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ANSWERS TO STUDY QUESTIONS CHAPTER 13 - Streams

1. 2000m / 50km = 40m / km; With 1000km of meanders the stream’s gradient becomes 2000m / 1000km = 2m / km. Thus meandering decreases gradient.

2. Streams with higher discharges tend to have faster velocities and larger cross-sectional areas. 

3. Base level is the lowest elevation to which a stream can erode it’s channel. The ultimate base level for the San Diego River is sea level, but reservoirs, such as El Capitan, act as local base levels.

4. A stream erodes its channel by solution, hydraulic action, and abrasion.

5. A stream transports its load via the dissolved load, bed load, and suspended load.

6. If you collect a jar of water from a stream the suspended load will settle to the bottom of the jar. Generally this is comprised of silt and clay sized particles. If the water does not evaporate, the dissolved load will not settle to the bottom no matter how long the jar is left standing.

7. a. Streams diverging from a central high area such as a dome, volcano, or laccolith - RADIAL
    b. Branching, "treelike pattern" - DENDRITIC
    c. A pattern that develops when bedrock is crisscrossed by joints and faults - RECTANGULAR

8. During a flood, a stream’s bed load is washed out of the channel and deposited on the flood plain near the channel. When the flood waters recede, these deposits become natural levees. 
Since natural levees are higher than the flood plain, drainage on the flood plain is poor. Water tends to accumulate in such areas forming back swamps. Tributaries will have similar problems draining into the main stream. Yazoo tributaries form when tributaries parallel the main stream for great distances until finding a gap in the levees through which they can join the main stream.
Artificial levees promote the accumulation of a stream’s bed load by reducing flood frequency. As the bed raises, levees must be raised if channel volume is to be maintained.

9. a. meanders which commonly touch the sides of the stream's flood plain - LATERAL EROSION
    b. braided stream - DEPOSITION
    c. rapids and waterfalls - DOWNCUTTING
    d. narrow, V-shaped canyon - DOWNCUTTING
    e. graded stream - TRANSPORTATION
    f. relatively straight course - DOWNCUTTING
    g. close to the ultimate base level - TRANSPORTATION
    h. natural levies - DEPOSITION
    i. delta - DEPOSITION
    j. back swamps, yazoo tributaries, oxbow lakes - TRANSPORTATION

10. Meandering streams do not make good political boundaries, because their channels shift position rapidly as flood plain sediments are eroded from the outside of meander bends and deposited on the inside of meander bends.

11. When the land over which a meandering stream flows is uplifted (or its base level lowers), it’s gradient increases, it flows faster, it down cuts into it’s meandering channel, and entrenched meanders are formed.
    When the land over which a down cutting stream flows subsides (or its base level raises), it’s gradient decreases, it slows down, deposits sediments, forms a floodplain and starts to meander. Levees, back swamps, oxbow lakes and yazoo tributaries may form. 
    When a down cutting stream flows over land that continuously uplifts as the stream down cuts, the stream’s gradient will not flatten as down cutting progresses. Gradient and velocity will remain high, so down cutting will continue as long as the land uplifts. Eventually a deep, narrow canyon forms.
 

Last Updated: 01/13/2015
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