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Glossary of Minimum Flows and Levels Terms

This section explains terms you might encounter when reading about minimum flows and levels.

Sides of a river or stream between which the water normally flows.

The stage of a river when the elevation of water is at the top of its banks but not yet overflowing. A heavy rain event will likely cause water to flow into the floodplain when a system is at bankfull.

A measure of the number of species and the proportion of those species within a system.

A measure of the quantity, usually by weight (i.e. kilograms), of fish populations within a given area at a given time.

The amount of time floodwaters are in the floodplain.

A sampling technique used by biologists to collect fish in lakes, streams, and rivers. Electrodes placed in the water allow an electric current to pass through the water, which stuns any nearby fish. Biologists can then collect the fish with a dip net.

A continuous line, typically established next to shoreline habitat, along which biologists use electrofishing to sample for fish. The waters along transects are sampled over a give time or distance.

A flat tract of land bordering a stream or river that is susceptible to flooding during times of high water

Occurs when a river overflows its banks and the instream portion of the river becomes linked by water to the adjacent floodplain. Floodplain connectivity occurs during flood events, the duration of the connectivity is influenced by the magnitude of the flood event. Nutrients and resources readily transfer between the river and floodplain ecosystems when the river and floodplain are connected.

An event that occurs when a river overflows its banks and the flat expanses of land adjacent to the riverbank are submerged under water.

Weather events, such as hurricanes, severe storms, and dry spells, that lead to flood or drought conditions within a river system.

Fish lengths are categorized into size-class categories, and then the frequency (the number of fish collected) of fish within each size category is plotted in order of increasing length (i.e. 10 cm to 50 cm). Higher frequencies indicate higher abundance of a given size class.

How far the floodwaters extend into the floodplain.

The frequency between flood events within a given span of time.

The frequency between flood events within a given span of time.

The time period that immediately precedes a flood event in which the river and floodplain ecosystems will become connected. Waters are within the riverbanks during the pre-inundation period.

A measure that compares the weight of an individual of a given length to a predefined standard weight. This is then used to determine how an individual or a population of individuals compares to a standard weight for that species. Individuals or populations that are above the pre-defined standard weight are said to be in good condition.

Fish-length grouping categories. Size classes are often categorized into centimeter group intervals. For example, all collected fish measuring between 100 and 109 millimeters (mm) would be part of a 10-centimeter (cm) size-class category, and all fish between 110 and 119 mm would be part of the 11-cm size class.

A ratio of the drop in stream elevation that occurs over a given distance within a stream. Stream gradients are usually measured in feet per mile or meters per kilometer. Stream gradients decrease from the headwaters to the mouths of the streams. Low gradient streams have smaller changes in elevation over a larger distance as compared to high gradient streams.

The time of year or season (winter, spring, summer, or fall) in which a flood event occurs.

Land that drains water into a particular stream, lake, or river.