Northwest Fisheries Science Center

Ecosystem Analysis Projects


Dr. Beth Sanderson
Program Manager
Staff Directory

Ecosystem Analysis Program

Glossary:  Conserving Thermal Habitat for Pacific Salmon

Airborne remote sensing

Airborne remote sensing is a method of data collection that relies on infared spectral imagery.  Because sensing is conducted from an aircraft, the method allows coverage of larger and more remote areas than could be surveyed from the ground.


An alevin is a newly hatched salmonid.  It is a free living embryo that is still attached to the yolk sac and that subsists on internal yolk reserves.


Entire land–drainage area of a river.  Also called watershed, drainage basin, or catchment.


Entire land–drainage area of a river.  Also called watershed, basin, or drainage basin.


Straightening, narrowing, and deepening of a stream channel.  Channelization may be deliberate to improve navigation, move water faster, or prevent flooding of human infrastructure.  It often includes removal of debris and channel obstructions that may impede flow.

DBH (diameter at breast height)

A measurement of tree diameter taken at breast height.

Drainage basin

Entire land–drainage area of a river.  Also called basin, catchment, or watershed.

EPT (Ephemeroptera, Plecoptera and Trichoptera)

Group of insect orders used as a biological metric for monitoring water quality.  Water quality is often interpreted based on the presence of insects from these orders, whose common names are Mayfly (Ephemeroptera), Stonefly (Plecoptera), and Caddisfly (Trichoptera).  Higer water quality is generally indicated by greater species richness (numbers of taxa) from these orders. 

ESU (Evolutionarily Significant Unit)

A conservation management unit comprised of a population or set of populations that is reproductively isolated from conspecific populations and represents an important component in the species’ evolutionary legacy.

Fine sediment (fines)

Sediment particals that are generally less than 2–mm in diameter and typically composed of clay, silt, or sand.  Compare coarse sediment.


A flat depositional feature of a river valley adjoining the channel, the floodplain is formed by climate and hydrological conditions and is subject to periodic flooding.


Field measurement of specific attributes that have been predicted from models, maps, or remotely sensed data for the purpose of assessing accuracy and precision of predictions.

Hydraulic regime

For a stream or river, hydraulic regime refers to seasonal changes in stream characteristics such as flow, temperature, and sediment load.  Influences on regime include precipitation, air temperature, local geography, and human activity.  For example, during a spring freshet, melting snow causes large increases in the rate and volumen of flow, and may lower the stream temperature. 

Hyporheic zone

The hyporheic zone refers to saturated interstitial areas both below the streambed and within the streambanks (or floodplain), where stream water and deep groundwater intermix and where a number of important chemical, hydrological, and biological processes take place.

Incised channel

An incised stream channel is one in which the stream bed is deepened to a point where flow is no longer connected the surrounding floodplain but cuts through the stream bed, resulting in further erosion and instability.  Incised channels are caused by erosion, usually resulting from an imbalance between sediment transport capacity and sediment supply to the stream. 

LIDAR (light detection and ranging)

 Using a principle similar to radar, the LIDAR instrument transmits light to a target and receives reflected or scattered light back for analysis.  Change in the properties of light enable measurment of various properties of the target, such as distance, speed, rotation, or chemical composition and concentration.


A geomorphically similar stream section or a section of stream as defined by two selected points.


A spawning nest constructed in the substrate of a lake or stream by a fish.

Remote sensing

Gathering data from a remote station or platform, as in satellite or aerial photography.


Shallow section of a river or stream, with moderate–to–rapid flow and surface turbulence.


The banks of a river or the terrestrial aquatic interface.  That part of a terrestrial landscape that exerts a direct influence on stream channels or lake margins, and the water or aquatic ecosystems.


Layer of large, durable materials such as rock used to protect a streambank from erosion; also may refer to the materials used, such as rocks or broken concrete.

Sediment budget

Accounting of sediment sources and transfer processes in a watershed. The complete budget quantifies sediment sources, transport, and storage within a watershed, usually tracking each process of sediment production or movement separately.

Sediment supply

Supply of sediment to a river system, where it is carried in suspension (see suspended load and wash load) or on the bottom (see bed load).

In forestry or forest management, the care, cultivation, and harvest of trees. In restoration ecology, the term generally refers to planting, removing, or growing trees and other vegetation to restore certain forest characteristics.

Stream order

A method of classifying streams based on size and number of tributaries. Typically smallest streams are given smaller numbers. For example, a first–order stream would be the smallest detectable headwater stream, a second–order stream would be formed by the formation of two first–order streams, etc.


Changes in species composition of plants and animals in an ecosystem with time, often in a predictable order. More specifically, the gradual and natural progression of physical and biological changes, especially in the trophic structure of an ecosystem, toward a climax condition or stage.

Suspended load

Part of the total stream load that is carried for a considerable period of time in suspension, free from contact with the streambed; it mainly consists of clay, silt, and sand. Note that sediment can move between suspended load and bed load as the stream discharge changes. Compare bed load and wash load.


Exposed former floodplain deposit that results when a stream begins downcutting into its floodplain. 


Line defining the lowest (deepest) points along the length of a stream.

Thermal Regime

Thermal regime in a stream or river refers to seasonal changes in stream temperature.  Influences on thermal regime include precipitation, air temperature, local geography, and human activity.  For example, during a spring freshet, melting snow may lower the stream temperature. 

Thermal Refuge

Thermal refuge refers to a section of habitat where an animal can temporarily escape unfavorable temperatures.   


Volume of water between mean higher high water (MHHW) and mean lower low water (MLLW).


Entire land–drainage area of a river.  Also called a basin, drainage basin, or catchment.


A structure that forms a barrier to obstruct flow in a stream or river without blocking it entirely.  It often takes the form of a low dam and can be constructed from earth, logs and rocks, timbers, or concrete.  Purposes of a weir also vary, but from a restoration standpoint, there are two: 

1.   To divert or retain water for various human uses such as to prevent flooding, maintain navigability, or monitor discharge.
2.   To create more natural stream conditions by forming a pool to trap gravel and sediments and to improve fish habitat.