Fluvial Forms Flashcards
List 5 fluvial bedforms
Ripples Dunes Plane bed Antidunes Obstacle marks
What are fluvial bedforms similar to?
Aeolian bedforms
What is the medium for fluvial bedforms?
Water
What is the medium for aeolian bedforms?
Air
What does larger material require to be moved?
Higher stream power
What does the presence of fluvial bedforms depend on?
Grain size
What are horizontal bedplanes indicative of?
Lower stage plane beds
In which direction do ripples migrate overtime?
Down flow
Which side do ripples erode?
Upstream side
Which side do ripples deposit?
Downstream side
Give a place where ripples can be seen?
The beach
What is meant by transient?
Adjust quickly to change
Are ripples transient?
Yes
What energy conditions are required for ripples to form?
Lower energy conditions
What transportation process allows ripples to form?
Suspension
What do ripples have a high rate of?
Aggradation
Are dunes visible?
Yes, they poke out of the water to a greater extent
What do dunes cause?
Surface waves that are out of phase with the water bed.
Is the amplitude of dunes higher or lower than that of ripples?
Higher
What can the amplitude of dunes reach?
10s of cm to 10s of m
What shows migration in dunes?
Cross stratification
In which direction do dunes migrate?
Downflow
How do dunes migrate?
By accretion of the lee side
Why are dunes in dynamic equilibrium?
The stoss side is eroding and the lee side is depositing
What are two important features of the upper stage plane bed?
Coarser material than lower stage
Some rocks
In what plane bed would you find ripples?
Lower stage plane bed
In what plane bed would you find dunes?
Lower stage plane bed
What are antidunes?
The opposite of dunes
What type of feature are antidunes?
Erosional
In which direction do antidunes migrate?
Upflow
What waves are antidunes associated with?
Breaking waves
What is the water flow like around antidunes?
Shallow but fast
In which way do antidune beds dip?
Upflow
Why is the stoss side of antidunes preserved?
Due to the dip
Which side of the antidune is eroded?
Lee side
Which side of the antidune moves upward?
Crest side
How long are antidunes preserved for?
They are very rarely preserved
What are two features of cluster bedforms?
Rocks dip into the flow
Coarser material
List 4 obstacle marks
Ice blocks
Secondary bedforms
Vegetation
Anthropogenic sources
What flow can ice blocks create?
Horse shoe flow
What can ice blocks cause?
Scouring due to horse show flow
What changes overtime in rivers?
Discharge
What two things do bars require?
Cohesionless sediment
Bedload
Why are bars difficult to define?
They depend upon flow depth and discharge
What are bars?
Attachments to channel margins
Where can bars be found?
Mid channel
What are bar types often associated with?
Channel morphological type
What transportation process causes bars?
Suspended load
Are bars formed in low or high energy environments?
Low energy
What bars can braided rivers have?
1st, 2nd and 3rd order bars
In what environments do braided rivers occur?
In a number of enviroments
Where are braided rivers usually found?
Where there is a lot of sediment
Give two examples of wondering gravel bed rivers
River Coquet, Northumberland
Fraser River, British Columbia
What can be done to find the age of island bars?
Tree coring
What can affect the location of erosion/ deposition?
Positioning of flow cells
What happens as the river channel widens? (3)
Flow reduces
Sediment transport reduces
Change in the type of material transported
What are the main features of Anastomosing rivers?
Parallel channels
Aligned by natural levees with flood basins inbetween
Define Anastomsing river
“A type of river channel with multiple interconnected, coexisting channel belts on alluvial flood plains, which most often form under low energy conditions near a local base level” Makaske 2001
When do braided rivers occur?
When erodibility of bank particles is more than their transportability
When do meandering rivers occur?
When erodibility and transportability of bank particles are equal
When do straight rivers occur?
When transportability of bank particles is higher than erodibility
What is the spacing like for pools and riffles?
It is regular
What property changes in pools and riffles can occur and why?
Major changes in hydraulic properties depending upon flow stage
What hypothesis is associated with pools and riffles?
Velocity reversal hypothesis
What is the velocity reversal hypothesis?
Velocities in pools increase at a higher rate than in riffles
Can rivers be damned by their own levees?
Yes
When do river terraces form?
After glaciers melt
Why do river terraces form after glaciers melt?
There is less discharge
What do river terraces reflect a change in?
River channel change in water and sediment flux
Briefly explain the magnitude and frequency concept
Argument over whether frequency of floods is more important than intensity. Medium magnitude floods occurring over intermediate timescales achieve most work in terms of sediment transport.
What is avulsion?
Rapid channel change
What is river terrace formation an example of?
Complex response