1. STREAMS & RIVERS
Chapter 6 1

2. watershed drainage basin animation
What is a Watershed?
watershed drainage basin animation

3. NORTH CAROLINA WATERSHEDS (drainage basins)

4. REVIEW…. The Water Cycle4

5. River Systems (structure)
6.1 Streams and Rivers
River Systems (structure)
Tributary- a stream that runs into another stream or river
River system-
a river and all of its
tributaries 5

6. ex) Mississippi River system
Drainage basin, or watershed- all the land that drains into the river either directly or through its tributaries
ex) Mississippi River system
Divide- high land that
separates one drainage
basin from another
Ex) Continental Divide
in the Rocky Mountains 6

7. Velocity- distance that water travels in a given amount of time
Related to the amount of energy that the water has
Erosion occurs more quickly
Other characteristics affect the velocity:
Gradient, Discharge, and Channel Characteristics
Gradient- steepness of the slope of a stream or river
Steep at its source; gradual at sea level

8. Channel- the path through which the water flows in a stream or river
Discharge- the amount, or volume, of water that passes a certain point in a given amount of time
Not constant over length of a river
Increases downstream as tributaries add more water
Not constant year-round- increased precipitation/melting snow
Channel- the path through which the water flows in a stream or river
Shallow, winding stream with many boulders has contact with surface area that causes it to slow down by friction
Straight channel that is wide and deep has less surface area in contact with water, so velocity is greater
Velocity is greatest at the top center of the stream
When it curves, zone of max. speed shifts to the outer bank
SEE FIGURE 3 (p.160)

9. Stream Flow & Erosion
There is more stream velocity in the middle/top of the stream
Erosion will be greater in the middle of the straight stream (increase depth)
Deposition will occur on the stream/river banks where the channel turns and the velocity of the waterway drops
SEE FIGURE 3 (p.160)

11. 6.2 The work of streams

12. Breaks up materials by mechanical means
Erosion
Running water wears down Earth’s surface by breaking up bedrock and by removing eroded rock and soil materials
Breaks up materials by mechanical means
Abrasion mainly; in time, creates rounded boulders, pebbles, and sand grains from the cutting tools

14. the process by which materials are deposited
DEPOSITION
Deposition
the process by which materials are deposited
Occurs because the river or stream no longer has enough energy to transport them

15. Potholes & Plunge Pools-
Erosion creates:
Potholes & Plunge Pools-
deep oval or circular basins formed when water falls either vertically or forward 15

16. Depositional Features
Delta- a fan-shaped deposit that forms when a river flows into a quiet or large body of water
River water comes to almost a standstill at a delta
Distributaries- branches formed by rivers flowing over its delta
Responsible for
delta’s Δ shape
Formation is
delicate balance
between
deposition
and erosion

17. Stream Deposition
River will deposit part of its load when either velocity or discharge decreases
Velocity may decrease if channel widens or river meets an obstruction (curving bank/rock outcrop)
Speed decreases at the inside of the curve and when the river empties into the sea- deposits the most material
Discharge and velocity increase during a flood, then decrease as flood waters subside 17

18. Meanders Meanders = side-to-side curves in a river or stream.
More likely in a FLAT area or a STEEP area?
FLAT!!
When a stream meanders, what happens to the speed?
SLOWS DOWN!! 18

19. Erosion likely to occur: OUTSIDE curves because velocity is faster
Deposition likely to occur:
INSIDE curves because velocity is slower

20. FLOODS:
Most caused by rapid spring snow melt or storms that bring heavy rains over a large region
Ex: Mississippi River in 1993
Measures to control flooding
Artificial Levees- earthen mounds built on the banks of the river
Flood-control dam- store floodwater and then let it out slowly
Limits on floodplain development- minimizing the development on floodplains
Floods 20

21. WATER & EROSION:
MEANDERING STREAM
DELTA FORMATION
OXBOW FORMATION

22. 22

23. Mississippi Watershed Floods (1993)
What happened?
50 deaths
Property damage = $12B
70,000 people left homeless
8.7 M acres farmland lost
Environmental Impacts
Pesticides & agricultural chemicals washed into Gulf of Mexico
Zebra mussels carried to new waters (AP EXAM ‘10)
Exacerbating factors:
(1) Draining wetlands
(2) Building on flood plains
(3) Constructing levees