Amateur Geologist Structured Geological Glossary: Rivers and Streams

Structured Geological Glossary: Rivers and Streams

active lobe	of a delta. The site on a delta where functioning distributary channels cause the delta to grow seaward.
suspension bed	The part of the sediment carried along by the water flowing above the stream bed.
suspended load	"Part of the total stream load that is carried in suspension free from contact with the stream bed; it consists mainly of clay, silt, and fine sand."
dissolved load	Part of the total stream load consisting of substances in dissolved form such as Ca2+, HCO-3, H4SiO4.
paleocompetence	Competence is a measure of a stream's abiility to entrain sediment particles, measured by the maximum grain size that can be transported. Empirical relationships between grain size and flow velocity or stream power are applied to paleoflood deposits to derive estimates of these same paleoflow parameters.
translocation	Physical or chemical migration of suspended particles or aqueous solute by moving water in a hydrochemical system or by animals and plants.
bed-load	The sediment that a stream moves along the bottom of its channel by rolling and bouncing.
macroturbulence	Flood flows of great depth and high velocity are characterized by special turbulent flow phenomena that are exceedingly powerful. Macroturbulence phenomena include powerful upward vortices called kolksintences shocks resulting from sudden pressure change known as cavitation and powerful roller vortices oriented parallel to flow. These features provide enormous shear stresses and stream power to flood flows.
alluvium	An unconsolidated terrestrial sediment composed of sorted or unsorted sand, gravel, and clay deposited during comparatively recent geologic time by a stream or river. Alluvial deposits include mid channel bar, point bar, floodplain deposits, alluvial fans, and fluvial terrace.
alluvail fan	A low, cone shaped deposit of terrestrial sediment formed where a stream undergoes an abrupt reduction of slope.
alluvlal fan	A low cone-shaped structure that form where an abrupt reduction in slope -- for example, the transition from a highland area to a broad valley -- causes a stream to slow down.
bajada	Multiple alluvial fans joining together to form an undulating landform.
bolson	In arid regions, a basin filled with alluvium and intermittent playa lakes and having no outlet.
gradient	The down valley slope of a steam bed.
graded stream	A stream whose smooth profile is unbroken by resistant ledges, lakes, or waterfalls, and which maintains exactly the velocity required to carry the sediment provided to it.
longitudinal profile	A cross section of a stream from its mouth to its head, showing elevation versus distance to the mouth.
Thalweg	A sinuous imaginary line following the deepest part of a stream.
base-level	" The level below which a stream cannot erode; usually sea level sometimes locally the level of a lake or resistant formation. "
mature	A stage in the geomorphic cycle in which maximum relief and well-developed drainage are othen present.
V-shaped valley	A valley whose walls have a more-or-less uniform slope from top to bottom, usually formed by stream erosion. While the valley takes on a V-shape the river itself flows in a U-shaped bed similar to that created by a glacier.
gully	A very small channel formed by running water. Gullies hold water for brief periods of time after a rain storm or snow melt.
pothole	A semispherical hole in the bedrock of a stream bed, formed by abrasion of small pebble and cobble in a strong current.
terrace	Level or near-level area of land, generally above a river or ocean and separated from it by a steeper slope. A river terrace is made by the river at some time in the past when the river flowed at a higher level. It A terrace may be made of river deposits such as gravel or sand, or it could be cut by the river on bedrock. A glacial terrace or outwash terrace is similar but is formed by a stream or river from a glacier upstream.
stream capture	A process of erosion where one stream erodes headward, diverting some of another stream’s drainage into its own channel. Also called stream piracy.
stream piracy	See stream capture
perennial stream	A stream that runs continuously throughout the year.
divide	A ridge of high ground separating two drainage basin emptied by different streams.
ephemeral stream	A stream drainage that is usually dry and fills with water only during brief episodes of rainfall. Many desert streams ephemeral.
wadi	A steep-sided valley containing an intermittent stream in an arid region.
wash	A normally dry stream bed that ocassionally fills with water.
arroyo	A steep-sided and flat-bottomed gully in an arid region that is occupied by a stream only intermittently, after rains.
dry wash	An intermittent stream bed in an arroyo or canyon that carries water only briefly after a rain.
disappearing stream	In karst areas, streams often disappear into the ground usually at a sinkhole.
flood plain	" A level plain of stratified alluvium on either side of a stream; submerged during flood and built up silt and sand carried out of the main channel. "
bankfull stage	The height of water in a stream that just corresponds to the level of the surrounding floodplain.
incised	A term used to describe down-cutting (downward erosion) by a stream. Incision deepens and often steepens the stream channel.
oxbow lake	A lake formed when a meander of a stream is cut off from the main stream by erosion.
levee	"A low ridge along a stream bank, formed by deposits left when floodwater decelerates on leaving the channel; also an artificial barrier to floods built in the same form. "
bar (stream)	An accumulation of sediment, usually sandy, which form at the borders or in the channels of streams or offshore from a beach.
overbank deposits	Silt and clay deposited on a flood plain by a flooding stream.
bar-finger sand	An elongated lens of sand deposited during the growth of a distributary in a delta. The bar at the distributary mouth is the growing segment of the bar finger.
delta	A body of sediment deposited in an ocean or lake at the mouth of a stream.
delta	A fan-shaped deposit that form where a stream enters a lake or ocean and drops its load of sediment.
distributary	One of the branches into which a river divide, typically at a delta.
braided stream	A stream that has many intertwining channels separated by bar of coarse sediment. Braided streams develop where sediment is supplied to the stream system at a very high rate on an alluvial fan, for example, or in front of a melting glacier.
meander	Broad, semicircular curves in a stream that develop as the stream erodes the outer bank of a curve and deposits sediment against the inner bank.
flood	A lake, stream, or other body of water that flows over its natural confining boundaries. During a flood, water flows out over land not normally covered with water.
trellis drainage	A system of streams in which tributaries tend to lie in parallel valleys formed in steeply dipping bed in folded belts.
internal drainage	"An area in which surface water cannot reach the ocean. Any water that falls into an area with internal drainage as rain or snow does not escape out of it; not one of the streams that originate within these basin ever find an outlet to the ocean. (see drainage basin)"
rectangular drainage	A system of streams in which each straight segment of each stream takes one of two characteristic perpendicular directions, with right-angle bends between. The streams are usually following two perpendicular sets of joint.
stream order	The hierarchical number of a stream segment in dendritic drainage
radial drainage	A system of streams running in a radial pattern away from the center of a circular elevation, such as a volcano or dome.
drainage basin	A region of land surrounded by divide and crossed by streams that eventually converge to one river or lake.
superposed stream	A stream that flows through resistant formation because its course was established at a higher level on uniform rocks before down-cutting began.
homopycnal	Describes water entering a lake that has the same density as the lake water.
hyperpycnal	Describes water that is denser than the water in the lake it enters.
discharge	The amount of water issuing from a spring or in a stream that passes a specific point in a given period of time.
dendritic drainage	A stream system that branches irregularly and resembles a branching tree in plan.
turbulent flow	A high-velocity flow in which streamlines are neither parallel nor straight but curled into small tight eddies (compare Laminar flow).
streaming flow	A tranquil flow slower than shooting flow.
wrong term	The movement of sand or fine sediment by short jumps above the ground or stream bed under the influence of a current too weak to keep it permanently suspended.
flowstone	A lake, stream, or other body of water that flows over its natural confining boundaries. During a flood, water flows out over land not normally covered with water.
flow rheology	Deformational character of the flow when stress is applied. Rheology varies due to differences in fluid strength, viscosity, density and sediment concentration.