Stream and River Deposits Chapter 11 Section 2

Stream and River Deposits Chapter 11 Section 2

The Ability to Erode • Gradient: Measure of change in elevation over a certain distance • Discharge: The amount of water a stream or river carries • Load: The material carried by a stream

Gradient • The steeper a stream is the more erosive energy it has

Discharge • The more water a river will discharge the more erosive power it will have.

Load • Load is affected by speed. – Fast = large particles – Slow = Smaller particles

Stages of a River • Rivers go through a “life cycle. ” • Youthful • Mature • Old

Youthful • Youthful rivers have a steep gradient, a steep and narrow channel, and many waterfalls. The channel will erode deeper, rather than wider.

Mature • Mature Rivers have a gradient that is not as steep as a youthful river. They have few falls and rapids. They will erode wider rather than deeper.

Old • Old rivers have a low gradient and little erosive energy. They deposit rather than erode.

Rejuvenated Rivers • Rejuvenated rivers are mature rivers that have a steeper gradient due to land rising because of tectonic activity.

Deposition

Delta • Rivers slow down when they empty into a large body of water. • This often causes a fan-shaped pattern of deposits called a delta.

Deltas (cont. ) • These deltas cause the coast line to grow. • Deltas are made of mostly mud. Some of the mud particles come from very far away.

Alluvial Fans • When a fast-moving mountain stream flows onto a flat plain, the stream slows very quickly. • The deposition forms an alluvial fan. • Alluvial fans form on dry land.

How do rivers deposit sediment? • Rivers pick up weathered sediment during erosion. • Then the sediment is dropped off or laid down. • This happens when the speed of water decreases.

Meandering Rivers • Constantly erode material - Cut bank • Constantly deposit material - Point bar • Change their channel course gradually • Create floodplains wider than the channel – Very Fertile soil – Subjected to seasonal flooding

Formation of Meanders

Point bar deposits

Cut bank erosion Point bar deposits } Meander loop

Formation of an Oxbow

Meandering stream flowing from top of screen to bottom

Maximum deposition Maximum erosion

Meander scars Oxbow Lake Oxbow cuttoff

Flood Plains • When there is a sudden increase in the volume of water flowing into a stream, it will overflow. • This is caused by a SUDDEN increase in precipitation or rapid snow melt. • The area around a river that forms from sediments deposited during a flood is called a floodplain. • Each flood adds another layer of sediment.

Good Farming • Floodplains are good for farming because the periodic floods bring in new, rich soil.

Review 1. What is the difference between a delta 2. 3. 4. 5. and an alluvial fan? Why are floodplains bad? Why are flood plains good? What causes sediment to be deposited. What is the relationship between weathering, erosion, and deposition?