LAB 06: FLUVIAL PROCESSES AND LANDSCAPES
Note: Please refer to the GETTING STARTEDmodule to learn how to maneuver through, and how to answer the lab questions, in the Google Earth () component.
KEY TERMS
You should know and understand the following terms:
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Alluvial fan |
Drainage divide |
Oxbow Lake |
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Basin |
Drainage pattern |
Sinuosity |
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Braided streams |
Entrenched meander |
Stream discharge |
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Cutbanks |
Hydrograph |
Stream order |
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Delta |
Meandering river |
Watershed |
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Drainage density |
Meander scar |
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LAB LEARNING OBJECTIVES
After successfully completing this module, you should be able to do the following tasks:
· Describe the concepts of sub-basins and watersheds
· Identify different human water uses of a river
· Construct a stream order for a river system
· Compute drainage density of a given basin
· Identify drainage patterns of river networks
· Explain how braided rivers and meandering rivers are formed
· Identify the physical features common to a meandering river system
· Describe the physical conditions necessary to form alluvial fans
INTRODUCTION
This module examines fluvial processes and landscapes. Topics include watersheds, drainage patterns and densities, stream order, meandering and braided streams, and alluvial fans. While these topics may appear to be disparate, you will learn how they are inherently related. The modules start with four opening topics, or vignettes, which are found in the accompanying Google Earth file. These vignettes introduce basic concepts of fluvial processes and landscapes. Some of the vignettes have animations, videos, or short articles that will provide another perspective or visual explanation for the topic at hand. After reading the vignette and associated links, answer the following questions. Please note that some links might take a while to download based on your Internet speed.
Expandthe INTRODUCTION folder and then select Topic 1: Introduction
Read Topic 1: Introduction
Question 1: Which of the following is a reason for the location selected for the first English settlement in the New World, Jamestown, VA?
A. Prime agricultural land
B. On the advice from the Native Americans
C. Deep water port
D. The land was already cleared
Read Topic 2: Rivers of Life
Question 2: If our ability to predict floods has improved significantly, why does economic loss continue to rise? (Check all that apply).
A. Increased urbanization
B. Increased population
C. Increased development along coasts
D. Increased real estate values
Read Topic 3: Rivers of Waste
Question 3: What are potential outcomes or conditions resulting from too much nitrogen running off from agricultural fields? (Check all that apply).
A. Eutrophication of water bodies
B. Decrease in crop production
C. Contamination of groundwater
D. Health issues in infants
Read Topic 4: Erosion
Question 4: List three ways in which humans contribute to stream bank erosion.
A. Vegetation removal
B. Increase in impervious surfaces
C. Wave from boats
D. Wind action on exposed banks
Read Topic 5: Transportation and Deposition
Question 5: What impacts do dams have on the transportation of sediment? Check all that apply.
A. Decrease in sediment transportation upstream from dam
B. Increase in sediment transportation downstream from dam
C. Decrease in sediment transportation downstream from dam
D. Increase in sediment transportation upstream from dam
Collapse and uncheckthe INTRODUCTION folder
For the remaining portions of this module, you will identify and explain the geographic distribution, patterns, and processes associated with fluvial environments. In doing so, you will recognize and appreciate the impact of rivers.
GLOBAL PERSPECTIVE
Expand the GLOBAL PERSPECTIVE folder and then expand the World Rivers folder. Double‑click and select any continent or world region. To display river information (name and approximate length) click any river in the Google Earth 3-D pane.
Collapse the World Rivers folder.
Major Cities on Rivers
Expand Major Cities on Rivers.
For each question below, type the latitude and longitude coordinates into the Search field and then press Enter. When you arrive at your destination, find the information that you will use to fill in the blanks below:
Question 6: 33 18 59 N, 44 23 33 E
City:
A. Atlanta
B. Baghdad
C. Cairo
D. Dusseldorf
River:
A. Mississippi
B. Euphrates
C. Tigris
D. Nile
Question 7: 30 03 29 N, 31 14 05 E
City :
A. Paris
B. Moscow
C. Cairo
D. Shanghai
River:
A. Ohio
B. Jordan
C. Zambesi
D. Nile
Question 8: 48 51 26 N, 2 21 04 E
City:
A. London
B. Madrid
C. Paris
D. Buenos Aires
River:
A. Rio de la Plata
B. Seine
C. Thames
D. Volga
Question 9:Montreal, Canada.
Latitude: A. 45° 30’S B. 73° 33’N C. 45° 30’N D. 73° 33’S
Longitude: A. 45° 30’E B. 73° 33’N C. 45° 30’S D. 73° 33’W
River:
A. Montreal
B. St. Lawrence
C. Hudson
D. Ottawa
Collapse anduncheck the GLOBAL PERSPECTIVE folder
WATERSHEDS AND DRAINAGE DENSITY
Expand the WATERSHEDS AND DRAINAGE DENSITY folder.
A drainage basin is an area of land in which a stream receives water, predominately by surface runoff, through flow, and groundwater flow. Drainage basins are topographically divided from each other by the highest points of elevation, so that all water from the ridges and hills flow into a given drainage basin and thereby into a given stream. This topographic delineation is commonly referred to as a watershed (the drainage divide between two drainage areas), although many in the United States use the term watershed interchangeably with drainage basin or catchment.
A large drainage basin can contain several smaller drainage basins or sub-basins. The nested nature of these sub-basins is determined by topography as well as where the water flows out of the drainage area, known as the outflow point.
In Figure 1, dash-lines A, B, and C demarcate the watersheds of the tributary streams, while dash-line D delineates the watershed of a larger drainage basin for the larger streams, which includes the smaller tributaries and their sub-basins.
Figure 1. Watershed map (Source: Maidstone Lake USGS 7.5 minute map).
Understanding watersheds are important because stream flow and water quality are influenced by the nature of and changes in the drainage basin. We can determine what is happening in our river basins by examining the water flow and water quality from a river’s outflow point. Changes to water flow or water quality in rivers could be due to either natural events (such as lightning induced forest fires increasing soil erosion) or human modifications (such as agricultural practices increasing pollution).
Double-click and select Columbia River Watershed.
The Columbia River watershed encompasses 258,000 square miles (approximately the size of France), with 220,000 square miles in the U.S. and 38,000 square miles in Canada. The length of the river is approximately 1243 miles, making it the 15th longest river in the United States.
Uncheck Columbia River Watershed.
Check the Columbia River Sub-basin US only folder. Click on each sub-basin in the Google Earth map pane to identify its name.
Question 10: How many Columbia River sub-basins in the United States are displayed on the map?
A. 7
B. 8
C. 9
D. 10
Uncheck Columbia River Sub-basin US only.
Expand the Columbia River Watershed – Fly Over folder.
The Google Earth flying simulation of the Columbia River shows how the basin is a multi-use watershed. Do the following steps to reduce confusion for the duration of the simulation:
1. Uncheck all the check boxes in the Google Earth’s Places and Layers panes.
2. Check only the Enable this check box for the tour check box to display the text in the simulation.
3. Double-click here to view the tour (Running Time: 2:06).
When the simulation stops, close the simulation control panel:
Question 11: What water uses did you see as you traveled upstream on the Columbia River? (Check all that apply).
A. Agriculture
B. Flood control
C. Power generation
D. Recreation
E. Ranching
Uncheck Columbia River Watershed – Fly Over.
Expand the Stream Orderfolder.
Stream Order
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Figure 2. Stream order (16.9 Arbogast 2nd. Ed.). |
Stream order is a measure of the size of a stream based on a hierarchy of tributaries. Using the Strahler stream order method, the smallest tributaries are assigned the value of 1. When two streams with different order numbers join, the resulting stream is assigned the value of the higher order numbered stream.
In Figure 2, two streams with an order number of 1 join to form a stream with an order number of 2. However, when one stream with an order number of 1 joins a stream with an order number of 2, the stream remains a 2. Large river systems typically have a higher stream order. The Mississippi River for example has a stream order of 10.
The Strahler stream order number for a given stream is dependent on the scale as which one views a stream network. A stream with an order number of 3 on a 1:24,000 map, for example, might have an order number of 1 on a 1:1,000,000 scale map, as fewer rivers are displayed on a smaller scale map.
Double-click and select the Willamette River folder.
In this particular map, the Willamette River has a Strahler stream order of 5. Though not all streams are labeled with their order, you should be able to determine how the stream ordering system works. You might have to zoom in to see the labels clearly.
Double-click and select the Snake River folder.
For Questions 12 to 15, identify the stream order number for rivers A, B, C, and D:
Question 12: River A:
A. 1
B. 2
C. 3
D. 4
Question 13: River B:
A. 1
B. 2
C. 3
D. 4
Question 14: River C:
A. 1
B. 2
C. 3
D. 4
Question 15: River D:
A. 1
B. 2
C. 3
D. 4
Uncheck the Stream Order folder.
Stream Density
Double-click and select the Stream Density folder.
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Figure 3. Drainage basins (16.8 Arbogast 2nd. Ed.). |
Notice the two sub-basins that are highlighted. The smaller one is the Willamette River watershed and the larger one is the Snake River watershed. The drainage density of a basin measures how well a watershed is drained and depends largely on the underlying bedrock and topography of the basin. Basins with high relief and exposed bedrock tend to have a higher drainage density.
Use the following formula to calculate the stream density of each sub-basin (show your work):
In other words, the [drainage density] equals the [total length of all streams] divided by the [area of the drainage basin]
Double-click and select Snake All Streams.
Double-click and select Willamette All Streams.
Willamette River watershed:
Question 16: What is the stream density of the Willamette River sub-basin?
A. 12800 / 11500 = 1.11
B. 11500 / 12800 = 0.90
C. 12800 / 11500 = 1.43
D. 11500 / 12800 = 0.95
Snake River watershed:
Question 17: What is the stream density of the Snake River sub-basin?
A. 108000 / 138000 = 0.78
B. 138000 / 108000 = 1.28
C. 108000 / 138000 = 0.83
D. 138000 / 108000 = 1.48
Collapse and uncheck WATERSHEDS AND DRAINAGE DENSITY folder.
DRAINAGE PATTERNS
Expand the DRAINAGE PATTERNS folder.
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Figure 4. Drainage patterns (16.7 Arbogast 2nd Ed.). |
The drainage patterns of a stream system (a network of streams and tributaries) depend largely on the topography on the land as well as the structure of the underlying bedrock. Areas subject to faulting often produce rectangular drainage patterns, while areas with folded topography (mountains) often have trellis drainage patterns. Volcanoes typically form radial drainage patterns. Dendritic drainage patterns are common in areas with non-porous, impermeable bedrock.
Double-click and select Drainage pattern 1.
Question 18: Identify Drainage pattern 1:
A. Radial
B. Trellis
C. Rectangular
D. Dendritic
Now that you have identified Drainage pattern 1, double-click and select drainage patterns 2 to 5 to identify them.
Question 19: Identify Drainage pattern 2:
A. Radial
B. Trellis
C. Rectangular
D. Dendritic
Question 20: Identify Drainage pattern 3:
A. Radial
B. Trellis
C. Rectangular
D. Dendritic
Question 21: Identify Drainage pattern 4:
A. Radial
B. Trellis
C. Rectangular
D. Dendritic
Question 22: Identify Drainage pattern 5:
A. Radial
B. Trellis
C. Rectangular
D. Dendritic
Collapse anduncheck the DRAINAGE PATTERNS folder
BRAIDED STREAMS
Double-click and select the BRAIDED STREAMS folder.
Fast moving streams originating from mountainous glacial areas or regions with an abundance of erodible sediment, often transport great quantities of coarse material such as sand and gravel within the channel. As the stream velocity decreases (topography becomes less steep) however, the discharge is insufficient and the stream can no longer carry the sediment load. In essence, the deposited bed load forms bars (or eyots) within the stream channel, forcing stream channel to diverge and converge among the deposits. These constantly shifting channels within the larger river channel are what give the stream its braided appearance.
The Delta River is an example of a braided stream near the town of Delta Junction, Alaska. Notice the network of broad yet shallow stream channels that diverge and converge, separated by bars of deposited bed load.
Question 23: Based on the location and the deposition type, explain why this stream forms a braided pattern.
A. The steep slope of the river means that water flows faster and can easily carve out a series of channels forming a braided stream
B. The slow flowing river means that not much sediment can be carried by the water and hence, the load is deposited forming a braided stream
C. The channels are stationary and it is the river that moves, thus creating a braided appearance.
D. The steep topography means the river is stationary and it is the channels that are constantly shifting, forming a braided stream
Question 24: Where does the sediment (deposition material) come from?
A. The sediment is actually in place and is not transported. It is merely disturbed by the river, which forms bars of deposited bed load
B. The sediment was actually deposited upstream by meandering rivers and over time headward erosion by the river created the braided stream
C. The sediment is from glacial erosion that is carried downstream by streams from the melting glacier
D. The sediment is finely sorted from upstream weathering and erosion of loess deposits
Uncheck BRAIDED STREAMS
MEANDERING STREAMS AND FLOODPLAINS
Expand the MEANDERING STREAMS AND FLOODPLAINS folder.
In contrast to braided streams, meandering streams are formed in landscapes with little relief, are generally slower moving, and carry finer sediments. In addition, water flow within meandering stream typically is constrained to a single channel. As their name suggests, meandering streams are identifiable by their sinuosity, or the bends and turns of the stream channel across a floodplain. The meander of the channel occurs with the scouring of the channel on the outside of the bend (where flow is faster) and deposition on the inside of the bend (where flow is slower). This constant erosion or removal of sediment from cutbanks and deposition of sediment from point bars produces the movement of the meander across the landscape, with past meanders evident from oxbow lakes and meander scars.
Click Stream Process Animation and view the animation.
Erosion and deposition occurs primarily during periods of flooding. Many rivers are prone to flooding, with some large flooding events changing the course of the stream channel (by bypassing the meander altogether and producing a straight reach). While natural or artificial levees might prevent a stream from flooding, large flood events compromise levees, with water and its suspended sediment spilling over the levees and depositing onto the surrounding floodplain.
Double-click and select Mississippi River – Identify Features.
Using the following list of meandering stream features, answer Questions 25 to 29 that apply to the Mississippi River map image in Google Earth.
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A. Oxbow Lake |
B. Point bar |
C. Meander scar |
D. Outside of meander |
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E. Island |
F. Inside of meander |
G. Deep channel (thalweg) |
H. Shallow channel |
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I. Floodplain |
J. Low ground |
K. Cut bank |
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Question 25: Stream Feature A:
A. Oxbow lake
B. Point bar
C. Meander scar
D. Outside of meander
E. Island
F. Inside of meander
G. Deep channel (thalweg)
H. Shallow channel
I. Floodplain
J. Low ground
K. Cut bank
Question 26:Stream Feature B:
A. Oxbow lake
B. Point bar
C. Meander scar
D. Outside of meander
E. Island
F. Inside of meander
G. Deep channel (thalweg)
H. Shallow channel
I. Floodplain
J. Low ground
K. Cut bank
Question 27:Stream Feature C:
A. Oxbow lake
B. Point bar
C. Meander scar
D. Outside of meander
E. Island
F. Inside of meander
G. Deep channel (thalweg)
H. Shallow channel
I. Floodplain
J. Low ground
K. Cut bank
Question 28: Stream Feature D:
A. Oxbow lake
B. Point bar
C. Meander scar
D. Outside of meander
E. Island
F. Inside of meander
G. Deep channel (thalweg)
H. Shallow channel
I. Floodplain
J. Low ground
K. Cut bank
Question 29: Stream Feature E:
A. Oxbow lake
B. Point bar
C. Meander scar
D. Outside of meander
E. Island
F. Inside of meander
G. Deep channel (thalweg)
H. Shallow channel
I. Floodplain
J. Low ground
K. Cut bank
Question 30: Identify the dominant land uses surrounding the river.
A. Agriculture
B. Mining
C. Forestry
D. Urban
E. Fishing
Double-click and select Mississippi River – Measure Distance.
Do the following steps to examine river sinuosity.
1 Verify that Mississippi River – Measure Distance is the only item checked in the Places pane.
2 Go to the Google Earth icon bar and click the Show Ruler tool .
Note: Verify that the simulation control panel is closed:
3
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Figure 2. Stream distance (image from Google Earth). |
In the Ruler window, click the Path tab and select Miles for the units.
4 Draw a straight line between the two points; that is, click point and then click point to determine the distance. This is the downvalley length.
5 Click Clear on the Ruler window to stop.
Question 31: What is the length, in miles, of the channel?
A. 29
B. 16
C. 38
D. 47
Measure the distance of the channel (the meander):
1 In the Ruler window, click the Path tab and set the units to Miles.
2 Click point and click you as trace the path of the river until you get to point . This is the channel length. Figure 7 shows an example of how your path might appear.
Question 32: What is the length, in miles, of the channel?
A. 29
B. 16
C. 38
D. 47
The sinuosity index (SI), also known as the meander ratio, calculates how much the stream channel deviates from the shortest path. Straight rivers have a SI close to 1, but this number increases the more a river meanders.
Question 33: Use the following formula to calculate the SI for this reach of the Mississippi River:
In other words, the [sinuosity index] equals the [channel length] divided by the [downvalley length].
A. 16 / 37 = 0.42
B. 47 / 29 = 1.62
C. 38 / 16 = 2.38
D. 38 / 29 = 1.31
Close the ruler tool. Uncheck Mississippi River – Measure Distance.
Double-click and select San Juan River – Compare Features.
The San Juan River is another meandering stream, yet we do not see the classic oxbow lakes and meandering scars we saw with the Mississippi River.
Question 34: Compute the SI of the San Juan River from point A to point B.
A. 20 / 4 = 5.0
B. 6 / 10 = 0.60
C. 6 / 2 = 3.0
D. 8.5 / 3 = 2.83
Question 35: Which river (Mississippi River or San Juan River) has a higher SI?
A. Mississippi River
B. San Juan River
C. They have the same
D. Unable to discern
Use the following navigation steps to examine the terrain:
Question 36: Explain why there are no classic oxbow lakes or meander scars.
A. They have been filled in by sediments from the river
B. The surrounding material is too soft to allow for their creation
C. The surrounding material is too hard to allow for their creation
D. The river is downcutting faster than it can change course
Collapse and uncheck MEANDERING STREAMS AND FLOODPLAINS
ALLUVIAL FANS
Expand the ALLUVIAL FANS folder. Double-click and select Alluvial Fan.
Alluvial fans are comprised of water-transported material or alluvium. Most alluvial fans consist primarily of coarse grained material. In Death Valley, California, notice the series of alluvial fans.
Do the following steps to get a better view of the landscape and to explore the topography:
1 Check the Nova Canyon 7.5 minute map check box and compare the contour lines on the alluvial fan to those contour lines on the northeast portion of the map. This make take a few minutes, depending on your Internet connection speed.
2 Zoom in to the Death Valley region.
3 To see the landscape in 3D:
PC: Press and hold the Shift key and use the scroll button on the mouse. You can also use the Ctrl or Shift keys in combination with the arrow keys to pivot and rotate the image.
Mac: Press Shift in combination with the up and down arrows. You can also use the mouse scroll wheel to zoom.
Question 37: What geographic and topographic land features are necessary to create alluvial fans? Hint: Where are the fans located physically as well as what features are required to develop them?
A. Humid, flat landscapes
B. Arid, steep landscapes
C. Humid, steep landscapes
D. Arid, flat landscapes
This concludes Module 16
