Braided and Meandering Rivers

Question 1

What controls channel morphology and therefore deposits?

Answer 1

• Gradient (not the steepest though as we looking at deposition)
• Type of sediment load
• Amount of sediment load
• Stream power and capacity
• Sediment cohesion

Question 2

Braided Morphology and Deposition

Answer 2

• Slightly steeper Gradient
• More sediment amount relative to amount of water
• Coarser types of sediment that are non-cohesive as moving as bedload

Question 3

Meandering Morphology and Deposition

Answer 3

• Flat Gradient
• Less sediment amount relative to amount of water
• Fine grain sediment type that tent to be very cohesive, thus making stronger banks and get suspended load

Question 4

Braided Rivers:

Answer 4

• Bars where sediment is being temporarily stored -> moved in floods
• Multiple subchannels within greater location
• Bed load dominant relate to suspended load
• High sediment load relative to stream capacity to transport the sediment

Question 5

Braided River Bars:

Answer 5

• Bars are migrating dunes during flood flows
• Really gradual stoss slope and lee slope which is being eroded by the other channels
• Gives you an indication that there is a of sediment in the system
• Bars modified by changes in flow levels from low to high to waning. Always changing flow conditions
• Expect that the dunes will have channels cut over them
• Bar morphology and modification: as floods get lower it carved channels in the middle -> river gets lower and moved.
• May have dune cross bedding or may have been destroyed by the reworking

Question 6

Meandering Rivers:

Answer 6

• Single Sinuous Channel encased in their mud/soil banks
• low sediment load relative to capacity
• High suspended load relative to bedload
• cohesive banks make it hard to erode -> same with tree roots etc

Question 7

Meander formation and migration

Answer 7

Determined by how water flows and is deflected by channel banks

• Water flows in a direction until it hits something it can’t erode
• erosion happens on the outside bend (cut bank)
• Deposition of the inside (point bar) and slightly downhill
• Corkscrew water motion on a curve helps cause erosion and deposition
• Eventually gets more extreme as it is eroded from the outside
• Varies from low to high sinuosity

Question 8

Meandering Rivers in flood:

Answer 8

When it floods, all the muds get transported onto the flood plains and deposited

Question 9

Levees and Crevasses Splays

Answer 9

During flood, as the water overtops the levees (banks), you deposit the sands as velocity drops, in a mini-delta called a crevasses splay. This fines further from channel
- Crevasses splay deposits show that channels have migrated laterally over time

Question 10

Oxbow lakes

Answer 10

Form when a meander loop cuts-off. Water often flows over point bars during smaller floods

Question 11

Floods are when changes happen:

Answer 11

• Deposits fines in flood plain
• Cut banks collapse and meander bend migrate
• Meander loop cut off forms and Oxbow lake

Question 12

River Avulsion in Meandering Rivers

Answer 12

As meanders migrate they form meander scrolls.