chapter 16 GEO

Hydrologic Cycle

The unending movement of water throughout the Earth’s spheres

Balanced Hydrologic cycle

The total amount of water vapor in the atmosphere remains about the same, therefore the annual precipitation worldwide must equal the quantity of water evaporated

Sheet flow

Thin sheets of water

rills

Tiny channels developed by sheer flow

Gullies

Rills join together to form these, gullies than later develops into brooks, creeks, or streams

Stream

Any water that flows in a channel regardless of size

River

Carries a substantial amount of water and has many tributaries

Drainage Basin / Watershed

A stream drains in this area of land

Divide

The imaginary line separating one basin from another

Continental Divide

A continent is divided into different drainage basins

3 zones of a river

• Sediment production

• Sediment transportation

• Sediment deposition

Sediment production

• Zone where most sediment is derived

• Located in the headwater region of a river system.

• Sentiment generated by

• -bedrock broken into smaller pieces

• - bank erosion.

Sediment transport

• Sediment is transported in trunk streams

- in balance, the amount of sediment being eroded equals the amount of sediment being deposited

Sediment deposition

• When a river reaches a large body of water, the energy decreases in the river deposits sediments.

• Typically only find sediments are deposited in oceans.

( Common Drainage Patterns ) Dendritic (treelike)

• The most common

• uniform underlying material

( Common Drainage Patterns ) Radial

• Typically forms on volcanic cones or domes

( Common Drainage Patterns ) Rectangular

• Bedrock is jointed or faulted

Trellis

• Bedrock consists of alternating bands of resistant and weak strata

Water gap

The steep wall notch followed by the river through a ridge of resistant rock

Antecedent stream

• stream existed before the ridge was uplifted

Superposed stream

• trims are eroded into a pre-existing structure, very beneath layers of relatively flat lying strata

Laminar flow

Water slowly flowing in a nearly straight path

Turbulent flow

Border moving quickly in a erratic fashion (both horizontal and vertical movement)

Factors affecting Flow velocity

• The slope, or gradient, of the stream

• channel shape

• channel size and roughness

• discharge

• monitoring streamflow characteristics

Wetter perimeter

The area where the river is in contact with each channel

Cross-sectional area

The most efficient channel has a small wetted perimeter compared to this

Bankfull

Maximum flow velocity occurs when a stream is this

Longitudinal profile

A cross-sectional view of a stream

• head or mouth is the source of the stream

• mouth is the downstream point where the stream empties into a larger body of water

Stream erosion

• dreams have the ability to deepen and widen their panels and have the capacity to transport large sediment

• dreams, cut channels by quarrying, abrasion, and corrosion

• Quarrying involves removing large blocks from the channel bed

Stream erosion Pt.2

• by scraping, bumping, and rubbing, abrasion both a road sediments and polishes them while cutting a bedrock channel

• potholes form when fast moving, swirling sediment in Eddies abrades a hole by acting like a drill into the steam-bed

• corrosion ( rocks, gradually dissolving and flowing water )

- can occur in limestone bedrock channels

All streams transport a kind of sediment, they do this in 3 ways

• dissolved load ( in solution )

• suspended load ( in suspension)

• Bed load ( sliding, skipping, or rolling along the bottom )

Dissolved load

• most of the dissolved load is brought to a stream via groundwater

• dissolved loads is not affected by stream velocity

• dissolved minerals precipitate when water chemistry change

-when the organisms create hard parts

-when water enters an inland “sea” where the evaporation raise is high

Suspended load

• the largest part of a streams load is carried in suspension

-usually only fine sand, silt, and clay are carried this way

-during a flood stage, larger particles can also be carried in suspension

• amount of material carried in suspension is controlled by stream, velocity and settling velocity of sediments

-settling velocity is a speed at which a particle fall through a steel liquid

Bed load

• horse, Sands, gravel, and boulders move along the stream bed by saltation ( skipping or jumping )

• larger particle, slide, or roll along the bottom

• less rapid and more localized than transport via suspended load

• horse gravels may only be moving during times of high flow while boulders move only during exceptional floods

Capacity

The maximum load of solid particles a stream can carry per unit time

• the greater than discharge, the greater the capacity

Competence

The maximum particle size a stream can transport

• streams with a faster velocity have a higher competence

Deposition of sediment by stream

• occurs when a stream’s velocity is less than a settling velocity

• particles of the same size are deposited at the same time in a process called sorting

-larger particles settle out first

• sediments deposited by streams are called alluvium

Bedrock channels

• bedrock channels are cut into the underlying strata

-typically form in the headwater region where these streams have a steep slope

-energetic flows tends to transport course particles that actively braided the bedrock channel

-steps and pools are common features of bedrock channels

-channel pattern is controlled by the underlying geology

Alluvial channels

• alluvial channels formed in sediment previously deposited in the valley

-typically associated with a flood plain

-channels can change shape as material is eroded and transported

-channel shape is affected by the average size of sediment, great gradient, and discharge

-channel patterns reflect the streams ability to transport load at a uniform rate while expending the least amount of energy

Alluvial channels Pt.2

• meandering channels

-stream transport suspense, sediment in broad, sweeping bands, called meanders

-relatively deep, smooth channels, primarily transporting mud

• meandering channels evolve over time

-the outside of a meander ( cutbank ) is a zone of active erosion

-the inside of a meander ( point bar ) is a zone of deposition

-through time, the bends in a channel can also migrate and eventually join together

-a meander that has been cut off from joining Benz is called a cut off Oxbow lake

Alluvial channels Pt.3

•Braided channels

-a braided channel is a complex network of converging and diverging channels that thread among numerous islands or gravel bars

-a large portion of the load is horse material

-stream has a highly variable discharge

Stream valley

The channel and the surrounding terrain that directs water to the stream

-Alluvial channels have wide Valley floors

-bedrock channels have narrow V shaped valleys

Base level

Lowest point to which stream can erode

-ultimate base level in sea level

-local or temporary base level includes lakes, resistant layers of rock, and large rivers

Graded stream

Only transport sediment

Floodplain

Flat valley floor

Erosional floodplain

Floodplain is being formed

Depositional floodplain

Produced by major fluctuations in base level or climate conditions

Incised meanders

Meander is flowing through steep, narrow, bedrock valleys

Terraces

The flat remnants of the old floodplain

Deltas

Form where sediment-laden streams, enter, relatively still waters of a lake, inland Sea, or ocean

Distributaries

The main channel divides into several smaller channels in the delta

Natural levees

Raised areas adjacent to the channel formed during flood events

• following a flood event, Levees prevent water from returning to the stream channel

Alluvial fans

Develop where a high gradient stream leaves a narrow valley in a mountainous valley

• Forms in response to abrupt drop ingredient

Flood

Occurs when the stream exceeds the capacity of its channel and overflows its banks

• The most common and most destructive geologic hazard hazard

• Magnitude and frequency is influenced by human activities

• Common floods:

-regional floods

-flash floods

-ice jam floods

-dam failure floods

Regional floods

Seasonal floods that typically result from spring rains or rapid melting of snow

Flash floods

• occur with little to no warning

• produce rapid rises in water levels and can have devastating flow velocities

• mountainous areas are extremely suspectible due to steep

Ice jam flood

• ice formed in rivers, creating dams that will break when temperatures rise

-common problem with north flowing rivers in the northern hemisphere

Dam failure floods

• dams designed to contain small or moderate floods face a larger volume flood event

• damn fail and release large amounts of water as a flash flood

Flood recurrent intervals

An estimate of how often a flood of a given size can be expected to occur

Artificial levels

• most common used stream-containment structures

• earth mounds built on riverbanks to increase the capacity of the channel

-not built two with Stan, and often fail in floods

-when exceptional floods threaten, openings are created to divide divert water out of the channel and into floodways

Channelization

• altering a stream channel to make flow more efficient