Stream/River Erosion & Deposition

1. Stream/River Erosion & Deposition

2. What is a Stream/River? • A stream is a moving body of water that eventually connects to an ocean A river is simply a LARGE stream!!

3. Velocity – how fast or slow the river is moving. • This determines the rivers ability to erode sediments Stream / River Characteristics Which river has a greater velocity?

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

5. Stream / River Characteristics 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 m3/s Mississippi River in USA has 7th greatest discharge at 17,300 m3/s

6. 4. Stream Channel – the course that the water flows in a river Stream / 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 valleyshere

8. Following a River from Source to Mouth • Alluvial Fan: A fan-shaped deposit of sediment that forms when a stream drops downward from a higher elevation and encounters the valley floor. The stream slows down, depositing fine silt, sand, or other sediments it is carrying.

9. Waterfall Formation The stream bed has soft and hard rock. The softer rock erodes MORE QUICKLY as the river flows over it. Eventually there is a big enough difference in the rock layers to form a waterfall.

11. 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. Tributaries

13. 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.

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

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

16. Lena River Delta in Siberia

17. New Orleans: Built on Mississippi River Delta

18. Ox Bow Lakes Meanders can turn into Oxbow lakes…here’s how

19. Ox Bow Lakes • Neck of meander is gradually eroded • Once cut off, the water takes the quickest/shortest route • What’s left behind is the Ox Bow lake

20. Sediment Transport in Rivers • Rivers & Streams carry sediment in 3 ways: • In solution (dissolved load) • In suspension (suspended load) • Scooting or rolling along bottom (bed load) http://www.youtube.com/watch?v=LhbEvV5hqCo

21. 1. Dissolved Load Sediments that are dissolved in river water

22. 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 floods

23. 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

24. Over 55% of U.S. rivers and streams are so polluted that they are no longer safe for fish and other aquatic life!!

25. Quiz Vocabulary • Stream • Velocity • Gradient • Discharge • Stream Channel • Source/Headwaters • Alluvial Fan • Tributaries • Base Level • Meander • Delta • Ox Bow Lake • Dissolved Load • Suspended Load • Bed Load