Deck 14: Streams and Floods: the Geology of Running Water

Question 1

What kind of drainage network is likely to form in a landscape with a uniform substrate and a constant and gentle slope at the surface?

A) dendritic
B) radial
C) rectangular
D) trellis

Answer 1

A

Question 2

A stream carrying sediment flows over the solid rock of its channel,polishing the rock and wearing it away.This is an example of __________.

A) scouring
B) abrasion
C) dissolution
D) saltation

Answer 2

B

Question 3

Running water dissolves soluble minerals.This material is most likely to be transported by a stream as _________.

A) suspended load
B) dissolved load
C) bed load
D) discharge

Answer 3

B

Question 4

Which river has the greatest discharge of any stream on the Earth?

A) Nile
B) Mississippi
C) Congo
D) Amazon

Question 5

Which landscape feature is most likely to form a drainage divide?

A) an mountain ridge
B) a lake
C) a canyon
D) a delta

Question 6

A trellis drainage network such as the one shown below is most like to form in landscapes develop on which type of geologic structure(s)or feature(s)?

A) volcanoes
B) heavily fractured bedrock
C) thick,uniform regolith
D) anticlines and synclines

Question 7

Over time,a stream tends to increase in length by eroding and extending its channel upstream,in a process called ________.

A) downstream piracy
B) headward erosion
C) downcutting
D) infiltration

Question 8

Water in a stream flows from its _________ to its __________.

A) mouth,headwaters
B) mouth,source
C) source,headwaters
D) headwaters,mouth

Question 9

The largest drainage basin in the United States drains into the:

A) Pacific Ocean
B) Arctic Ocean
C) Gulf of Mexico
D) Atlantic Ocean

Question 10

A stream is ________.

A) flowing water confined to a channel
B) a small river found near its headwaters
C) a small river near the mouth
D) a large river near its source

Question 11

What is the term for the land area drained by all of the streams that empty into a tributary?

A) a drainage divide
B) a watershed
C) a drainage network
D) a meander

Question 12

The main stream that is supplied by all tributaries within a drainage network is termed a ________ stream.

A) lead
B) trunk
C) taproot
D) pirate

Question 13

In an ephemeral stream,the groundwater table lies _________ the streambed.

A) on the right side of
B) upstream from
C) above
D) below

Question 14

What kind of drainage network is likely to form in a landscape characterized by a parallel series of ridges and valleys?

A) dendritic
B) radial
C) rectangular
D) trellis

Question 15

What is runoff?

A) water that infiltrates into groundwater
B) water contained in lakes and reservoirs
C) flowing freshwater water on the Earth's surface
D) water flowing over waterfalls

Question 16

Ephemeral streams ________.

A) consist of a series of intertwined channels that are overloaded with sediment
B) have flowing water either episodically or during only a portion of the year
C) have a channel that is highly sinuous (curvy)
D) are those that divert flow from streams they have intersected through stream erosion

Question 17

What kind of drainage network is likely to form in a landscape characterized by a uniform and steep slope and a relatively weak substrate?

A) dendritic
B) parallel
C) rectangular
D) trellis

Question 18

A parallel drainage network such as the one shown below develops on a very steep slope.What type of geologic processes can be inferred from the presence of a parallel drainage network?

A) recent retreat of a glacier
B) a dried-out lake bed
C) recent uplift,such as along a fault
D) seasonal flooding

Question 19

What kind of drainage network is likely to form in a landscape where the bedrock is broken by a regularly-spaced grid of joints and fractures?

A) dendritic
B) radial
C) rectangular
D) trellis

Question 20

A radial drainage network is likely to indicate a current or former _______ in the landscape.

A) landslide
B) volcano
C) mountain belt
D) glacier

Question 21

The deepest part of a curved stream channel,where the flow is fastest,is called the ________.

A) base level
B) point bar
C) stream gradient
D) thalweg

Question 22

A "bird's foot" delta such as the Mississippi River delta forms when the ________.

A) oceanic current exceeds the river current
B) oceanic current is so strong that all sediment is removed as it arrives
C) river and oceanic currents are equal
D) river current exceeds the oceanic current

Question 23

The distinction between a valley and a canyon is ________.

A) nonexistent; the two terms are synonymous
B) that the sides of a canyon are more steep than those of a valley
C) that the sides of a valley are more steep than those of a canyon
D) that valleys are often cut by streams,whereas canyons are eroded by the wind

Question 24

The average velocity of water in a stream

A) is the velocity of the water at the surface of the stream.
B) is the velocity on in the inside of curves in the stream's path.
C) is the velocity at which all of the water is moving.
D) is an approximation to account for friction and turbulence.

Question 25

What physical property of the underlying rock would lead to the formation of a cliff over which a waterfall may form?

A) a high resistance to erosion
B) high porosity
C) large permeability
D) very fine grain sizes

Question 26

Repeated flooding outside a stream channel and across an entire floodplain can result in a pair of low ridges on either side of a stream termed

A) cut banks.
B) natural levees.
C) pirated streams.
D) oxbow lakes.

Question 27

If over time a stream experiences a decrease in its base level or increase in discharge,a(n)________ is likely to form.

A) alluvial terrace
B) slot canyon
C) meander
D) waterfall

Question 28

The base level of a tributary would ________ if a dam and a reservoir were constructed where it flowed into a trunk stream.

A) be unchanged
B) become unpredictable
C) fall
D) rise

Question 29

In some cases,the push of flowing water cause large particles to bounce or roll along a streambed.These pieces are then carried along the bottom of the stream as _________.

A) suspended load
B) dissolved load
C) bed load
D) discharge

Question 30

A geologist finds an old report on stream discharge and reads a value of "20",but the rest of the page is cut off.Which of the following could be the appropriate value and units for the discharge of a stream?

A) 20 meters per second
B) 20 cubic meters per second
C) 20 square meters per second
D) 20 seconds per cubic meter

Question 31

Meandering streams ________.

A) consist of a series of intertwined channels that are overloaded with sediment
B) have flowing water either episodically or during only a portion of the year
C) have a channel that is highly sinuous (curvy)
D) are those that divert flow from streams they have intersected through stream erosion

Question 32

Which of the following is most likely to make up the suspended load of a stream?

A) ions that formed when minerals dissolved in groundwater
B) large boulders that fell into the stream during a landslide
C) gravel that washed into the stream during a flood
D) small grains of clay and silt

Question 33

The discharge of a river traveling through a temperate region will typically ________ downstream; the discharge of a river traveling through an arid region will typically ________ downstream.

A) increase; increase
B) decrease; decrease
C) increase; decrease
D) decrease; increase

Question 34

Why do deltas form?

A) because tidal currents carry sediment from elsewhere along the shoreline
B) because when streams reach base level,the sediment they carry settles out and is deposited
C) because stream sediments cannot be transported in seawater
D) because in places,stream water sinks into the ground where it meets the oceans,leaving behind sediments

Question 35

The shape of a delta is primarily determined by ________.

A) the shape of the river channel near the mouth
B) the average grain size of the suspended and bed loads
C) whether river currents or ocean currents are locally predominant
D) the type of rock that is weathering at the outcrop near the headwaters of the river

Question 36

What shape does the longitudinal profile of a typical stream follow? A longitudinal profile plots elevation of a streambed with distance,showing the streambed elevation from its highest point upstream to the lowest point at base level.

A) a straight diagonal line
B) a straight horizontal line
C) concave upward
D) a line with random high and low points

Question 37

Ultimately,the base level of a stream valley cannot be lower than ________.

A) the average elevation of the continent on which it is found
B) sea level
C) the average elevation of the local catchment
D) the maximum elevation of the local catchment

Question 38

The flat-lying area surrounding a river channel is termed the ________.

A) base level
B) floodplain
C) stream gradient
D) thalweg

Question 39

Braided streams ________.

A) consist of a series of intertwined channels that are overloaded with sediment
B) have flowing water either episodically or during only a portion of the year
C) have a channel that is highly sinuous (curvy)
D) are those that divert flow from streams they have intersected through stream capture

Question 40

In the picture below,fragments of bed load bounce along the bed and knock other grains up into the flow to move downstream for short distances.This process is called

A) saltation.
B) meandering.
C) stream piracy.
D) base level.

Question 41

What is a point bar?

A) a rocky barrier in a streambed
B) a place where base level rapidly changes along a stream's length
C) the inside curve of a stream's meander where sediment is deposited
D) a place where two tributaries meet in a watershed

Question 42

Sketch a meandering stream in map view.Your drawing should include (labeled)the channel,floodplain,meanders,and at least one oxbow lake.How does an oxbow lake form?

Question 43

Describe what happens to the amount and grain size of sediments carried by a stream when it transitions from high flow velocity to lower velocity.Give an example of where on a landscape such a transition could occur.

Question 44

Recent tectonic uplift or a drop in base level can result in downcutting into a landscape that had previously been eroded close to base level,in a process called

A) meander migration.
B) flooding.
C) stream piracy.
D) stream rejuvenation.

Question 45

Which of the following scenarios is more likely to cause a flash flood than a slow-onset flood?

A) the melting of snowpack in the spring time,coupled with rain
B) sustained rains during a distinct wet season
C) the failure of a stream channel's levees
D) the sustained presence of a storm over a region

Question 46

Which of the following is MOST likely to result in stream rejuvenation?

A) the discharge of a stream decreases
B) the base level of a stream drops
C) the land surface beneath a stream subsides
D) a drainage reversal occurs

Question 47

Using the image below,label the stream channel,meander,floodplain,headwaters,and mouth.Additionally,sketch a cross-section of this stream from A to A' and from C to C'.

Question 48

What are some of the ways that urbanization can change how stream discharge responds to rainfall and runoff and affect flooding?

Question 49

Urbanization of a watershed is most likely to result in __________.

A) increased infiltration of rainwater
B) a longer lag time between storms and the onset of flooding
C) an increase in the volume of water entering streams after rainfall
D) a decrease in the likelihood of flash flooding

Question 50

If a 50-year flood occurs on the Mississippi River this year,what is the probability that a flood of the same magnitude will occur in the following year?

A) 0 percent
B) 1 percent
C) 2 percent
D) 50 percent

Question 51

A meander that is cut off to become completely isolated from the main channel but which retains water is called a(n)________.

A) meander neck
B) cut bank
C) oxbow lake
D) thalweg

Question 52

Which of the following best describes a "100-year flood"?

A) has a 1 percent chance of occurring in any given year
B) occurs once every 100 years
C) lasts for 100 years
D) is twice as deep as a 50-year flood

Question 53

What is a flash flood? Suggest two circumstances that might lead to flash flooding.

Question 54

Contrast the gradient of a typical stream at its headwaters versus its mouth.Sketch the longitudinal profile of a typical stream.

Question 55

Which of the following conditions would cause the largest stream capacity?

A) high velocity and high discharge (i.e.,a large,fast-moving river)
B) high velocity and low discharge (i.e.,a small,fast-moving mountain creek)
C) low velocity and high discharge (i.e.,a large but slow-moving river)
D) low velocity and low discharge (i.e.,a small and sluggish lowland creek)

Question 56

Describe some of the methods that have been used for flood control,and explain why these methods have limitations or do not always work.

Question 57

Differentiate between dissolved load,suspended load,and bed load.

Question 58

Two 100-year floods can occur in two consecutive years.Use the concept of recurrence interval to explain how this is possible.

Question 59

Runoff from farm fields entering a stream system is likely to be __________ than that from naturally vegetated fields.

A) greater and more sediment-laden
B) smaller but more sediment-laden
C) greater but less sediment-laden
D) smaller and less sediment-laden

Question 60

Geologists are trying to determine the discharge of a river.The stream is semicircular in shape with a width of 10 m and depth of 5 m.They measure the velocity of the river to be 0.2 m/s.What is the discharge of the river? Sketch this cross-section,and show your work.Recall that the area of a circle is πr²,and a semicircle is one-half of that.