River Systems

what is erosion in fluvial systems?

dislodging, dissolving, or removing of weathered surface material, the material gets transported to new locations (fluvial transport), and is laid down by deposition

what is sheet flow?

a thin unconfined sheet of water formed when soil becomes saturated

what is the “evolution” of run off?

sheet flow→ rills → gullies → steams

what are rills?

tiny channels

what are drainage basins?

the area contributing water to a river

what is a drainage divide?

the imaginary line that separates one drainage basin from another

what are the three ways fluvial landscapes are created?

erosion, transport, deposition

The energy of a stream to accomplish geomorphic work depends on…

gradient, base level, and volume of flow (discharge)

what is the gradient of a stream?

the drop in elevation per unit distance; generally steeper near headwaters and more gradual downstream

what is the base level?

the lowest point to which a stream can vertically erode its channel

what is ultimate base level?

sea level

what is discharge?

the volume of flow passing a point

discharge increases as…

distance downstream increases

laminar flow

water flowing slowly in a nearly straight path

turbulent flow

water moving quickly in an erratic fashion horizontally and vertically

what are headwaters?

the source of a stream

how is sediment generated?

weathering, bank erosion, scouring of the channel bed

what are trunk streams?

channel network along stream sections that transport sediment

where is most sediment deposited?

at the mouth of the stream and forms a delta (where the stream empties into a larger body of water)

where is finer sediment deposited?

in the ocean; coarser sediment is deposited before streams reach the ocean

what are the three processes that erode stream channels?

hydraulic action, abrasion, and dissolution

what is hydraulic action?

erosion by water pressure; turbulent flow loosens and lifts particles

where is hydraulic action the highest?

upstream tributaries of a drainage basin where sediment load is low and flow is turbulent

what is abrasion?

the scouring of the bed by sediment carried in the flow (the grinding of particles), moves and breaks down sediments

what is dissolution?

the chemical weathering of soluble bedrock; chemical reactions break apart mineral molecules and the ions disperse into the water decomposing the mineral

what are the three types of load in fluvial transport?

dissolved load, suspended load, and bed load

what is dissolved load?

material is carried and transported as dissolved ions in the flow

what is suspended load?

fine-grained particles that are transported in the flow (floating); usually only fine grained sand, silt, and clay carried this way

what prevents suspended load from settling?

stream turbulence

which type of bed load transports the most sediment?

suspended load

where is dissolved load typically?

warm, moist, relatively flat areas with lush vegetation and soluble bedrock

what is bed load?

coarse particles that move along the bed (sand sized and larger depending on the discharge)

what is a difference between bed load and suspended load?

unlike suspended load bed load is not always in motion and is only in motion during flood stage

what form of transport is seen in bed load?

saltation and traction

what is saltation?

bouncing motion

what is traction?

rolling motion

what is a streams capacity?

the maximum load of solid particles a stream can carry

what is a streams competence?

the maximum particle size that can be transported by a stream

what is a multiple-thread channel (or braided channels)?

excess sediment and fluctuation discharge creates a series of interconnected channels

what are the two types of single-thread channels?

meandering or straight

where do straight channels occur?

headwater areas where gradient is high (steep drop in elevation)

where do meandering streams occur?

lower gradient areas (more gradual drop) with finer sediments

what is a meandering stream?

more sinuous snake-like form weaving back and forth across the landscape

where is the fastest flowing water in a straight channel?

in the centre just below the surface where there is the least friction

where is the fastest flowing water in a meandering stream?

shifts to the outside of each bend

what is a cut bank and how is it formed?

when the maximum velocity is defected to the outside of a meander and erosion occurs

what is a point bar and how is it formed?

the inside of a meander where the lowest velocity occurs and sediment is deposited

the more contact with bed and banks…

the more friction

what is an oxbow lake and how is it formed?

the abandonment of a meander which becomes a standing body of water

what is a neck?

narrow piece of land between adjacent cut banks

how is a cut off formed?

when there is a flood and the neck breaches

what are alluvial channels?

self forming and self adjusting to accommodate change

what is sorting?

when particles of a similar size or deposited together; larger particles are deposited first followed by finer particles

what is a flood plain?

flat, low-lying area adjacent to a channel and subjected to recurrent flooding

how are flood plains formed?

when a river overflows its channel

natural levees

raised areas adjacent to the channel formed during flood events

back swamps

formed in flood plains after flood events subside

yazoo tributaries

growing levees prevent tributaries from joining the main stream, forcing them to flow in the back swamp area before reaching the main stream channel

what are incised or entrenched meanders?

meanders flowing through steep, narrow bedrock valleys

what is an alluvial terrace?

form as a river incises

what are alluvial fans?

fan-shaped alluvial deposits formed where a high gradient stream leaves a narrow valley in mountainous terrain, coming out onto a broad flat plain

what is a river delta and how is it formed?

when a river reaches a standing body of water and its sediment load is deposited (coarse sediment is deposited first closest to the rivers mouth)

deltas grow outwards as long as…

the stream supplies more sediment than is being eroded by waves