1. Erosion and Deposition
Water Sculpting the Earth’s Surface

2. Water
Water covers over 70 percent of the surface of the planet..

3. Hydrologic Cycle
A continuous renewal of the Earth’s supply of fresh water
Sources:
The Ocean – Largest source
All other bodies of water

4. Processes of the Water Cycle
The water cycle operates through a series of
processes. These processes are:
Evaporation – from ocean, lakes, rivers
Condensation – water vapor cools and forms clouds
Precipitation – falls to the Earth’s surface as rain, snow, etc.

5. After falling to the ground…
1 of 3 process can occur: 1. Infiltration - absorbed into the ground 2. Runoff – moves across the Earth’s surface into lakes, rivers, oceans 3. Transpiration – absorbed by plants and then released back into the atmosphere

6. The Water Cycle
Water’s movement between the atmosphere, earth and biosphere makes up the water cycle.

7. Stream flow
Influenced by gravity. The time that it takes water to flow from the land to the sea depends on the water’s velocity.

8. Where rivers run straight, their velocity is fastest at midstream
Where rivers run straight, their velocity is fastest at midstream. In bends, water runs fastest along the outer banks.

12. Stream flow
The ability of a stream to erode and transport sediment depends on velocity
Three factors that determine velocity of a stream
Gradient
Channel Characteristics
Discharge

13. Gradient - The steepness of a stream channel.
- The steeper the gradient, the more energy the water has therefore more erosion will take place
Mississippi River

14. Channel Characteristics
A stream channel is the course the water follows. As the water flows, it encounters friction from the stream’s sides and bottom. Large smooth streams flow the most. Small rough streams flow the least.

15. Discharge
Discharge is the amount of water passing a point in a given time. Discharge is usually measured in meters3/second.

16. Factors affecting discharge
1. Precipitation: As additional water reaches the stream due to precipitation, discharge increases.
2. Stream Channel Width: The wider the stream channel, the more water it discharges
3. Stream Contour: The smoother the stream channel, the more the discharge.

17. The world’s largest river, the Amazon, has a discharge rate of 212,000 meters3/second.

18. Changes Between Upstream and Downstream
While gradient decreases between the head waters and the tail waters of a river, discharge increases. This is because all along its course, rivers are fed by tributaries.
Mississippi
River
Basin

19. Base Level
At Base level (or sea level) rivers enter wide, flat valleys. Here rivers and streams begin to bend back and forth and form meanders.
Thames River,
England

20. Meanders

21. Erosion Streams and rivers eroded their channels by : 1. abrasion
2. grinding
3. dissolving soluble materials.

22. Sediment Transport Streams transport sediment in three ways:
In solution
In suspension
Rolling material along the bottom.

23. In solution
Material carried in solution by a river is called its dissolved load.

24. In suspension
Material in suspension is called its suspended load. The majority of sediments carried by a river is its suspended load.

25. Rolling material along the bottom.
These materials are called the bed load.

26. Competence versus Capacity
A streams competence measures the largest particle it can carry. Competence increases with velocity.
Capacity is the maximum load that a stream can carry. Capacity is directly related to its discharge.

27. Deposition
Deposition occurs when stream flow drops below a critical velocity thus allowing a particle to settle out.
Alluvial
Iron deposits in a
Steam in
New Zealand

28. Deposition
During deposition, like-sized particles tend to fall out. This causes deposits to be constructed of similar-sized particles. This process is called sorting. These deposits are called alluvium.
Alluvial deposits
following the
eruption of Mt.
St. Helen

29. Depositional Environments
When a river enters the relatively still waters of a lake or ocean, its velocity decreases and forms deltas, or broad, fan-shaped alluvial deposits.
Niger River
delta

30. Depositional Environments
When streams overflow their banks, they create mounds of sediment parallel to the stream called natural levees.

31. Stream Valleys Narrow Valleys
V-shaped valleys with rapids and waterfalls
The primary work of the stream is downcutting toward base level

32. Stream Valleys - continued
Wide Valleys
Flat valley floors or floodplains, streams with meanders
Downcutting becomes less and as a result the stream’s energy is directed against the sides widening the valley

33. Floods and Flood Control
Most floods are caused by rapid snowmelts in the Spring and heavy rains over a large region..
Upper
Mississippi
River Valley
Flood-1993

34. Measures to Control Flooding
Artificial Levees
Limiting Development
Flood-control Dams