Streams and Rivers

Question 1

Where is the majority of our water?

Answer 1

97% is saltwater (oceans)
Freshwater is mainly in glaciers
Accessible freshwater is mainly in groundwater
The last bit is surface water

Question 2

What is discharge? How do we calculate it?

Answer 2

Volume of water flowing past a specific point (higher discharge = can carry more material and move larger sediments)
Changes based on seasons, elevation, bends, etc.

Height x Width x Speed

Question 3

Laminar Flow

Answer 3

Laminar = flows smoothly in a straight path
Uncommon in nature: water must slow-moving, deep, or partially frozen

Question 4

Turbulent Flow

Answer 4

Stream paths mix, cross, and form chaotic swirls

Question 5

Source aka Headwaters

Answer 5

Furthest point upstream (highest elevation)
- large grains

Question 6

Mouth

Answer 6

Furthest point downstream (lowest elevation, usually where it empties into a lake, ocean, etc.)

Question 7

Longitudinal Profile

Answer 7

Tracing the river’s decreasing slope from source to mouth

Question 8

Base Level

Answer 8

Lowest level that a stream will erode to (sea level)

Question 9

Floodplains

Answer 9

A flat area next to the river that floods when the stream overflows

Question 10

Stream Terraces

Answer 10

Broad, flat benches that mark former levels of the floodplain

Question 11

In what 3 ways do streams erode?

Answer 11

Removal of rock debris (pick up + carry away)
Downcutting by abrasion = canyons, V-shaped valleys, + potholes
Headwater erosion (point of highest energy)

Question 12

What are the characteristics of a meandering river?

Answer 12

Meandering: single channel, no set pattern, needs vegetation to create stable banks, not wide, deeper, relatively constant flow, transports fine sediments (suspended load), slowly changes shape across time

Question 13

What are the characteristics of a braided river?

Answer 13

Braided: network of converging and diverging channels, shallow, wide, highly variable load depending on seasons/rain, little to no vegetation, high sediment load (mainly coarse/bed load), can change shape very quickly

Question 14

Point bars vs Cut banks

Answer 14

P.B. = the point where a meandering river is slower (inside the bend), leading to sediment deposition
C.B. = the point where a meandering river is fast (outside of the bend), leading to erosion

Question 15

Oxbow Lake

Answer 15

A meander loop gets cut off and isolated from the stream as the bends merge and close the path
Shaped like a horseshoe

Question 16

Drainage Basin

Answer 16

The total land that empties water into a stream system
Boundaries (like mountains) can separate one drainage basin from another
Drainage patterns can also change based on surrounding geology

Question 17

Suspended Load

Answer 17

Fine-grained material is lifted and carried in suspension
75% of sediment is transported this way

Question 18

Dissolved Load

Answer 18

Ions dissolved in the water

Question 19

Bed Load

Answer 19

Particles that are too heavy or large to be carried instead roll/skip along the bottom, becoming smaller and rounder

Question 20

Traction vs Saltation

Answer 20

Traction: intermittent sliding, dragging, or rolling along the bottom

Saltation: briefly lifted in a series of hops or skips

Question 21

Capacity vs Competence

Answer 21

Capacity = the max amount of sediment a stream can carry
Competence = the largest particle a stream is capable of moving (controlled by the speed of the river)

Question 22

Natural Levees

Answer 22

A ridge of coarse-grained sediment next to the stream channel caused by deposition during floods
As they build up, it makes it harder for the channel to overflow

Question 23

Deltas

Answer 23

Braided rivers form as a stream empties into the ocean

Stream speed decreases quickly when it reaches the ocean, depositing most of the sediment

They grow in size over time and can change location based on sea level rise and fall (b/c of changing base level)

Question 24

Alluvial Fans

Answer 24

Similarly shaped to deltas (like a D), they are aprons of sediment that form at the mouths of dry mountain canyons because of intermittent rainfall

Sediment is carried down mountains via water, wind, and gravity, but once it hits the base, velocity quickly decreases

Question 25

What are some pieces of evidence for alluvial fans?

Answer 25

Broken pieces of trees because of how powerful the force of the water is
Reverse grading (with the smallest sediments at the bottom)

Question 26

How do plate tectonics relate to streams and alluvial fans?

Answer 26

Alluvial fans only form near mountains, which are typically made on convergent plate boundaries
All streams will flow from high to low elevation

Question 27

Man-made Levees

Answer 27

Building up the height of stream banks manually in an attempt to contain water and divert flow to other areas during floods
However, if they’re breached, the flooding persists and the water takes longer to recede