Glossary of Terms


Bars

In-channel accumulations of sediment that are often only inundated at bankfull flows. Very important to channel form and function – bars are an important
part of hydraulic roughness, deflect flow, and active migration of bar forms (slow movement over years, can be re-arranged by big floods) is an important component of sediment transport.

Mid-channel bar: common in zones of rapid deposition (rivers overloaded with
coarse bedload), at channel widenings, etc. As these become common they will
split flow into multiple threads.
Alternate bars: side-channel bars formed in straight channels (mobile bed) – a
natural flow/sediment transport instability that will always form: positive
feedbacks from virtually any initial perturbation to a straight, flat-bed channel.
Point bars: bar forms produced by deposition on the inside of meander bends,
critical to meander migration and alluvial stratigraphy
Back-bar chute: high flow channel often formed at top, inside edge, of point bar.

Braiding Parameter - Measures the number of bars or islands in a channel. The parameter is defined as the number of bars or islands per meander wavelength (Rust 1978).

Crevasse-splay - Fan-shaped wedges of coarse sediment deposited downstream of levee breaks during floods.

Counterpoint Bar - a term for all concave bank deposits. The bars may be deposited in a slack water created by flow separation around a tightly curved meander bend (Smith 1987). These bars are often separated from the bank by a small secondary channel.

ECS - Epsilon Cross-Stratification (also see Meandering Channel Systems)

Floodplain - Level land along the course of a river formed by the deposition of sediment during periodic floods. Floodplains contain such features as levees, backswamps, delta plains, and oxbow lakes. Floodplains may be extensive, such as below the conflux of the Ohio and the Mississippi, where they have a width up to 80 mi (130 km).

Floodplain Channels - Smaller channels important in the flooding and draining of the floodplain (and in the distribution of sediment, development of stratigraphy).

LAS - (lateral accretion surfaces). These are the bounding surfaces in ECS units and generally represent the topographic surface of the bar at a point in time. LAS can be either surfaces of erosion or deposition. LAS can often be identified texturally by the paucity of coarse silt, due to their eolian origin (Shepherd 1987).

Scroll-bar topography - Series of arcuate topographic ribs left behind a migratingmeander loop – related to migrating bar forms and back-bar chutes.

Sinuosity - Sinuosity is defined as the ration of thalweg length to channel valley length (Rust 1978).

Thalweg - The line defining the lowest points along the length of a river bed or valley.

Valley Length - The straight line distance down the river valley