River Erosion and Deposition

Question 1

What is the movement of sediment from one location to another called?

Answer 1

Erosion (Weathering is the actual breaking of existing rock into sediment)

Question 2

What is the placement of sediment called?

Answer 2

Deposition

Question 3

In the upper course of a river, what is the shape of the channel?

Answer 3

The channel is narrow, straight, with more erosion of the bed than the sides.

Question 4

In the upper course of a river, why is the water moving quickly?

Answer 4

The upper course of a river has a steeper slope than the middle and lower courses.

Question 5

In the middle course of a river, how does the channel change?

Answer 5

The channel widens, and meanders form.

Question 6

What is a meander?

Answer 6

A curve in the river channel that forms when faster water erodes one bank, while slower water deposits sediment on the opposite bank.

Question 7

What is a levee?

Answer 7

A natural or artificial build up of the banks of a river channel.

Question 8

How do natural levees form?

Answer 8

During a flood, sediment-rich water will deposit larger pieces near the banks of the river.

Question 9

How does a floodplain form?

Answer 9

During a flood, sediment-rich water will carry finer particles until the water speed slows enough to deposit them.

Question 10

Why are many cities and towns built near rivers?

Answer 10

Rivers provide fertile soil for agriculture. They can be a source of freshwater. They can be used to transport goods.

Question 11

Why should artificial levees be built away from the banks of the river?

Answer 11

The sedimentation process from periodic flooding replenishes soil. The river channel is not constricted, which decreases pressure on the levees.

Question 12

What is a floodway?

Answer 12

A channel or area adjacent to a river where floodwaters are diverted to prevent damage to buildings and people.

Question 13

How can dams be used to control floods?

Answer 13

Dams are built upstream to control the amount of water in the channel near a populated area.

Question 14

What is a tributary?

Answer 14

A smaller stream that flows into a larger stream.

Question 15

How does a alluvial fan form?

Answer 15

When the slope of the land abruptly changes from the upper course to the middle course, larger pieces of sediment are deposited at the base of mountains.

Question 16

What is a delta?

Answer 16

A triangular-shaped deposit of sediment that forms where a river enters a larger and slower body of water.

Question 17

In what order is sediment usually deposited in a delta?

Answer 17

The largest sediment will be near the mouth of the river: gravel, sand, silt, and clay.

Question 18

How does draining wetlands affect an area’s ability to deal with flooding?

Answer 18

Draining wetlands compacts sediments, which can lower the elevation and create areas for flood waters to fill. Draining wetlands can also increase erosion during flooding.

Question 19

What is a tidal surge?

Answer 19

A wall of water that comes on to the shore during a hurricane?

Question 20

What are two problems associated with building near coasts that are prone to hurricanes?

Answer 20

Increase number of people and buildings that can sustain damage. Removal of seagrass and other vegetation that can buffer the coasts from tidal surges.

Question 21

What are distributary channels?

Answer 21

A series of small streams that flow out from the main river and transport sediment to form a delta.

Question 22

What is the mouth of the river?

Answer 22

The location where the river enters a larger body of water.

Question 23

What are the headwaters of a river?

Answer 23

The location where precipitation or other water source forms a channel that will become a river.

Question 24

Why might more water be located in the middle course of a river than in the upper course?

Answer 24

Tributary channels converge to add water to the river.

Question 25

Why might deltas have different shapes?

Answer 25

The shape depends on the amount and size of sediment entering the body of water, the speed of the river as it enters the body of water, and the amount of erosion.

Question 26

How might humans affect the shape of a delta?

Answer 26

Structures such as dams and levees can control the amount of sediment and speed of the river water. Removing vegetation can increase the amount of erosion that occurs. Building on the delta can compact the sediments.

Question 27

What sized particles form the sedimentary rock conglomerate?

Answer 27

Larger sediment such as gravel or pebbles.

Question 28

What sized particles form the sedimentary rock shale?

Answer 28

Mostly clay and some silt-sized particles

Question 29

Peat is partially decayed plant matter. Over geologic time, which sedimentary rock can it form?

Answer 29

Coal

Question 30

The remains of microscopic marine organisms can form which sedimentary rock?

Answer 30

Limestone