Commonly Used Terms

Annual High Water Level

The high water mark typically reached on an annual basis within a channel. Also referred to as the Ordinary High Water Mark (OHWM or OHW).

Armoring (bank)

Protective covering, such as rocks, logs, vegetation or engineered materials used to protect and stabilize streambanks.


The sudden change in the course of a river channel (often during a flood), potentially causing the separation of land from one property and its attachment to another.

Bald & Golden Eagle
Protection Act (BGEPA)

Federal Regulation which prohibits anyone, without a permit issued by the Secretary of the Interior, from “taking” bald or golden eagles, including their parts, nests, or eggs.


The mark or flow of a stream at which it is about to overtop its banks. Typically, this flow would occur every 1.5 years; therefore, it is sometimes used in reference to a 1.5 year event.

Bank Stabilization

The process by which eroding or failing banks are modified to resist the channel velocities or protect steep slopes with structural aspects such as boulders, logs, retaining walls and/or vegetation.

Bank Stability

The ability of a streambank, including its soils and vegetation, to resist erosion from water flows and gravity.


Using natural materials, such as boulders, soil, logs and plants to create an ‘engineered’ solution. In the case of this Handbook, most bioengineering measures are related to bank stabilization.


The study of living organisms.

Clean Water Act (CWA)

The 1972 amendment to the Federal Water Pollution Control Act of 1948 with the objective to maintain and restore the integrity of the nation’s waters by regulating pollutants discharged into them.

Colorado Noxious Weed Act

Under this Act, the Colorado Department of Agriculture (CDOA) has implemented a noxious weed control program. The aim of this program is to prevent the introduction of new invasive species, eradicate species with isolated or limited populations and manage well-established and widespread noxious weeds.

Conditional Letter of Map Revision (CLOMR)

FEMA’s comment on a proposed project that would, upon construction, affect the hydrologic or hydraulic characteristics of a flooding source and thus result in the modification of the existing regulatory floodway, the effective Base Flood Elevations (BFEs), or the Special Flood Hazard Area (SFHA).


A tunnel carrying a stream or open drain under a road or railroad.


A nearly vertical cliff produced by erosion of the banks of a stream.


Sediment (including rocks and sand) settling out of moving water and being added to the streambed, bank, or floodplain.


The physical removal of water from a stream or lake via an engineered structure. Often used to divert water for irrigation, municipal, industrial, or storage purposes.

Drop Structure

Structures that create vertical or near vertical elevation changes in a stream in order to reduce the slope of the stream upstream and/or downstream of the structure.


A system, or a group of interconnected elements, formed by the interaction of a community of organisms with their environment.

Endangered Species Act (ESA)

A federal regulation to protects animals and plants that are in danger of extinction (endangered) or are threatened to become endangered (threatened) and the habitat upon which they depend.

Endangered/ Threatened Species

Endangered: any species which is in danger of extinction throughout all or a significant portion of its range. Threatened: any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range.


A way of measuring the relationship between a stream and its floodplain. Often measured as a ratio of the width of the flood-prone area to the surface width of the bankfull channel.


A stream channel in which erosion and deposition are relatively balanced, resulting in little or no change to the channel shape over time.


The movement of soil or rock by wind, water, or other natural processes.

Fish Passage

The capability for a stream section to allow fish to move upstream and
downstream through it.

FEMA Flood Insurance Rate Map (FIRM)

The official map of a community on which FEMA has delineated both the special hazard areas and the risk premium zones applicable to the community.

Flood Fringe

The area outside of the floodway, but still within the 100 year floodplain.


An area of low-lying ground adjacent to a river, formed mainly of river sediments and that is subject to flooding. Typically separated into zones based on the probability of flooding frequency.

Floodplain Conveyance

The amount of water that can flow through a floodplain for a given section.


The channel of a stream or other watercourse and the adjacent land areas through which flood waters will flow most efficiently.

Fluvial Geomorphology

The study of how a stream interacts with its geologic surroundings.


The study of the physical properties of the earth.


Relating to the form of the landscape and other natural features of the earth’s surface.


Study of the characteristics and history of landforms.


Strong synthetic fabrics used to stabilize loose soils and prevent erosion.

“Good Wood”

Large woody material that does not pose a flood risk and provides a variety of environmental benefits, including habitat, bank stabilization and improved hydraulic function.


The act of altering the ground surface to a desired grade or contour by cutting, filling, leveling, and/or smoothing.

Grade Control

A natural or engineered structure on the channel bed which locally prevents bed erosion, creating a stable channel slope (or “grade”).


An erosional feature of some streams where an abrupt vertical drop in the stream bed occurs (also known as a knickpoint). A headcut will typically migrate upstream as it progresses.

Hydric Soil

A soil that formed under conditions of saturation, flooding or ponding long enough during the growing season to develop anaerobic conditions in the upper part. Found in wetlands.


A graph showing the rate of flow (discharge) versus time past a specific point in a river, or other channel or conduit carrying flow.


The study of water on the earth, in the earth and in the atmosphere.

Hydraulic Engineering

The study and design of how fluids move in relation to their environment.


A material that does not allow fluid to pass through it (e.g., concrete).


When a stream has a cut vertically downward through its bed, and has lost connection with its floodplain.

Large Woody Material (LWM)

Dead trees, branches, limbs or logs, often left behind by flood events.

Letter of Map Revision (LOMR)

FEMA’s modification to an effective Flood Insurance Rate Map (FIRM), or Flood Boundary and Floodway Map (FBFM), or both.

Migratory Bird Treaty Act (MBTA)

Federal Regulation which makes it illegal for anyone to take, possess, import, export, transport, sell, purchase, barter, or offer for sale, purchase, or barter, any migratory bird, or the parts, nests, or eggs of such a bird except under the terms of a valid permit issued pursuant to Federal regulations.


A twist, turn or curve in an active channel of a river, stream or creek. See Oxbow for the historical/past curves of a river.

No-Rise Certification

A hydraulic certification supported by technical data and signed by a registered professional engineer, showing that work in the floodway will result in a zero-rise or a decrease in base flood elevations.

Noxious Weeds

Aggressive non-native plants that invade an area, displacing native vegetation and reducing agricultural productivity.

Office of Emergency Management (OEM)

An agency at the local, state or national level that holds responsibility of comprehensively planning for and responding to and recovering from all manner of disasters, whether man-made or natural.

Ordinary High Water Mark (OHWM)

The high water mark typically reached on an annual basis within a channel. Also referred to as Annual High Water Level.


The place where an irrigation ditch, drain or sewer pipe empties into a water body.

Overflow Channel

Sections of stream that do not normally carry water during average daily flows, but will become active during larger flow events to carry excess water.


A naturally abandoned or cutoff portion of a historic meander bend; while a meander is part of an active channel, an oxbow is the non-active area remaining after a meander is cut off from the channel.

Plugs (Plants)

Individual wetland or riparian plants that are established by a professional wetland plant nursery and installed in predetermined areas along a stream or wetland to expedite plant establishment.

Primary Streambed Material

The most common aggregate found in a streambed; examples include boulders, cobble, gravel and sand.

Rheotactic Salmonids

Fish of the Salmon family (i.e. salmon, trout, char and whitefish) that generally turn to face into an oncoming current.


A stretch of a stream or river, the boundaries of which are often defined by physical or political changes.


Of, relating to, or situated or dwelling on the bank of a river or other body of water.

River Dynamics

How a river function and moves.


The result of swiftly moving water eroding soil, causing a hole or depression in the stream bed.


Solid fragments of inorganic or organic material that come from the weathering of rock and are carried and deposited by wind, water, or ice.


Sloped areas alongside streams, creeks and rivers that connect the stream to its floodplain.

Stream Corridor

A stream corridor is an ecosystem that usually consists of three major areas or zones: stream channel, streambank, upland transition.

Stream Slope

The vertical distance that a stream drops over a given horizontal length.

Stream Stewardship

The act of supervising or taking care of the larger stream system.

Stream Steward

Someone who understands and respects the value of a healthy stream system and treats the stream in ways that will benefit the entire stream corridor and watershed.

Stream Restoration

A large variety of ecological, physical, spatial and management measures and practices aimed at restoring the natural state and functioning of a stream or river system in support of biodiversity, recreation, flood management and landscape development.

Toe of Bank

The bottom of a streambank where the bank meets the baseflow water level of a channel.


Dry areas away from the stream channel.


A river, canal, or other body of water serving as a route or way of travel or transport.


An area of land consisting of a network of streams, rivers and lakes that drains to a single point.


A natural or artificial channel through which water flows or a stream of water (such as a river, brook, or underground stream).


Area that is inundated or saturated by surface water or groundwater at a frequency and duration sufficient to support, and that under normal circumstances support, a prevalence of vegetation typically adapted to life in saturated soil conditions. Wetlands often need to be identified and delineated by a professional environmental consultant based on the available water, types of soils and types of vegetation.


The ratio of the bankfull surface width to the mean depth of the bankfull channel. The width/depth ratio is key to understanding the distribution of available energy within a channel, and the ability of various discharges occurring within the channel to move sediment.


Plant community characterized by, relating to or requiring only a small amount of moisture.