Week 8: Rivers Flashcards
What is a stream?
Any flowing body of water, regardless of size
What is a river?
A major branch of a large stream system
What is a channel?
The stream passageway
What is a load?
The sediment carried by the stream
What is discharge?
The quantity of water passing a given point
Name and describe the two processes by which water in a stream moves.
Laminar Flow:
Straight or gently curved streamlines that run parallel to one another without mixing or crossing
Turbulent Flow:
A complex pattern of movement with streamlines crossing and forming swirls and eddies
What is a suspended load?
All the material temporarily or permanently suspended in the flow
What is a bed load?
The material carried by the stream along its bottom by sliding and rolling
What is saltation?
The intermittent jumping of sand grains as they are lifted off the bottom, carried a short distance and then settle out
What is abrasion?
A sandblasting action from sediments in the suspended and bed load that cause erosion on rocks the stream runs over or alongside.
What is a stream valley?
The entire area between tops of the slopes on both sides of a river
What is a stream channel?
A channel that carries all the water during normal, nonflood times.
What is a flood plain?
A flat area about level with the top of the stream valley
List the 2 common stream channel patterns.
- Meanders
- Braided Streams
What are Meanders?
- Curved and bent river channels that wind across a floodplain
- Common in streams with a low gradient that typically cut through unconsolidated material
- Migrate over years, eroding the outside banks of the stream where current is strongest
What are point bars?
Curved sandbars that deposit on the inside bank where current is slower in a meandering stream channel.
What is an oxbow lake?
The crescent-shaped, water filled loop that is created when the meander loop neck becomes so narrow that the loop is bypassed by the river
What are braided streams?
- High energy streams that have many channels instead of one single channel
- Channels split apart and then rejoin in a patter resembling braids of hair
What is the gradient of a stream?
The distance the stream falls between two points
What is a stream’s Long Profile?
- A line drawn along the surface of the stream from its source to its mouth
- It is a concave upward curve due to decreases in gradient downstream
What is the base level?
It occurs where a river enters a body of standing water
What is the discharge?
The amount of water in m3/s that passes down the river
Why does the velocity of streams increase downstream?
Because the streams are deeper downstream and have less resistance from the stream bed, even though the gradient has decreased
When does a flood occur?
When a stream’s discharge exceeds the capacity of the channel and the stream overflows its banks.
Why are floods of significance and cause a large impact?
Because they increase both the discharge of the stream and its velocity. This means that a much greater amount of load is carried by the stream as well as the size of material. It results in a large amount of erosion and redeposition.
Large impact also because many communities are built on floodplains.
What is a Recurrence Interval?
Commonly expressed as 10 year or 100 year flood events. Found by plotting the occurrence of past maximum discharges, including floods of different sizes on a probability graph.
What is alluvium?
Sediment material deposited out of a stream
Why does the size of sediment carried by a stream decrease in the downstream direction?
Because, although the velocity increases downstream, sorting leaves the larger particles upstream and abrasion reduces particles in size.
What is a floodplain?
The part of the stream valley inundated with flood waters
What is a levee?
A broad low ridge of sediment built along the side of the river channel
What is a terrace?
The remains of an abandoned flood plain that is no longer used due to down-cutting of the river.
What is an alluvial fan?
A fan shaped body of alluvium built where a stream leaves a steep mountain valley and the sudden decrease in gradient and velocity causes it to deposit its load on the valley floor.
What is a Delta?
A sedimentary deposit that forms where a stream flows into a standing body of water and the velocity decreases rapidly causing the sediment loads to drop out.
What is a drainage basin?
The total area that drains into the stream
What are first order streams?
The smallest streams that lack tributaries
What are second order streams?
Where two first order streams join and form a second-order stream
What are third order streams?
Where two second order streams join. They can have first and second-order tributaries
What is a Dendritic stream pattern?
Where branching channels are treelike
It reflects massive and/or flat-like rock strata where the rock imposes little control on stream patterns
What is a Radial stream pattern?
Where channels radiate out - forms around a topographic high, such as a dome or volcanic cone
What is a Rectangular stream pattern?
A rectangular arrangement of channels marked by right-angled bends.
It forms in areas where rocks are heavily jointed and fractured
What is a Trellis stream pattern?
A rectangular arrangement of channels in which principle tributaries are parallel and very long.
It reflects dipping or folded strata in which the edges of rock units are exposed on the surface
What are Placer Deposits?
Deposits of heavy minerals that have been concentrated mechanically (e.g. gold deposits).
For example, gold is of higher density and does not get removed by a lower stream flow which will remove most other minerals. The gold is then left behind and becomes concentrated.
