1. Stream Erosion & Deposition Chapter 6 sections 1 and 2

2. What is a Stream? A stream is a moving body of water that eventually connects to an ocean Note: Today we will be discussing large streams called rivers!

3. River Characteristics 1. Velocity – how fast or slow the river is moving; this determines the rivers ability to erode sediments Which river has a greater velocity?

4. 2. Gradient – the slope or steepness of the river; the steeper the gradient, the more energy River Characteristics

5. 3. Discharge – the amount of water moving by a certain point of the river in a set time The Amazon River in South America has greatest discharge 212,400 m 3 /s Mississippi River in USA has 7 th greatest discharge at 17,300 m 3 /s River Characteristics

6. 4. Stream Channel – the course that the water flows in a river River Characteristics

7. Following a River from Source to Mouth A river begins at the source/headwaters –This is usually where you find the steepest gradient –You may also find V-shaped valleys here

9. Following a River from Source to Mouth Alluvial fans – fan-shaped sediment deposit that forms when a high gradient stream leaves a narrow valley

10. Following a River from Source to Mouth As the river continues, you will also find many tributaries – this is where one stream empties into another As more tributaries add water to the main river, the amount of discharge increases

12. Following a River from Source to Mouth As the river moves downhill, it will erode its channel until it hits base level Base level is the lowest point to which a river can erode its channel

13. Following a River from Source to Mouth As a river approaches base level, it can develop meanders – bends in the stream channel

14. Following a River from Source to Mouth Delta - a fan-shaped sediment deposit where a river empties into an ocean at mouth

16. New Orleans: Built on Mississippi River Delta

17. Note: Meanders can turn into Oxbow lakes…here’s how

18. Sediment Transport in Rivers Streams carry sediment in 3 ways: –In solution (dissolved load) –In suspension (suspended load) –Scooting or rolling along bottom (bed load)

19. 1. Dissolved Load Sediments that are dissolved into river water

20. 2. Suspended Load Fine-grained sediment (like sand, silt, clay) that remains in the water during transportation –Usually what you see that makes a river look dirty –Most sediment carried by a stream is suspended –This amount increases dramatically during flood

21. 3. Bed Load Heavier, coarse grained sediments that travel along the bottom of a stream. –Causes the most stream erosion! –Sediment may not move frequently