measure the health or integrity of the ecosystem.

Ecoregion - A region defined by similarity of climate, landform, soil, natural vegetation, hydrology or other relevant variables.

Ecosystem Restoration - Restoration of all or part of the functions and structures of a previously degraded ecosystem.

Eddy - A circular current or a current of water running contrary to the main current, usually resulting from an obstruction.

Effective Discharge - The discharge that transports the largest fraction of the annual sediment load. The effective discharge results in the average morphologic characteristics of a channel and at which channel maintenance is the most effective.

Embeddedness - The degree to which the coarse channel bed materials (boulders, cobble, gravel, sand) are surrounded or covered by fine sediments, usually measured as percent coverage by finer sediments.

Entrenched Channel - A channel that has eroded downward or was constructed such that it no longer has access to its original floodplain during moderate flow events.

Entrenchment Ratio - The ratio between the flood-prone width and the bankfull width.

Environmental Indicator (Source: OEPA) - A measurable feature which singly or in combination provides managerially and scientifically useful evidence of ecosystem quality, or reliable evidence of trends in quality.

Ephemeral Stream - A water course that is usually dry but sporadically contains stream flow, typically during significant rain or snowmelt events.

Erosion - The wearing away of rock or soil by the action of water, wind, ice or other mechanical or biological forces.

Extirpated - Describes a local population of a species that has been eliminated because of loss of habitat, a catastrophic event, or chronic impairment, but still can be found in another location.



F


Fill - Soil or other material placed as part of a construction activity. Often used to raise the ground level of a floodplain or wetland to make it suitable for construction or other human activities.

Flash Flood - A flood that crests in a short length of time and is often characterized by high velocity flows.

Flashiness - Term that describes the degree to which a watershed is able to attenuate the intensity of stormflows through infiltration, retention, detention, … A "flashy" watershed has a high degree of impervious surface resulting in fast, intense flood peaks.

Flood - The temporary inundation of normally dry land areas resulting from the overflowing of the natural or artificial confines of the stream channel.

Flood Attenuation - To lessen the amount, force or severity of high flows.

Flood Peak - The highest value of stage or discharge achieved by a flood. Flood crest is equivalent to peak stage.

Flood Routing - The process of determining progressively the flood elevation (or flood "wave") at successive points along a stream.

Flood Stage - The gage height at which the stream begins to overflow its banks.

Floodplain - According to Leopold (1994), a floodplain "is a level area near a river channel, constructed by the river in the present climate and overflowed during moderate flow events."

Floodplain Bench - A small level area that forms at the effective discharge stage within an over-wide, entrenched channel.

Flood-Prone Area - A term coined by Rosgen (1996) to describe the area flooded at flows twice the maximum depth of flow at the effective discharge.

Floodway - The stream channel and those parts of the floodplain adjoining the channel that are required to carry and discharge the floodwaters or flood flow of the stream.

Flow Attenuation - See Flood Attenuation.

Fluvial - Relating to a stream or river; produced by stream action.

Forb - A non-grass herbaceous plant.

Froude Number - Dimensionless number expressing the ratio of inertial force to gravity force in a fluid.

Function - The physical, chemical and biological processes, services and values that occur in an ecosystem (e.g., floodplain, stream, wetland) as a result of their structure and composition.



G


Gaging Station - A particular point on a stream of known cross-section where systematic observations of water depth or discharge are obtained.

Gaining Stream - A stream or reach of stream whose flow is being increased due to an inflow of ground water.

Geologic Control - A local rock formation or clay layer that limits the vertical or lateral movement of a stream at a particular point.

Geomorphology - The branch of geology that studies the nature and origin of land forms. The natural forces that shape landforms include water, ice, wind, gravity and time. Fluvial geomorphology is the study of the formation of landforms by the action of flowing water.

Glide - Shallow, low gradient stream sections with slow current and fine substrate.

Grading - Term used to denote the variability and distribution of sediments and bed materials. A well-graded material will be sorted by size. A poorly-graded material will consist of a single sediment size or all size materials uniformly mixed.

Gradient - The rate of change in (vertical) elevation per unit of horizontal distance.



H


Habitat - Those parts of the environment on which particular plants or animals depend, directly or indirectly in order to carry out their life processes (modified from Newbury and Gaboury, 1993). That provide provisions for life.

Headcutting - The process by which the stream is actively eroding the streambed downward (degrading, incising, downcutting) to a new base level. Because of the resultant high gradient change, this erosional action progresses upstream. Often suggests adjustment to changing stream hydrology or sediment load.

Headwater Stream - Stream with a small drainage area (Ohio EPA defines as streams with drainage area < 10 mi2).

Healthy System (Source: OEPA) - Ecological systems that support numerous and complex processes, produce desirable biomass and exhibit other attributes such as high diversity and sensitive organisms.

Hester-Dendy - The Hester-Dendy is a standardized multiple-plate, artificial substrate sampler used to measure macroinvertebrate populations in streams.

Heterogeneity - Diversity. In an ecosystem context, composed of varied components, functions or organisms. Depth or flow heterogeneity describes the variability and diversity of the channel that provides required habitat for a diversity of organisms.

Hydraulic Gradient - The change in hydraulic head over some specified distance.

Hydraulic Jump - Abrubt, turbulent, noisy transition from super-critical flow to sub-critical flow. Entrains air into the stream.

Hydraulic Radius - Corss-sectional area divided by the wetted perimeter.

Hydraulics - The study of the properties, movement and behavior of water flowing in open channels or pipes.

Hydric Soils - Soils that are ponded, flooded, or saturated long enough during the growing season to develop anaerobic conditions.

Hydrograph - A graph showing flow, stage, velocity or discharge with respect to time, for a given point in the stream.

Hydrologic Cycle - The constant circulation of water from the sea to the atmosphere, to the land and back to the sea by surface, underground and atmospheric pathways.

Hydrology - The study of the properties, movement and behavior of water on the land surface and under ground.

Hyporheic Zone - Zone of substrate in a stream bottom extending 1 to 2 meters below the surface of the stream bed.



I


Impairment - Impact that damages the biological integrity of a water body such that attainment of the designated use is prevented.

Impervious Surface - Surfaces, such as roads, parking lots and roofs, whose properties prevent the infiltration of water and increase the amount of stormwater runoff in a watershed.

Impoundment - A body of water, such as a pond, lake or reservoir, formed by confining a stream or other surface flow.

Incised Channel - A stream that, through degradation, has cut its channel into the bed of the stream valley.

Index of Biotic Integrity (IBI) - A combination of 10 metrics collectively used to describe the health (production, function, tolerance, and reproduction) of the fish community in a stream.

Infiltration - The downward movement of water through soil or porous rock.

Intermittent Stream - A stream that flows periodically or seasonally, and is dry part of the year.

Interstitial Flow - Water flow through bed (i.e., riffle) and bar materials.

Invertebrate Community Index (ICI) - A combination of 12 metrics collectively used to describe the health (production, function, tolerance, and reproduction) of the macroinvertebrate community in a stream.



J



K



L


Laminar Flow - Streamline or parallel flow near a solid boundary. Contrast to turbulent flow.

Losing Stream - A stream or reach of stream from which some water flows from the stream bed into the ground.



M


Macroinvertebrates - Stream-dwelling arthropods (insects, crustaceans) without a backbone that can be viewed without magnification. Examples include crayfish, leeches, water beetles and the larva of dragonflies, caddisflies, and mayflies. Macroinvertebrates are an important food source for many species of fish.

Manning's "n" - Manning's n-value is a coefficient used to describe boundary roughness of a channel or pipe. "n" incorporates the roughness of the bed material, vegetation, bends, junctions and other irregularities.

Mass Wasting - Large slope failures associated with downcutting stream channels and undermined support of steep slopes. Contrast to Rotational Failure (global) or Bank Erosion.

Meander - Bend or curve in a stream channel.

Meander Belt - The area between lines drawn tangential to the extreme limits of fully developed meanders. The meander beltwidth is the distance between the tangential lines marking the extremes of successive meanders, measured normal to the downvalley progression of the stream. Meander length is the distance between corresponding points in two successive meanders, or twice the distance between crossover or inflection points.

Meandering Stream - A stream characterized by a clearly repeated pattern of meanders as seen from above.

Metric (Source: OEPA) - A characteristic of the biota that changes in some predictable way with increased human influence.

Mitigation - To alleviate, or compensate for, the impact of environmental degradation, often through replacement of lost ecological functions or values at a nearby location.

Most Probable Form - The form toward which the channel tends given the local parameters such as discharge, sediment load, sediment type and slope.

Multi-disciplinary Approach - An approach that utilizes the skills, knowledge and experience of professionals from several fields to develop a more holistic understanding and treatment of the components, issues, problems and variables of a project.



N


Native Vegetation - Vegetation indigenous to an area and adapted to local conditions.

Nick Point - A usually less erosive material, such as bedrock or a fallen log, that tends to slow the downward erosion of the stream channel and the upstream migration of a headcut.

Non-Point Source - Extensive or disperse source of pollution. Examples include agriculture, lawns, parking lots and septic systems.



O


Overbank - Water flow over the top of bank.

Oxbow - A cut off and abandoned meander of a river.



P


Particle Size Distribution - See Substrate Analysis.

Peak Flow - The highest discharge achieved during a storm event.

Pebble Count - Method for determination of the size distribution of channel bed materials.

Perennial Stream - A stream that normally contains flowing water at all times.

Planform - The shape of an object as viewed from above. Stream planform can be developed from aerial photographs.

Point Bar - An accumulation of alluvium - usually sand or gravel - caused by a decrease in sediment transport capacity on the inside of a meander bend.

Point Source - Source of pollution from a single, well-defined outlet. Examples include wastewater treatment outfalls, combined sewer overflows, and industrial discharge pipes.

Pool - A deep, usually wide, section of stream with slow currents at low flow. Usually occurs between two riffles. Natural streams often consist of a succession of pools and riffles.

Population - The total number of a single species (i.e., group of interbreeding organisms) inhabiting a particular locality.



Q



R


Radius of Curvature - The radius of the circular arc that best describes the outside bend of a stream meander.

Rating Curve - See Stage-Discharge Relationship.

Reach - A length of channel uniform with respect to discharge, area and slope. More generally, any length of a stream.

Recession Curve - That part of a hydrograph after the flow peak showing decreasing runoff or discharge following a period of rain or snowmelt.

Recharge - The process by which rain, snowmelt or surface water infiltrates and replenishes ground water reserves.

Recurrence Interval - The interval of time, on average, between occurrences of a hydrologic event of a certain magnitude.

Redd - Shallow depression in the streambed gravel in which a female salmonid (e.g., trout) deposits her eggs. More generally, the spawning ground or nest of various fishes.

Reference Site/Reach - A minimally impaired site that is representative of the expected or desired ecological conditions and integrity of other sites in the region.

Refugia - Places of shelter from danger or pursuit

Regulatory Floodplain - Floodplain defined for some regulatory purpose, e.g., for flood insurance. Often reflects the estimated extent of some extreme flood event, e.g., the 100-year flood.

Rehabilitation - To restore to a former state or capacity. To restore to a condition of health.

Restoration - Bring back to a former, natural condition. Alternately, the recovery of biological and hydraulic function such that the biological integrity and health of an ecosystem can be self-sustained over time.

Return Period - See Recurrence Interval.

Revetment - A facing of stone, rootwads, cut trees, or other durable material used to protect a streambank against erosion.

Reynold's Number - Dimensionless ratio of inertial force to viscous force used to describe the characteristics of fluid flow in a channel or pipe. The critical Reynolds number occurs at the point between laminar and turbulent flow.

Riffle - Shallow, steeper, section of stream with fast currents at low flow. Sometimes called a rapid. Where most invertebrates will be found. Termed "the larder of the lotic environment".

Riparian - Related to the banks or floodplain area of a natural watercourse.

Riparian Buffer - An undisturbed, vegetated strip of land adjacent to a water course.

Riparian Corridor/zone - Area adjacent to a river or stream. "Those areas that are saturated by ground water or intermittently inundated by surface water at a frequency and duration sufficient to support the prevalence of vegetation typically adapted for life in saturated soils." (Beschta 1991)

Riverine - Relating to rivers or streams.

Run - Shallow stream section with moderate currents.

Runoff - That portion of rainfall or snowmelt that moves across the land surface into streams and lakes.



S


Sandbar - An accumulation of alluvium - usually sand or gravel - caused by a decrease in sediment transport capacity in an overwide channel.

Scour Pool - An area of deeper water created by the scouring action of water. These generally occur downstream of obstructions or along the outside of a meander bend.

Sediment - Soil particles (sand, silt, clay) that have been transported away from their previous location by the action of water.

Sedimentation (Siltation) - The deposition of sediment.

Sediment Yield (Sediment Discharge) - The total sediment (i.e., bed load and suspended sediment load) outflow from a drainage basin in a specific period of time.

Shear Stress (Shear Velocity/Shear Force) - Force applied parallel to (rather than normal to) a surface. The tractive force that removes material from a streambank as flow moves over the surface.

Sinuosity - The relative curviness of a stream channel. Quantified as the total stream length divided by valley length.

Sorting/Bed Sorting - Natural separation of stream bed substrate into different size classes due to variability in flow velocities and the differential depositional characteristics of those bed materials.

Spawning - The production and/or deposition of eggs by a fish or other aquatic animal.

Spoil - Dirt or rock that has been removed from its original location.

Stable Channel - State in which a stream develops a stable dimension, pattern and profile such that, over time, channel features are maintained and the stream system neither aggrades nor degrades (Rosgen, 1996)

Stage - The height of water above an established datum. Stream depth at a given discharge.

Stage-Discharge Relationship/Curve - A graph showing the relation between gage height (or stage) and the amount of water flowing in the channel.

Stratigraphy - The arrangement of strata or geologic layers. Also, the branch of geology that studies the origin, composition and distribution of strata.

Streambank - The side slopes of a channel between which the streamflow is normally confined.

Stream Gage - A device used to measure the water surface elevation in relation to an established datum.

Stream Morphology - The form (dimension, pattern and profile) and structure of the stream channel.

Stream Order - A method for classifying streams as part of a drainage network. The smallest unbranched mapped tributary is classified as first order, the stream receiving the tributary is classified as second order and so on. Streams that have no branches or tributaries are first order. Streams that receive only first order streams are second order. Streams that receive only first and second order streams are third order. The mainstem always has the highest order.

Stream Power - Measure of energy available to move sediment, or any other particle in a stream channel. It is affected by discharge and slope.

Stream Profile (or Longitudinal Profile) - A graph of elevation vs distance along a stream channel. At a minimum, should include channel invert and water surface. Can also include bankfull, floodplain or terrace elevations.

Stream Stability (Source: Rosgen, 1996) - A stream is stable when it maintains its dimension, pattern and profile such that, over time, channel features are maintained and the stream system neither aggrades nor degrades.

Sub-critical Flow - Relatively tranquil flow that occurs at depths greater than the critical flow depth (Froude number < 1)

Substrate - Channel bed materials (silt, sand, gravel, cobble, boulders, organic debris,)

Substrate Analysis - Any test utilized to determine the size or size distribution of substrate, e.g., core analysis, sieve analysis or pebble count. A Particle Size Distribution is a plot showing the cumulative percent of substrate smaller than a given particle diameter. The percent smaller than a given diameter is denoted by a "D". For example, the median particle diameter, or D50, is larger than 50 percent of channel material as determined by a substrate analysis. Other substrate size indices, such as the D84 (i.e., the particle diameter larger than 84 percent of channel material as determined by a substrate analysis) are often used as indicators of stream power and the ability of the stream to mobilize that particle size during a given discharge event.

Supercritical Flow - Relatively rapid flow that occurs at depths smaller than the critical flow depth (Froude number > 1).

Suspended Sediment/Suspended Sediment Load - The soil particles lifted into and transported within the streamflow. Contrast to Bedload.



T


Terrace (or Floodplain Terrace or Low Terrace) - A relatively flat surface in a valley, at some elevation above the existing floodplain, representing a previous, abandoned floodplain of the stream.

Thalweg - The path connecting the deepest points along a stream channel.

Time of Concentration - The time required for water to flow from the farthest point in the watershed to the gaging station.

Total Maximum Daily Load (TMDL) - An estimate of the total quantity of pollutants from all sources (point, non-point, natural) that may be allowed into waters without exceeding applicable water quality standards.

Tractive Force - The drag or shear stress on a stream bank or stream bed caused by passing water which tends to pull soil particles along with the stream flow.

Transport Capacity - The ability of a stream, for a given flow condition, to transport a volume (or weight) of sediment material of a specific size per unit time.

Tributary - A stream that contributes its water to another stream or body of water.

Turbidity - Cloudiness caused by the presence of suspended sediments in water, typically measured with a Secchi disk or turbidity tube.

Turbulent Flow - Fluid flow in which the velocity at any point varies erratically in magnitude and direction. Contrast to laminar flow.

Two-Stage Channel - A ditch or channel with a second well-defined channel within the larger channel. In a two-stage channel, a floodplain bench forms (or is constructed) at the effective discharge stage.



U


Undercutting - The process by which the lower portion or "toe" of the streambank is eaten away by erosion leaving a concave, overhanging section of stream bank. Often occurs on banks at the outside of stream bends.



V


Vanes - An artificial structure used to direct flows in a stream.

Velocity - The speed at which water is flowing, typically reported in feet per second. Mean Velocity is the speed of flowing water integrated over the entire channel cross-section.

Vortex (pl: vortices) - A mass of fluid with a whirling or circular motion that tends to form a cavity in the center of the circle and that draws materials toward its center. An eddy or whirlpool.



W


Water Quality - A term used to describe the physical, chemical and biological characteristics of water with respect to its suitability for a particular use.

Watershed - Area that drains to a common outlet. For a river or stream, it is all the land that drains to it or its tributaries. Variously called Basin, Drainage Basin or Catchment. A Sub-basin or Subwatershed is a discriminate drainage basin within a larger watershed, typically defined for planning or modeling purposes. The size of a watershed is termed its Drainage Area.

Watershed Function - Any of the many services provided by landscape elements (soil, floodplain, riparian corridor, stream channel) within a watershed. Watershed functions include: collection, storage and conveyance of water; flow attenuation (i.e., flood control); sediment management; chemical (nutrient and pollutant) filtering, transformation and assimilation; and biological habitat. Collectively, the degree of performance of the above named functions.

Weir - An artificial structure to construct water levels in a stream.

Wetted Perimeter - The boundary of wetted contact between a stream of flowing water and its containing channel at a given discharge, measured in a direction perpendicular to the flow.

Woody Debris - Any large, relatively stable woody material that intrudes into the stream channel.



X



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Sources


Sources include:

1. Federal Interagency Stream Restoration Working Group. 1998. Stream Corridor Restoration: Principles, Processes, and Practices.

2. Fischenich, C. 2000. Glossary of Stream Restoration Terms. U.S. Army Corps of Engineers, ERDC TN-EMRRP-SR-01, Vicksburg, MS.

3. Langbein, W.B. and K.T. Iseri. 1995. Manual of Hydrology: Part 1. General Surface-Water Techniques. USGS Water Supply Paper 1541-A, html version - http://water.usgs.gov/wsc/glossary.html

4. Leopold, L. 1994. A View of the River. Harvard University Press, Cambridge, MA.

5. Newbury, R.W. and M.N. Gaboury. 1993. Stream Analysis and Fish Habitat Design: A Field Manual. Newbury Hydraulics Ltd., Gibsons, British Columbia, Canada.

6. Ohio EPA. 1988a. Biological Criteria for Protection of Aquatic Life, Volume I: The Role of Biological Data in Water Quality Assessment. Ohio EPA, Columbus, OH.

7. Rosgen, D. 1996. Applied River Morphology. Wildlands Hydrology, Pagosa Springs, CO.

8. U.S. Army Corps of Engineers. 1993. EM 1110-2-1416.

9. Webster's New Collegiate Dictionary. G & C Merriam Co., Springfield, MA.

10. Wetland and Watershed Protection Tool Kit - http://www.aswm.org/lwp/nys/glossary.htm

11. Yoder, C.O. and E.T. Rankin. 1998. The role of biological indicators in a state water quality management process. Environmental Monitoring and Assessment 51: 61-88.



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