Chapter 14: Running Water: The Geology of Streams and Floods flashcards |

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alluvial fan

A gently sloping apron of sediment dropped by an ephemeral stream at the base of a mountain in arid or semi-arid regions.

alluvium

Sorted sediment deposited by a stream.

annual probability

The likelihood, expressed as a percentage, that an event (e.g., a flood of a given size) will happen in a given year.

antecedent stream

A stream that cuts across an uplifted mountain range; the stream must have existed before the range uplifted and must then have been able to downcut as fast as the land was rising.

bar

(1) A sheet or elongate lens or mound of alluvium; (2) a unit of air pressure measurement approximately equal to 1 atm.

base level

The lowest elevation a stream channel's floor can reach at a given locality.

braided stream

A sediment-choked stream consisting of entwined subchannels.

capacity

The total volume of sediment that a stream can carry.

channel

A trough dug into the ground surface by flowing water.

competence

The ability of flowing water to carry sediment, as represented by the largest clast size that the stream can transport.

delta

A wedge of sediment formed at a river mouth when the running water of the stream enters standing water, the current slows, the stream loses competence, and sediment settles out.

discharge

The volume of water in a conduit or channel passing a point in one second.

distributaries

The fan of small streams formed where a river spreads out over its delta.

downcutting

The process in which water flowing through a channel cuts into the substrate and deepens the channel relative to its surroundings.

drainage basin

An array of interconnecting streams that together drain an area.

drainage divide

A highland or ridge that separates one watershed from another

drainage network

An array of interconnecting streams that together drain an area.

ephemeral stream

A stream whose bed lies above the water table, so that the stream flows only when the rate at which water enters the stream from rainfall or meltwater exceeds the rate at which water infiltrates the ground below.

flash flood

A flood that occurs during unusually intense rainfall or as the result of a dam collapse, during which the floodwaters rise very fast.

flood

An event during which the volume of water in a stream becomes so great that it covers areas outside the stream's normal channel.

floodplain

The flat land on either side of a stream that becomes covered with water during a flood.

headward erosion

The process by which a stream channel lengthens up its slope as the flow of water increases.

longitudinal profile

A cross-sectional image showing the variation in elevation along the length of a river.

Meander

A snake-like curve along a stream's course.

natural levees

A pair of low ridges that appear on either side of a stream and develop as a result of the accumulation of sediment deposited naturally during flooding.

permanent stream

A stream that flows year-round because its bed lies below the water table, or because more water is supplied from upstream than can infiltrate the ground.

point bar

A wedge-shaped deposit of sediment on the inside bank of a meander.

Rapids

A reach of a stream in which water becomes particularly turbulent; as a consequence, waves develop on the surface of the stream.

recurrence interval

The average time between successive geologic events.

seasonal flood

Floods that appear almost every year during seasons when rainfall is heavy or when winter snows start to melt.

sheetwash

A film of water less than a few millimeters thick that covers the ground surface during heavy rains.

stream

A ribbon of water that flows in a channel.

stream piracy

The situation in which headward erosion causes one stream to intersect the course of another, previously independent stream, so that the intersected stream starts to flow down the channel of the first stream.

stream rejuvenation

The reed downcutting of a stream into a floodplain or peneplain, caused by a relative drop of the base level.

stream terrace

A flat surface, underlain by alluvium, that borders a stream; terraces form when the stream cuts down into the alluvium that it had deposited previously.

superposed stream

A stream whose geometry has been laid down on a rock structure and is not controlled by the structure.

tributary

A smaller stream that flows into a larger stream.

V-shaped valley

A valley whose cross-sectional shape resembles a V; the valley probably has a river running down the point of the V.

waterfall

A place where water drops over an escarpment.

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