Lecture 13: Surface Water Flashcards
-River Morphology -Flooding -Fluvial Depositional Landforms -Lakes
River morphology
Refers to the shape of a river channel and the evolution of the channel shape over time.
Bedrock channels
Are places where the river is directly incised in bedrock, and are typical of the higher gradient (headwaters) region of a river.
- Typically form a series of pools and falls
- Rock is removed by both physical erosion and chemical dissolution of the underlying rock
Alluvial channels
Are made up of unconsolidated sediment - called alluvium
- Normally further downstream in lower gradient environments
- Morphology changes more rapidly
The two kinds of alluvial channels
- Braided channels
2. meandering channels
Braided channels
Comprised of multiple channels separated by bars typically comprised of relatively coarse material (sand and gravel)
Where do braided channels form?
Common in glacier-fed rivers
- where discharge is variable over time
- where banks are easily eroded
Meandering channels
Forms large sinuous loops - each bend is a meander
Where is coarser bed material located in meandering channels?
On the outside, where the flow is faster.
How is an oxbow lake formed?
When the migration of a meander in a meandering channel slows due to a more resistant bank material, which results in slower erosion. The meander behind it may catch up and cut off a portion of the river.
Cutbanks
Erosion on outer bank
Point bars
Deposition on inner bank
River valleys
Where a river sits, which includes the river channel and the region nearby that feeds water to the river.
Bedrock channel valleys
Deep, narrow, v-shaped valleys
Alluvial channel valleys
Wide, shallow valleys
Floodplains
An area of low-lying ground adjacent to a river.
Floods
Occur when a river’s discharge exceeds the capacity of its channel.
Leeves
Embankments along the sides of the river - from due to repeated flooding.
-During a flood, the river his carrying more sediment and this sediment deposits onto the floodplain near the river, this causes leeves to form.
What are gauging stations?
Stations used to monitor the discharge and water height (stage) of major rivers.
-Used to predict the magnitude and frequency of floods
Recurrence interval
The average period of time between two floods of the same magnitude.
Terraces
The bench or steps up the sides of the river valley.
-Represent different floodplain levels.
Downcutting
Downward erosion of a river through its bed.
What three things cause downcutting?
- Sea level falls
- Tectonism removes an obstacle
- River discharge increases
What are three deposition landforms?
- Floodplains
- Alluvial fan
- Delta
What is an alluvial fan?
A fan-shaped body of alluvium deposited as the flow of a river decreases in velocity.
What is a delta?
A triangular shaped deposit formed when a stream enters standing water of a sea or lake.
What are the two kinds of lakes?
- Open lake
2. Closed lake
What is an open lake?
Hav inlet and outlet streams, which cause the water level in the lake to stay relatively constant in the short term.
-Sediments are usually muds, with sands near the shore.
What is a closed lake?
Have no outlet stream, which causes water levels to fluctuate due to evaporation.
-Sediments are usually salt deposits formed by evaporation.
