Geology Chapter 16 Running Water

How many stream terraces can exist along a single valley?

No limit exists. Stream terraces will keep forming as long as lateral erosion and downcutting continue.

How does water get from the oceans onto land?

Ocean water evaporates to form gaseous water and moves into the atmosphere, where it condenses into liquid water and falls out of the atmosphere to land as rain.

Are stream terraces depositional or erosional landforms?

Stream terraces can be either depositional or erosional.

What does the hydrologic cycle describe?

The hydrologic cycle describes how liquid and gaseous water move between the ocean, atmosphere, and land.

What would happen to the oceans if surface runoff and groundwater flow did NOT occur?

The oceans would become smaller.

What will happen to the water level in the stream if the water table is below the level of the stream channel?

The stream will lose water to the groundwater system.

Running water is the single most important erosional agent sculpting Earth's land surface.

True

How will channel velocity change along the longitudinal profile of a stream?

Velocity will start low and gradually increase toward the mouth due to increasing discharge downstream

How does an alluvial fan form?

When a stream with a steep gradient emerges onto a relatively flat lowland, its gradient drops, and it deposits a large portion of its sediment load in a pattern that looks like a fan from above.

What is a floodplain?

a flat surface next to a river channel

What is a stream terrace?

a remnant of an older floodplain that sits above the stream valley

What is a natural levee?

a ridge of flood deposits next to a river channel

What is a graded stream?

a stream that neither erodes material nor deposits it but merely transports it

Dam-Failure Floods

artificial containment structures fail.

Where is most of Earth's freshwater found?

as ice at Earth's surface

Suspended Load

fine sediments that are held up by the water and carried throughout the water column.

Levee

formed by floodwaters on either side of a stream.

Alluvial Fan

formed by mountain streams emerging onto a flat plain.

Ice-Jam Floods

frozen material creates a temporary dam on a thawing river.

Which of the following would increase flow velocity?

having a narrow, deep channel

Dissolved Load

ions in solution that are dispersed throughout the flow.

Bed Load

larger sediments that bounce, roll, or slide along the bottom.

According to scientists and engineers, which of the following is the best type of flood control?

limiting the amount of development within a flood plain

Which ocean is Earth's largest?

the Pacific Ocean

Imagine a valley containing four stream terraces. Where would the youngest stream terrace be found?

the lowest terrace

What is evapotranspiration?

the transfer of water directly from the land's surface into the atmosphere

Which of the choices below is not a factor that causes infiltration and runoff to vary from place to place and from time to time?

time of the day

When do streams erode laterally?

when downcutting is occurring in easy-to-erode sediment or rock

When do stream terraces form?

when streams exist under alternating erosional and depositional conditions

According to the hydrologic cycle, once precipitation has fallen on land, what paths might the water directly take?

~runoff into the sea ~evaporation/transpiration ~infiltration into the ground ~runoff into a river

What are some drawbacks to some flood-control strategies?

-River channelization can accelerate bank erosion. -Artificial levees cannot withstand periods of extreme flooding. -Flood-control dams are costly to maintain.

In general, how do the channel width, channel depth, flow velocity, and discharge change between the headwaters and the mouth of the stream?

The channel width, channel depth, flow velocity, and discharge all increase as the stream approaches the mouth.

What is the longitudinal profile?

The cross-sectional area from the headwaters to the mouth

Delta Delta

form where streams enter large lakes or oceans.

What type of drainage pattern develops on highly jointed bedrock?

rectangular

The Great Flood of 1993 in the Upper Mississippi River basin is an example of which type of flood?

regional flood

Regional Floods

seasonal Floods.

Bar

small deposits that form in the stream channel.

What percentage of Earth's water is in the form of seawater?

97.2%

How much of Earth's surface water exists in the oceans?

Almost all of Earth's surface water exists in the oceans.

Briefly describe a general drainage basin.

An area drained by a stream is called a drainage basin, which is bounded by an imaginary line called a divide. The divide can be clearly visible as a sharp ridge, or it could be difficult to determine in subdued topography.

Which of the choices below correctly defines base level and differentiates between ultimate base level and local (temporary) base level?

Base level is generally defined as the lowest elevation to which a stream can erode its channel. The ultimate base level is sea level; local base levels are lakes, resistant layers of rock, and rivers that act as base levels for their tributaries.

Which part of a stream's sediment load moves the slowest?

Bed load

Where are bedrock channels more likely to be found?

Bedrock channels are typically found in the headwaters of river systems where streams have steep slopes.

The ________ is an elevational point that divides an entire continent into large drainage basins.

Continental Divide

Which of the following choices correctly describes two processes that cut channels into bedrock?

During abrasion, the bed and the banks of the river are constantly bombarded by the particles carried in the water. During corrosion, soluble bedrock such as limestone is gradually dissolved by the flowing water.

Flash Floods

Floods with high precipitation in a short time.

How do natural levees form?

Levees form as the result of the repeated flooding of a river within a floodplain. Each time the floodwaters recede, the suspended load that had been carried by the water is deposited, building up levees along the banks of the river.

Which of the following beds would be easiest for a stream to erode?

Lined with silt

Which of the following scenarios represents the best nonstructural approach to flood control?

Managing a floodplain to limit development in sensitive areas

What are the differences between laminar flow and turbulent flow?

-Unlike a laminar flow, a turbulent flow erodes by lifting sediment from the streambed. -A laminar flow moves in nearly straight-line paths parallel to the stream channel; a turbulent flow moves in an erratic fashion with horizontal and vertical swirling motions. -Unlike laminar flow, a turbulent flow occurs where the flow resistance in the channel is the greatest.

What factors would decrease flow velocity?

-a decrease in gradient of the stream -a decrease in stream discharge -having a rough channel

Which of the following is a characteristic of a graded stream? CHOOSE ALL THAT APPLY.

-meanders -well-developed floodplain

Why are urban areas susceptible to flash floods?

A high percentage of the surface area is covered with cement, asphalt, and other impervious materials

How does the formation of a natural levee impact flooding?

Natural levees raise the height of the stream channel, reducing the amount of flooding that will occur on the floodplain.

Why doesn't sea level drop even though oceans have a higher rate of evaporation than precipitation?

Surface water running off into the oceans makes up the difference between evaporation from the oceans and precipitation into the oceans, creating a balance.

What would happen to atmospheric water if Earth were mostly covered with land?

The atmosphere would contain less water.

Transpiration moves water from _______.

biosphere to the atmosphere

A ________ stream consists of a complex network of converging and diverging channels that weave around channel bars.

braided stream

The process that causes dissolution of limestone bedrock in a stream is ______.

corrosion