EDUC 217: Chapter 9

What feature may form where a stream enters the relatively still waters of a lake, an inland sea, or an ocean?

Delta

potholes

circular depression in a bedrock stream channel created by the abrasive action of particles swirling in fast-moving eddies

How does an oxbow lake form?

An oxbow lake forms when the bend of a meandering river is isolated from the river when it is cut off from the main river channel. This isolated bend becomes the oxbow lake.

infiltration

movement of surface water into rock or soil through cracks and pore spaces

turbulent flow

movement of water in an erratic fashion, often characterized by swirling, whirlpool-like eddies. most streamflow is of this type

factors that influence flow velocity and control a stream's potential to do "work"

(1) channel slope or gradient (2) channel size and cross-sectional shape (3) channel roughness (4) the amount of water flowing in the channel

stream valley

the channel, valley floor, and sloping valley walls of a stream

suspended load

the fine sediment carried within the body of flowing water

laminar flow

the movement of water particles in straight-line paths that are parallel to the channel. the water particles move downstream, without mixing.

settling velocity

the speed at which a particle falls through a still fluid. the size, shape, and specific gravity of particles influence settling velocity

capacity

total amount of sediment a stream is able to transport

alluvium

unconsolidated sediment deposited by a stream

runoff

water that flows over the land rather than infiltrating into the ground

5 factors for the amount of water that runs off the ground

(1) the intensity and duration of rainfall (2) amount of water already in the soil (3) nature of the surface material (4) slope of the land (5) extent and type of vegetation

Which of these options accurately describes settling velocity?

Settling velocity is the speed at which a particle falls through a still fluid. This velocity is influenced by the size, specific gravity, and shape of the settling particle. Settling velocity has no effect on the dissolved load of a stream.

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.

Which situations(s) would trigger the formation of incised meanders?

The base level of a stream drops, causing a meandering stream to begin downcutting, The land over which a meandering stream is flowing uplifts, causing the stream to begin downcutting

Where is the majority of water stored in the hydrosphere?

The oceans

When 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.

point bar

a crescent-shaped accumulation of sad and gravel deposited on the inside of a meander

longitudinal profile

a cross section of a stream channel along its descending course from the head to the mouth

oxbow lake

a curved lake produced when a stream cuts off a meander

rectangular pattern

a drainage pattern characterized by numerous right-angle bends that develops on jointed or fractured bedrock

stream terrace

a flat, bench-like structure produced by a stream, which was left elevated as the stream cut downward

meander

a looplike bend in the course of a stream

incised meander

a meandering channel that slows in a steep, narrow valley. incised meanders form either when an area is uplifted or when base level drops

competence

a measure of the largest particle a stream can transport; a factor that is dependent on velocity

distributary

a section of a stream that leaves the main flow

cutoff

a short channel segment created when a river erodes through the narrow neck of land between meanders

braided channel

a stream channel that consists of numerous intertwining channels

dendritic pattern

a stream system that resembles the pattern of a branching tree

trellis pattern

a system of streams in which nearly parallel tributaries occupy valleys cut in folded strata

radial pattern

a system of streams running in all directions away from a central elevated structure, such as a volcano

yazoo tributary

a tributary that flows parallel to the main stream because a natural levee is present

channelization

altering a stream channel in order to speed the flow of water and prevent it from reaching flood height

delta

an accumulation of sediment formed where a stream enters a lake or ocean

natural levee

an elevated landform that parallels some streams and acts to confine their waters, except during flood stage

divide

an imaginary line that separates the drainage of two streams; often found along a ridge

alluvial fan

A fan-shaped deposit of sediment formed when a stream's slope is abruptly reduced

back swamp

A poorly drained area on a floodplain resulting when natural levees are present.

Which choice describes how an erosional floodplain develops?

A stream approaches a graded condition, stops eroding, and starts meandering. As the stream meanders, it widens the valley by continuously eroding the banks on both sides. This widened valley is an erosional floodplain.

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.

Which are characteristic of flash floods, but not of regional floods?

Being influenced by topography, Being influenced by surface conditions, High flow velocities

What is the difference between capacity and competence?

Capacity is the maximum load of solid particles a stream can transport per unit of time, whereas competence is a measure of a stream's ability to transport particles based on size rather than quantity.

Which are correctly described flood-control strategies?

Channelizing (altering a stream channel to speed water flow) to prevent the stream from reaching flood levels, Creating levees (artificial earthen or cement mounds or walls on either side of the river) to artificially increase flood levels within the main channel, Limiting certain activities or land uses, and implementing appropriate zoning regulations in high-risk flood areas

What are distributaries, and why do they form?

Distributaries are channels that are shorter and have higher gradients than the original stream channel. They form when the original channel becomes choked with sediment and carry water away from this channel.

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.

How might a stream channel become braided?

If a large portion of a stream's sediment load consists of coarse material and the stream has a highly variable discharge, a stream channel can become braided.

Why do V-shaped valleys often contain rapids or waterfalls?

In many V-shaped valleys, resistant bedrock upstream creates rapids by acting as a local base level, whereas downcutting occurs in less resistant bedrock downstream.

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 drops out, building up levees along the banks of the river.

What is meant by a nonstructural flood control strategy?

Limiting certain activities or land uses and implementing appropriate zoning regulations in high-risk flood areas

regional floods

Rapid melting of snow and/or major storms that bring heavy rains over a large area

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

Runoff into a river, Evaporation/transpiration, Infiltration into the ground, Runoff into the sea

continental divide

splits the entire continent into enormous watersheds

cut bank

the area of active erosion on the outside of a meander

bar

the common term for sand and gravel deposits in a stream channel

floodplain

the flat, low-lying portion of a stream valley that is subject to periodic inundation

watershed

the land area that contributes water to a stream. also called a drainage basin

drainage basin

the land area that contributes water to a stream. also called a watershed

base level

the level below which a stream cannot erode (1) ultimate base level: sea level (2) temporary, or local, base levels: lakes, resistant layers of rock, and main streams that act as base levels

flood

the overflow of a stream channel that occurs when discharge exceeds the channel's capacity. floods are the most common and destructive type of geologic hazard

dissolved load

the portion of a stream's load that is carried in solution

sorting

the process by which solid particles of various sizes are separated by moving water or wind. also, the degree of similarity in particle size in sediment or sedimentary rock

discharge

the quantity of water in a stream that passes a given point in a period of time

gradient

the slope of a stream; generally measured in feet per mile

saltation

transportation of sediment through a series of leaps or bounces

hydrologic cycle

unending circulation of Earth's water supply. powered by energy from the sun. has continuous exchanges of water among the oceans, atmosphere, and continents. (it is balanced)

flood-control dams

built to store floodwater and then let it out slowly

evapotranspiration

combined effect of evaporation and transpiration

sediment production

where most of the sediment is derived is located in the headwater region of the river system

artificial levees

earthen mounds built on the banks of a river to increase the volume of water the channel can hold

headward erosion

extension upslope of the head of a valley due to erosion

flash flood

little warning and are potentially deadly because they produce rapid rises in water levels and have devastating flow velocities

evaporation

process of converting a liquid to a gas

transpiration

release of water vapor to the atmosphere by plants

bed load

sediment that is carried by a stream along the bottom of its channel

artificial cutoffs

shortening the stream, the gradient and the flow velocity are both increased