Deck 14: Floods and Human Interactions

Question 1

How does failure of an artificial levee differ from failure of a natural levee?

A)The water spills slowly over the levee into its floodplain, dropping coarser particles next to the main channel.
B)The water flows faster, and the areas next to the levee are commonly buried under sand and gravel.
C)The water flows slowly, depositing valuable topsoil in the floodplain.
D)The water flows at the same speed as the river, limiting erosion.
E)There is no difference between failure of an artificial and a natural levee.

Answer 1

B

Question 2

Damage from debris flows can be limited through construction of walls to deflect flows to an undeveloped area.

Answer 2

True

Question 3

To reduce exposure to damage from debris flows, buildings and streets should be built perpendicular to the downslope direction of flow.

Answer 3

False

Question 4

Why is living on a floodplain behind a levee safe from flooding?

A)Levees are rarely overtopped.
B)Water cannot seep under levees to flood the floodplain.
C)Levee banks are rarely eroded enough to fail.
D)Once a levee is built high enough to contain a 100-year flood, it will never flood.
E)Actually, 100-year flood levels often continue to get higher with time.

Question 5

In which logging method are felled trees skidded downslope to be loaded on trucks?

A)tractor yarding
B)selective cutting
C)slope collecting
D)saw cut loading
E)skid sloping

Question 6

How does a bridge promote erosion in a channel?

A)The bridge pilings interfere with the water flow, causing additional sediments to be deposited.
B)The water velocity decreases, due to restricted flow over the floodplain.
C)The water velocity increases, due to restricted flow over the floodplain.
D)The channel height decreases, and large particles fall out, creating more surfaces for erosion to occur.
E)A bridge does not promote erosion.

Question 7

Artificial levees are almost always built downstream of natural levees.

Question 8

The U.S. average annual death rate caused by floods over a recent 10-year period exceeded 100.

Question 9

How does streambed mining affect a stream?

A)It increases erosion in the downstream channel.
B)It carries greater sediment load downstream.
C)It slows stream water velocity.
D)It increases groundwater supplies away from the stream.
E)It steepens the channel gradient downstream.

Question 10

When a large flood first breaches a levee, what are the characteristics of the water crossing the breach?

A)relatively clear, highly eroding
B)relatively cloudy, highly eroding
C)relatively clear but not prone to strong erosion
D)relatively cloudy but not prone to strong erosion
E)about the same average sediment load as the flooding stream

Question 11

Wing dams are used to constrict river channels to increase river depth for barge traffic during low flow.

Question 12

Debris flows can happen even on slopes of less than 30° covered with thick brush or forest.

Question 13

U.S. taxpayers pay the cost of any loss under the federal flood insurance program.

Question 14

Which is NOT a common method of levee failure?

A)seepage
B)bank erosion
C)interweaving
D)slumps into the channel
E)piping

Question 15

A dam built to store water for irrigation may lead to high reservoir levels behind the dam and too little remaining water storage in the reservoir to prevent downstream flooding during high rainfall or snowmelt.

Question 16

Building on the outside bend of a meander is the best location to reduce the possibility of bank erosion during a flood.

Question 17

Which is NOT an unintended consequence of building an artificial levee?

A)It causes the stream to flow faster.
B)It raises the water level during flooding.
C)It causes more upstream flooding.
D)It causes more downstream flooding.
E)It protects towns from flooding for a time.

Question 18

Dams cause erosion of the upstream channel.

Question 19

What is/are the best material(s) for building a levee?

A)locally available material from the floodplain
B)sand and mud
C)coarse gravel
D)clay
E)crushed rock

Question 20

What is NOT a way in which development affects floods?

A)pavement and rooftops increase runoff
B)excavation of sand and gravel changes river sediment loads
C)artificial concrete channels minimize floods
D)logging increases runoff
E)logging decreases sediment loading

Question 21

Rising floodwater in a river increases groundwater pressure, which can push water to the surface on the floodplain, where it can potentially rise to nearly the water level in the river. With prolonged flooding, that water often reaches the surface as _______________.

Question 22

The Teton Dam, in the state of _______________, failed June 5, 1976, took 11 lives, and caused more than $3.2 billion in damage.

Question 23

Where likely sources of debris flows are a short distance upstream and the channel gradient is high, ____.

A)a trip wire is more effective than an acoustic flow meter for debris flow warnings
B)sirens should not be used in debris early warning systems
C)warning time for a debris flow may be too short to allow for evacuation
D)the danger to humans from a debris flow is minimized
E)debris flows and mudflows will never be covered by flood insurance

Question 24

A(n) _______________ is a permeable structure meant to trap debris flows.

Question 25

Water _______________ cm deep and above the vehicle floorboards can push a vehicle off the road and potentially drown the occupants.

Question 26

Which event did NOT occur during and after the flooding of the Cumberland River near Nashville in the spring of 2010?

A)Levees were overtopped.
B)Most of the damage was outside the floodplain.
C)Over 30 people died.
D)Many houses were filled with 2 m of water.
E)Most people evacuated, since the failure occurred gradually.

Question 27

Which type of dam is built to control downstream flooding?

A)flood-control dam
B)wing dam
C)hydroelectric dam
D)spillway dam
E)all types of dams

Question 28

The national flood insurance program formally separates the flood plain into the floodway and the _______________.

Question 29

Sometimes a levee breach will lead to _______________, where the main channel of a river is redirected through the breach.

Question 30

What is NOT a reason that a levee originally built to contain a 100-yr flood would be insufficient?

A)Major floods occur more frequently as areas are developed.
B)Floods larger than a 100-year flood can occur at any time.
C)Flood levels generally rise over time.
D)Sediment deposited by tributary streams degrades the levee.
E)Levees are of varying quality.

Question 31

What do rivers continually strive to do?

A)Build up their sediment load.
B)Disburse their sediment load.
C)Minimize the energy they expend.
D)Maximize the energy they expend.
E)Maintain as straight a path as possible.

Question 32

Which factor did NOT contribute to the flooding around Jakarta, Indonesia, in February 2007, which killed dozens and forced the evacuation of more than 400,000 people?

A)torrential rains
B)deforestation of hillsides near the city
C)a volcanic eruption that occurred just prior to the flooding
D)storm drains and rivers clogged with trash
E)inadequate urban planning

Question 33

The 10-m high Hope Mills Dam in _______________ failed twice, once in 2003 and once in 2010.

Question 34

The growth of _______________ is a major problem in buildings that have been flooded.

Question 35

When a flood breaks through the walls of a levee, it is called a(n) _______________.

Question 36

Which is NOT a type of early warning system for debris flows?

A)trip wires
B)acoustic flow monitors
C)sirens
D)weather alerts for increased hazard conditions
E)alluvial fan monitors

Question 37

Levees are ____.

A)less susceptible to failure when built from local materials
B)an alternative to spillways for protection of structures from floods
C)always artificial, not natural
D)sometime intentionally breached during floods
E)reinforced by piping and sand boils

Question 38

Which was the most disastrous dam failure in recent decades?

A)Lake Vyrnwy Dam in Wales
B)Gordon Dam in Tasmania
C)Cougar Dam in Oregon
D)Banqiao Dam in China
E)Buffalo Bill Dam in Wyoming

Question 39

Which factor does NOT influence the hazard potential of a failing dam?

A)the population's distance downstream
B)the amount of upstream erosion
C)the valley topography
D)the height of the dam
E)the volume of water released

Question 40

A structure that allows for controlled release of water from a levee is known as a(n) _______________.

Question 41

Although a levee may be initially of sufficient height to constrain a 100-year flood, the stream will eventually _______________ the levee in a larger flood.

Question 42

How does vegetation removal affect the contribution of sediment to streams?

Question 43

Every time we build a new levee to protect something on a floodplain or to facilitate shallow-water navigation, we _______________ the width of the flood-flow part of the river.

Question 44

List some regions of the U.S. where there are significant populations living on alluvial fans. Why is it dangerous to build there?

Question 45

Why would building a levee from locally-available material make it susceptible to failure?

Question 46

A bill passed by the U.S. Senate in 2008 requires that people buy _______________ if a levee breach will result in their homes being flooded.

Question 47

Describe coastal effects of removing sediments from a stream, as is done during mining.

Question 48

Flood insurance is provided by the _______________.

Question 49

Why is it dangerous to drive in a shallow flooded area?

Question 50

Compacted clay resists erosion and is nearly impermeable to floodwater but can fail by _______________.