Week 6: Following Rivers Through Time

Using My World to Study Human Impacts on River Sediments through Time

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Key Questions:

• How has the flow of the Mississippi River changed over time?
• What is the evidence of ancient rivers in modern soils?
• How do rivers transport and deposit sediments to balance the erosion and subsidence of their deltas?

Introduction

Meanders and their importance to soil erosion and transport

Rivers are constantly changing their course, meandering through time and space, forming new features and erasing old ones. Meander amplitudes get wider because the soil erosion carrying capacity increases with the width of the river. As in any process, the random places where the water is able to travel faster start eroding more material causing meanders to grow toward the side of the river that is moving faster and eroding. This forces the current to move toward that side, which subsequently erodes the bank more. Eventually, the meander grows to be wide enough that the return meander starts to make a closed loop. Meanders that grow close enough to close the loop form a cutoff, which deprives the meander from water current. This deprivation of current causes the ends of the meander to fill with silt, eventually becoming an oxbow lake. In this investigation you will explore the patterns left behind by rivers and their meanders.

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Launch My World and Open the Project File

• Launch My World by double-clicking its icon on your desktop or by clicking its icon in the Dock (Mac) or Launch Bar (Win).
• Choose File > Open Project..., navigate to Applications/My World /data/LouisianaMW, select the LA_Rivers.m3vz file, and click Open.
  
• A map of Louisiana is displayed when the project opens. Parishes are shown in tan and the Mississippi River is blue.

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Observe Patterns left by Old River Meanderings

Prepare the map for investigation

• Turn on the Parishes layer and make it the active layer.
• Double click on the layer name to open the Edit Appearance window.
• Make the Parishes layer transparent, by moving the Transparency slider to 100%.
• Move the la_lndsat7.tif layer above the U.S. States Layer.
Show me how
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1. Turn on the Parishes layer and make it the active layer.
2. Double click on the layer name to open the Edit Appearance window.
3. Make the Parishes layer transparent, by moving the Transparency slider to 100%.
   
4. Choose Fill Color of the layer by NAME of the parishes.
5. The names of the parishes are now listed in the Legend to the right of the map.
6. Move the la_lndsat7.tif layer above the U.S. States Layer. By clicking and dragging it up the Layer list.

• Make Parishes the active layer then click on the Show Table of Layer button and use the Find button to find Pointe Coupee parish.
Show me the how to use the find tool
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1. Make Parishes the active layer by clicking once on its name in the Layer List. Then click on the Show Table of Layer button. In the table of the layer click on the Find button.
2. Type in Pointe Coupee in the value box.
   
3. Click make Selection from Rows.
   
4. Name your selection, "Pointe Coupee".
   
5. Close the Table of Layer and return to the map. Point Coupee is highlighted in yellow on the map.
   
• Pan and Zoom in on the Parish. Once you have found it, click the All (highlighting off) radio button to turn the yellow highlighting off.
  


• Examine the two oxbow lakes left behind from the time when this was the channel of the Mississippi River.
Show me the Oxbow Lake
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Measure and compare the Mississippi and the Pearl

• Zoom to the extent of the la_lndsat7.tif image..
• Make the Mississippi River the active layer.
• In the Edit Appearance window, change the properties of the Mississippi River layer.
  Select the following options:
  • Choose Color by: Uniform Yellow
  • Choose Line Width by: Uniform
  • Line Width narrow (the second line).
  • Dashes Dash –dot –dash
• Close the Edit Appearance window.
Show me how to change the Edit Appearance
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1. Make the Mississippi River the active layer.
2. In the Edit Appearance window, change the properties of the Mississippi River layer.
   Select the following options:
   • Choose Color by: Uniform Yellow
   • Choose Line Width by: Uniform
   • Line Width narrow (the second line).
   • Dashes Dash –dot –dash
   
   
• On the la_lndsat7.tif satellite image of the river, measure the width of theMississippi River in 3 locations. You will need to zoom and pan around on the image to find locations to measure. Record the data in on a piece of paper or a data table.
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Measuring with My World
• To measure, click on the Measure tool in the toolbar.
• Choose My World GIS > Preferences... to set the measurement units, choose the meters option for the measuring units.
• On the Satellite image , click and drag perpendicularly across the river from one side to another. Notice the measurement in the lower right corner of the map window.
• Double click to end a segment of measure.
• Record the data in on a piece of paper or a data table.


Show me how to measure
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1. To measure, click on the Measure tool in the toolbar.
2. Choose My World GIS > Preferences... to set the measurement units, choose the meters option for the measuring units.



3. On the Satellite image , click and drag perpendicularly across the river from one side to another. Notice the measurement in the lower right corner of the map window.
4. Double click to end a segment of measure.
5. Record the segment data in on a piece of paper or a data table. Click the image for a larger view.



• Average the data that you recorded in the three measurements. Answer the question; what is the average width of Mississippi in this region of Louisiana?
Show me the answer
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The Mississippi is approximately 1300 meters in width.
• Measure the length and amplitude of the meanders of the Mississippi in 3 locations. Record your data.






• Turn on the Pearl River layer and LA_Pearl.tif
• Turn off the Landsat.tif
• Zoom to the Pearl River
• In the Edit Appearance window, change the appearance of the Pearl River layer. Select the following: Shape Dotted line, Color Yellow, Size narrow.
• Zoom in to the Pearl River.


Show me the result
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Measure the width of the Pearl River in 3 locations. Record your data.

• Measure the length and amplitude of several of the meanders in northern section the Pearl River.
• Compare the measurements of these two rivers and answer the following question:
  • Which river is capable of carrying a larger volumes of water and hence, large volumes of soil?
    Show me the answer
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    The Mississippi on average is nearly 10 times wider than the Pearl.

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Pan along the course of the Pearl River and examine river features

Examine the satellite image for the following features along the Pearl River: Meanders, Meander Scars, Cutoffs, and Oxbow Lakes .

Turn off the Pearl River layer and the Pearl.tif image

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Soils and River Patterns

What is soil?

Soils, in general, are composed of broken down rock mixed (regolith) and living or previously living matter (humus). Soils also contain empty spaces between their particles, which fill with air, and water. Soils form in the normal process of mass wasting, or moving from high places to lower altitude places through gravity assisted processes such as free falls, or they are transported by other agents such as wind or water (erosion). Soil textures are generally classified by the size of the particles that compose it. Particle sizes, ranging from largest to smallest, are sand, silt, and clay.

• Turn on the Louisiana Soils layer.
• Zoom to the extent of the Louisiana Soils layer.
• Classify and Symbolize the Louisiana Soils layer.
• Select the following:
• Choose Fill Color by: MAPDES2
• Color Scheme Soil Texture
• Transparency 60% Click Apply and Close.
• In Edit mode make a new annotations layer to name the soils.
• Return to the Edit Appearance window for the Mississippi River and set it back to Blue, Solid and narrow.

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How do rivers deposit soil?

The Louisiana Soils layer is now classified into six groups. Each type of soil displayed on the map has a slightly different origin and composition. The soils are also in different locations.

On the Legend, click on the name of the Soil types to highlight them on the map in yellow. After clicking on each name in the legend. Read the description of the individual soil's origin and relationship to river flow described in the paragraphs below.




Answer the following questions about Louisiana Soils:

• Which types of soils are closest to the river's channel?
  Show me the answer
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  The Natural Levees are closest to the river channel.
• Which types of soils are nearest its outlet into the Gulf of Mexico?
  Show me the answer
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  The Delta Plains are closest to the Gulf.
• Which types of soils are important for agriculture?
  Show me the answer
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  The Alluvial soils are best for agriculture.

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Subsidence and Loss of Wetlands

View the 7 minute animated story, Last Chance for Mississippi Delta

• Add USGSLandLossSatImage1932-2050.jpg image.
  This image shows land loss from 1932-2050. The land loss up to 2000 is historical, the land loss after 2000 is projected if no further corrective actions are taken.
  Show me how to add the image
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  Click the Import Layer from File button and navigate to the LouisianaMW Folder. Select the image, USGSLandLossSatImage1932-2050.jpg and click OK. The image coordinates are set so just click OK in the next dialog box that opens.
• Move the image above the U.S. States layer.
• Zoom to the delta region of Louisiana where the Land Loss image is located.
Show me the map with the image added
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• Turn the soils layer on and off to better view the image. Zoom, Pan and turn layers on and off, as needed to see the relationships between soil types and subsidence.
Answer the following questions:
• What types of soils are vanishing?
  Show me
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  Delta plain
• Why are wetlands important to coastal protection?
  Show me
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  They provide buffer from storms.
• What other ecosystem services do wetlands provide?
  Show me
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  Wetlands provide habitat for fish and other wildlife.

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Explore More

• Look for patterns between soils and river meander features such as Oxbow Lakes and Meander Scars. These features show where was river in the past. How does soil fit in?
• Turn on the Atchafalaya River layer and add US ACE Levees and Lake Ponchatrain layers (from the data folder). Discuss the man made levees and why they were built. Use the information and pictures in the Resources section below.
• Turn on the Louisiana Cities layer again. Find New Orleans and other coastal cities. Are they in the zones that are subsiding? If you were a city planner or government official, what plans might you make for the future based on this lesson?

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Resources

The Times-Picayune article: Last Chance

Last Chance Series of Articles: Part 1 - Coastal Erosion

Last Chance Series of Articles: Part 2 - Losing Ground

Last Chance Series of Articles: Part 3 - Laying the Groundwork

Animation of River Meanders forming: Meander and Floodplain Animation

COSEE: Central Gulf of Mexico educational resource site COSEE Resource Site

Louisiana Costal Wetlands Conservation and Restoration Task Force: LaCoast - Excellent source of satellite images, maps and animations

TERRA Image of Mississippi Meanders TERRA satellite image of Mississippi Meanders

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