1. Exploring Geology Chapter 16 Rivers and Streams
Goals for this chapter:
Processes associated with rivers, such as erosion and deposition
Features of rivers, including meanders, floodplains and deltas
Importance of rivers to society, such as flooding
Headings in notes:
3D Information about what is on the 3D file accessed via the 3D link in the lower right corner of slide, if present
INSTRUCTIONS TO STUDENTS Instructions that the instructor can give to students
OBSERVATIONS What students might see during an observation exercise
EXPLANATION Additional aspects that can be explained by the instructor
EXERCISE Instructions to students about possible in-class exercise
NOTES Miscellaneous notes
Note on PowerPoint Animations
The PowerPoint files are set up so that text and figures appear sequentially on slides. As a cue to the instructor, the figure number goes away when the next click will advance the presentation to the next slide. If the figure number is still showing, another click will reveal something else on that slide (or hide the figure number for slides with no animated text).
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1

2. Yukon Delta
Bering Sea
Observe features on this satellite image that may be related to rivers
MEDIA
1600a1_Yukon_Delta.mov
1600a1_Yukon_Delta.kmz
1600a2_Yukon_Delta_VE3.scene
Note that north is to the right in image; colors are more vibrant in the media file than the figure on slide.
INSTRUCTIONS TO STUDENTS
Observe this satellite image of the Yukon Delta, identifying some obvious features that may be related to rivers. Colors are from the satellite data, not actual colors of the delta.
OBSERVATIONS
Many lakes and wetlands
Distributary system
Bulge in coastline
More vegetation on the delta
Light-colored water (sediment rich) along the coast
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3. Yukon Drainage Area Yukon Delta Yukon River 3 MEDIA
1600a2_Yukon_Drainages_pano.mov
Zoom and scroll map; drainages in blue
EXPLANATION
Location of delta
Drainage network
Runoff and sediments from this large region head toward the delta
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4. Drainage Basins Observe the red and blue areas and their boundary
Red area drained by one stream, and blue area by another: each is a drainage basin
MEDIA
1601b1_Drainages.mov
1601b1_Drainages_VE1.scene
INSTRUCTIONS TO STUDENTS
Observe the red and blue areas of this terrain and their mutual boundary
Boundary between basins is a drainage divide
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5. Volume of Flow Versus Time
Plot of discharge versus time is a hydrograph
This hydrograph shows discharge (flow) increasing during a flood, then decreasing as flood ends
Runoff from steep drainage basin is fast and most water arrives downstream at once
EXPLANATION
Scientists measure the amount of water flowing through a specific measuring site in a stream
Plot these data on a hydrograph, which portrays how the flow rate (discharge) varies through time
Higher parts of the graph signify more flow
Steep curve indicates a more rapid change in flow rate
Runoff from basin with gentle slopes is spread out over time; less peak flow
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6. Discharge Versus Basin Shape
Simple drainage basin: runoff reaches main drainage in orderly way
Has simple hydrograph
More complex basin shape: water shows up at different times
EXPLANATION
Brown insets are map views of drainage basins
Configuration of the drainage network influences when water from a precipitation or snowmelt event reaches areas downstream
When water arrives depends on the distance it has to travel and its rate of flow (size of stream, etc.)
NOTES
The top figure is not in the textbook but included here for comparison (book compares bottom figure here with top hydrograph from previous slide)
More complex hydrograph reflects something about basin shape
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7. How Do Rivers Vary Over Time?
Rivers vary in discharge during the year due to snowmelt, wet/dry seasons, etc.
INSTRUCTIONS TO STUDENTS
Observe the pattern on this graph of discharge versus time of year, and suggest some situations that could cause such a pattern
EXPLANATION
Vary in discharge, such as peak flow during Spring snowmelt, or during a rainy season that begins in the middle of the Summer
Smaller fluctuations record individual events, like a storm or especially warm week that results in more snowmelt in the Spring
Suggest some factors that might explain this pattern above (many possible answers)
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8. Tributaries and Drainage Networks
Smaller subsidiary channels are tributaries
Tributaries spread out discharge over time
Types of Drainage Patterns
EXPLANATION
Dendritic drainages are branching and tree-like, with smaller tributaries feeding into larger ones
Radial drainages flow outward in all directions, like off a circular mountain
Structurally controlled drainages follow tilted or folded layers, faults, joint patterns
Rivers can cut across layers (ridges), like in Appalachian Mountains
Structurally controlled
Dendritic
Radial
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9. North American Drainage Basins
Observe these drainage basins and find where runoff in your area ends up
INSTRUCTIONS TO STUDENTS
Observe these drainage basins and try to determine where runoff in your area ends up
Can you name the major rivers shown?
Answer (from right to left)
St. Lawrence, Ohio, Mississippi, Missouri, Arkansas, Rio Grande, Colorado, Snake, Columbia, Saskatchewan
EXPLANATION
Continental Divide generally used to refer to boundary between drainages that flow to Pacific versus those the flow to the Atlantic and Gulf of Mexico, but other regional divides are important
Interior drainage means area does not drain into the sea (drainage patterns disrupted by Basin and Range faulting in Nevada and Utah)
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10. How is Material Transported and Deposited?
Fine particles can be carried in suspension (floating) in water
Soluble ions are dissolved in and carried by moving water
Sand grains can roll and bounce along
EXPLANATION
Can introduce terms saltation, traction, solution
Cobbles and boulders mostly roll and slide during high flows
Material moving on river bed is bed load
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11. What Processes Erode Material?
Clasts can be picked up by turbulence and low pressure caused by moving water
Moving clasts collide with other clasts and obstacles, chipping away or launching pieces
EXPLANATION
Soluble material could include salt, gypsum, and calcite in limestone and travertine
Turbulence loosens and lifts pieces of streambed
Soluble material is dissolved and removed
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12. Turbulence
Viscosity (resistance to flow) and surface tension act to keep water smooth, as in slow-moving water
Upward- flowing eddies can pick up loose material
Moving water has inertia (tries to keep moving with same speed and direction)
EXPLANATION
Inertia means that a moving object tends to keep moving in the same direction and with the same speed unless affected by a force, such as from friction or an obstacle
At higher velocities or near obstacles, flow becomes more chaotic (turbulent), forming a swirl called an eddy
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13. Observe how river gradient changes downstream
Gradient = change in elevation for a horizontal distance (small blue triangles)
Expressed as m/km or ft/mile, degrees, or percentage
EXPLANATION
Steepest gradient on this figure is 15m/km
Note the very large vertical exaggeration that is about 50 times – gradients for most rivers are very low (Lower Mississippi is less than 0.1m/km)
EXERCISE
Provide students with pairs of elevation drop and distance, and have them calculate gradient
Practice converting units, such as feet/mile to meters/kilometer
Steeper gradient: river drops more for a given distance
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14. How Does a River Change Down Stream?
T1-T3 = tributaries H = headwaters D = delta M = mouth
INSTRUCTIONS TO STUDENTS
(With only the map showing) Predict how discharge, flow velocity, and sediment load will vary from the headwaters, past a tributary, across the delta, and to the mouth of the river
EXERCISE
(More difficult for students) Sketch a graph for each factor where vertical axis represents the amount of that quantity (like water velocity) and the horizontal axis represents distance downstream; sketch one example, such as total sediment load, that would be more difficult for them on their own
NOTES
The increase in discharge follows from the increase in channel size (cross section) and flow velocity.
It is not intuitive that water velocity increases downstream. It looks higher in steep mountain streams, but turbulence greatly slows the average rate.
Although purposely not shown and probably no need to mention here (deltas are covered later), water velocity generally slows dramatically near the mouth of the river, as the river encounters a lake or sea; this results in sediment deposition and decrease in maximum grain size.
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15. Sediment Size Versus Current Velocity
At high velocity, sand and smaller particles carried in suspension
At moderate velocity, silt and clay remain suspended but sand moves as bed load (rolls, etc.)
NOTES
The main point of this graph is that whether and how sediment is carried depends on stream velocity, and that different sediment sizes can be carried by different mechanisms, depending on the velocity
At lowest velocity, sand dropped but silt and clay remain in suspension
Observe and interpret this graph of stream velocity versus mode of transport for different sizes of sediment
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16. How Do Rivers Change Downstream?
Observe this profile of a river. How would you describe this pattern to someone?
INSTRUCTIONS TO STUDENTS
Observe this profile of a river that goes from the Appalachians eastward to the Atlantic Ocean
It crosses several provinces, including the Piedmont and Coastal Plain
OBSERVATIONS
Steeper in the mountains
Gentle downstream
Very gentle in Coastal Plain
Bump in middle
EXPLANATION
Concave-up shape
Drop from Piedmont to Coastal Plain is at the Fall Line
Rivers tend to be steep near their origin, such as in hills and mountains
Most rivers become less steep (more gentle) down stream (profile is concave upward)
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17. Base Level The lowest level to which a river can erode: base level
High above base level: much erosion
Closer to base level: less erosion
EXPLANATION
Base level can be the sea, lake, or closed basin
High above base level, streams and rivers can have steeper gradients and erode sharply into terrain
Closer to base level, streams have lower gradient so less erosion
Roughness of landscape reflects decreasing gradient of rivers (curved profile)
Landscape reflects decreasing gradient and how high above base level
Sea level is ultimate base level
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18. Curves in Rivers and Streams
Observe these satellite images of rivers
This river is braided
This river has meanders
MEDIA
1601a1_Brahmaputra_Brading.mov
This movie is of a different area, but shows excellent large-scale braiding.
INSTRUCTIONS TO STUDENTS
Observe the characteristics of each river, identifying smaller features along each river, and difference between the two rivers
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19. Curves in Rivers and Streams
Observe the channels in three rivers
INSTRUCTIONS TO STUDENTS
Observe the channels in three rivers
Braided: network of interweaving channels
Low sinuosity: gently curved
Meandering: very curved; high sinuosity
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20. What Processes Operate on Meanders?
Small graphs show profiles across the river channel; observe the channel profiles for different parts of the river
Straight channel: symmetric, fastest in center
Outside bend: deeper and faster; erosion of cutbank
MEDIA
1605b1_Meander_Profiles.mov
Movie rotates the block, displaying cross sections of the river in different segments
INSTRUCTIONS TO STUDENTS
Observe the small profiles across the channel (blue and white graphs) relative to their location on curves or straight segments of the river
EXPLANATION
Straight channel: fairly symmetric with highest velocity in center
Inside of bend: channel shallower and velocity lower, so deposition forms a point bar
Outside of bend: channel deeper and velocity faster, so erosion forms a cutbank
Erosion of cutbank and deposition of point bar may be balanced, so river maintains width
Inside bend: shallow and slower; deposition of point bar
Erosion and deposition may be balanced
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21. How Do Meanders Form and Move?
Faster side erodes and deepens
Deep side faster and more water, so erosion
Inside slower and less water, so deposition
Erode outside bend, increasing curvature; migration outward and downstream
MEDIA
1605c1_Meander_Formation.mov
Movie plays to show how water flows and causes meanders to form
INSTRUCTIONS TO STUDENTS
Do not take detailed notes here as the information is in the book
EXPLANATION
Curve begins when the velocity is faster on one side; gets eroded and deepens
Deeper side carries more and faster water so get more erosion, forming a cutbank
Inside has less and slower water so has deposition, forming a point bar
Meander erodes its outside bend, increasing curvature; meander migrates outward and downstream
Continued erosion or overflow during a flood can cut off meander and form an oxbow lake
Erosion or overflow erosion: cutoff meander and oxbow lake
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22. Landforms in the Headwaters of Streams
Waterfall
MEDIA
1606a3_Alaska_Headwaters.mov
1606a3_Alaska_Headwaters_VE1.scene
Rotate the scene about 180 degrees to duplicate this above view.
EXPLANATION
Waterfall: where resistant rocks or tributary valley higher than main valley
Rapid: turbulent river due to an obstruction, like debris from tributary, landslide, or bedrock in channel
Mountain lake: water impounded by some obstruction or where bedrock scoured deeply
NOTES
Could show photographs of waterfall, rapid, and steep headwaters
Rapid: turbulent segment
Mountain lake
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23. Landforms of Mountain Streams and Rivers
Incise into bedrock; narrow canyon if incision faster than widening
Dump debris when reaching more gentle terrain
MEDIA
1606b3_Mountain_River_Landforms.mov
1606b3_Mountain_River_Landforms_VE1.scene
Covers a larger area than the figure
EXPLANATION
Rivers erode into (incise) bedrock; narrow canyon if incision is faster than widening of canyon walls
Steep drainages may dump their debris when reaching more gentle terrain
Incised channels can become braided as they reach less steep areas
NOTES
Could show photographs of braided streams and alluvial fans
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Braided channels in less steep areas 23

24. Observe this view of a braided river
River has steep gradient onto plain
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Glaciated mountains: abundant sediment supply
MEDIA
1607a1_South_Island.mov
1607a1_South_Island_NZ_VE2.scene
INSTRUCTIONS TO STUDENTS
Observe this terrain, which has rivers that start in the mountains and reach the sea
EXPLANATION
River drains steep mountain range with glaciers and an abundant sediment supply
River exits mountains with a steep gradient and flows onto a sloping plain
Sediment-rich river is braided all the way to the ocean
NOTES
The topography and satellite image are from Canterbury, New Zealand, but were flipped for layout purposes in the textbook figure, but are not flipped in the media files
Sediment- rich river braided to ocean 24

25. Close-Up Views of Braided River
Braided channels: steep gradients, abundant supply of sediment, and variable flows
MEDIA
1607a2_Mountain_Braided_River.mov
1607a2_Mountain_Braided_River_VE1.scene
1607a4_Closeup_Braided_Stream.mov
1607a4_Closeup_Braided_Stream_VE6.scene
Close-ups of different segments of same river shown on previous slide; for textbook layout reasons, first figure is rotated 90 degrees compared to media files and second figure is flipped compared to media files.
EXPLANATION
Rivers have braided channels where there are steep gradients, abundant supply of sediment, and variable flows
Braided channels may be part of river with fairly straight path
NOTES
These views are of same river as last slide
Part of fairly straight river
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