Lecture 11

Question 1

How does a system stay balanced

Answer 1

Sediment supply must be equal to stream power otherwise either aggregation or degradation will take place

Question 2

What geological feature can lead to high amounts of sediment

Answer 2

Techtonic

Question 3

What can increase stream power

Answer 3

Slope, depth, rainfall, stream order

Question 4

How does climate impact sediment and water

Answer 4

Sea level rise, more rainfall then more sediment,

Question 5

How can vegetation impact river systems

Answer 5

More stable banks, water control and uptake

Question 6

Where do we get little records of what a river is doing

Answer 6

Little sediment with little aggregation, no new locations, channel belt is stable

Question 7

Where will we get high rates of preservation and sediment movement

Answer 7

High sediment with high channel aggregation

Question 8

What is a key aspect of channel change

Answer 8

Sediment supply

Question 9

What is the channel belt

Answer 9

The whole channel shape which the river runs in

Question 10

What is an avulsion

Answer 10

A abrupt shift of the entire channel belt to a new location, inter avulsion period can be 1000s years

Question 11

How long does it take for an avulsion to complete

Answer 11

May be almost instant, but may take longer for the whole channel to fill in or move

Question 12

What is the hop length

Answer 12

Distance that the new channel shifted

Question 13

What is avulsion length

Answer 13

distance that the channel belt is before is rejoins the channel

Question 14

what is the hop length

Answer 14

size of the channel movement

Question 15

what was the relationship between channel belt width and distance it was moving

Answer 15

almost a 1 correlation. 2.5 times channel belt width is how much it is moving over.

Question 16

What is the set up

Answer 16

what would make the channel belt [perfect for switching to a new location

Question 17

What is the trigger

Answer 17

The chance of the river avulsing after it has been set up to do so

Question 18

what are the two theory for set up

Answer 18

superelevation and gradient advantage

Question 19

what is super elevation

Answer 19

levee’s build up either side of the channel, channel starts to become perched above the flood plain.

Question 20

what happens when the depth of the channel is the height of the land cover

Answer 20

channel depth above floodplain, when spills out all old channel is lost

Question 21

What is gradient advantage

Answer 21

is there a tilt in the flood plain itself, water will move on the gradient, cutting a new channel

Question 22

What is a trigger event

Answer 22

large flood which starts the avulsion

Question 23

what can happen in really big floods

Answer 23

avulsion can take place even without set up

Question 24

what is a key control on the avulsion processes

Answer 24

sediment supply.

Question 25

Where do we get heigher avulsion frequency

Answer 25

more sediment.

Question 26

What does bed load do to channels

Answer 26

build the channel up creating more channel height and therefore more avulsion chance

Question 27

what does suspended sediment do to banks

Answer 27

builds up levees

Question 28

How do we get a perched channel

Answer 28

some suspended sediment for levees and some bedload to build channel height

Question 29

If you had little coarse sediment but lots of fine sediment what would happen

Answer 29

hinder avulsion, larger levees shallower channel

Question 30

In south America what has seen to be linked with avulsions

Answer 30

la nina events cause avulsions, 51 in la nina only 5 with el nino

Question 31

When can avulsions be linked climatically

Answer 31

high rainfall events

Question 32

what were rivers like pre 450ma

Answer 32

no vegetation, braided rivers were much more avulsive with no vegetation growth

Question 33

When was the older rhine-meuse avulsions

Answer 33

8000ya, nearer to the coast

Question 34

what drives the original avulsions

Answer 34

sea level rise, reduce the slope, sediment deposition

Question 35

What was the second avulsion stage caused by

Answer 35

subsidence of the crust, more low lying area

Question 36

What is the rhine avulsion duration

Answer 36

325 years

Question 37

If sea levels wall what happens to the land

Answer 37

erosion and incision

Question 38

How was the bridge karssenberg

Answer 38

based on the rhine system, numerical system model

Question 39

what is sediment transport a function of

Answer 39

the discharge

Question 40

How will channel incision change river shape

Answer 40

more sediment released if more incsion

Question 41

What can happen to the original channel after evolution

Answer 41

single channels can create multiple channels

Question 42

what are the two probability factors that lead to channel avulsion

Answer 42

Ps, birfurcation, super elevation, Pd, probability of a yearly flood discharge

Question 43

If you've had one avulsion what is the probability of another one happening

Answer 43

it drops

Question 44

What can happen to channel belt size

Answer 44

they can widen

Question 45

How does the model know which channel to give more water

Answer 45

slope

Question 46

What happens if we get lots of connected channels together

Answer 46

can find aquifers below the soil

Question 47

what is base level?

Answer 47

the lower limit to which a river can erode its valley (powell 1875)

Question 48

what are the 3 river planform types

Answer 48

straight, braided, meander

Question 49

what is the equation for stream power

Answer 49

water density x gravity x discharge x slope

Question 50

What is unit stream power

Answer 50

stream power divided by width

Question 51

What are the 5 basic degrees of freedom in a channel system

Answer 51

Slope, width, depth, platform, bed roughness

Question 52

What is the efficient transfer of water

Answer 52

Hydraulic efficiency

Question 53

What is the primary movement process of larger bed load

Answer 53

Saltation

Question 54

What is the typical longprofile of a river

Answer 54

Concave from source to mouth

Question 55

What does curved channel result in

Answer 55

Super elevation of the waters surface higher at the outside of the bend

Question 56

Other than a flood, how else can avulsions occur

Answer 56

water build up after downstream blockage

Question 57

How much has the po river in Italy moved in 3000 years

Answer 57

50km

Question 58

how much has the yellow river moved laterally over 4200 years

Answer 58

800km

Question 59

what happens when avulsive rivers stay separate and both channels filled over a large length of time

Answer 59

they are termed anastomosed

Question 60

when do inter avlusion periods decrease

Answer 60

when base sea level rises

Question 61

what is the average inter avulsion period of the river kosi

Answer 61

4-44 years

Question 62

how does the flow of the kosi river change

Answer 62

gradual transfer of flow form one channel to another

Question 63

how were some of the po's avulsions created

Answer 63

man made movement of channels

Question 64

when does avulsion frequency increase

Answer 64

with increasing deposition rate in the channel belt

Question 65

how might tectonic activity effect avulsions

Answer 65

may occur as a response to an individual tectonic event., or gradual tectonic shift

Question 66

tectonically, where to avulsing channels concentrate

Answer 66

in areas of tectonic subsidence

Question 67

how are belts seen over time

Answer 67

seen to be stacked on top of each other laterally

Question 68

What must the diversion of a channel to a new system result in

Answer 68

channel incision

Question 69

what did some scientists use dune movement to estimate

Answer 69

bed load movement

Question 70

what did kostachuk find about lagging with river dunes structure

Answer 70

dune height and length lagged behind changes in channel velocity leading to a hysteresis effect

Question 71

in migrating dunes, how much trapped sediment was suspension

Answer 71

95%