McKnight's Physical Geography: Chapter 16 notes

True or False: Interfluves consist of ridge tops or mountain crests

False. They can, but some are made up of broad, flatish divides

Fluvial Processes

Processes that involve running water

Most important agent of erosion and deposition

Running water

True or False: The flow of water in streams probably contributes more to shaping landforms than all other external processes combined.

True, this is because water is so ubiquitous

Stream

Any channeled flow of water

Overland flow

Unchanneled downslope movement of surface water

Streamflow

The channeled movement of water along a valley bottom

Two topographic elements that make up the continents

Valleys and interfluves

Valley

Is that portion of the terrain in which a drainage system is clearly established. It includes the valley bottom, which is partially or totally occupied by the channel of a stream, as well as the valley walls that rise above the valley bottom on both sides. The upper limit of a valley is not always readily apparent, but it can be clearly conceptualized as a lip or rim at the top of the valley walls above which drainage channels are indistinct or absent.

Interfluve

the higher land above the valley walls that separates adjacent valleys.

True or False: All parts of the terrain that aren't in a valley are part of an interfluve

True

Drainage basin/ Watershed

All of the area that contributes overland flow, streamflow, and groundwater to that stream. In other words, the drainage basin consists of a stream's valley bottom, valley sides, and those portions of the surrounding interfluves that drain toward the valley.

Drainage divide

The line of separation between runoff that descends in the direction of one drainage basin and runoff that goes toward an adjacent basin; this is where the drainage basin terminates.

Continental Divide of North America

The set of ridges separating the drainage basins of streams that flow eastward or southward

Stream Order

Describes the arrangement and organization of all streams within a watershed

First order stream

Smallest stream, has no tributaries

Third order stream

When two second order streams join

Gradient

Elevation change over a given distance

True or False: average stream length generally increases with increasing order, average watershed area generally increases with increasing order, and average stream gradient decreases with increasing order

True

Penstocks

Pipes where water exits a resevoir

True or False: Dams require no power, a small workforce, and can be turned on quickly

True

% of the world's rivers that have been dammed

60%

Deposition

Movement of eroded materials

True or False: Fluvial erosion ends when rain starts to fall

FALSE. It begins when rain starts to fall

During heavy or continued rain:

Infiltration is diminished and most of the water moves downslope as overland flow.

Sheet Erosion

The water flows across the surface as a thin sheet, transporting material already loosened by splash erosion

Rills

Sheet flow broken into tiny channels by turbulence

Gullies

When rills begin to coalesce into fewer and larger channels

Stream flow speed is determined by:

The gradient, by the resistance of the bedrock, by the shape of the channel, and by the volume of the flow.

Stream flow turbulence determined by:

Flow speed, and roughness of channel.

True or False: Any water moving downslope can transport rock

True

Stream Load

All materials moved by a stream

Dissolved Load

Materials, mostly salt, dissolved in the water

Suspended Load

Very fine particles of clay and silt carried in suspension, moving along with the water without ever touching the streambed. Moves very slowly.

Bedload

Sand, gravel, and larger rock fragments

Saltation

A series of jumps or bounces that moves the smaller particles in the stream load

Traction

Rolling or sliding along the streambed. This is how larger particles in the load are moved.

2 concepts used to describe the load a stream can transport.

1. Competence
2. Capacity

Competence

diameter of largest particles that can be moved

Stream Capacity

A measure of the amount of solid material a stream has the potential to transport, normally expressed as the volume of material passing a given point in the stream channel during a given time interval.

Where are stream deposits found

At the mouths of canyons, on floodplains, and along the inside bank of river bends.

Alluvium

The general term for stream-deposited sediment

Alluvium Properties

- Alluvium is typically smooth and round due to the battering the rocks receive from each other as they flow downstream. Over the great distances of many stream systems, this battering and abrasion (along with chemical weathering) eventually reduces larger rocks (boulders, cobbles, and pebbles) to smaller sizes (sand and silt).

- Alluvial deposits often display distinct strata, or layers, due to episodes of deposition following periodic floods.

- Alluvium is often "sorted"—that is, an alluvial deposit often consists of rocks of just about the same size. Sorting can occur when the speed of water flow diminishes. As stream competence drops, the heaviest (and therefore largest) rocks are deposited first, while smaller rocks are carried away and deposited elsewhere.

Perennial Streams

Permanent streams. Very common in humid regions

Ephemeral Streams

Carry water only during and immediately after a rain.

Discharge

The volume of flow per unit time.

True or False: The "wet season" can be as short as a day or two

True

Gage height

Local water height in a stream

Recurrence Interval

The probability of a given-size flood occurring. A "100-year flood" refers to stream discharge that has a 1 in 100 (1 percent) probability of being exceeded in any single year.

Laminar Flow

All of the water moves smoothly downstream in parallel paths.

Four stream channel categories

1. Straight
2. Sinuous
3. Meandering
4. Braided

Straight channels

Short and uncommon

Sinuous Channels

Winding and occur in almost every type of topographic setting. Their curvature is usually gentle and irregular. Stream channels are likely to be sinuous even when the stream flows down a steep slope. Where gradients are low (over flatter land), many stream channels tend to develop greater sinuosity and begin to meander.

Meandering Channels

Exhibit an extraordinarily intricate pattern of smooth curves.

Braided Channels

Consist of multiple interwoven and interconnected channels separated by low bars or islands of sand, gravel, and other loose debris

Consequent stream

Normally the first to develop on newly uplifted land, and many streams remain consequent throughout their evolutionary development.

Subsequent streams

Streams that develop along zones of structural weakness

Antecedent stream

A stream that predates the uplift

Dendritic drainage pattern

Consists of a random merging of streams. Tributaries always join streams at angles less than 90 degrees. More common than all other patterns combined.

Trellis drainage pattern

Forms in areas of hard and soft bedrock in close contact, shape modified by structure of bedrock

Radial drainage

Streams descend from concentric uplift

Centripetal drainage

Opposite of radial

Annular Pattern

Forms in areas of hard and soft domes or basins, flow follows soft bedrock and is confined by hard bedrock

Downcutting

Lowering of the streambed, produces a deep valley with steep sides and often a V-shaped cross section. Downcutting is most prevalent in the upper reaches of a stream, where the gradient is usually steep and the valley narrow.

Base level

Lower limit to how much downcutting a stream can do

Graded Stream

A stream in which the gradient has adjusted to the point of allowing just the transportation of its load

Knickpoints

Part of a river or channel where there is a sharp change in channel slope, such as a waterfall or lake.

Knickpoint migration

When harder material erodes away, so the position of the knickpoint migrates upstream with a successively lower profile until it finally disappears and the channel gradient is smoothed. Niagra falls is example.

Lateral Erosion

Erosion on the outside of the curves, where the water speed is greatest.

Headward Erosion

Erosion at the origin of a stream channel, which causes the origin to move back away from the direction of the stream flow, and so causes the stream channel to lengthen.

Stream Capture

When a stream or river drainage system or watershed is diverted from its own bed, and flows instead down the bed of a neighboring stream. Example is West Africa.

Delta

A triangular tract of sediment deposited at the mouth of a river, typically where it diverges into several outlets.

Aggradation

General term that refers to process of deposition

Floodplains

Low-lying, nearly flat alluvial valley floor that is periodically inundated with floodwaters. Valley bottom is also termed a floodplain.

Bluffs

A steep cliff, bank, or promontory.

Natural Levee

Commonly form around lowland rivers and creeks without human intervention. They are elongate ridges of mud and/or silt that form on the river floodplains immediately adjacent to the cut banks. Like artificial levees, they act to reduce the likelihood of floodplain inundation.

Yazoo Stream

A tributary stream entering a floodplain cannot flow directly into the main channel because it encounters prominent natural levees.

Stream Terrace

Remnant of the previous valley floor. Often occur in pairs.

Superimposed Streams

original drainage pattern incised into underlying sequence of rocks of a different structure

Which part of the valley has the fastest moving water?

Cut bank. Slowest is the point bar.

Entrenched river

a river or stream that flows in a narrow trench or valley cut into a plain or relatively level upland.

Equilibrium Theory

Variations in influence of crustal movement and resistance of underlying rock. Prime theory used today.

Nearly all streams in arid regions are:

Ephemeral