3 streams and floods

Question 1

Rivers

Answer 1

By far the most important agent of erosion and deposition on the surface of the Earth

Question 2

Drainage networks

Answer 2

dominate earth’s surface

Question 3

Drainage Basins and Divides

Answer 3

Drainage basin
The area drained by a certain river system
All streams flow to the ocean
Except not quite
we live in a basin that doesn’t reach the ocean because we have divides on all sides

Divides
Boundaries that separate one drainage basin from another
Mountains: always a higher point in

Question 4

Drainage patterns: dendritic

Answer 4

Dendritic
Horizontal bed layers of soft rock
looks like a tree

Question 5

drainage patterns: radial

Answer 5

radial
isolated peaks
star shaped around a peak

Question 6

Drainage Patterns: rectangular

Answer 6

rectangular
jointed bed rock at 90 degree angles
keep eroding in the patterns of deformations

Question 7

drainage patterns: trellis

Answer 7

trellis
deformed strata with alternating weak and resistant rock
see screen shot
like railroad track symbol

Question 8

drainage patterns: parallel

Answer 8

parallel
steep sided hills with less vegetation
like lines on a paper

Question 9

river vs. creek vs. stream vs. brook vs. etc.

Answer 9

Informal
River > Stream > Creek ~ Brook ~ Burn ~ Crick
Geology
River or Stream no matter the size
Any flowing channelized water
Permanent vs Ephemeral (temporary)

Question 10

river systems

Answer 10

Any body of water that flows downhill in well defined channel
Streams erode the valleys through which they flow
valleys weren’t there until the stream cut down into it

River system parts
Collecting
Transporting
Dispersing

Question 11

River Systems: collecting

Answer 11

Collecting
Occurs in tributaries
“Headwaters” top
Erosion= primary geologic characteristic
Transportation-some
Deposition-not much
Have the most energy

Question 12

River Systems: Transporting

Answer 12

Transporting
Occurs in main “trunk”
Erosion-some
Transportation-main
Deposition-some

Question 13

River Systems: dispersing

Answer 13

Dispersing
Occurs in distributaries
“Mouth” end
Erosion-not much
Transportation-some
Deposition-main

Question 14

Stream Flow Variables

Answer 14

Discharge
Gradient
Velocity
Sediment load
Base level

Question 15

Stream Flow Variables: Discharge

Answer 15

Volume of water flowing past a given point in the river in a certain amount of time

Varies with season and weather

Weir (like we saw on the bridge in rock canyon) Measured in cubic meters per second

Question 16

Stream Flow Variables: Gradient

Answer 16

Slope of the river channel
Rise over the run
Changes over length of river
Steep at headwaters
- Sediments are coarse
Nearly flat at mouth
- Sediments are fine

Question 17

Stream Flow Variables: Velocity

Answer 17

Directly related to gradient and volume
Higher gradient, higher velocity
Higher volume, higher velocity
Not uniform in stream channel
Highest in middle/center and top of channel

Question 18

Stream Flow Variables: Sediment Load

Answer 18

Material carried by the stream

Three types
Suspended load
- Fine particles (makes it look dirty/murky)
- Usually largest fraction of mat’l carried

Bed load
- Coarse particles
- Rolling, sliding, or saltation (bouncing)

Dissolved load
- Ions in solution (not visible)

saltation see sediment load screenshot, little rocks jumps and land and bump another and that makes it jump and so on

Question 19

Stream Flow Variables: Base Level

Question 20

sediment load considerations

Answer 20

Capacity
Amount of sediment the stream can carry
Depends on velocity and volume
Varies seasonally, with weather, over time

Competence
Largest size of sediment the stream can carry
Depends on velocity and volume
Varies seasonally, with weather, over time

Question 21

“dry” riverbeds

Answer 21

“Wadi”,“Wash”,“Arroyo”,“Slot Canyon”
Desert soils don’t soak up torrential rains
Hazardous flash floods after storms
Sometimes miles and miles away from the rain
deadly

Question 22

base level

Answer 22

Level to which a stream will erode
Won’t erode lower than base level
Sea level is the ultimate base level
Local base level
Lakes/Reservoirs
Elevation of the stream’s mouth
Head: start of stream
Mouth: end of stream

Question 23

great basin

Answer 23

Internal drainage
No outlet to the ocean
Topographic barriers
see screenshot for location west

Question 24

What is the ultimate base level of the Provo River?

Answer 24

great salt lake

Question 25

river erosion

Answer 25

Removal of regolith
Downcutting
The stream channel
Headward erosion

Removal of regolith (weathering products)
Washed downstream
About 6 cm/1000 yr removed from the continents

Question 26

river erosion: v shape

Answer 26

Downcutting the stream channel
Abrasion by sand and gravel dragged across the sides and bottom
Most rapid during high flow
Slope retreat
V-shaped valley formation

Question 27

canyons

Answer 27

Hard rock will not slump as easily as softer rock/regolith

Question 28

valley and canyon

Answer 28

stair step canyon alternating soft and hard, see screenshot

Question 29

headward river erosion

Answer 29

Headward erosion
Erosion rates are highest where gradients are highest
New channels develop at stream head

Question 30

stream piracy

Answer 30

headward erosion can cause
Stream Piracy, me hearties
Headward erosion may allow one stream to capture the tributaries of a different stream
see screenshot

Question 31

river erosion: braided streams

Answer 31

Braided Streams
High sediment load streams with relatively low water levels
Most common in tributary systems: near the head of the river
Distinctive stream pattern
Multiple channel system with lots of islands
Common in arid regions and in front of glaciers

Question 32

river deposition

Answer 32

Primarily in the transporting and dispersing systems
Flow velocity reduction
Creates
Floodplains
Deltas
Alluvial valleys and fans

Question 33

river deposition: floodplains

Answer 33

Floodplains
Flat area bordering a stream channel
Stream channel meanders through time across the floodplain
Natural state
Stream channel position changes
Artificial state
Stream channel remains same

Question 34

river deposition: deltas

Answer 34

Deltas
Depositional place of most of river’s sediment
Where the river hits base level
Sudden drop in velocity
Stream drops everything off
May be modified by waves

Question 35

deltas

Answer 35

Distributaries
As sediment is dropped off, a tributary channel becomes clogged
May split off into two smaller channels to seek easier route

Avulsion
Shift in main course
The Mississippi wants to switch to the Atchafalaya channel
Leaving New Orleans high and dry

Question 36

river deposition: alluvial valleys and fans

Answer 36

Alluvial valleys and fans
Dry basin deposits
Rapid velocity drop as stream comes out of confined canyon
Spreads out from canyon mouth
High sediment load
Usually found in arid climates

Question 37

bajada

Answer 37

Coalesced alluvial fans
Common in at the base of desert ranges

Question 38

river deposition; meandering streams

Answer 38

Meandering Streams
Common in floodplains
Sinuous pattern
Erosion on one back, deposition on the other
changes course of river

Erosion – Cutbank: knocks into river bank
Deposition – Point bar: slower side of river more deposition

see screen shots for cutbank and evolution of meadnering streams

Question 39

meandering streams

Answer 39

Meander: loop
- Point bar: deposition and cutbank: erosion
- Cutoff: bends back on itself creatingVVV
^^^^Oxbow lakes
Natural levees: sand ridges that parallel the channel
- Embankment created during flood stage: sediments dropped when the water enters a valley
- Sand ridges that parallel the channel
Yazoo streams: run down from high places and pareallel to river , but are blocked from entering the river by deposited material that creates river banks
Backswamps:?