Chapter 10 - part 2

Question 1

23. 3 flood control measures in common use.

Answer 1

The way to control a flood is to keep excess water in the channel, or if it won’t stay in the channel, a place for it to go. 1. ARTIFICIAL LEVEES 2. ARTIFICIAL CHANNELS 3. FLOOD PLAINS

Question 2

ARTIFICIAL LEVEES

Answer 2

Raised banks of the river channel intended to increase the size of the channel and keep more water in it.

Question 3

ARTIFICIAL CHANNELS

Answer 3

Extra river channels made to accommodate excess water and keep it moving.

Question 4

FLOOD PLAINS

Answer 4

The Large areas of Land next to the active channel intended to store water temporarily.

Question 5

23. How do all three flood control measures alter the river system?

Answer 5

All three of these control measures may alter the river system by either changing:

the size or shape of the river channel

the number of channels

or the nature of the whole system

Question 6

Levee drawbacks.

Answer 6

While these are cheap and effective, they do have drawbacks: Sediment that would normally leave the channel during a flood remains there. This sediment will start to fill the channel, reducing its depth. Levees can also make a flood worse because they can act as a barrier to the return of water into the channel.

Question 7

26. Levee

Answer 7

A bank or levee is a raised portion of the floodplain next to the channel.

Question 8

27. What are the 3 ways that water can escape a river channel during a flood?

Answer 8

Water can exit a channel in 3 different ways. 1. Over top of the bank 2. Through the bank 3. Underneath the bank as groundwater.

Question 9

Water escaping a river channel : over the top of the bank

Answer 9

Once bankful discharge is reached and exceeded, water spills out of the channel over top of the bank.

Question 10

Water escaping a river channel : through the bank

Answer 10

Water exits the channel through a breach in the bank.

Question 11

Water escaping a river channel : underneath the bank as groundwater

Answer 11

Water exits the channel as groundwater because of the weight of the higher water in the channel pushing around.

Question 12

28. Avulsion

Answer 12

When water leaves the channel through a breach in the bank, it is an avulsion.

Question 13

Landforms created by Avulsion

Answer 13

A Crevasse-splay. A fan shaped deposit that is thicker and coarser near the breech changing to thinner and finer away from the channel.

Question 14

29. What is Channelization?

Answer 14

The modification of a natural river channel so as to control the flow of water in it. This may include straightening the channel. Channelization can also mean changing the banks and bottom of a channel.

Question 15

30. What affect does channelization have on streamflow?

Answer 15

It creates a rigid, fixed channel separate from the surrounding ground. Groundwater cannot enter the channel nor can river water leave as groundwater.

Question 16

31. Effects of fire, logging and animal grazing on stream behaviour.

Answer 16

Most often this means vegetation is removed. Once vegetation is gone, there is nothing to intercept precipitation and nothing to keep this water from rapidly collecting on and moving across the land. More surface water means more sediment that eventually reaches the river channel. A larger sediment load in a river can alter the river system.

Question 17

32. What effect does streambed sand and gravel mining have on the behaviour of the stream?

Answer 17

Sediment - sand and gravel - mining (removal of sediment from a river channel) of a river bed changes the size and shape of the channel and the flow conditions in it.

Question 18

33. What effect does stream flow have on a concrete pillar that has been placed in a river channel? (SEE PHOTO)

Answer 18

At (A), as water moves around the concrete post in the river, turbulence increases and water velocity drops on the lee slide/down current side. At (B), water velocity increases as it accelerates around the post. The end result is scouring (erosion) of sediment away from the front of the position and deposition of a pile of sediment behind it.

Question 19

how do levees worsen a flood?

Answer 19

because they can act as a barrier to the return of water into the channel.