Week 6: Following Rivers Through Time

Week 6: Following Rivers Through Time

Using ArcGIS to Study Human Impacts on River Sediments through Time

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

top of page

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.

Download Geographic Data About Louisiana


Shortcut1
  • Right-click the link below to download the zipped file to your computer.
  • LouisianaAM2.zip (Zip Archive 26.1MB Mar22 10)
  • Unzip the file. A folder called LouisanaAM2 will be created.
  • Move the entire LouisanaAM2 folder into the C:/eyesinthesky2/week6 folder or the area you have designated for your Eyes in the Sky 2 work. Data folder. (Path: C:/eyesinthesky2/week6/LouisianaAM2)
top of page

Launch ArcGIS and Open the Project File

  • Launch ArcGIS ArcMap by double-clicking its icon on your desktop or by clicking its icon on the Launch Bar.
  • Choose File > Open, navigate to C:/eyesinthesky2/week6/LouisanaAM2, select the LA_Rivers.mxd file, and click Open.
    02 Open Project
  • A map of Louisiana is displayed when the project opens. Parishes are shown in tan and the Mississippi River is blue.
top of page

Observe Patterns left by Old River Meanderings

Prepare the map for investigation

  • Turn on the Louisiana Parishes layer.
  • Right click on the layer name to open the Properties window.
  • Make the Louisiana Parishes layer transparent, by giving it No Color fill.
  • Label the Louisiana Parishes layer with the NAME of the parishes.
    1. Turn on the Louisiana Parishes.
    2. Right click on the layer name to open the Properties window.
    3. Make the Louisiana Parishes layer transparent, by giving it No Color fill.
      1 Louisiana Parishes No Color
    4. Label the Louisiana Parishes layer with the NAME of the parishes.
      Label Parishes
    5. This is what the map looks like after labeling.
      Labeled Map

  • Use the Find Find Tool tool to find Pointe Coupee parish.
    1. Click on the Find tool. Select Louisiana Parishes from the In pull down box.
      6 Find Louisiana Parishes
    2. Type in Pointe Coupee in the Find box.
      7 Find Pointe Coupe
    3. Right click the correct entry from the list in the box at the bottom of the Find window. Click on Select to hightlight Point Coupee in blue on the map.
      8 Find Pointe Coupe Select
    4. Move your Find window without closing it to view your map.
      9 Find Pointe Coupe Selected
    5. Right click again Pointe Coupee list in the box at the bottom of the Find window. Click on Zoom To to zoom into the parish of Point Coupee.
      11 Find Window Zoom to
    6. Your map will look like this.
      12 Pointe Coupee Zoomed In
  • Turn off the US States layer.
  • Once you have found your selected county Pointe Coupee, it is no longer necessary to have it highlighted. Click the Clear Selections 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.
top of page

Measure and compare the Mississippi and the Pearl

  • Turn off the labels on the Parishes layer. You can do this by right clicking on the Louisiana Parishes layer and uncheck the Label Features menu option.
  • Right click the Mississippi River layer.
  • In the Properties window, change the properties of the Mississippi River layer.
    Select the following options:
    • Features using: Single Symbol
    • Style Dash line
    • Color Yellow
    • Size 2.
  • Close the Properties window.
    1. Right click the Mississippi River layer.
    2. In the Properties window, change the properties of the Mississippi River layer.
      Select the following options:
      • Features using: Single Symbol
      • Style Dash line
      • Color Yellow
      • Size 2.

    14 Mississippi Yellow
  • On the la_lndsat7.tif satellite image of the river, measure the width of the Mississippi River in 3 locations. You will need to zoom and pan around on the image to find locations to measure. Record the data on a piece of paper or a data table.
  • top of page
    Measuring with ArcGIS
    • To measure, click on the Measure tool 14 Measure Tool in the toolbar. Click on the drop-down menu arrow, choose the Distance, Meters option for the measuring units. Move the measurement window off to the side so that you can see the satellite image.
    • On the Satellite image, click and drag perpendicularly across the river from one side to another on a section of river of your choosing. Notice the measurement in the measurement box.
    • Record the data on a piece of paper or a data table.

      1. To measure, click on the Measure tool 14 Measure Tool in the toolbar. Click on the drop-down menu arrow, choose the Distance, Meters option for the measuring units.

      2. 16 Measure Meters
      3. On the Satellite image, click and drag perpendicularly across the river from one side to another. Notice the measurement in the upper left corner of the map window.
        18 Measure Window
      4. Record the segment data in on a piece of paper or a data table. Click the image for a larger view.

      5. 25 Measuring First Section of Mississippi
    • 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?
    • 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 Riverlayer and LA_Pearl.tif
  • Turn off the Landsat.tif
  • Zoom to the Pearl River Hint: Right click on the Pearl River layer and click on Zoom to Layer.
  • In the Properties window, change the appearance of the Pearl River layer. Select the following: Style Dashed 2:2, Color Yellow, Size 1.

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

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

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.

  • Meander The bends in a river as it progresses.
  • Cutoff Occurs when the river takes a short-cut rather than following a meander that may have grown too large. In a cutoff, the river will be following its original path as well as running along the short-cut.
  • Oxbow Lake The horseshoe shaped bend of a river that becomes separated from the main part of the river after it has been a cutoff.
  • Meander Scars An oxbow lake that has become filled in with soil.


  • Turn off the Pearl River layer and the Pearl.tif image
  • top of page

    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 US States layer.
    • 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:
      • Symbology tab: Categories, Unique values
      • Field for Values MAPDES2
      • Color Scheme Random
      • Display tab: 60% Transparent
    • In the Properties window for Soils, click the Labels tab to label the features using the Field MAPDES2. Accept the default color and size. Click OK then.
    • Return to the Properties window for the Mississippi River and set it back to Blue, Solid and Size <2.
    top of page

    How do rivers deposit soil?


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


    Right click on the Louisiana Soils layer, click on Open Attribute Table and resize the table so that you can see both the table and the map at the same time.
    Click on the box to the far left on the Attribute Table to highlight each soil type on the map in bright blue one record (line) at a time. After clicking on each line in the Attribute Table, read the description of the individual soil's origin and relationship to river flow described in the paragraphs below.
    Alluvium soils are Highlighted. 23 Soils and Attribute Table Highlighted

    Soils higher in sand are generally more porous and settle out streams carrying them quickly when the water slows down. Rivers that flood slow down drastically when water leaves the main channel. The larger suspended particles settle quickly and end up creating Natural levees close to the sides of the riverbanks. Levee soil types are also good indicators that rivers must have existed in an area in the past. Natural levees are nature's way of building up the sides of the river to control future flooding.

    The silty Alluvium soils settle out in calmer waters and would be more typical away from the rivers in backwater swamps or just throughout the flood plain. They are typically rich in nutrients and these regions are well suited to growing vegetation and supporting healthy riparian (river edge) plant communities. People settling the area would have found these areas good for farming.

    Delta plains are soils deposited by river action as it reaches a lake or in this case, the Gulf. The materials being deposited in the delta plains have come from erosion somewhere higher in the fresh water environment. Particle sizes are become smaller and include more clay. Clays are the last type of particle to settle out in the slower moving environment of the gulf.

    The Chenier plains are composed of high percentages of clay particles as well. Over time, the Gulf currents have reworked these soils. As these soils were deposited in deeper water and more anaerobic environments and were influenced by salt water the organic material was less able to readily decay. Therefore they are darker and higher in organic content. The Chenier plains compose the majority of the current and past shorelines of the Louisiana coastline.

    Answer the following questions about Louisiana Soils:
    • Which types of soils are closest to the river's channel?
      The Natural Levees are closest to the river channel.
    • Which types of soils are nearest its outlet into the Gulf of Mexico?
      The Delta Plains are closest to the river channel.
    • Which types of soils are important for agriculture?
      The Alluvial soils are best for agriculture.

    top of page

    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

    • Close the Attribute Table and Clear Selections.
    • 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.
      Click the Add Data button and navigate to the LouisianaAM2 Folder. Select the image, USGSLandLossSatImage1932-2050.jpg and click Add.
    • Move the image above the US 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 and pan as needed to see the relationships between soil types and subsidence.
    • Answer the following questions:
      • What types of soils are vanishing?
        Delta plain
      • Why are wetlands important to coastal protection?
        Buffer from Storms
      • What other ecosystem services do wetlands provide?
        Wetlands provide habitat for fish and other wildlife.
    top of page

    Explore More

    • Look for patterns between soils and river meander features such as Oxbow Lakes and Meander Scars. These features show where the river was in the past. How does soil fit in?
    • Turn on the Atchafalaya Riverlayer and add US ACE Levees and Lake Ponchartrain 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 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?

    top of page

    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
    top of page