Week 6: Following Rivers Through Time

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

A river meandering through Innoko National Wildlife Refuge. Source: US Fish and Wildlife Service.

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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?


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

My World Icon
  • 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.
    5 LA Rivers project 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.
  • Make Parishes the active layer then click on the Show Table of Layer button and use the Find find button button to find Pointe Coupee parish.
  • 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.
    9 oxbow lake

  • Examine the two oxbow lakes left behind from the time when this was the channel of the Mississippi River.
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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.
  • 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.

    • 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?
    • 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.

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?
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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?
    • Which types of soils are nearest its outlet into the Gulf of Mexico?
    • Which types of soils are important for agriculture?

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    Subsidence and Loss of Wetlands

    delta from last chance Mississippi Delta.
    Source: Ted Jackson / Times-Picayune.

    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.
    • Move the image above the U.S. States layer.
    • Zoom to the delta region of Louisiana where the Land Loss image is located.
    • 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?
      • Why are wetlands important to coastal protection?
      • What other ecosystem services do wetlands provide?
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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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    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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