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300. Surface Water. Chapter 13. The Role of Streams & Rivers. What role do streams & rivers play on Earth? ~½ of the water that falls to Earth’s surface eventually ends up in a stream or river & most drain to oceans essential part of the water cycle Most important agent of surface erosion.

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the role of streams rivers
The Role of Streams & Rivers
  • What role do streams & rivers play on Earth?
    • ~½ of the water that falls to Earth’s surface eventually ends up in a stream or river
      • & most drain to oceans
        • essential part of the water cycle
    • Most important agent of surface erosion
river systems
River Systems
  • What is a river system?
    • a river and all of its tributaries
      • What is a tributary?
        • a stream that runs into another stream or river
drainage basins watersheds
Drainage Basins/Watersheds
  • What is a drainage basin (or watershed)?
    • all the land that drains into the river either directly or through its tributaries
      • Lgst drainage system in U. S. = Mississippi River system

Continental Divide

Appalachian Mountains

divides
Divides
  • What is a divide?
    • high land that separates one drainage basin from another
      • Continental Divide (Rocky Mountains) is the major divide in the U. S.
        • rain falling to east flows to (Gulf of Mexico &) Atlantic
          • by way of Mississippi River system
        • rain falling to west flows to the Pacific

Continental Divide

stream river characteristics velocity
Stream/River Characteristics: Velocity
  • What is “velocity”?
    • distance water travels in a given amount of time
  • How is velocity measured?
    • float method
    • flow meter

Measuring Stream Velocity Video

slide7
Stream/River Characteristics: Velocity
  • What affects a stream’s velocity?
    • amount of energy a stream has
      • What affects a stream’s energy?
        • 1. gradient (slope or steepness)
        • 2. discharge (amount of water)
        • 3. channel (stream path)
          • size (width & depth)
          • shape of the path (straight/curved)
stream river characteristics velocity1
Stream/River Characteristics: Velocity
  • How is stream velocity related to the size of the particles it can transport?
    • faster = larger particles
stream river characteristics gradient
Stream/River Characteristics: Gradient
  • What is “gradient”
    • steepness of the slope
      • gradient = change in elevation

change in distance

slide10
Stream/River Characteristics: Gradient
  • What affects a stream’s gradient?
    • closer to head (source)
      • steeper
    • closer to mouth
      • gentler
stream river characteristics gradient1
Stream/River Characteristics: Gradient
  • How is gradient related to velocity?
    • steeper
      • faster
    • gentler
      • slower
stream river characteristics discharge
Stream/River Characteristics: Discharge
  • What is “discharge”?
    • volume of water that passes a certain point in a given amount of time (related to velocity)
stream river characteristics discharge1
Stream/River Characteristics: Discharge
  • What affects a stream’s discharge?
    • # (& volume) of tributaries
stream river characteristics discharge2
Stream/River Characteristics: Discharge

Youthful

  • What affects a stream’s discharge?
    • age of stream
      • older
        • more discharge
      • younger
        • less discharge

Mature

Old Age

stream river characteristics discharge3
Stream/River Characteristics: Discharge
  • What affects a stream’s discharge?
    • time of year
      • late winter to mid-summer
        • greatest discharge
      • late summer to mid-winter
        • lowest discharge

Mean of monthly stream flow at Peachtree Creek for each month (for the years 1958 to 2002) The January value of 174 cubic feet per second (ft3/s) was computed by averaging the 44 mean January stream flows (1959-2002).

stream river characteristics discharge4
Stream/River Characteristics: Discharge
  • How is discharge related to velocity?
    • greater discharge
      • greater velocity
    • lower discharge
      • lower velocity
stream river characteristics channel
Stream/River Characteristics: Channel
  • What is a stream’s “channel”?
    • path through which the water flows
stream river characteristics channel1
Stream/River Characteristics: Channel

Youthful

  • What affects a stream’s channel?
    • age of stream
      • older
        • wider & deeper
      • younger
        • narrower & shallower

Mature

Old Age

stream river characteristics channel2
Stream/River Characteristics: Channel
  • How is a stream’s channel related to its velocity?
    • straight, wide, & deep
      • small surface area in contact with the water
        • less friction
          • faster (especially at center near surface)
stream river characteristics channel3
Stream/River Characteristics: Channel
  • How is a stream’s channel related to its velocity?
    • shallow & winding
      • large surface area in contact with water
        • greater friction
          • slower
      • fastest on outside of curve
how streams weather erode material
How Streams Weather & Erode Material
  • mostly mechanical weathering
      • split rocks due to pounding
      • abrasion
        • by “cutting tools”  sand, pebbles, boulders, etc.
          • rounded & smoothed
how streams weather erode material1
How Streams Weather & Erode Material
  • What is a “pothole”?
    • Deep, rounded basin
      • formed when sand, pebbles, & small boulders swirl around in whirlpools & grind into the rocks
  • What is a “plunge pool”?
    • basin worn away at the base of a waterfall
      • formed by the action of falling water and abrasion of churning particles
stream erosion
Stream Erosion
  • Streams are effective agents of erosion.
    • gravity pulls water downhill
      • soil & rock carried with it
stream erosion1
Stream Erosion

How Streams Transport Materials

  • What is a stream’s “load”?
    • eroded rock & soil materials that are transported downstream
      • transported 3 ways:
        • 1. solution (dissolved)
        • 2. suspension (floating)
        • 3. bed load
stream erosion2
Stream Erosion
  • What are two measures used to describe the ability of a stream to erode materials?
    • competence
      • maximum size of particles stream can carry
    • capacity
      • total amount of sediment stream can carry
slide27
The size and amount of sediment carried by a stream depends on:

•velocity (speed of stream)

• discharge (volume of water)

choice A

choice B

Which stream carries larger/more sediment?

stream deposition
horizontal sorting in a stream animation

deposition patterns

Stream Deposition

settling rate by size, shape, density animation

vertical sorting animation

  • When a stream flows to base level (lake/ocean), what happens to its energy?
    • It decreases.
      • What happens…?
        • graded (sorted) deposition occurs
          • largest closest to mouth & smallest farthest out
          • largest on bottom & smallest on top
depositional features
Depositional Features
  • What is a delta?
    • fan-shaped deposit of silt & clay at mouth of river
      • forms when river flows into quiet or large body of water & energy decreases
  • How do the rates of erosion & deposition affect the size of the delta?
    • If deposition > erosion  delta grows.
    • If erosion > deposition  delta shrinks.
  • A river flowing into a delta splits into distributaries.
    • smaller channels that bring sediment to front of delta
river valleys youthful streams
River Valleys: Youthful Streams
  • What is the gradient of youthful stream like?
    • steep
      • How does the river flow?
        • in a straight line
      • In which direction does the river erode?
        • downward
  • What is the shape of the resulting valley?
    • V-shaped (a.k.a. canyon, gorge, chasm)
      • steep, almost vertical sides and narrow bottom
  • Is the discharge large or small?
    • small
river valleys mature streams
River Valleys: Mature Streams
  • What happens to the gradient as a stream matures?
    • gradient decreases
      • How does the river flow?
        • slight curves b/c velocity decreases
      • In which direction does the river erode?
        • outward b/c less erosion of bed & more erosion of sides
river valleys mature streams1
River Valleys: Mature Streams
  • What is the shape of the resulting valley?
    • wider, broad floor, gently sloping walls
  • Is the discharge large or small?
    • medium
slide33
River Valleys: Old Age Streams
  • What happens to the gradient in an old age stream?
    • gradient decreases to almost horizontal (stream approaches base level)
      • How does the river flow?
        • wide meanders across floodplain
          • can form oxbow lakes
      • In which direction does the river erode?
        • outward b/c less erosion of bed (bottom) & more erosion of sides
slide34
River Valleys: Old Age Streams
  • What is the shape of the resulting valley?
    • valley floor widens into a floodplain
  • Is the discharge large or small?
    • large
slide35
Life of a Stream

Youthful

Mature

Old Age

slide36
Stream Flow, Erosion, & Deposition
  • Why does water move faster in center?
    • less friction
  • What does the profile of a straight section of a stream look like?

Slow

Fast

Slow

Slow

Fast

Slow

------------

Slow

slide37
Stream Flow, Erosion, & Deposition
  • What happens when a stream meanders?
    • erosion in some areas
      • cut banks
    • deposition in other areas
      • point bars
slide38
Stream Flow, Erosion, & Deposition
  • What does sediment size tell us?
    • large  water moving fastest (only lg sediments left behind)
    • small  water slowed down (& dropped small sediments)
  • point bar
  • deposition of small sediments
  • shallow

--------------

  • cut bank
  • erosion of small sediments, large sediments left behind
  • deep

Cross-section on next slide

slide39
Stream Flow, Erosion, & Deposition
  • In a meander where does water move fastest?
    • outside of bend
  • In a meander where does water move slowest?
    • inside of bend
  • What does the profile of a meandering stream look like?

slow

fast

point bar

deposition

shallow

cut bank

erosion

deep

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