Deck 13: Floods And Human Interactions

Question 1

What is avulsion?

A) A flooding stream permanently leaves its old channel to form a new floodplain channel.
B) A stream tends to avoid moving in a straight line: it tends to meander.
C) Streams often drop most of their sediment load quickly as the water velocity drops after a flood peak.
D) Streams tend to maintain a nearly constant meander radius for a given discharge.
E) Streams tend to be locked into their meandering channels, avoiding changing channels during a flood.

Answer 1

A

Question 2

What pattern exists in the annual cost of U.S.flood damages from 1910 to 2010?

A) an increase due to population increases and floodplain development
B) an increase due to a decline in building codes
C) a decrease due to restrictions on floodplain development
D) a decrease due to greenways, park systems, golf courses and ball parks
E) no increase or decrease due to subsidized flood insurance

Answer 2

A

Question 3

What physical effect do most bridges have on the streams they cross?

A) They restrict flood flow on the floodplain, so water under the bridge is deeper and faster.
B) They minimize flooding upstream because the water upstream moves more slowly.
C) They decrease erosion under the bridge because they slow the water.
D) They decrease water level just downstream because the water there moves more slowly.
E) They cause vehicles crossing the bridge to get swept up in the flood.

Answer 3

A

Question 4

Which of the following is NOT a common reason cited for building large dams on rivers?

A) flood control
B) hydroelectric power
C) water supply (or irrigation)
D) raise groundwater levels upstream
E) recreation

Question 5

What human action does NOT negatively impact stream processes and cause excessive erosion?

A) logging
B) overgrazing
C) planting trees
D) deforestation
E) fire

Question 6

What process does NOT lead to the failure of a river levee?

A) water overtopping the levee
B) erosion of the levee by the river currents
C) slumping of banks of the levee into the river
D) sandbagging the levee to raise its height
E) piping or seepage through the levee

Question 7

Why does removal of vegetation cause more surface runoff and thus more erosion?

A) It permits more water to directly strike the ground and run off.
B) All of the plants covering the surface slow the runoff.
C) Roots of the plants hold the soil together and prevent erosion.
D) It reduces the amount of vegetation available for forest fires.
E) It results in increased grazing and compaction of the soil.

Question 8

Where do people most commonly get the material to build an artificial river levee?

A) from quarries in the nearby hills
B) from the local sand and gravel company
C) from the river channel, by dredging
D) from coastal dunes or beaches
E) old composted landfill material

Question 9

As dictated by current restrictions,what is the maximum amount the level of a 100-year flood can be encroached (raised)as a result of building?

A) 3 feet
B) 6 inches
C) 0.3 meters
D) 1 meter
E) 18 inches

Question 10

A study of more than 8000 U.S.dams by the Army Corps of Engineers indicated that what proportion of the dams were unsafe?

A) 1/10
B) 1/5
C) ¼
D) ⅓
E) ½

Question 11

Which of the following does NOT cause increased erosion in a stream channel?

A) building a dam across the stream
B) mining gravel from the stream channel
C) planting native trees in the flood fringe
D) building a bridge across the stream, with roadway fill across the floodplain
E) channelizing the stream upstream

Question 12

Roughly what depth of flowing stream is dangerous to drive through?

A) 10 cm (4 inches)
B) 30 cm (1 foot)
C) 60 cm (2 feet), since water would then be over the axles
D) 120 cm (4 feet), since water would then be window-height
E) 180 cm (6 feet), since water would then be above the roof of the car

Question 13

What are the best detection devices to warn people of an already-moving debris flow?

A) a tripwire
B) natural sounds created by the flow
C) an acoustic flow monitor
D) a visual film monitor
E) a natural barrier

Question 14

Which of the following is NOT a good use for floodplains?

A) agriculture
B) parks
C) playing fields
D) golf courses
E) shopping centers

Question 15

Which of the following statements is NOT true about the effects of mining sand or gravel from a streambed or banks?

A) There aren't any negative effects; the stream merely brings in more sand and gravel.
B) Removal of sediment makes the stream erode its channel deeper.
C) Increased erosion by the stream can affect roads and bridges.
D) Deepening the channel lowers the water table and affects agriculture.
E) Deepening the channel can affect water supplies.

Question 16

How long before a flood can someone purchase insurance from the National Flood Insurance program?

A) one week
B) 30 days
C) 3 months
D) 6 months
E) 1 year

Question 17

Why is it almost impossible to keep water from seeping under a levee and out onto a floodplain?

A) Bigger rocks are typically placed at the bottom of levees, and they are most permeable.
B) Levees are built on floodplains marked everywhere by old permeable stream channels.
C) People building levees often forget to line the stream channel with plastic.
D) Piping (large tubes) are built near the top of the levee to prevent overtopping.
E) Metallic walls that are placed into the ground rust and fail after two or three years.

Question 18

What is the significance of a sand boil?

A) formation of a boiling spring in a sand layer
B) a bulbous mass of sand at the toe of an active landslide
C) a sign of seepage under a river levee
D) sand and water that sprays up from the ground because of loading the ground by a nearby landslide
E) sand and water that bubbles up from an artesian well

Question 19

Which effect do levees NOT have on a stream?

A) They raise the flood level.
B) They increase the water velocity next to the levee.
C) They raise water level just downstream.
D) They raise the water level upstream.
E) Over time, they deepen the stream channel bottom.

Question 20

Which of the following is NOT a feature of a modern debris flow trapping structure?

A) spillway
B) water overflow pipes
C) permeable dams
D) cross-linked steel pipes
E) sand and mud from the floodplain

Question 21

What are causes of dam failure? What determines the hazard potential of dam failure for people living downstream?

Question 22

What are the four main reasons cited for building large dams on rivers?

Question 23

Define and explain the process of streambed mining.What are the consequences of streambed mining?

Question 24

What is a debris flow? What areas are most affected by debris flows? What is the best solution to minimize the impact caused by these dangerous flows?

Question 25

What are common levee failures? What makes levees more susceptible to these types of failures?

Question 26

What is avulsion?

Question 27

Why are artificial levees so easily eroded and fail so often?

Question 28

Where do people most commonly get the material to build an artificial river levee?

Question 29

A levee breach forms when a levee fails or is overtopped during flood.Why doesn't flow through the breach lead to avulsion or permanent change in the path of the main channel of a river such as the Mississippi?

Question 30

What is urbanization and how does it contribute to flooding?

Question 31

Why does a stream typically erode its channel downstream from a newly constructed dam?

Question 32

If you find a sand boil on a floodplain,what does that indicate?

Question 33

Why is it almost impossible to keep water from seeping under a levee and out onto a floodplain?

Question 34

What are human activities that can impact stream processes and contribute to flooding? What happens to the streambed as a result of these activities? Identify and explain each activity and the ways in which it affects flooding.

Question 35

Why does the channel bed of a river confined between levees gradually build higher with time?