1. River Systems
Chapter 15

2. 15.1 – The Water Cycle

4. Water Cycle Evapotranspiration Evapotranspiration increases
Total loss of water by an area
Evaporation + transpiration by organisms
Evapotranspiration increases
With temperature
With vegetation
With wind

5. Water Budget Precipitation = Evapotranspiration + Runoff
Globally balanced
Locally not balanced
Factors affecting local water budget
Temperature Vegetation
Wind Rainfall amounts

6. Global Water Oceans (97%) – too salty too use Ice caps (2%)
Ground Water (<1%)
Rivers, lakes, reservoirs…(<0.01%)

7. Water Use in U.S. ~ 100 – 150 gallons/day/person (municipal)
~ 2000 gallons/day/person total use
Agriculture, hydroelectric, industry

8. 15.2 – Stream Erosion

9. How rivers develop
A river system begins to form when precipitation exceeds evapotranspiration in a given area.
After soil soaks what it can hold, excess water moves downslope as runoff.
Runoff erodes rock & soil & may form a ditch called a gully
Eventually develops into a permanent stream

10. River System Parts
Tributaries
Feeder streams into main stream

11. River System Parts Lake Lanier Watershed Area Watershed
Area that drains into a particular stream
White
Lumpkin
Dawson
Habersham
Lake Lanier Watershed Area
Hall
Forsyth

12. River System Parts
Divide
Separates watersheds

13. Channel Erosion Headward Erosion
Channel erodes at river head in opposite direction of flow

14. Headward Erosion

15. Headward Erosion

16. Headward Erosion Niagara Falls

17. Stream Piracy One stream takes over and begins to drain an area
Pirate stream erodes faster
Pirate stream

18. Stream Load Suspended load Bed load Dissolved load Fine sand and silt
Larger materials bouncing down stream
Dissolved load
Transported in liquid form

19. Stream Load Suspended load: particles of fine sand and silt
Bed load: larger, coarser materials (sand, gravel, pebbles)
Dissolved load: mineral matter suspended in liquid solution

20. More River System Parts
Stream Discharge
Volume of water that a stream transports
Higher velocity = higher discharge

21. More River System Parts
Stream gradient
Steepness
Generally steeper near headwaters
Steeper means higher velocity

22. Gradients Steep Gradient Gentle Gradient Yellowstone River, WY
Near headwater
Gentle Gradient
Far from headwater
Yellowstone River, WY
Mississippi River, New Orleans

23. Meandering Channels Slow moving streams tend to wander
They form meanders
Winding patterns of wide curves
Slowness causes bank erosion as opposed to bed erosion

24. Meander on the Mississippi Near Baton Rouge

25. Louisiana Meander

26. Meandering Stream Rocky Mountain National Park

27. Meanders and Lakes
Oxbow Lakes: A meander curves and forms a narrow neck.
When this narrow neck is cut off, the meander is isolated
from the river and forms an oxbow lake.
Oxbow lakes

28. Braided Streams
Stream with multiple channels that divide and rejoin around sediment bars
Result of large sediment load

29. 15.3 – Stream Deposition

30. Deltas
Fan-shaped mass of deposited material at the mouth of a stream or river

31. Alluvial Fan Deltas formed on land
Caused by temporary streams (run off)

32. Floodplains
The part of a valley floor that may be covered with water during a flood.

33. Natural Levees
When a stream overflows its banks and spreads out over the floodplain, the stream slows down and deposits coarse sediment on the river banks.
This sediment builds up and raises the height of the river banks.
This is a natural levee.
Finer sediments are washed out into the floodplain.

34. Flood Control
Human activities contribute to flooding: logging & clearing land of vegetation lead to increased erosion.
Natural events like fires can increase likelihood of flooding.

35. Flood Control
Direct: Building artificial structures that redirect flow of water
Examples: dams, levees

36. Flood control
Indirect methods: structures are not specifically built and natural methods are used like soil & forest conservation
These prevent excess runoff during periods of heavy rainfall

37. Living in Floodplains
Sediments deposited during floods are rich in minerals and nutrients.
Rich soils draw people to live there for farming.
Convenient access to river for shipping, fishing, and transportation also make people want to live here.

38. Life Cycle of Lakes
Precipitation forms in a depression and forms a lake.
A lake loses water as it drains or evaporates.
A common cause of excess drainage? An outflowing stream erodes its bed below the level of the lake basin.
As water is lost, the lake basin may eventually become dry land.
Lakes can also fill up with sediment and disappear.
Sediments are carried by streams or in runoff from land.