Deck 15: Streams and Floods

Question 1

Which of the following statements concerning graded streams is NOT true?

A) A graded stream responds instantaneously to any change in sediment load or discharge in such a way as to establish a new graded state.
B) After a sudden decrease in sediment load, the gradient decreases, as does stream velocity.
C) The equilibrium of a graded stream is temporary and lasts only until the next change in its environment.
D) After a sudden increase in sediment load, the gradient increases, as does stream velocity.

Answer 1

B

Question 2

The tectonic activity that produces trellis stream patterns would be:

A) falling sea level.
B) rising sea level.
C) convergence.
D) divergence.

Answer 2

C

Question 3

A graded stream is one in which an equilibrium has been reached so that:

A) only deposition occurs.
B) only erosion occurs.
C) changes in the stream's environment no longer cause changes in the stream's erosion or deposition.
D) there is little net erosion or deposition.

Answer 3

D

Question 4

Which of the following statements concerning a stream's sediment load is NOT true?

A) Dissolved load is strongly affected by velocity.
B) Both flat and low- density particles tend to remain within the suspended load.
C) Large stones that cannot be carried within a stream's suspended load can sometimes be transported by traction in the stream's bed load.
D) Fine particles of clay are likely to be transported as part of the suspended load.

Question 5

Geologists use the term "stream" to refer to:

A) tributaries to rivers.
B) all the above.
C) major rivers.
D) small local creeks.

Question 6

Stream piracy occurs when:

A) a stream cuts through a separating strip and bypasses a stream meander.
B) one stream captures the headwaters of another stream on the opposite side of a drainage divide.
C) degradation causes the stream to erode its bed and reduce its gradient.
D) erosion causes a waterfall to migrate upstream and reduce its height until it no longer exists.

Question 7

A stream crossing a delta splits into a network of distributaries because:

A) an increase in stream velocity and discharge causes the stream to cut a new stream channel away from the delta.
B) as waves and shoreline currents erode the delta, the stream seeks new areas in which to deposit its load.
C) as the delta grows, the decreased stream gradient causes greater sedimentation and clogging of the delta channels.
D) the stream eventually encounters erosion- resistant rocks that steer it away from the delta.

Question 8

Which of the following conditions is most favorable for delta formation?

A) Where waves and currents immediately sweep away most of the river's delivered sediments.
B) Where a large sediment load is delivered to quiet coastal waters.
C) Where powerful storm waves carry all of the river's delivered sediment.
D) Where a small sediment load is delivered along the river's short path to quiet coastal waters.

Question 9

The volume of a stream's dissolved load is dependent on all of the following factors EXCEPT:

A) climate.
B) topography.
C) stream velocity.
D) bedrock composition and acidity of the water.

Question 10

Which of the following statements about the processes of stream erosion is NOT true?

A) Potholes in bedrock are evidence of stream erosion by dissolution.
B) Hydraulic lifting is erosion by water pressure.
C) Abrasion and hydraulic lifting are more efficient in fast, turbulent streams than in slow ones.
D) Each year, dissolution is responsible for the removal of an estimated 3.5 million metric tons of rock from the continents.

Question 11

In a curved section of a stream channel, the fastest water is:

A) near the outside of the curve.
B) relatively equal throughout the stream.
C) in the middle of the stream.
D) near the inside of the curve.

Question 12

Which of the following statements about deltas is NOT true?

A) The term comes from the Roman word for stream.
B) Topset beds are sediments deposited in horizontal layers on top of inclined foresets.
C) Bottomset beds are sediments deposited in horizontal layers farther away from the mouth of the stream.
D) Foreset beds are coarse sediments deposited first, close to the mouth of the stream.

Question 13

Streams meander because:

A) streams typically carry a larger sediment load than their velocity can maintain.
B) streams are steered by slight elevation changes within their floodplain.
C) streams are steered around materials that are more resistant to erosion.
D) erosion occurs on the outside of curves while deposition occurs on the insides of curves.

Question 14

The Mississippi River will soon take a shorter route to the Gulf of Mexico by way of:

A) The birdfoot delta.
B) Lake Pontchartrain.
C) The Atchafalaya River.
D) The Balize delta.

Question 15

Streams with large amounts of coarse, bed- load sediments deposit what bedform?

A) Mid- channel bars.
B) Floodplain.
C) Levees.
D) Backswamp.

Question 16

All of the following are factors that would probably reduce the amount of runoff from heavy rains EXCEPT:

A) clay- rich soil.
B) extensive vegetation.
C) flat topography.
D) highly fractured granite bedrock.

Question 17

The stream that erodes through its divide to capture the other slope drainage does so because of its:

A) steeper slope.
B) less resistant streambed rocks.
C) greater discharge.
D) all of the above.

Question 18

Natural levees result when:

A) hard, erosion- resistant rocks become part of a stream's banks.
B) yazoo streams flow parallel to a main stream and deposit material on the stream bank.
C) streams flood their banks and deposit sediment directly on top of the banks.
D) streams erode downward in their channel, leaving their banks higher relative to the surface of the stream.

Question 19

Braided streams are caused by:

A) an exceptionally high discharge.
B) an exceptionally steep gradient.
C) an exceptionally high sediment load.
D) an exceptionally high velocity.

Question 20

All of the following could initiate the formation of stream terraces within a floodplain EXCEPT:

A) a local tectonic movement that lowers the stream's base level.
B) a long- term increase in sediment load.
C) a long- term increase in precipitation.
D) a decrease in global sea level.

Question 21

Every stream carries water from a watershed that is separated from other watersheds by a:

A) floodplain.
B) tributary.
C) drainage basin.
D) drainage divide.

Question 22

Flood prediction is based primarily on:

A) the statistical probability of a flood occurring within a given time.
B) monitoring of flood precursors, such as increased groundwater levels and unusual plant behavior.
C) computer models of meteorological cycles.
D) monitoring global levels of atmospheric moisture.

Question 23

The primary difference between a superposed stream and an antecedent stream is that:

A) superposed streams do not meander, whereas antecedent streams have continually migrating meanders.
B) younger superposed streams follow stream beds created by ancient antecedent streams.
C) superposed streams erode deeper rock layers, whereas antecedent streams erode into a landscape that is being slowly uplifted.
D) antecedent streams build up their floodplains through deposition, while superposed streams erode downward in their floodplains.

Question 24

During a flood, a stream's erosive power increases dramatically. The increase in erosive power is approximately equal to:

A) the square of the increase in velocity.
B) two times the increase in discharge.
C) the increase in discharge.
D) the increase in velocity.

Question 25

A 10- year flood is a flood that:

A) occurs once every 10 years.
B) occurs once each year for 10 years.
C) does not occur every 10 years.
D) lasts for 10 years.

Question 26

Which of the following statements about stream transport is NOT true?

A) A stream's competence is a measure of the diameter of the largest particle that the stream can transport.
B) A stream's capacity is proportional to the square of its discharge.
C) A stream's competence is proportionate to the square of its velocity.
D) A stream's capacity is a measure of the maximum quantity of sediment the stream can transport.

Question 27

In the Big Thompson flood of 1976, which factor contributed most to the disaster?

A) Excessive snowmelt.
B) Highly fractured granite bedrock.
C) Steepness of the slopes in the area.
D) Earlier forest fires removed vegetation.

Question 28

A river provides "good news" to a city with all of the following EXCEPT:

A) fertile soils adjacent to rivers grow crops.
B) floods damage property and disrupt transportation.
C) steady supply of water for home use.
D) source of clean hydroelectric power.

Question 29

Waterfalls tend to:

A) remain stationary but decrease in height as erosion cuts downward in the upper channel.
B) migrate downstream and become larger as sediment deposits accumulate on their edge.
C) migrate upstream and become smaller as erosion wears away their edge.
D) remain stationary but increase in height as the falling water erodes deeper into their plunge pool.

Question 30

The highest point along a meandering stream floodplain would be:

A) the point bar deposits.
B) the levees.
C) the yazoo streams.
D) the channel bank.

Question 31

Niagara Falls migrates upstream about 1 meter per year because it:

A) erodes a soft shale on top of a resistant dolostone.
B) erodes a hard sandstone on top of a soft shale.
C) erodes a hard sandstone on top of a soft limestone.
D) erodes a soft shale beneath a resistant dolostone.

Question 32

A stream's base level is:

A) the elevation of the head of a stream.
B) the lowest level to which a stream can erode its channel.
C) the gradient of the stream where it enters the ocean.
D) the average elevation of the stream channel.

Question 33

The primary difference between a delta and an alluvial fan is that:

A) alluvial fans result from deposition into inland lakes, while deltas result from deposition into the ocean.
B) alluvial fans are erosional features, whereas deltas are depositional features.
C) alluvial fans are formed on low- land plains, while deltas are formed in a standing body of water.
D) alluvial fans form at the source of a stream and deltas form at the mouth of a stream.

Question 34

Stream valleys have a distinctive V- shape because:

A) as a valley is cut, overland flow and mass movement remove loosened material from its slopes.
B) as a stream erodes downward, it encounters material more resistant to lateral erosion.
C) as a stream erodes downward, it becomes graded and accomplishes less lateral erosion.
D) as a valley becomes established, there is less lateral meandering.

Question 35

All of the following statements concerning the Earth's water resources are true EXCEPT:

A) meteoric water is the portion of Earth's water that is contributed by meteorites.
B) the total amount of water has remained fairly constant for the last 1 billion years.
C) all but 1% or less is in the oceans or frozen in glaciers and snow.
D) some water is stored for thousands of years as snow on mountain peaks or as ice in glaciers.

Question 36

A swift- flowing, relatively sediment- free stream transporting large boulders along its bed would be considered to have a:

A) high capacity and low competence.
B) high capacity and high competence.
C) low capacity and high competence.
D) low capacity and low competence.

Question 37

A rectangular stream pattern characterizes a topography of:

A) numerous joints or fractures, many with right angles.
B) a gently sloping basin uniform in structure and composition.
C) narrow valleys with soft rocks are separated by ridges of hard rocks.
D) a central high area with outward radiating drainages.

Question 38

Artificial flooding on the Colorado River in 1996:

A) replenished beaches and sandbars along the river.
B) scoured sediment and vegetation along the banks.
C) cleared debris from tributaries.
D) all of the above.

Question 39

The most likely effect of stream channelization is that:

A) stream gradient and velocity will both increase.
B) stream gradient will increase, and velocity will decrease.
C) stream gradient and velocity will both decrease.
D) stream gradient will decrease and velocity will increase.

Question 40

The most common structural flood control measure is:

A) flood- control dams.
B) diversion channels.
C) artificial levees.
D) none of the above.

Question 41

Which of the following statements about stream drainage patterns is NOT true?

A) A dendritic drainage pattern occurs in areas with newly exposed coastal muds and massive plutonic igneous or metamorphic rocks.
B) A rectangular drainage pattern occurs in areas that are nearly flat, such as the Midwestern and Great Plains states.
C) A trellis drainage pattern occurs in areas containing narrow valleys separated by parallel ridges.
D) A radial drainage pattern occurs around topographic peaks, such as young volcanic cones.

Question 42

List and describe the parts of a stream system.

Question 43

Define the mechanisms by which streams erode their channels.

Question 44

Explain the concept of a graded stream.

Question 45

Stream terraces indicate what overall geologic process?

A) Local flooding in the stream valley.
B) A local rise in base level.
C) Stream deposition in its channel.
D) Stream erosion in its channel.

Question 46

In a straight section of a stream channel, the fastest water is:

A) near the bank just below the surface.
B) in the middle just below the surface.
C) in the middle at the bottom.
D) near the bank at the bottom.

Question 47

A 150- kilometer- long stream has a gradient of 10 feet per kilometer. The streams velocity at a point X, exactly halfway between the source and the mouth, is 5 meters per second. The depth of the stream is 2 meters, and the width is 8 meters. What is the correct estimate of the stream's discharge at point X?

A) 400 cubic meters per second.
B) 600 cubic meters per second.
C) 40 cubic meters per second.
D) 80 cubic meters per second.

Question 48

Which of the following statements concerning stream activity and water on Mars is NOT true?

A) Most of Mars' stream- related features are near sites of ancient volcanic activity.
B) It is likely that most of Mars' water is trapped as ice beneath the regolith.
C) Mars probably has abundant surface water, as on Earth.
D) Because of low atmospheric pressure, any liquid water found at the surface of Mars would vaporize instantaneously.

Question 49

List and explain the three ways in which streams transport sediments.

Question 50

What causes a stream to eventually abandon a delta?

Question 51

Accumulations of gold, platinum, or silver would most likely be found:

A) distributed evenly throughout the stream bed.
B) in point bars on the inside of meander curves, where stream velocity is the slowest.
C) on the outside of meander curves, where the high velocity of the water has embedded them in the banks.
D) in potholes in the stream bed because their high density would cause them to sink lower than other sediments.

Question 52

How does stream velocity differ in different parts of a stream channel?

Question 53

The world's oceans contain approximately what percentage of the Earth's water?

A) 75%.
B) 83%.
C) 86%.
D) 97%.

Question 54

Discuss methods used to predict major floods.

Question 55

How do natural levees form?

Question 56

Explain why Mars, a virtually waterless planet, exhibits stream landforms.

Question 57

Describe how superposed and antecedent streams develop.