Why study streams

Question 1

Why study streams?

Answer 1

• They provide water and deposit fertile soil for agriculture
• They’re pathways for commerce and trade
• They erode, flood, and sculpt the landscape

Question 2

Evapotranspiration:

Answer 2

Moves water into the atmosphere and precipitation brings it back to earth

Question 3

Drainage basin:

Answer 3

Is the area that drains into a stream.

Question 4

Divides

Answer 4

Are ridges that serrate basins

Question 5

What is the largest river basin?

Answer 5

The Mississippi basin

Question 6

Discharge

Answer 6

Is the amount of water that flows through a channel

Question 7

Where does sediment come from?

Answer 7

• Loosened particles from weathering are picked up in surface runoff and transported to the stream channel
• Mass movement events may move loose material downslope into the stream channel
• The stream itself may also erode the banks of its channel

Question 8

Sediment moves as…

Answer 8

Bedload and suspended load

Question 9

Bedload:

Answer 9

Is large grains that cannot be picked up, but still are able to be moved. They roll, bounce, and slide along the bottom
- When a stream is at bankfull, all sizes of particles move due to increased stress

Question 10

Suspended Load:

Answer 10

Small sediment grains that mix with the flowing water are transported above the bed, rarely touch the bottom, and came make the water cloudy/muddy

Question 11

Dissolved load:

Answer 11

The hidden load. Ions in solution form chemical weathering are also carried by water in streams

Question 12

Alluvial Stream

Answer 12

Is where the channel is in water transported sediment. It has a different energy structure than a bedrock stream which is cut into solid rock

Question 13

How do streams pick up sediment?

Answer 13

Force, not velocity is exerted on a particle to move it.

Question 14

When does shear stress increase?

Answer 14

Shear stress increases with increasing water depth and increased slope. Both cases require shear force to overcome the resisting forces of friction and cohesion

Question 15

Do small particles take as much shear force as large particles?

Answer 15

Yes, small particles of silt and clay actually have large cohesive forces for their size that keeps them in place

Question 16

Stream power:

Answer 16

Is the result of shear stress and velocity .

Question 17

A stream must..

Answer 17

Lose power to move sediment when it switches form erosion to deposition

Question 18

Loss of shear stress will cause..

Answer 18

Deposition

Question 19

Loss of velocity will cause…

Answer 19

Deposition

Question 20

Loss of discharge will cause…

Answer 20

Deposition because without water, there is no shear stress or any velocity

Question 21

Increase of water depth…

Answer 21

Increases shear stress, which increases stream power which results in Erosion

Question 22

Decrease in water depth…

Answer 22

Decreases shear stress, which decreases stream power which results in deposition

Question 23

Increase in channel slope…

Answer 23

Increases shear stress, which increases stream power which results in erosion

Question 24

Decrease in channel slope…

Answer 24

Decreases shear stress, which decreases stream power which results in deposition

Question 25

Increase in flow of velocity…

Answer 25

Increases velocity, which increases stream power, which results in erosion

Question 26

Decrease in flow of velocity…

Answer 26

Decreases velocity, which decreases stream power which results in deposition

Question 27

When does deposition happen?

Answer 27

Deposition happens where water depth decreases and stream power drops off

Question 28

An alluvial fan forms where…

Answer 28

The stream goes from confined to unconfined

Question 29

Where do deltas form?

Answer 29

They form where streams enter the ocean or lake

Question 30

What factors determine channel pattern?

Answer 30

• Meandering Patterns

- Braided patterns

Question 31

Meandering Patterns:

Answer 31

Is a single main channel that has various loops and/or curves down its length. It is longer and has a lower average slope.

Question 32

Braided Patterns:

Answer 32

Are a series of small channels that are interwoven into a larger whole

Question 33

Channel Patterns:

Answer 33

Are most often a combination of meandering and braided patterns

Question 34

How do banks determine channel pattern?

Answer 34

• Bank erodibility influences channel pattern

- Stable banks are due to clay, vegetation or a narrow, deep, and sinuous channel

Question 35

Why do streams flood?

Answer 35

• Discharge exceeds a stream channels capacity

- The drainage basin cannot absorb the water from precipitation or snowmelt and then must runoff onto the surface

Question 36

Causes of floods:

Answer 36

• Extreme rainfall
• Rapid snowmelt
• Storm surge
• Breaching of dams/embankments

Question 37

Flash floods

Answer 37

Associated with canyons and are generally the deepest and most damaging. They are rapid and difficult to predict

Question 38

Prolonged floods:

Answer 38

Last more than two days and inundate large areas

Question 39

Storm surge

Answer 39

Strong onshore winds cause ocean water to ‘pile up’ along the shore which raises the level of all rivers flowing into that coastal area