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These definitions have been compiled from various sources, including the USGS's Water Resources Data, Weather Service Operations Manual, Chapter E-90, and Glossary of Meteorology (AMS, 1959).

backwater effect

The effect which a dam or other obstruction has in raising the surface of the water upstream from it.

backsight

A rod reading taken on a point of known elevation, a benchmark or a turning point. Backsights are added to the known elevation to arrive at the height of the instrument. With a known height of the instrument, the telescope can be used to determine the elevation of other points in the vicinity.

backwater curve

The longitudinal profile of the surface of a liquid in a non-uniform flow in an open channel, when the water surface is not parallel to the invert owing to the depth of water having been increased by the interposition of an obstruction such as a dam or weir. The term is sometimes used in a generic sense to denote all water surface profiles; or for profiles where the water is flowing at depths greater than the critical.

backwater flooding

Upstream flooding caused by downstream conditions such as channel restriction and/or high flow in a downstream confluence stream.

bank

The margins of a channel. Banks are called right or left as viewed facing in the direction of the flow.

bankfull stage/elevation

An established river stage, or water surface elevation, at a give location along a river which is intended to represent the maximum water level which will not overflow the river banks or cause any significant damages from flooding.

backsight

A rod reading taken on a point of known elevation, a benchmark or a turning point. Backsights are added to the known elevation to arrive at the height of the instrument. With a known height of the instrument, the telescope can be used to determine the elevation of other points in the vicinity.

backwater flooding

Upstream flooding caused by downstream conditions such as channel restriction and/or high flow in a downstream confluence stream. barrage

barrage

Any artificial obstruction placed in water to increase water level or divert it. Usually the idea is to control peak flow for later release.

base flood

The national standard for floodplain management is the base, or one percent chance, flood. This flood has at least one chance in 100 of occurring in any given year. It is also called a 100 year flood.

base station

A computer which accepts radio signals from ALERT gaging sites, decodes the data, places the data in a database, and makes the data available to other users.

base width

The time duration of a unit hydrograph.

baseflow

Streamflow, or runoff, which results from precipitation which infiltrates into the soil and eventually moves through the soil to the stream channel. Also known as dry-weather flow and groundwater flow.

basin

see drainage basin

basin boundary

The topographic dividing line around the perimeter of a basin, beyond which overland flow (i.e., runoff) drains away into another basin.

basin lag

The time it takes from the centroid of rainfall for the hydrograph to peak.

basin recharge

Rainfall which adds to the residual moisture of the basin in order to help recharge the water deficit. Water absorbed into the soil which does not take the form of direct runoff.

bed load

Sand, silt, gravel, or soil and rock detritus carried by a stream on or immediately above its bed. The particles of this material have a density or grain size such as to preclude movement far above or for a long distance out of contact with the stream bed under natural conditions of flow.

bed material

The sediment mixture of which a streambed, lake, pond, reservoir, or estuary bottom is composed.

benchmark

A permanent point whose known elevation is tied to a national network. These points are created to serve as a point of reference. Benchmarks have generally been established by the USGS, but may have been established by other Federal or local agencies. Benchmarks can be found on USGS maps.

black ice

1. Transparent ice formed in rivers and lakes.
2. Ice which forms on horizonal surfaces, such as roads, which is nearly transparent due to the absence of trapped air bubbles.

border ice

An ice sheet in the form of a long border attached to the bank or shore. Also known as shore ice.

brackish ice

Ice formed from brackish water.

braided stream

A stream characterized by successive division and rejoining of streamflow with accompanying islands. A braided stream is composed of anabranches.

brash ice

Accumulation of floating ice made up of fragments not more than about 6 feet (2 meters) across; the wreckage of other forms of ice.

breakup

The time when a river whose surface has been fromzen from bank to bank for a significant protion of its length begins to change to an open water flow condition. The event is signaled by the breaking of the ice and often associated with ice jams and flooding.

breach

The failed opening in a dam.

bubbler gage

A water stage recording device capable of being attached to a LARC for data automation purposes.

buttress dam

Buttress dams are comprised of reinforced masonry or stonework built against concrete. They are usually in the form of flat decks or multiple arches. They require about 60 percent less concrete than gravity dams, but the increased form work and reinforcement steel required usually offset the savings in concrete. Many were built in the 1930s when the ratio of labor cost to materials was comparatively low. However, this type of construction is not competitive with other types of dams when labor costs are high.