Exam 4 pt.3

Point bars

A crescent-shaped accumulation of sand and gravel deposited on the inside of a meander.

Oxbow lake

A curved lake that's created when a stream cuts off a meander

Downcutting

A dominant erosional process where the lowering of the streambed toward base level as turbulent water lifts unconsolidated material or when bedrock channels are lowered by means of quarrying, abrasion, and corrosion.

Sorting

A process in which solid particles are separated; explains why particles of similar size are deposited together

Braided channel

Channels that consists of interwoven appearance of converging and diverging channels that thread their way among numerous islands or gravel bars; Form where a large portion of a stream's sediment load consists of coarse material and stream has a highly variable discharge. B/c bank material is readily erodible, they're wide and shallow.

Bedrock channels

Channels that cut into underlying strata and typically form in the headwater of river systems where streams have steep slopes. The energetic flow tends to transport coarse particles that actively abrade this; Steep version of this often develop a sequence of steps and pools, relatively flat segments (pools) where alluvium tends to accumulate and steep segments (steps) where bedrock is exposed. The steep areas contain rapids or waterfalls.

Stream valley

Consists of a channel and the surrounding terrain that directs water to the stream which includes the valley floor, which is the lower, flatter area that's partially or totally occupied by the stream channel, and the sloping valley walls that rise above the valley floor on both sides. Alluvial channels often flow in the valley that has wide valley floors consisting of sand & gravel deposited in the channel and clay & silt by floods. Bedrock channels tend to be located in the narrow V-shaped valley. In some arid regions, where weathering is slow and rock is particularly resistant, narrow valleys having nearly vertical walls (slot canyons) are also found; exist on a continuum from narrow, steep-sided valleys to valleys that are so flat and wide that the valley walls aren't discernible.

Terraces

Flat surfaces that are the remnants of former floodplains

Erosional floodplain

Floodplain produced by erosion.

Alluvial channel

Form in sediments that was previously deposited in the valley; When the valley floor reaches sufficient width, material deposited by the stream can form a floodplain that borders the channel. B/c the banks and beds of alluvial channels are composed of unconsolidated sediment, they can undergo major changes in shape as material is continually eroded, transported, and redeposited; Major factors affecting the shapes of these channels: average size of the sediments being transported, the channel's gradient, and discharge; reflect a stream's ability to transport its load @ a uniform while expending the least amount of energy meaning that the size and type of sediment being carried help determine the nature of the stream channel; 2 most common type: meandering and braided

Local/temporary base level

Includes lakes, resistant layers of rock, and rivers that act as base levels for their tributaries and all limits a stream's ability to down cut its channel.

Incised meanders

Meandering channels that flow in steep, narrow bedrock valleys; Formed on the floodplain of a stream that was in balance w/ its base level meaning that a change in base level caused the stream to begin downcutting due to their steep gradient. One of 2 will occur: Either the base level dropped, or the land on which the river was flowing was uplifted

Competence

Measure of a stream's ability to transport particles based on size rather than quantity; Directly correlated w/ flow velocity; Increase proportionally to the square of flow velocity meaning; the Higher amount of this makes it easier to transport large particles.

Floodplain

Named b/c when a river overflows its banks during flood stage, it inundates this; broad, flat valley floor covered with alluvium. Over time this will widen to a point where the stream is actively eroding the valley walls only in a few places.

Depositional floodplain

Produced by major fluctuations in conditions like changes in base level or climate.

Settling

Speed @ which a particle falls through a still fluid; larger particle = more rapid settling; also influenced shape and specific gravity; flat grains settle more slowly than spherical grains and dense particles sink faster than less-dense particles

Graded stream

Stream that has the necessary slope and other channel characteristics to maintain the minimum velocity required to transport the material supplied on it; neither eroding or depositing material but simply transporting it. When a stream reaches equilibrium, it becomes a self-regulating in which a change in on characteristic causes a change in the others to counteract the effects

Meandering channel

Streams that transport much of their load in suspension generally move in sweeping bends; flows in relatively deep, smooth channels and primarily transport mud, sand, and occasionally fine gravels; evolves over time as individuals migrate across floodplains where most of the erosion is focused at the outside of the meander, where velocity and turbulence is the greatest.

Cutoff

The area of active erosion outside of a meander; A short channel segment created when a river erodes through the narrow neck of land between meanders

Base level

The levels below which a stream can't erode; lowest elevation to which a stream can erode its channel; the level @ which the mouth of a stream enters the ocean, a lake, or a trunk stream.

Capacity

The max. Load of solid particles a stream can transport per unit time; directly correctly with discharge and flow velocity.

Ultimate base level

Sea level; the lowest level to which stream erosion could lower the land.

Alluvium

Sediment deposited by the stream; Makes up many different depositional features where some occur w/in stream channels, some occur on the valley floor adjacent to a channel, and some are found at the mouth of the stream.

Bed load

Sediment move along the bottom by the moving water, or particles move along the ground surface by the wind; Sediment that makes up this move by rolling, sliding, and saltation; Movement of this throughout a stream network tends to be more localized than the movement of suspended load and is much slower. Depending on discharge & slope of the channel, coarse gravels may only be moved during times of high flow, while boulders only move during powerful floods; This can't be carried at all until it's broken into smaller particles.

Saltation

Sediments that move by this appears to jump or skip along the stream bed; This occurs as particles are propelled upward by collisions or lifted by the current and then carried downstream a short distance until gravity pulls them back to the back of the stream; Large/heavy particles moved by this through rolling/ sliding along the bottom, depending on their shapes