Characteristics of Characteristics of Straight, Straight,

Meandering, and Meandering, and Braided ChannelsBraided Channels

RareRare

Low velocity due to Low velocity due to low gradient low gradient (slope)(slope)

Bars = piles of sediment within the channel.

Straight ChannelsStraight Channels

Velocity in a straight river channelVelocity in a straight river channelVelocity is always greatest in the middle away from the Velocity is always greatest in the middle away from the banks and bed of the channel (area 4)banks and bed of the channel (area 4)

Meandering ChannelsMeandering ChannelsLatin word for WANDERING.Cutbank = outside curve of meander.

High erosion and velocity

Point bar = inside curve of a meander.

High deposition Low velocity

This continual erosion and deposition causes the channel to move and bend across a river valley.Creates a floodplain and Oxbow Lakes

Flat land next to a river that can floods.

Oxbow Lakes – Oxbow Lakes – lake formed when a meander lake formed when a meander

of a river is cut off from the main channelof a river is cut off from the main channel

Braided ChannelsBraided Channels

Low gradientLow gradient

End of a riverEnd of a river

Usually happens at Usually happens at deltas.deltas.

DeltasDeltas

Stream enters standing body of water.

Velocity drops and sediment is deposited.

They build outward from coastline.

Can only survive in low current and velocity.

The Stream CycleThe Stream Cycle

As a river erodes its banks and bed, it As a river erodes its banks and bed, it changes the landforms it passes though changes the landforms it passes though and alters its own course. The and alters its own course. The development of a river system is divided development of a river system is divided into three stages:into three stages: Youthful Mature Old

A river can become rejuvenated

A youthful stream usually erodes its bed more rapidly than it erodes its banks.V-shaped valley with steep sidesWaterfalls and rapids are commonRelatively few tributaries.No Floodplain

Flat area next to a river that can floodSomewhat straight channelSteep gradientFew pointbars

Youthful Youthful RiversRivers

Yellowstone Yellowstone RiverRiver

Mature Mature RiversRivers

V-Shaped valley is not as deep

Floodplain develops

Increased meanders

Gradient begins to reduce

Erosion is sideways instead of downward

Divides become rounded

Erosion and deposition at near equal rates

Pointbars and cutbanks develop

Old RiversOld RiversLand worn to nearly flat surface

No downward cutting taking place

Very low gradient

Rivers meander across extremely wide, flat flood plains

Natural levees may form

Oxbow lakes form

Oxbow Lakes

Rejuvenated RiversRejuvenated Rivers

Uplift of Land (Lowering of Sea Level, sometimes greater stream flow) causes stream to speed up and cut deeper.

Stream valley takes on youthful characteristics but retains features of older stages as well.

Can happen at any point in the cycle.

Rejuvenation of an old-age landscape

Rejuvenation of an early mature landscape