Characteristics of Straight, Meandering, and Braided Channels

Straight Channels Rare Low velocity due to low gradient (slope) Bars = piles of sediment within the channel. Rare because of constant deposition and erosion

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

Meandering Channels Latin 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 – lake formed when a meander of a river is cut off from the main channel

Braided Channels Low gradient End of a river Usually happens at deltas.

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

Youthful Rivers V-shaped valley with steep sides A youthful stream usually erodes its bed more rapidly than it erodes its banks. V-shaped valley with steep sides Waterfalls and rapids are common Relatively few tributaries. No Floodplain Flat area next to a river that can flood Somewhat straight channel Steep gradient Few pointbars Youthful Rivers

Yellowstone River

Mature Rivers 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 Rivers Land 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 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