Glossary of Stream Terms
NOTE: Italicized words within a definition are defined elsewhere within this glossary.
aggradation (aggrading) – A progressive build-up or raising of the channel bed and floodplain due to sediment deposition. The geologic process by which streambeds are raised in elevation and floodplains are formed. Aggradation indicates that stream discharge and/or bedload characteristics are changing.
aquatic habitat – Physical attributes of the stream channel and riparian areathat are important to the health of all or some life stages of fish, aquatic insects and other stream organisms. Attributes include water quality (temperature, pH), riparian vegetation characteristics (shade, cover, density, species), stream bed sediment characteristics, and pool/riffle spacing.
bankfull depth – The depth from the elevation of water surface at the bankfull discharge to the deepest point in the channel.
bankfull discharge – The discharge (or flow) that occurs, on average, every 1.2 to 2.0 years. This discharge, from relatively frequent storms, is largely responsible for the shape of the stream channel within the floodplain.
bankfull width – The width of the water surface at the bankfull discharge.
base flood elevation – The height of the base flood, usually in feet, in relation to the National Geodetic Vertical Datum of 1929, the North American Vertical Datum of 1988, or other datum referenced in the Flood Insurance Study report, or average depth of the base flood, above the ground surface.
bedload – Sediment moving on or near the streambed and transported by jumping, rolling or sliding on the bed layer of a stream.
berm – A mound of earth or other materials, usually linear, constructed along streams, roads, embankments or other areas. Berms are often constructed to protect land from flooding or eroding, or to control water drainage (as along a road-side ditch). Some berms are constructed as a byproduct of a stream management practice whereby stream bed sediment is pushed out of the channel and mounded on (and along the length of) the stream bank - these berms may or may not be constructed for flood control purposes; some are simply piles of excess material. These berms often interfere with other stream processes such as floodplain function, and can exacerbate flood-related erosion or stream instability.
boulder – In the context of stream assessment surveys, a boulder is stream sediment that measures between 256 mm and 4096 mm (about 10 inches to 13.3 feet).
braided – A stream form in which the channel splits into 3 or more separate sub-channels, often crisscrossing to produce a “braided” pattern of connected channel with large or small islands between them. Islands formed between the channels can be either bare gravel or cobble materials, or contain mature forest vegetation.
channel-forming flow – see bankfull discharge
clay – Clay is the smallest sediment size present in a stream, measuring less than 0.0039mm in size. Clay can be identified by its smooth and slippery texture. Clay deposits can be seen in sections of the stream, and can produce turbidity in stream water when it is disturbed either during floods or by activity in the stream.
cobble – In the context of stream assessment surveys, cobble material is sediment that measures between 64 mm and 256 mm (about 2.5 inches to 10 inches).
cohesive - Soil types such as clays and silts that are held together owning to attraction between like molecules.
confluence – The location of the joining of two separate streams, each with its own watershed.
cross-section (see also monitoring cross-section) – In the context of stream assessment surveys, a cross-section is a location on a stream channel where stream morphology is measured perpendicular to the stream flow direction (as if taking a slice through the stream), including width, depth, height of banks and/or terraces, and area of flow.
culvert – A closed conduit for the free passage of surface drainage water (Lo, 1992). Culverts are typically used by the Town and County to control water running along and under the road, and to provide a crossing point for water from road side drainage ditches to the stream, as well as for routing tributary streams under the roads. Culverts are also used by landowners to route roadside drainage ditch water under their driveways to reduce or prevent erosion.
degradation (degrading) – The process by which a stream reach or channel becomes deeper by eroding downward into its bed over time, also called “downcutting”, either by periodic episodes of bed scouring without filling, or by longer term transport of sediment out of a reach without replacement.
demonstration stream restoration project, (demonstration project) – A stream(stability) restoration project that is designed and located to maximize opportunities for monitoring of project success, public and agency education about different stream restoration techniques, and interagency partnerships for funding and cooperation.
discharge (stream flow) – The amount of water flowing in a stream, measured as a volume per unit time, usually cubic feet per second (cfs).
embankment – A linear structure, usually of earth or gravel, constructed so as to extend above the natural ground surface (Lo, 1992). Similar to a berm, but usually associated with road fill areas, and extending up the hillside from the road, or from the stream up to the road surface.
entrenched – In stream classification (see stream type), entrenchment (or entrenchment ratio) is defined by stream cross-sectional shape in relation to its floodplain and valley shape, and has a specific numerical value that in part determines stream type. For example, if this number is less than 1.4, the stream is said to be highly entrenched, if between 1.4 and 2.2 it is mildly entrenched, and greater than 2.2 it is not entrenched. Entrenchment ratio is used with other stream shape data to determine stream type, and define baseline data for future monitoring (Rosgen, 1996).
equilibrium (see also Astable @) – The degree to which a stream has achieved a balance in transporting its water and sediment loads over time without aggrading (building up), degrading (cutting down), or migrating laterally (eroding its banks and changing course).
erosion BThe wearing away, detachment, and movement of the land surface (sediment), by running water, wind, ice, or other geological agents, including such processes as gravitational creep or slumping (New York Guidelines for Urban Erosion and Sediment Control, 1972). In streams, erosion is a natural process, but can be accelerated by poor stream management practices.
exotic plant – see invasive plants
floodplain BThe portion of a river valley, adjacent to river channel, which is covered with water when river overflows its banks at flood stage. The floodplain usually consists of sediment deposited by the stream, in addition to riparian vegetation (Rosgen, 1996). The floodplain acts to reduce the velocity of floodwaters, increase infiltration (water sinking into the ground rather than running straight to the stream - this reduces the height of the flood for downstream areas), reduce stream bank erosion and encourage deposition of sediment. Vegetation on floodplains greatly improves their functions.
Geographic Information System (GIS) BDesktop software with a graphical user interface that allows loading and querying, analysis and presentation of spatial and tabular data that can be displayed as maps, tables and charts (ArcView GIS, 1996). The maps in the East Branch Delaware River Stream Corridor Management Plan were produced with GIS, and can be updated as new information becomes available.
Global Positioning System (GPS) B A satellite B based positioning system operated by the U.S. Department of Defense (DoD). When fully deployed, GPS will provide all-weather, worldwide, 24-hour position and time information (GPS Pathfinder Office: Getting Started Guide, 1999). The stream assessment survey done for the East Branch Delaware River Stream Corridor Management Plan included the use of a GPS unit to document the locations of all mapped stream features. This information was added to the GIS to produce the maps.
gravel – In the context of stream assessment survey, gravel is sediment that measures between 2 mm and 64 mm (about 0.08 inches to 2.5 inches).
head-cut – A marked change in stream bed slope, as in a A step @ or waterfall, that is unprotected or of greater height than the stream can maintain. This location also referred to as a A knick point @ , moves upstream, eventually reaching an equilibrium slope.
imbricate - Having the edges of bed material overlapping in a regular arrangement like roof tiles or the scales of a fish. Rocks in a riverbed often end up leaning on each other, their tips pointing downstream in an imbricated pattern.
instability (see also A unstable @ ) B An imbalance in a stream = s capacity to transport sediment and maintain its channel shape, pattern and profile.
incised – Erosion of the channel by the process of degradation to a lower base level than existed previously or is consistent with the current hydrology.
invasive plants – Non-native species that are able to compete with and replace native species in natural habitats, also referred to as Aexotic @ plants.
Japanese Knotweed (see also invasive plants) – An invasiveplant, not native to the Catskill region, that colonizes disturbed or wet areas, especially stream banks, road-side ditches and floodplains. This plant out-competes natives and other beneficial plants, and may contribute to unstable stream conditions.
left bank – The left stream bank as looking or navigating downstream. This is a standard used in stream assessment surveys.
matrix – The framework material within which other materials are lodged or included. For example, cobbles could be embedded in a matrix of sand and fine gravel.
meander – Refers both to a location on a stream channel that is curved (a “meander bend”), and to the process by which a stream curves as it passes through the landscape (a “meandering stream”).
monitoring – The practice of taking similar measurements at the same site, or under the same conditions, to document changes over time.
monitoring cross-section – For the purposes of the East Branch Delaware River Stream Corridor Management Plan, this is a location where metal rebar rods have been used to permanently locate an actively eroding stream bank. At this site, detailed data have been gathered to document the stream condition. The site ispermanently marked to enable future measurements that, when compared to the existing condition, provide information about the stream’s change. Measuring change over time is considered ‘monitoring,’ and this information provides early warning to stream managers about important but perhaps visually imperceptible changes in the stream.
monumented – Refers to a location, usually a cross-section, that is marked with a permanent or semi-permanent marker, or “monument”, to enable future monitoring at the same place.
morphology, stream morphology – The physical shape, or form, of a landscape or stream channel, that can be measured and used to analyze stream or landscape condition, type or behavior.
morphometry - The quantitative measurement of the form especially of living systems, such as watershed and its stream network.
nutrient – The term "nutrients" refers broadly to those chemical elements essential to life on earth, but more specifically to nitrogen and phosphorus in a water pollution context. In a water quality sense nutrients really deals with those elements that are necessary for plant growth, but are likely to be limiting -- that is, where used up or absent, plant growth stops.
physiography – The physical features of the earth’s surface, including landforms, currents of the atmosphere and climate, ocean and distribution of flora and fauna or the general “look” of the land.
planform – The general shape and layout of the river as viewed from above.
pool – A small section of stream characterized by having a flat or nearly flat water surface compared to the average reach slope (at low flow), and deep and often asymmetrical cross-sectional shape.
reach – A section of stream with consistent or distinctive morphological characteristics (New York Guidelines for Urban Erosion and Sediment Control, 1972).
reference reach, stable reference reach – A stable portion of a stream that is used to model restoration on an unstable portion of stream. Stream morphology in the reference reach is documented in detail, and that morphology is used as a blueprint for design of a stream stability restoration project.
revetment – Any structural measure undertaken to stabilize a road embankment, stream bank or hillside.
riffle – A small section of stream characterized by having a steep water surface slope compared to the average reach slope (at low flow), and a shallow and often uniform cross-sectional shape.
right bank – The right stream bank as looking or navigating downstream. This is a standard used in stream assessment surveys.
riparian (area, buffer, vegetation, zone) – The area of land along stream channels, within the valley walls, where vegetation and other land uses directly influence stream processes, including flooding behavior, erosion, aquatic habitat condition, and certain water quality parameters.
rip-rap – Broken rock, cobbles, or boulders placed on earth surfaces, such as a road embankment or the bank of a stream, for protection against the action of water; materials used for soil erosion control (New York Guidelines for Urban Erosion and Sediment Control, 1972).
rotational failure (translational failure) – A geotechnical term referring to the shape and mechanism of a hillslope failure that results in a section of land surface that falls, or “fails”, by rotating out of place along a curved plane surface (as opposed to sliding along a straight line or flat plane surface). This type of failure is common in the East Branch Delaware River valley, easily recognized by “back leaning” trees on displaced sections of the slope, separated by fault scarps (cracks in the ground surface perpendicular to the failure direction, also often curved) as these blocks of land rotate downward and outward.
runoff – The portion of precipitation (i.e., rainfall) that reaches the stream channel over the land surface.
sand – In the context of stream assessment surveys, sand material is sediment that measures between 0.063 mm and 2 mm (up to 0.08 inches).
sediment, stream bed sediment – Material such as clay, sand, gravel and cobble that is transported by water from the place of origin (stream banks or hillsides) to the place of deposition (in the stream bed or on the floodplain) (Lo, 1992).
sediment discharge – The combination of washload plus bedload material.
silt – In the context of stream assessment surveys, silt material is sediment that measures between 0.0039 mm and 0.063 mm.
sinuosity – The ratio of channel length to direct down-valley distance. Also may be expressed as the ratio of down-valley slope to channel slope.
slump – The product or process of mass-wasting when a portion of hillslope slips or collapses downslope, with a backward rotation (also a rotational failure).
stable (see also equilibrium) – A stable stream is defined as maintaining the capacity to transport water and sediment loads over time without aggrading (building up), degrading (cutting down), or migrating laterally (eroding its banks and changing course). Stable streams resist flood damage and erosion, and provide beneficial aquatic habitat and good water quality for the particular setting.
stability – In stream channels, the relative condition of the stream on a continuum between stable (in equilibrium or balance) and unstable (out of equilibrium or balance). Stream stability assessment seeks to quantify the relative stability of stream reaches, and can be used to rank or prioritize sections of streams for management.
stacked rock wall – A boulder revetment used to line stream banks for stabilization. Stacked rock walls can be constructed on a steeper angle that rip-rap, so they take up less of the stream cross-section, provide a wider road surface, and provide less surface area for solar heating, allowing stream temperature to remain cooler relative to banks lined with rip-rap. These features can be augmented with bioengineering to enhance aquatic habitat and stability functions.
stage – In streams, stage refers to the level or height of the water surface, either at the current condition (i.e., current stage), or referring to another specific water level (i.e., flood stage).
stream assessment, stream assessment survey – The methods and summary information gathered in a stream reach or series of reaches, primarily focused on stream morphology. Stream assessment for the East Branch Delaware River included detailed characterization and mapping of stream channel patterns, cross-section shapes and slope.
stream flow (discharge) – The amount of water flowing in a stream, measured as a volume per unit time, usually cubic feet per second (cfs).
stream stability restoration (design, project) – An unstable portion of stream that has been reconstructed, using morphology characteristics obtained from a stable reference reach in a similar valley setting, that returns the stream to a stable form (that is, to a shape that may allow the stream to transport its water and sediment load over time without dramatic changes in its overall shape).
stream type – As defined by Rosgen (1996), one of several categories defined in a stream classification system, based on a set of delineative criteria in which measurements of channel parameters are used to group similar reaches.
terrace – A level area in a stream valley, above the active floodplain, that was deposited by the stream but has been abandoned as the stream has cut downward into the landscape. These areas may be inundated (submerged) in higher floods, but are typically not at risk in more common floods.
thalweg – The line followed by the majority of the stream flow (New York Guidelines for Urban Erosion and Sediment Control, 1972). In stream assessment, this location is used as a reference location for surveys and other measurements, and is most often associated with the deepest point in the stream cross-section (i.e., the stream channel that would still have water flowing in it at even the lowest flow conditions).
toe – The bottom, or base, of a stream bank or embankment.
tributary – A stream that feeds into another stream; usually the tributary is smaller in size than the main stream (also called “mainstem”). The location of the joining of the two streams is the confluence.
turbidity – A measure of opacity of a substance; the degree to which light is scattered or absorbed by a fluid. Streams with high turbidity are often referred to as being “turbid”.
unstable(see also instability) – Describing a stream that is out of balance in its capacity to transport sediment and maintain its channel shape, pattern and profile over time.
washload – The finest-grained fraction of the total sediment load, consisting of particles whose settling velocity are so low that they are transported in suspension at approximately the same speed as the flow and only settle out when flow velocity are much reduced.
watershed – A unit of land on which all the water that falls (or emanates from springs) collects by gravity and runs off via a common outlet (stream) (Black, 1991).
waters of the United States
- All waters which are currently used, or were used in the past, or may be susceptible to use in interstate or foreign commerce, including all waters which are subject to the ebb and flow of the tide;
- All interstate waters including interstate wetlands
- All other waters such as intrastate lakes, rivers, streams (including intermittent streams), mudflats, sandflats, wetlands, sloughs, prairie potholes, wet meadows, playa lakes, or natural ponds, the use, degradation or destruction of which could affect interstate or foreign commerce including any such waters:
- Which are or could be used by interstate or foreign travelers for recreational or other purposes; or
- From which fish or shellfish are or could be taken and sold in interstate or foreign commerce; or
- Which are used or could be used for industrial purpose by industries in interstate commerce;
- All impoundments of waters otherwise defined as waters of the United States under the definition;
- Tributaries of waters identified in paragraphs (1)-(4) of this definition;
- The territorial seas;
- Wetlands adjacent to waters (other than waters that are themselves wetlands) identified in paragraphs (1)-(6) of this section.
wetland – An area that is saturated by surface water or ground water with vegetation adapted for life under those soil conditions, as in swamps, bogs, fens, and marshes.
velocity – In streams, the speed at which water is flowing, usually measured in feet per second.
