Chapter 13. Streams and Flooding

What is a floodplain?

A broad strip of land built up by sedimentation on either side of a stream channel and covered with water during a flood (Ridges of sediment deposited in or on the sides of streams are called point bars.)

Rank in order from the beginning (at the top) the processes necessary to create entrenched meanders.

A meandering river flows across a floodplain. A tectonic event causes an uplift, causing the river to erode downward. Further incision by the river creates more entrenchment.

What is a drainage divide?

A ridge or strip of high ground separating one drainage basin from another

What is a drainage network?

A series of interconnected streams that when combined drains a larger area that any one stream

Which of the following statements are true with regard to a stream's formation of cessation (ending)? (Choose all that apply.)

Changing the amount of water or sediment supplied to a basin can cause the formation of a stream or cause its end Changing the slope of the land can cause the formation or cessation of a stream (A drop in sea level can provide the gradient needed to start a stream, and a rising sea can swamp or drown a stream.)

Rank the following particle sizes transported by water from smallest to largest. (Place the smallest particle size at the top.)

Clay Silt Sand Cobbles Boulders

Match the condition on the left with the effect on the river or drainage system on the right.

Dam: Changes the base level because of sediment buildup Tectonism: Can increase the slope and supply of coarse sediments Runoff: Increases flow, causing flooding Geology: Streams erode soft rocks more easily than hard rocks Vegetation: Plants stabilize stream bank and protect against erosion

__________ are formed as rivers slow down when they reach their mouth and empty into an ocean.

Deltas

Rank the formation of terraces by rivers from the first stage at the top to the last stage on the bottom.

Deposition of sediment occurs on the floodplain. A drop in the base level of the river results in downcutting through deposits. Further downcutting occurs, and the river abandons the previously formed floodplain. The oldest floodplain becomes isolated as the river downcuts, leaving a terrace.

Match the type of sediment load to its description.

Dissolved: Chemically soluble ions transported by the river Suspended: Clay and silt carried indefinitely above the riverbed Bed: Material carried on the bottom of a river by pushing, bouncing, rolling, and sliding; usually sand and gravel

Select common features located along low-gradient rivers. (Choose all that apply.)

Floodplains Single channels Meanders River terraces

What does downstream mean?

It is the direction of flow in which the water is moving. (In rivers, downstream is the direction of flow from higher elevation to lower elevations.)

Match the location of the diagram with a description of the shape of the river.

Left-side diagram: Braided river Middle diagram: River with low sinuosity Right-side diagram: Meandering River

Select two ways that mountain streams obtain their sediments.

Soil and/or sediment slides down into the drainage area. Tributaries bring sediments into the drainage area.

Match the river drainage patter with the appropriate description of its geology.

Structurally controlled pattern: Drainage occurs on eroded layers or structures and then cuts across a ridge to follow a different weak layer. Radial drainage pattern: Drainage is found on symmetrical mountains such as volcanoes. Dendritic drainage pattern: Treelike pattern develops on rocks with similar resistance to erosion.

Why does the discharge of a stream change during the course of a year? (Select all that apply.)

The type of precipitation can vary during the year. The amount of precipitation can vary by season. Influx from groundwater can vary during the course of a year.

Which of the following describes the headwaters of mountains streams? (Choose all that apply.)

They have turbulent flow. They have the ability to carry large boulders. They have steep gradients.

What is the name of the subsidiary channels that join up with the main river channel?

Tributaries

Select consequences to a river when a dam is constructed. (Choose all that apply.)

Water released from the dam is clear (no sediment) and has a new capacity to erode and transport sediments downstream. The dam creates a temporary base level for the river. The dam causes the river to deposit its sediment load upstream of the dam. (A reservoir is created, providing new and better habits.)

Define the landforms associated with the headwaters of mountain streams.

Waterfall: Occurs when a stream or river's gradient is so steep that water goes over a ledge or cliff Rapid: Occurs along a river and is characterized by turbulent water Lake: Occurs where water is impounded by some obstruction Pool: Occurs when water slows down and piles up upstream of a rapid

Rank the seasons from the lowest discharge of water to the highest for a river located in the Upper Midwest of the U.S. (Place the season with the lowest discharge on top.)

Winter Fall Summer Spring

The erosional base level of a river can be ____________. (Choose all that apply.)

a closed land basin a lake an ocean

The erosional base level of a river can be _____________. (Choose all that apply.)

a closed land basin a lake an ocean

Streams that carve directly into the rocks that compose a mountain or other area are _______________ streams.

bedrock

A(n) __________ is formed where a river meets the sea, slows down, and deposits its sediments.

delta

When rivers enters a lake or an ocean, they slow down and lose their capacity to carry sediments, forming ________________.

deltas

Rivers and streams ______________ the landscape, carry the materials, and later deposit the sediments, thereby acting as major sculptors of Earth's surface.

erode

Meanders cause differences in water velocity in the river channel. On the outside of a meander, water velocity is ___________ and causes erosion, while on the inside of a meander, water velocity is ___________ and deposition of sediments occurs.

faster; slower

Viscosity is the resistance to ____________ exhibited by fluids.

flow

The largest rivers last ______________ as features on the landscape.

for along time (The oldest river systems are many millions of years old.) (Changes in tectonics and climate will eventually end all rivers.)

What is the word used to describe the change in elevation for a given stream or river over a horizontal distance?

gradient

Rivers are dynamic systems driven by precipitation and _____________. (Hint: the answer is just one word.)

gravity

The driving force behind a river's flow is _________________.

gravity

The origin of a river is called its _________________, and the end of a river called its ____________.

headwaters; mouth

The area of the origin of a river is its ____________, the ___________ the end of the river.

headwaters; mouth is

The production of ice sheets during global cooling results in ______________ sea levels. These ice sheets can depress the __________, causing river drainages to flow toward the ice sheets.

lower; crust

The base level of a river is the ____________ elevation to which the river can erode.

lowest

The discharge of a river is measured in cubic _________ metes per second,

meters (Discharge also is measured as cubic feet per second.)

What type of lake is created when a cutoff meander becomes isolated? The answer is just one word.

oxbow

A stream or river that flow all year is ________________.

perennial

A depositional feature that has been built on the inside of a curve because of lower velocity is a ________________.

point bar

Erosion and deposition by _______________ are the principal processes that sculpt Earth's landscape.

rivers

The type of sediment transport that involves a series of leaps or bounces off the bottom of a streambed is _______________.

saltation

The total amount of sediment carried by a river is the ______________.

sediment load

When is sediment most likely to be deposited? When the ______________.

sediment supply exceeds a stream's capacity to transport it

The amount that a river or stream channel curves in a given length is called its ______________________.

sinuosity

Rainwater creates _________ erosion as it hits the ground.

splash

Stream terraces are composed of either __________ or ___________. (Choose the two that apply.)

stream-derived sediment composing former floodplains an erosion surface cut into bedrock

River _____________ are relatively flat benches that are perched above a river or stream and stair-step upward and outward from the active channel.

terraces