18.7: Review and Additional Resources

Review

Figure \(\PageIndex{1}\)

Review and assess your learning. Start with the "Important Terms and Concepts" to ensure you know the terminology related to the topic of the chapter and concepts discussed. Move on to the "Review Questions" to answer critical thinking questions about concepts and processes discussed in the chapter. Finally, test your overall understanding by taking the "Self-assessment quiz".

Important Terms and Concepts

• drainage basin

  fundamental unit of study for fluvial processes

• watershed

  fundamental unit of study for fluvial processes

• perennial stream

  flow all year

• tributary stream

  small streams that enter into the main stream

• intermittent stream

  only flow during wetter times of the year

• interfluve

  The upland between tributaries

• drainage divide

  represents the boundary between adjacent drainage basins and determines into which basin precipitation flows

• exotic stream

  those that originate in a humid region but flow through an arid region

• Davisian Cycle of Erosion

  a theory of landscape development that describes a cycle of erosion which shapes the land surface

• Dynamic equilibrium theory

  equilibrium state is determined by the balance between inputs and outputs from the system. Over time, the channel achieves an equilibrium state between inputs (water) and outputs (sediment)

• dendritic drainage pattern

  the most common form and looks like the branching pattern of tree roots

• parallel drainage pattern

  form where there is a pronounced slope to the surface. A parallel pattern also develops in regions of parallel, elongate landforms like outcropping resistant rock bands

• trellis drainage pattern

  look similar to their namesake, the common garden trellis

• rectangular drainage pattern

  found in regions that have undergone faulting. Streams follow the path of least resistance and thus are concentrated in places were exposed rock is the weakest; makes sharp bends and enter the main stream at high angles.

• radial drainage pattern

  develops around a central elevated point. This pattern is common to such conically shaped features as volcanoes.

• centripetal drainage pattern

  opposite of the radial as streams flow toward a central depression

• deranged drainage pattern

  develop from the disruption of a pre-existing drainage pattern

• accordant stream

  correlated with the structure and relief over which they flow

• discordant stream

  rocks over which they flow are either antecedent or superimposed

• antecedent stream

  flowed across bedrock structures prior to uplift

• superimposed stream

  appear to be superimposed over the rock layers that they presently flow over

• cross-sectional area

  determined by multiplying channel depth by channel width along a transverse section of the stream

• wetted perimeter

  the portion of the channel that is "wet"

• flow velocity

  how fast the water is moving through a cross-section

• discharge

  the volume of water passing through a particular cross-section in a unit of time, measured in units like cubic meters per second or cubic feet per second

• hydrograph

  a graphical way of portraying the change in discharge over time, and how it relates to inputs of water and the environment in which the stream is located

• rising limb (hydrograph)

  the part of the graph where it rises to a peak

• recessional limb (hydrograph)

  where the graph declines back to its base flow

• straight channel

  relatively straight; rarely is a channel perfectly straight in nature

• meandering channel

  one that takes twists and turns over its length

• braided channel

  created when a stream channel is divided into several smaller ones by the accumulation of in-channel deposits

• sinuosity ratio

  the distance between two points on the stream measured along the channel divided by the straight line distance between the two points

• stream (channel) slope (gradient)

  the difference in elevation between two points on a stream divided by the distance between them measured along the stream channel.

• stream erosion

  the detachment of material from the bed or sides of the channel

• stream transportation

  the movement of earth material by water

• traction

  a scooting and rolling of particles along the bed

• saltation

  a bouncing-like movement

• suspended load

  comprised of sediment suspended and transported through the stream

• bed load

  that which is moved across the bed of the channel

• solution (dissolved) load

  comes primarily from groundwater seepage into the stream. Ions in solution also come from the solution of materials that line the channel

• stream deposition

  sediment moving through the stream accumulate on the bed

• floodplain

  the relatively flat area that borders a stream which is periodically inundated with water during high flow periods

• natural levee

  a narrow ridge of alluvium deposited at the side of the channel

• back swamp

  located some distance away from the stream channel on the floodplain; important "sponges" that retain water that might cause severe flooding downstream.

• meander

  a bend in a stream

• point bar

  forms on the inside bank of a meander and rising from the channel as an accumulation of alluvium

• alluvium

  sediment carried by stream

• bar and swale topography

  a succession of bars with intervening swales

• neck

  the upland between opposing meanders of a stream

• cutoff

  occurs when the neck between river meanders is eroded away and the meanders join to shorten the length of the channel

• oxbow lake

  A river cut-off; typically crescent shaped - like that of an oxbow

• meander scar

  remnants of the oxbow

Review Questions \(\PageIndex{1}\)

Describe the various stream system features found in a drainage basin.

Answer

The drainage divide represents the boundary between adjacent drainage basins and determines into which basin precipitation flows. Streams within the drainage basin are either perennial or intermittent in flow. Perennial streams flow all year. The base flow of these streams is provided by groundwater seepage into the channel. Tributary streams are small streams that enter into the main stream. Tributary streams, especially the smaller ones around the periphery of the basin, are intermittent. Intermittent streams only flow during wetter times of the year. Much of their flow is provided by surface runoff and when the water table is higher as a result of moist conditions. The upland between tributaries is called an interfluve.

What is an exotic stream? Give an example.

Answer

A stream that originates in a moist region that flows into and through a drier region. The Nile River is considered an exotic stream.

Explain the basic difference between the Davisian Cycle of erosion and the Dynamic Equilibrium theory.

Answer

The Davisian theory begins with the uplift of land or fall of base level, initiating a cycle of erosion from youth characterized by downcutting, to mature (valley widening), and finally old age stage (formation of a peneplain). The cycle is renewed with uplift or a fall in base level. The dynamic equilibrium theory describe stream development as constantly adjusting to inputs (water) and outputs (sediment)s to the stream system. Over time, the channel achieves an equilibrium and remains in this state until a disturbance alters the inputs and outputs within the stream system.

Describe the stream network pattern and structural control over dendritic, rectangular, parallel, radial, centripetal, trellis and deranged (contorted) drainage patterns.

Answer

A dendritic drainage pattern is the most common form and looks like the branching pattern of tree roots. It develops in regions underlain by homogeneous material. A parallel drainage pattern forms where there is a pronounced slope to the surface. A parallel drainage pattern also develops in regions of parallel, elongate landforms like outcropping resistant rock bands. Tributary streams tend to stretch out in a parallel-like fashion following the slope of the surface. A trellis drainage pattern looks similar to their namesake, the common garden trellis. Trellis drainage develops in folded topography like that found in the Appalachian Mountains of North America. The rectangular drainage pattern is found in regions that have undergone faulting. Faulting off-sets the direction of the stream with tributary streams making sharp bends and entering the main stream at high angles. The radial drainage pattern develops around a central elevated point. This pattern is common to such conically shaped features as volcanoes. The centripetal drainage pattern is typical of basins in arid regions with interior drainage. During wetter portions of the year streams feed ephemeral lakes, which evaporate away during dry periods leaving salt flats. A deranged (also know as contorted) pattern develops from the disruption of a pre-existing drainage pattern.

Compare and contrast antecedent and superimposed streams.

Answer

Antecedent streams flowed across bedrock structures prior to uplift. Slow mountain building permitted stream erosion to keep pace with uplift. The Columbia River that cuts across the Cascade Mountains is an example of an antecedent stream. Superimposed streams expose buried geologic structures and cut through them.

Define cross-sectional area, channel slope, and wetted perimeter.

Answer

The cross-sectional area of the stream is determined by multiplying channel depth by channel width along a transverse section of the stream. Channel slope is the difference in elevation between two points on a stream divided by the distance between them measured along the stream channel. The wetted perimeter is the portion of the channel that is "wet". The wetted perimeter is the width plus twice the depth that the water touches.

Describe how cross sectional area related to stream discharge and velocity.

Answer

Generally, the larger the discharge, the smoother the channel, greater the stream velocity. Cross-sectional area and discharge increases down stream due to tributary and ground water flow into the channel.

Why doesn't stream velocity progressively increase in the downstream direction?

Answer

As streams grow larger their down stream slope decreases, preventing a continuous buildup of energy and creating a more uniform distribution of stream energy along its length.

Describe how a stream erodes its channel.

Answer

Solution: dissolving rock from the sides and bed of the channel. Hydraulic action: lifting sediment from the sides and bed of the channel through hydraulic action. Abrasion: materials suspended in the water are used to scour the bed and sides of the channel.

What is the sinsuosity ratio and how does it describe stream channel shape

Answer

The sinuosity ratio is used to determine whether a channel is straight or meandering. It is calculated as the distance between two points on the stream measured along the channel divided by the straight line distance between the two points. If the sinuosity ratio is 1.5 or greater the channel is considered to be a meandering one.

Compare and contrast straight, meandering, and braided channels.

Answer

Straight channel exhibit a linear though rarely is a channel perfectly straight in nature. A meandering channel is one that takes twists and turns over its length. Abraided channel is one in which the main channel is separated into several smaller channels by bars.

Self-Assessment Quiz \(\PageIndex{1}\)

1. An oxbow lake
   1. is created by the cutoff of a meander
   2. is formed by stream aggradation
   3. is formed by flooding
   4. none of the above
2. Deposition of alluvium
   1. takes place on the outside bank of a meander
   2. occurs when stream velocity increases
   3. takes place on the inside bank of a meander
   4. occurs with an increase in discharge
3. Under constant discharge, an increase in the width of a channel
   1. will decrease the cross-sectional area of the stream
   2. will likely decrease stream velocity
   3. will likely increase stream velocity
   4. will do none of the above
4. Point bar formation is found
   1. on the inside bank of a meander
   2. on the outside bank of a meander
   3. in the middle of the channel
   4. at any of the above locations
5. The highest velocity of flow is found
   1. at the side of the channel
   2. at the floor of the channel
   3. in the middle of the channel just below the surface
   4. on the inside bank of a meander
6. Vertical cutting and channel deepening primarily occurs
   1. prior to reaching equilibrium
   2. after reaching equilibrium
   3. occurs once the stream has achieved base level
   4. during the Old Age stage of Davis's cycle of erosion.
7. Which of the following drainage patterns typify the Ridge and Valley physiographic province of North America?
   1. Rectangular
   2. Centripetal
   3. Radial
   4. Trellis
8. Which of the following physiographic features would display a rectangular drainage pattern?
   1. The Appalachian Mountains
   2. The San Andreas Fault
   3. Mount Rainer
   4. The Black Hills of South Dakota
9. The upland between two tributaries is called
   1. an interfluve
   2. a neck
   3. a levee
   4. none of the above
10. A drainage basin that has undergone urbanization
    1. is likely to experience higher peak discharges
    2. decreased infiltration
    3. shorter lag times
    4. all the above

Answer

1. A
2. D
3. B
4. B
5. C
6. A
7. D
8. B
9. A
10. D

Additional Resources

Use these resources to further explore the world of geography

Focus on The Physical Environment: "Floods: Using Satellites to keep Our Heads above Water. (NASA Earth Observatory)

Physical Geography Today: Water Watch - USGS

Connections: Army Corps Project Pits Farmland Against Flood Threat. (NPR 2015) Flood protection pits farmland against local communities.

Active Learning: Virtual River (Cal State-LA)

Multimedia

"Running Water I: Rivers, Erosion and Deposition" (Annenberg/CPB:) Earth Revealed "Rivers are the most common land feature on Earth and play a vital role in the sculpting of land. This program shows landscapes formed by rivers, the various types of rivers, the basic parts of a river, and how characteristics of rivers — their slope, channel, and discharge — erode and build the surrounding terrain. Aspects of flooding are also discussed." Go to the Earth Revealed site and scroll to "Running Water I: Rivers, Erosion and Deposition". One-time, free registration may be required to view film.

"Running Water II: Landform Evolution" (Annenberg/CPB) Earth Revealed "The Colorado River is a powerful geologic agent — powerful enough to have carved the Grand Canyon. This program focuses on how such carving takes place over time, looking at erosion and deposition processes as they relate to river characteristics and type of rock. The evolution of rivers is covered, along with efforts to prevent harmful consequences to humans." Go to the Earth Revealed site and scroll to "Running Water II: Landform Evolution". One-time, free registration may be required to view film.

"Work of Rivers" (National Archives/Google) 1935 video by the Department of Interior. Interesting from a historical perspective on geomorphic theory (eg. Davisian theory) at the time.

Three Gorges" In this July 8, 2002 segment of All Things Considered NPR's Rob Gifford reports from the Yangtze River in central China as the Three Goreges Dam was nearing completion. (Real Media)

Readings

Flood: Using Satellites to keep our Head Above Water (NASA EOS)

Web Sites

Water Resources of the United States (USGS)