Rivers and the Environment Flashcards
How are rivers and people related?
Rivers shape the landscape and people shape rivers!
What is a drainage basin or watershed?
Area of land drained by a river system
What is a drainage divide?
The boundary between watersheds
What are the 3 main fluvial processes through which rivers shape the landscape?
- Erosion
- Transport
- Deposition
What is the spatial patterns of erosion and deposition along a streams course like?
- Upper Course - steep, fast flowing river with little water. lots of erosion
- Middle Course - river starts to slow down. More water. Still eroding
- Lower course - river very slow, much more water. depositing here, not eroding.
What is erosion and how does it start?
Removes bedrock and soil from original position. It stats with splash erosion from raindrops
What do streams do to channels as they move downstream? How does this happen?
Streams erode larger and larger channels moving downstream.
- Sheetflow - before channelization
- Rills – small channel formed by soil erosion—beginning of channelization
- Gullies - channels become larger
- Finally Stream Channels develop
What is rill erosion?
Rill erosion is the removal of soil by concentrated water running through little “streamlets”
What are gullies?
Gullies are formed by advanced rill erosion to the point that they cannot be smoothed over by normal tillage
Is the stream channel itself an erosional feature?
yes
What does the stream channel do when it has different volumes of water passing though it?
The stream channel continuously adjusts its shape and path according to the volume of water passing through it at any point
What is discharge? What does a higher discharge mean?
Cubic meters of water per second. High discharge means more erosion
What transports eroded material and what are the three types of transportation?
Streams transport eroded material
- Suspended Load
- Solution Load (Dissolved)
- Bedload
What does the size particles a stream can move depend on?
On its discharge. A high discharge means large material
How do floods effect streams and erosion?
Streams can carry much larger rocks during floods than average streamflow
What does the slow moving stream transport? What does it transport that cannot be seen?
Suspended mud
By contrast, Solution load (Dissolved load) is INVISIBLE.Usually composed of ions such as calcium, chloride, potassium, sulfate that may precipitate out in quiet water such as ponds
What happens to transported material when water slows down?
It drops its load….deposition
What is all material deposited by streams called? What is this material typically like and why?
All material deposited by streams is called alluvium. It is typically smooth and rounded because has been worn down by the river
How are rocks similar and different to alluvium?
Rocks also weather out of the bedrock in place; they are not deposited by the river, so NOT alluvium.
Note they are sharp and angular
Are river rocks alluvium or not?
Rounded ones are alluvium, the sharp ones are not.
What is a floodplain?
A floodplain is an area of land adjacent to a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge
Is a floodplain erosional or depositional? What is it made of?
It is depositional and is made of alluvium
What are natural levees?
A depositional feature that is a pair of low ridges that appear on either side of a stream and develop from accumulation of sediment deposited by natural flooding.
Why would natural levees develop?
slide 26
Where do meandering stream channels form? And are they erosional or depositional features?
Meandering stream channels (erosional features) form where streams are moving across a relatively flat landscape, usually near the lower end of its course. Remember the channel is constantly moving across landscape
What does increased velocity in meandering streams cause?
Causes erosion (cut bank)
What does decreased velocity in meandering streams cause?
Causes deposition (point bar)
What do cut banks and points bars look like?
Slide 30
What are oxbow lake and meaner scars evidence of?
Channel migration through time and the spatial history of the river
What does channel migration look like?
Slide 33
