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EASC 225 (Geomorphology) > Fluvial Processes > Flashcards

Fluvial Processes Flashcards

1
Q

What are some characteristics of rivers?

A
  • sculpts landscapes
  • move large amounts of sediment
  • is defined at any natural stream of water that flows in a channel with defined backs
  • channelized flow is the defining element
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2
Q

What is discharge? how is it calculated?

A
  • discharge is the amount of water passing through a cross section of the river during a specified interval of time
  • calculated by using the width and depth of the river section, and the velocity
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3
Q

What is the relationship between precipitation and discharge? what factors will effect this relationship?

A
  • typically with more precipitation we have an increase in discharge
  • however, there is a “lag” in the relationship, where discharge follows precip.
  • this lag depends on the basin drainage, which depends on pre-existing soil moisture, vegetation, topography, temp (snow vs rain) etc.
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4
Q

What are bedrock channels?

A
  • fluvial channels that are controlled by bedrock structure
  • do not store much sediment
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5
Q

What are alluvial channels?

A
  • modify materials laid down by the river itself
  • lots of sediment, gravel sand silt and clay
  • can look braided in nature
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6
Q

describe the 3 fluvial processes

A

Erosion: entrainment of sediment
Transport: movement of sediment
Deposition: settling of sediment

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7
Q

________ is the primary control of fluvial processes

A

VELOCITY

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8
Q

What is the Hjulstrom curve?

A
  • curve that allows us to determine based on the particle grain size and stream velocity, if material will be transported, eroded, or deposited.
  • is really two curves, the critical velocity curve and the settling velocity curve
  • the critical erosion velocity curve defines the shear stress necessary to initiate motion
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9
Q

What are some kinds of fluvial transport?

A
  • bedload
  • suspended load
  • dissolved load
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10
Q

What is bedload?

A

type of fluvial transport, where material is transported in contact with the bed, including rolling of particles, hopping particles (saltation)

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11
Q

What is suspended load?

A
  • type of fluvial transport, where sediment and particles are carried within the water column
  • typically silt and clay
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12
Q

What is dissolved load

A
  • a type of fluvial transport where ions are carried as dissolved material within the water column
  • also called chemical load
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13
Q

What are the two driving forces of fluvial processe?

A
  • slope
  • discharge
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14
Q

How do slope and discharge drive fluvial processes?

A
  • with increased slope, there will be increased velocity
  • with increased discharge, there will be increased velocity
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15
Q

What are the resisting forces of fluvial processe?

A
  • channel roughness (+ channel characteristics, width and depth)
  • velocity and turbulence
  • VISCOSITY
  • vegetation
  • man-made influences
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16
Q

What is channel roughness? How does this resist fluvial processes?

A
  • channel roughness is related to bed material size
  • typically if the roughness is increased, there will be a decrease in velocity
17
Q

What is Froude Number?

A
  • used to differentiate between different types of turbulent flow.
  • If we decrease the depth, the Fr number goes up, meaning the water is fast flowing and shallow)
  • If we increase the dept, Fr goes down, meaning fast flowing, but deep water.
  • if we increase the velocity, Fr also goes up
18
Q

What is Reynolds number?

A
  • number that relates to the viscosity and turbulence of fluvial processes
  • Re number dictates if a river has laminar flow (calm) or turbulent flow (chaotic)
  • turbulent flows are better at eroding and transporting sediment, more likely to change landscapes
19
Q

Re number greater than 500 means…..

Re number less than 500 means……

A

Re> 500 = Turbulent flow

Re< 500 = Laminar flow

20
Q

For Froude numbers…
(Fr<1)=…
(Fr=1)=…
(Fr>1)=…

A

(Fr<1)= TRANQUIL FLOW
(Fr=1)= CRITICAL FLOW
(Fr>1)= RAPID FLOW

21
Q

What are bedforms?

A
  • the organization of the bed relative to the velocity, turbulence, and sediment load of the water
22
Q

What is ‘baselevel’

A
  • the degree of gradient a river has with the land it is on
  • baselevel is always the ocean for rivers.
23
Q

What is fluvial equilibrium?

A
  • where the erosional rates (where the ground is) equals the depositional rates (where the water is)
  • equilibrium is if there was a nearly equal elevation between land and water basin/baselevel
24
Q

what are 5 major channel properties for fluvial channels?

A
  1. width or width to depth ratio
  2. sinuosity index, ratio of channel length to valley length
  3. sediment load
  4. gradient (slop of channel)
  5. bank sability
25
Q

What are two main types of channels?

A
  • bedrock
  • alluvial
26
Q

Channel morphology is greatly dependent on ….

A
  • discharge
  • materials present on the banks
27
Q

What are channel patterns? What are the 4 main types?

A
  • reflects how channels have adjusted in order to transport discharge most efficiently
  • Straight, meandering, braided, anabranching
28
Q

What are the characteristics of straight channels?

A
  • low width:depth ratio
  • low gradient
  • cohesive banks
29
Q

What are the characteristics of meandering channels?

A
  • most common pattern
  • erosion/deposition pattern (cut bank and point bar)
  • low width:depth ratios
  • sandier bank size
  • cutoffs may form oxbow lakes
30
Q

What are the characteristics of braided channels?

A
  • steep gradient
  • wide and shallow
  • unstable bars that move frequently
  • lots of gravels bars and sand bars
  • commonly associated with an overload of bedload
  • pretty much outwash plains
31
Q

What are the characteristics of Anabranching channels?

A
  • multiple channels separated by semi-permanent alluvial islands (bars, usually vegetated)
  • formed by cutoffs, channels avulsions, or mid-channel deposition
  • may be confused with braided rivers
32
Q

What are flood plains

A
  • valley bottom areas influenced by modern fluvial processes
  • mosaic of landforms: cutbanks, pointbars, natural levees, oxbow lakes, etc.
33
Q

What are river terraces?

A
  • older remnants flood plain surfaces, that are higher in elevation
  • like step stones moving towards the river, where the river is at the lowest elevation
34
Q

What are alluvial fans?

A
  • fan shaped fluvial deposits that accumulate at the base of streams, where it flows out from a steep gradient

EASC 225 (Geomorphology) (9 decks)

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