Final: Fluvial Processes

Geography 120 with Greene/marin-spiotta at University of Wisconsin - Madison

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Created: 2012-05-05
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Fluvial processes

those that involve running water, encompass both the unchanneled downslope movement of surface water, called overland flow, and the channeled movement of water along a valley bottom, called streamflow

Valleys and interfluve

valleys normally have clear-cut drainage systems; interfluves do not

Valley

portion of the terrain in which a drainage system is clearly established. it includes the valley bottom that is partially or totally occupied by the channel of a stream, as well as the valley walls that rise above the valley bottom on both sides.

Interfluve

the higher land above the valley walls that separates adjacent valleys

Drainage basin or watershed

the area that contributes overland flow, streamflow, and groundwater to that stream. consists of a stream's valley bottom, valley sides, and those portions of the surrounding interfluves that drain toward the valley

Drainage divide

line of separation between runoff that descends in the direction of one drainage basin, and runoff that goes toward an adjacent basin

Splash erosion/sheet erosion

impact of raindrops
lands on the wet soil surface, producing a miniature crater
Grains of clay and silt are thrown into the air and the soil surface is disturbed
When rain splash has broken down soil aggregates and created larger openings, water cannot infiltrate and overland flow continues to remove the soil in thin layers (sheet erosion)

Rill erosion

as overland flow moves downslope and its volume increases, the resulting turbulence tends to break up the sheet flow into multitudinous tiny channels called rills. this more concentrated flow picks up additional material and scores the slope with numerous parallel seams = rill erosion

Gully erosion

when a rill channel becomes broader and deeper and as the gullies get larger and larger, they tend to become incorporated into the drainage system of the adjacent valley, and the flow changes from overland flow to stream flow

Fluvial transport

- dissolved load: some minerals, mostly salts, are dissolved in the water and carried in solution

- suspended load: very fine particles of clay and silt are carried in suspension, moving along with the water without ever touching the streambed. have a very slow settling speed, even in still water (fine clay may require as much as a year to sink 100 ft in perfectly still water)

-bedload: sand, gravel, and larger rock fragments. the smaller particles are moved along with the general streamflow in a series of jumps or bounces collectively referred to as saltation. coarser pieces are moved by traction, which is defined as rolling or sliding along the streambed. bedload is normally moved spasmodically, especially during floods: debris is transported some distance, dropped, then picked up later and carried farther

Stream flow

erosion usually takes place along the outside of a turn where the stream is deepest (thalweg) and fastest, while alluvial deposition takes place along the inside of a turn where the water speed is slowest

Valley deepening: knickpoints

-irregularities in stream bed. zones of intense weathering on rocks

-faster, more turbulent flow digs down into the stream bed and eats away at weaker strata. stream bed can lower

-upstream migration of knickpoints overtime.

-valley deepens upstream

_________\

resistant /

weak /

resistant/____________

*waterfalls and rapids are often found in valleys where downcutting is prominent

Valley widening: lateral erosion

erosion that occurs when the principal current of a stream swings laterally from one bank to the other, eroding where the velocity is greatest on the outside bank and depositing alluvium where it is least on the inside bank

Floodplain features

-cutoff meander: a meander loop is by-passed as the stream channel shifts through lateral erosion and cuts a new channel across its neck and starts meandering again, leaving the old meander loop as a cutoff meander

-oxbow lake: the cutoff portion of the channel may remain for a period of time as an oxbow. they eventually fill with sediment and vegetation to become oxbow swamps

-meander scars: a dry former stream channel meander through which the stream no longer flows

-natural levees: an embankment of slightly higher ground fringing a stream channel in a floodplain; formed by deposition during floodtime

-yazoo stream: a tributary unable to enter the main stream because of natural levees along the main stream

Valley lengthening: headward erosion

erosion that cuts into the interfluve at the upper end of a gully or valley. the channeled streamflow wears back the top of the interfluve. overtime this erosion extends the valley headward at the expense of the interfluve

*basis of rill, gully, and valley formation and extension

Valley lengthening: delta formation

rivers widening; reach oceans

--downstream

-gets deposited where water slows down

gulf of mexico, bottom of U.S.

overtime create fertile soil

Meandering streams

higher velocities on outside of meanders (bends in the channel) lead to erosion to cut banks lower velocities on inside of meander loops lead to deposition of point bars. a meander shifts its location almost continuously, and migrate across the floodplain and also tend to shift downvalley, producing rapid and sometimes abrupt changes in the channel

complex network of stream channels separated by low bars or islands of sand, gravel, and other loose debris; heavy sediment load, high velocity, variable discharge, easily erodible banks. common in arid environments: prominent dry seasons and periods of low stream discharge

Straight channels

short and uncommon and usually indicative of strong control by the underlying geologic structure. a straight channel doesn't necessarily mean straight flow: thalweg ( deepest parts of the channel) wanders back and forth across the channel

About this deck

By: Anonymous
Created: 2012-05-05
Size: 19 flashcards
Views: 44

About StudyBlue

“Simply amazing. The flash cards are smooth, there are many different types of studying tools, and there is a great search engine. I praise you on the awesomeness.”
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