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Natural Hazards > Chapter 10 - part 1 > Flashcards

Chapter 10 - part 1 Flashcards

1
Q
  1. What is a drainage basin?
A

The area of land drained by a river or river system.

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2
Q
  1. How does a typical drainage basin vary from its highest point to its lowest point?
A

At the highest point,

  • the gradient is steeper - higher velocity
  • channel size: smaller
  • shape/ratio: higher width to depth ratio at top
  • sediment load: coarser sediment at the top
  • discharge: more water at the bottom
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3
Q

How is sediment created in a river?

A

Weathering creates sediment.

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4
Q

How does EROSION occur in a river?

A

because of the impact of:

MOVING WATER
IMPACT of other moving sediment
HYDRAULIC LIFT

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5
Q

How does TRANSPORT occur in a river?

A

SOLUTION

SUSPENSION

SALTATION

TRACTION

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6
Q

How does DEPOSITION occur in a river?

A

Occurs when water velocity drops.

Solution deposition occurs with precipitation.

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7
Q
  1. How does a river erode, transport and deposit sediment?
A

Basic processes:

  1. WEATHERING creates sediment.
  2. EROSION in a river occurs because of the impact of moving water, impact of other moving sediment and hydraulic lift
  3. TRANSPORT (through solution, suspension, saltation and traction)
  4. DEPOSITION occurs when water velocity drops (solution deposition occurs with precipitation)
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8
Q
  1. When does a river erode, transport and deposit most of its sediment load?
A

Most sediment movement takes place during rare, brief episodes of increased discharge (a flood).

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9
Q
  1. BRAIDED RIVER
A
  1. Number of channels:more than 1
  2. Size of channel:smaller
  3. Shape of Channelhigher w/d ratio
  4. Discharge:variable
  5. Sediment Load:poorly sorted coarse or large moving as bedload
  6. Gradient:Steep
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10
Q
  1. MEANDERING RIVER
A
  1. Number of channels:1
  2. Size of channel:larger
  3. Shape of ChannelLower w/d ratio
  4. Discharge:consistent and stable (uniform)
  5. Sediment loadwell sorted, fine or small moving in suspension
  6. Gradient

shallower

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11
Q

Braided Rivers are found ____ in the drainage basin

A

higher up in the drainage basin

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12
Q

Meandering Rivers are found ____ in the drainage basin

A

lower down in the drainage basin

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13
Q
  1. DISCHARGE
A

The volume of water moving in a river in a certain amount of time.

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14
Q
  1. BANKFULL DISCHARGE
A

The maximum amount of water in the channel. (Often the dominant discharge)

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15
Q
  1. DOMINANT DISCHARGE
A

The volume of water in the channel that does the most work.

Work is measured by the amount of sediment that is moved.

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16
Q
  1. DOMINANT DISCHARGE
A

The volume of water in the channel that does the most work.

Work is measured by the amount of sediment that is moved.

This is often bankfull discharge.

17
Q
  1. FLOOD
A

A flood is an even when there is more discharge than the channel can accommodate.

(this extra water leaves the channel and goes onto the flood plain; assuming there is one.)

18
Q
  1. FLOODPLAIN
A

A flat, low-lying area along a stream channel. The area of land next to the river channel used to store excess water (temporarily) and sediment (longterm)

19
Q
  1. How often do rivers flood?
A

Rarely.

20
Q
  1. Which river, braided or meandering is most likely to produce a catastrophic flood?
A

Both rivers are capable of creating a catastrophic flooding event.

While a flood in a braided river may be more violent (faster water), it will be shorter in duration.

A flood in a meandering system may be less violent (slower water) but last longer.

Also, a flood in a braided system will arrive sooner, whereas in a meandering system it may arrive later after the precipitation event.

21
Q
  1. Flooding in a braided system (see photo)
A

The excess water of a flood will enter the channel very soon after the rainfall event.

Discharge will increase quickly and reach a maximum value quickly

Just as quickly, discharge will drop as this excess water passes through the river.

Potentially a lot of sediment will be moved.

Braided rivers usually lack a flood plain so water and sediment continue to move during a flood.

22
Q
  1. Flooding in a braided system (see photo)
A

The excess water of a flood will enter the channel very soon after the rainfall event.

Discharge will increase quickly and reach a maximum value quickly

Just as quickly, discharge will drop as this excess water passes through the river.

Potentially a lot of sediment will be moved.

Braided rivers usually lack a flood plain so water and sediment continue to move during a flood.

23
Q
  1. Flooding in a meandering system (see photo)
A

Excess water from precipitation will enter the system more slowly.

This means that discharge will increase starting later after precipitation, reach a lower maximum value over a longer period of time, and then decrease slow over time.

In a meandering river, less sediment may be removed from the system. More might be deposited or simply moved within the system.

24
Q
  1. Explain the effects that saturated ground has on flooding
A

Where the ground is saturated with water, any extra water will remain on the surface.

As a result it will travel quicker into the river contributing to a more rapid increase in discharge.

25
Q
  1. Hydrograph
A

A hydrograph is a chart that compares discharge (maximum Q) over time.

26
Q
  1. Urban flood hydrograph PHOTO
A

An urban setting is less permeable:

  • There are many hard surfaces that prevent water from infiltrating into the ground.
  • There is also artificial drainage (i.e. sewers) that will channel water quickly into a river.

These both contribute to sudden increases and decreases in discharge.

27
Q
  1. Rural flood hydrograph PHOTO
A

In a rural setting, there are a lot of permeable surfaces (fields, forests etc. ) that allow water to infiltrate into the ground.

There is also little or no artificial drainage that will move quickly.

There is also lots of vegetation that can intercept and absorb water, slowing water movement over the surface.

28
Q
  1. Explain the unique circumstances surrounding the behaviour of a north flowing river in the Northern Hemisphere when it floods. Give an example.
A

In Canada, many rivers flow north.

As they flow north the landscape changes; permafrost is encountered. Permafrost makes the ground impermeable.

Precipitation is therefore quickly channeled into the river adding to a faster increase in Q.

Also, if there is flooding, this excess water will remain on the surface, making the flood worse.

During the winter, most rivers in Canada are frozen over. They behave like a pipe in that the water moving in them is confined to a fixed channel site.

In spring, North flowing rivers in Canada thaw first in the south. Here the extra water from snow melt eventually flows into a channel to the North that is still sealed with ice. Here water velocity increases.

At the same time, water pressure under the ice increases eventually causing the ice to break, sometimes suddenly and violently.

29
Q
  1. Explain the unique circumstances surrounding the behaviour of a north flowing river in the Northern Hemisphere when it floods. Give an example.
A

In Canada, many rivers flow north.

As they flow north the landscape changes; permafrost is encountered. Permafrost makes the ground impermeable.

Precipitation is therefore quickly channeled into the river adding to a faster increase in Q.

Also, if there is flooding, this excess water will remain on the surface, making the flood worse.

During the winter, most rivers in Canada are frozen over. They behave like a pipe in that the water moving in them is confined to a fixed channel site.

In spring, North flowing rivers in Canada thaw first in the south. Here the extra water from snow melt eventually flows into a channel to the North that is still sealed with ice. Here water velocity increases.

At the same time, water pressure under the ice increases eventually causing the ice to break, sometimes suddenly and violently.

30
Q
  1. Explain the effects that saturated ground has on flooding.
A

Permafrost/frozen ground makes the ground impermeable.

Precipitation is therefore quickly channeled into the river adding to a faster increase in Q.

If there is flooding, this excess water will remain on the surface, making the flood worse.

Natural Hazards (20 decks)

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