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Naturalists at Large: Rivers watersheds
The streams found in mountains are likely young, with V-shaped valleys and steep gradients. They move fast upstream, carrying large rocks and boulders, but slow downstream where they deposit small silts and clays. This sorting process forms the soils in valleys. Grand Canyon took 1-3 million years to form as the river cut through rock. Rivers slow and widen as they approach base level, forming broad floodplains and meanders.
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Naturalists at Large: Rivers watersheds
- 2. The streams found in mountains are likely to have formed relatively recently.
- 3. These young streams typically have V-shaped valleys.
- 4. The rivers tendto move fast in their upstream portions, although, some are slowed by the large rocks and boulders in the river channel.
- 5. The young mountain streams tend to have a steep slope or gradient. Slope or Gradient
- 6. Rivers move agreat deal of material. The faster the water moves, the larger material that can be carried down stream.
- 7. Fast moving upstreamportions can often move rocks and boulders. Downstream portions usually only transport small silts and clays.
- 8. This process tendsto sort materials by size. Have you ever wondered why we have so much silt and clay in our soil?
- 9. Valleys with very steep, almost vertical sides are called canyons or gorges.
- 10. How long do you think it took to form the Grand Canyon?
- 11. Most scientists believeit took 1 to 3 million years!
- 12. A stream orriver can not cut its bed any lower than the body of water into which it flows. As the stream approaches this base level, the slope and speed of the stream decrease.
- 13. The river channel becomes wider, deeper, and the volume is bigger as there are more tributaries contributing to the volume.
- 14. The river valleyalso changes at this point. It becomes more open, more of a U shape with a wider river floor.
- 15. The lower or downstream portion of the river is at its deepest, widest and slowest speed. It also has the largest volume and a very gentle gradient.
- 16. The river valleytends to be broad, flat and bounded by bluffs. These bottom lands are often areas that flood.
- 17. Lower portions ofrivers often start to meander or form a s-shape river pattern.
- 18. Erosion is greateron the outside of the bend, deposition more on the inside.
- 19. The river caneventually cut through the meander, leaving a straighter section and an ox-bow lake.
- 20. To view ananimation of this process click on this web site. http://www.school-portal.co.uk/GroupDownloadFile.asp?file=21606
- 21. Rivers deposit the sediment they have carried as they slow down. This sediment load will often form deltas as the river flows into the quiet waters of a bay or gulf.
- 22. The river tendsto be split into channels by its own deposits as it drops more sediment. As the deposits grow, they resemble the Greek letter ▲(delta).
- 23. Alluvial Fans An alluvialfan differs from a delta in several ways. The deposit is formed on land, not in water.
- 24. Alluvial Fans Also, the sediments of these deposits are coarse sands and gravels, rather than fine silts and clays of the deltas.
- 25. Watershed A watershed, or drainage basin includes all of the land that drains into a river or bay either directly or through its tributaries.
- 26. Watershed The high land that separates one river valley or watershed from the next, is called the divide.