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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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Surface water

300

Surface Water

Chapter 13


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


Surface water

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


Surface water

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 discharge5

Stream/River Characteristics: Discharge


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


Surface water

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


Surface water

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


Surface water

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


Surface water

Life of a Stream

Youthful

Mature

Old Age


Surface water

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


Surface water

Stream Flow, Erosion, & Deposition

  • What happens when a stream meanders?

    • erosion in some areas

      • cut banks

    • deposition in other areas

      • point bars


Surface water

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


Surface water

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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