1. STREAMS & RIVERS
Chapter 6

2. REVIEW…. The Water Cycle

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

4. separates one drainage basin from another
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

5. Characteristics
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

6. Characteristics continued…
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)

8. Different types of Stream Channels

9. Base Level
Base Level = lowest point to which a stream can erode its channel.
Base level is usually the level at which the mouth of a stream enters the ocean or the next body of water.
Temporary Base Level vs. Ultimate Base Level
Temporary = lake Ultimate = sea level
A stream in a broad,
flat-bottomed valley
that is near its base level
often develops many meanders.

10. 6.2 Stream Erosion and Deposition
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

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

12. Stream Flow & Erosion SEE FIGURE 3 (p.160)
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)

13. Erosion & Deposition Features in an Old Stream/River

14. Erosion cont… Potholes-
deep oval or circular basins formed when water in a river develops small whirlpools, and materials grind potholes in the bedrock

15. consists of dissolving soluble minerals
Plunge pool-
a basin that has been
worn away at the base
of a waterfall by the
action of falling water
Dunn River Falls
Chemical weathering
consists of dissolving soluble minerals
Calcite is dissolved, which may form pits and holes in the riverbed
Widens existing cracks and holes

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 shape
Formation is
delicate balance
between deposition
and erosion

17. Alluvial fan- fan-shaped deposit
May form when a steep mountain stream meets dry, level land at the base of a mountain
Differs from a delta
Deposit is formed on land, not in water
Sediments are coarse sands and gravels rather than fine silt and clay
Surface is sloping,
not flat like that of a
delta

18. Transported Material
Load- the eroded rock and soil materials that are transported downstream by a river
Suspension- a state in which rock materials carried by a river are stirred up and kept from sinking by the turbulence of stream flow
Materials are heavier than water, but the turbulence keeps them stirred up
The faster a stream flows, the more turbulent and muddy it becomes
Bedload- sand, pebbles, and boulders that are moved along the bed of a stream and that are too heavy to be carried in suspension

19. Transporting Materials
Two measures are used to describe the ability of a stream to transport materials
Competence- a measure that describes the maximum size of the particles a stream can carry
Capacity- a measure of the total amount of sediment a stream can carry
Depend on the velocity and discharge
Vary along a stream and change throughout the year
High velocity + High discharge = large amount of sediment and larger sizes of sediment particles

20. 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

21. Meanders – write your own notes!
Erosion occurs along the OUTSIDE of a meander…
…because the water is FASTER there (more velocity, more energy to erode)
Deposition occurs along INSIDE curves, (it’s slower & water cannot transport sediment any longer)

22. Stream Valleys Narrow valleys Wide valleys
narrow V-shaped valley shows
that the stream’s primary work
has been down cutting toward
base level
Rapids and waterfalls
Wide valleys
Downward erosion is less dominant
More energy is directed side to side
Floodplain- the flat, low-lying portion
of a stream valley subject to periodic flooding

23. Linville Gorge Carved out of the bedrock by the river forming a river valley.

24. Floodplains Streams that flow on floodplains move in meanders
Cutoffs- shorter channel segments
Oxbow lakes- abandoned bend of a river/stream

25. Oxbow Lake Formation
Meander forms (because the stream is close to base level)
Far side of curves erode faster, inching closer & closer together.
Curves join, and water moves past the bypass loop
Deposition occurs at the ends of the loop (because velocity drops), cutting off the oxbow lake.

27. 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

28. Flood plains & Levees
Developing in flood plains causes great economic loss.
What can we do to help this??
Build smaller levees farther apart…
Less expensive to build…
Improves habitat in the flood plain.