Lecture 7 - Channel Pattern

Question 1

What are the 3 river channel patterns?

Answer 1

Straight - straight channel

Meandering - curving channel

Braided - channel with multiple channels

Question 2

Which channel pattern is mostly man-made?

Answer 2

Straight channels.

Most natural river channels are either meandering/wandering or braided

Question 3

What is the channel sinuosity of a straight and meandering channel?

Answer 3

s = 1.0 - straight

s = 1.3-1.5 - threshold

s = > 1.5 - meandering

Question 4

What is anabranching?

Answer 4

Where multiple channels have bars with vegetation on them, reducing the erosion of the bars

Question 5

What is the difference between power and energy?

Answer 5

Energy is defined as the amount of work that can be performed.

Power is the rate at which work is performed.

Question 6

Why do different planforms develop?

Answer 6

Thresholds can be observed where a change occurs in either:
- sediment
- velocity
- slope

Question 7

Straight channel planforms

Answer 7

• Low slope angle
• Low power (Ω)
• Relatively narrow and deep channels

Question 8

Braided channel planforms

Answer 8

• Wide and shallow channels
• High slope angle
• High power (Ω)
• High discharge Variability
• High sediment load

Question 9

Meandering channel planforms

Answer 9

• Intermediate - enough energy for erosion, but bank resistance is enough to maintain a single channel

Question 10

What is the natural evolution of river channels?

Answer 10

Straight channels will start to meander due to differences in erosion rates and velocity within the channel.

Meandering channels will continue to meander and eventually have enough power to start braiding.

Braided channels are not common in the uk due to the unstable and sensitive conditions in sediment load and discharge