1. The Work of Streams

2. Introduction Streams are: Channels of Erosion Transporters of Sediment
Creators of features

3. Erosion Streams erode their channels by lifting loose particles by:
Abrasion
Grinding
Dissolving
The faster the current of a stream, the more erosion takes place.

4. Sediment Transport Streams transport sediment in three ways:
In solution (dissolved load)
In suspension (suspended load)
Scooting or rolling along the bottom (bed load)

5. Load Types
Dissolved load: Particles tiny enough to be dissolved in the water (dust, particles of sand, etc)
Suspended Load: Particles that are small enough to get carried by the current downstream.
Bed Load: Solid material that is too large to get carried by the current. These tend to roll along the bottom of a stream in the same direction as the current.

6. Deposition
Deposition occurs as streamflow drops below the critical settling velocity of a certain particle size.
TRANSLATION? The stream slows down and particles drop out!
Alluvium: The material that is dropped out of a stream.

7. Deposition – continued!
Deltas: An accumulation of sediment formed where a stream or river enters a lake or ocean.

8. Deposition - Continued
Natural Levees – a “wall” that forms along the banks of a flat river that floods repeatedly. The natural levee can protect the land from future flooding.

9. Stream Valleys Narrow Valleys Wide Valleys V-shaped
Formed from Down-cutting.
Rapids and Waterfalls found in this type.
Wide Valleys
Formed from erosion on the side of the stream channel.
Has a flat valley next to it called the floodplain.
Move in meanders:
Erodes the outside of the bends and deposits on the inside.

10. Floods
A flood occurs when the discharge of a stream becomes so great that it overflows its banks.
Most are caused by rapid snow melts or storms with heavy rain.

11. How do we control flooding?
Artificial Levees – mounds of earth built on the side of a river.
Flood Control Dams – smaller dams built across streams that can be opened or closed to control stream flow.
Limiting Development – Planning is done to avoid building on floodplains.