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Streams and Rivers


Streams and Rivers Carry water over land to oceans Almost of the water that falls to Earth s surface eventually ends up in a stream or river. – PowerPoint PPT presentation

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Title: Streams and Rivers

Streams and Rivers
  • Carry water over land to oceans
  • Almost ½ of the water that falls to Earths
    surface eventually ends up in a stream or river.
  • Essential part of the water cycle
  • Account for most of the erosion of Earths
    surface (most important agent of erosion)

Chapter 13 Section 1
River Systems
  • river system- a river and all of its tributaries
  • tributary- a stream that runs into another stream
    or river
  • Carry water and sediment to a main river which
    eventually flows into a lake or ocean
  • Sediment is deposited there because the water
    slows down

River Systems
River Systems
  • drainage basin/watershed- includes all the land
    that drains into the river either directly or
    through its tributaries
  • Largest drainage system in U. S. is Mississippi
    River system
  • Boundaries
  • West Continental Divide
  • East Appalachian Mts

River Systems
  • divide- the high land that separates one drainage
    basin from another
  • Continental Divide in Rocky Mountains is the
    major divide of the U. S.
  • Rain falling to east
  • flows to the Atlantic
  • Rain falling to west
  • flows to the Pacific

Characteristics of Streams and Rivers
  • velocity- distance water travels
  • in a given amount of time
  • Related to the amount of energy
  • a river has
  • Determined by a number of factors
  • 1. Gradient (slope or steepness)
  • 2. Discharge (amount of water)
  • 3. Channel
  • Size (width depth)
  • Shape of the path (straight/curved)
  • Texture (smooth/rough)
  • A fast-moving stream can erode materials more
    quickly and carry larger particles.

(No Transcript)
Characteristics of Streams and Rivers
  • gradient- steepness of the slope
  • Steeper (larger) slope ? closer to vertical
  • Gentler (smaller) slope ? closer to horizontal
  • To figure out gradient
  • gradient change in elevation
  • change in distance

Characteristics of Streams and Rivers
  • discharge- amount (volume) of water that passes a
    certain point in a given amount of time
  • Often increases downstream (tributaries add
  • Not constant year-round
  • As discharge increases,
  • velocity increases
  • Becomes wider, deeper,
  • and may flood banks

Characteristics of Streams and Rivers
  • channel- the path through which the water flows
    in a stream or river
  • Size and shape affects velocity of water
  • Shallow and winding (a lot of boulders)
  • A lot of surface area in contact with water
  • Greater friction
  • slower
  • Straight, wide, and deep
  • Less surface area
  • Less friction
  • faster

Stream Erosion Deposition
  • Streams are effective agents of erosion because
    as gravity pulls the water downhill, the water
    carries soil and rock materials with it.
  • When the streams energy decreases, these
    materials can no longer be transported are
    dropped or deposited.
  • This is known as deposition.

Deposition Patterns
Chapter 13 Section 2
How Streams Weather Erode Material
  • Running water breaks up bedrock (weathering) and
    removes the rock and soil materials (erosion).
  • Mostly mechanical weathering
  • Split and move rocks
  • Abrasion (by cutting tools sand, pebbles,
    boulders, etc.)
  • Produces the rounded and smoothed rocks and sand
    grains that are commonly found in streams/rivers.

Potholes Plunge Pools
  • Pothole
  • Deep, oval/circular basins
  • Form when sand, pebbles, and small boulders swirl
    around in whirlpools and grind into the rocks
  • The cutting tools are often found at the bottom
  • Plunge pool
  • Basin worn away at the base of a waterfall
  • Form by the action of falling water and abrasion
    of churning particles

How Streams Transport Material
  • load eroded rock soil materials that are
    transported downstream
  • Carried in 3 ways
  • 1. solution
  • 2. suspension
  • 3. bed load

How Streams Transport Materials
1. Solution
  • Minerals are dissolved from the bedrock carried
    in the water
  • Commonly include calcium, magnesium,
  • Most comes from groundwater seeping into river

2. Suspension
  • particles are swept up and carried in the water
    as it swirls around (turbulence)
  • Particles do not touch the bottom
  • Includes clay, silt, and fine sand
  • often looks muddy

3. Bed Load
  • Larger particles rolled along the bottom of a
  • Includes sand, pebbles, boulders that are too
    heavy to be carried by suspension
  • Move by rolling, sliding, jumping, or bouncing

2 Measures used to describe the ability of a
stream to transport materials
  • Competence maximum size of the particles a
    stream can carry
  • Capacity the total amount of sediment a stream
    can carry

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
  • Rock materials and sediments transported by
    running water are eventually deposited.
  • Happens when velocity or discharge decreases
  • Results in graded (sorted) material

vertical sorting animation
settling rate by size, shape, density animation
Horizontal sorting in a stream animation
Depositional Features
  • Delta fan-shaped deposit of silt clay that
    forms when a river flows into a quiet or large
    body of water
  • Resembles a triangle, surface is flat
  • Results from a decrease in the rivers energy
  • Balance between erosion and deposition
  • Deposition (sediment supply) greater than erosion
    ? delta grows
  • Erosion greater than sediment supply (deposition)
    ? delta shrinks
  • A river flowing into a delta splits into

How is a delta formed?
Depositional Features
  • Alluvial fan fan-shaped deposit formed when a
    steep mountain stream meets dry, level land at
    the base of the mountain
  • Differs from a delta in several ways
  • Formed on land (not in water)
  • Sediments are coarse
  • sands and gravels
  • (instead of silt and clay)
  • Surface is sloping not flat

River Valleys
Chapter 13 Section 3
Headward Erosion
  • Formation of river valley starts on small scale
  • Temporary stream forms small valley called gully
  • Gully grows in length, width, depth each time
    it rains
  • Headward erosion the process by which land is
    worn away at the head of a stream or erosion
  • Lengthens streams or gullies
  • Eventually cuts down far enough to become
  • When join tributary gullies river system is formed

Canyons and V-Shaped Valleys
  • Youthful Stream
  • Steep gradient (slope)
  • Flow in a straight line
  • Erodes downward
  • V-shaped valley (canyon, gorge, chasm)
  • steep, almost vertical sides and narrow bottom
  • Form
  • in areas of less rainfall
  • when river cuts into bed rapidly
  • when rock is resistant to erosion

Rapids and Waterfalls
  • Temporary features of streams
  • Because erosion is greatest here
  • Causes undermining
  • Water falling into the plunge pool at the base
    erodes rock there, leaving the rocks at the top
    to overhang
  • Pieces break off
  • waterfall recedes further upstream
  • Ex. Niagra Falls

Waterfall animation
Base Level
  • The level of the largest body of water into which
    a stream flows
  • Lowest level a stream can erode to
  • Lakes and rivers ? local base level (temporary)
  • Ocean (sea level) ? ultimate base level (final)
  • As stream approaches base level
  • Gradient decreases (flatter)
  • Velocity decreases (slower)
  • Less erosion of bed, more erosion of sides
  • Valley--wider, broad floor, gently sloping walls

Floodplains Floods
  • Flood when a river overflows its banks
  • Floodplain the area of the valley floor that is
    covered when a river floods its banks

Chapter 13 Section 4
Features of a Floodplain
  • Mature Stream
  • Small gradient (slope)/flatter
  • Meandering (winding, bends)
  • Erodes wider instead of deeper
  • More discharge

Old Age Stream
  • Very small/shallow gradient (almost horizontal)
  • Meanders across flood plain
  • Sometimes forms oxbow lakes
  • More sediment deposited on sides

Life of a Stream
Old Age
Stream Deposition
1. Small sediments are deposited where the
stream slows down.
Friction causes slow down
2. Large Sediments show where current was flowing
faster All smaller sized sediments washed away
3. Since streams tend to separate sediments by
size, the sediments deposited are SORTED (or
4. Profiles- a side view
Large Sediment (Pebbles)
Small Sediment (Sand)
Fast Water
Slow Water
Cross Section on next slide
Cross Sectional View of a Meander
Cut Bank
Point Bar
Sediments fall (Deposition)
Cuts into curve (erosion)
Profile of a Straight Section of a Stream
5. Formation of an Oxbow Lake
The river becomes so s-shaped, that the next time
the river floods
it is easier for the water to "take a short cut"
and go straight across the flood plain.
Natural Levees
  • When a river overflows onto its floodplain, the
    velocity decreases sediment is immediately
  • Thick deposits build up along stream banks
  • Form elevated (raised) ridges called levees

  • Naturally occurring
  • Can be constructive (helpful) or destructive
  • Temporarily relieve river of water/sediment
  • Deposit minerals nutrients on floodplains
  • Making land fertile for agriculture
  • Destructive for people living near river
  • Most result from heavy or long-lasting rain, the
    melting of winter snow, or both
  • Flash floods occur quickly, usually from short,
    heavy rains in areas of young, narrow streams
  • Human activity can worsen or even cause floods by
    increasing runoff (decreasing water absorption)
  • Cover land with buildings or pavement
  • Removal of vegetation
  • Removal of wetlands

Flood Prevention Control
  • Restore natural flood protections that humans
    have altered
  • Replant vegetation
  • Build damshowever, they can also cause more
    erosion of floodplain, which worsens flooding
  • Build artificial levees
  • Can cause more erosion (due to more water
  • Build spillways (channels running parallel to
  • Natural floodplain management (preserve sections
    of floodplain, restore wetlands, discouraging
    development of flood-prone areas)