The Missouri River at Alton, Illinois on 3 August 1993
The 1993 Mississippi Flood at St. Louis

Objective

The objective of this exercise to model the 1993 Mississippi River flood at St. Louis, Missouri. You will use a Digital Elevation Model (DEM) produced by the U.S. Geological Survey to approximate the flood during late July and early August, 1993. You will create a shaded hillslope model to show the extent of the flood.

The 1993 flood was one of the most severe ever recorded in the entire Mississippi Valley. It caused tremendous damage in the upper Midwest, although relatively few lives were lost due to the long period of onset as well as adequate warning and emergency preparation.. The immediate cause of the flood was unusually high precipitation in Iowa, Missouri, and Kansas beginning in late spring and peaking in June. Tributaries of Mississippi began to flood in June and the water steadily moved south and east into the main channels. The peak of the flood came in late July and early August, although the water remained above flood stage in many areas well into September. You can study the damage caused by the flood in a set of 1993 Flood Damage Maps available from the Army Corp of Engineers that includes the damage subdivided by state. One of the most interesting is the overall Flood Extent map that shows how precipitation sweep through the upper tributaries of the Mississippi.

The area you will map around St. Louis, a region hard hit by the flooding because it is at the confluence of the Mississippi, Missouri and Illinois Rivers. Here are a few of the many satellite images of St. Louis during the flood. These other images cover most of the area of the East St. Louis DEM that you are using for your modeling of the flood.. Here is a road map of St. Louis to help you get your bearings.

What to Turn In

For this exercise, you will turn in an MPEG flyby animation of the Mississippi River at St. Louis.


New ArcView Procedures and Commands

You already know most of the commands that you will use to create this map. There are a few new procedures you'll need to work with the elevation data contained in the DEM. The following points cover the new ArcView features. Once these are familiar you can experiment with others and use your previous experience with ArcView to layout your complete map.

PART I: Creating the Terrain Model

1) Using ArcView Extensions

With the project window active, be sure the necessary ArcView extensions are loaded. Choose:

File | Extensions. Check 1) 3D Analyst and 2) Spatial Analyst. Check the default box to load these extensions everytime you start ArcView on the computer. However, since you may use different lab computers from session to session, always check to see that the necessary extensions are loaded.

2) Copying the gridded data for East. St. Louis

With a View window open and active, choose:

File | Manage Data Sources. Use this dialog box to copy the grid map source from the lab's Z: scratch disk to your ZIP drive. Use Source Type: Grid. The name of the file you want to copy from the scratch disk is: stlouise (short for St. Louis East 250,000 scale DEM quadrangle.

3) Opening the gridded data in a view

Add gridded data to a view just as you would with other themes--by using the Add Theme icon or by choosing:

View | Add Theme. Use the dialog box to point to the copy of the stlouise grid that you copied to your ZIP disk. Specify Data Source Type: Grid Data Source.

Once the theme has loaded, make it visible by checking the legend box.

4) Adjusting the contour levels and color patterns.

By default, the grid theme is classified into 9 categories using equal intervals from the lowest to highest elevation. Also, by default one of the monochromatic color ranges is usually applied to the map. The elevations in this DEM range from 102 to 377 meters. The theme is in units of latitude-longitude measured in decimal degrees.

To get oriented to this contour map, you may wish to study a road map of St. Louis . On the road map, even low-lying areas in the Mississippi and Missouri floodplains are symbolized as land, making the river channels appear quite narrow.

Double click on the theme legend to open the Legend Editor dialog window. Under Classify, pick 9 categories and Natural Breaks. For Color Range, try: Elevation #2 or perhaps Terrain Elevation #2.

The first category (102-139 meters) contains the channel and most of the floodplains of the rivers. It also includes some low-lying areas to the east in Illinois and within the City of St. Louis proper. Most of these were protected from flooding by levees and dams.

Flood stage for the Mississippi River at St. Louis is 30 feet. This is the point of elevation above the level of average flow where a flood is judged to begin The 1993 flood stayed above flood stage for weeks and actually reached 40 feet in late July and early August.

The difficulty of modeling this peak flow using the DEM is that flood stage is a relative measure--relative to average flow along the gradiant of the river. The DEMs give absolute elevation and do not allow us to differentiate an exact boundary between land and water. In fact, the Mississippi River drops about 20 meters from the north of the DEM to the south. This means that the the flood stage within this DEM falls within a band of elevation, very roughly the first category of the Natural Breaks classification (about 30-37 meters).

5) Creating a 3-dimensional model

To create a shaped 3-dimensional model, make sure the View window and Stlouise theme are active, then choose:

Surface | Compute Hillshade.

A dialog box appears that allows you to set the position of the light source for modeling the shading. The azimuth sets the horizontal angle of the light source (0 to 360 degrees around the image clockwise). The altitude (0 to 90 degrees) sets the angle above the image. You may wish to experiment with this settings to see if you can improve the visibility of the terrain. Altitude is critical to determining the shadowing that appears on your map.

Make this theme visible on your map as soon as ArcView finishes its calculations..

This hillshade model makes it easier to pick out the main channels of the Mississippi and Missouri rivers as well as some of the benches within their flood plains.

6) Combining the maps to show the flood event in the hillshade model .

Now combine the the hillshade and color contour maps.

First select the color contour map (Stlouise) with your mouse and slide it to the top of the legend bar. This is so it will display in the foreground above the hillshade model.

Double click on the color contour map to open the Legend Editor . Leave (or set) the first category to a blue fill. Change each of the other fill selections to no color--the box with the X on the Color Palette. Once you apply these choices, the hillshade model will show through the color contour map. The blue fill represents the flood surge.

7) Saving your work

Be sure to create an ArcView project file (.apr) to save your work. Be sure to save the project file to your ZIP disk, preferably in the same folder as the gridded St. Louis data. If you don't specify the location of the project file, ESRI will default to the C: or Z: drives meaning you are likely to lose your work..

8) Completing your map

There is more to do before you have a complete map, but you have finished the basics of this exercise. Before you finish you can experiment with other features of ArcView's 3D Analyst and Spatial Analyst if you wish. Otherwise you can use the ArcView commands you already know to produce a complete map layout. You may print your final map in color, but please be sure to test your layout first on the black-and-white laser printer. Get everything right before you print on the more expensive color printer.


PART II: Creating the Flyby Animation


1) Adding another ArcView Extension

With the project window active, add the ArcView "Flyby Animation Builder" extension. Choose:

File | Extensions. Check 1) Flyby Animation Builder. While in the extension menu make sure that the 3D Analyst and Spatial Analyst are still selected.

2) Open the hillshade model you created in Part 1. If you saved an ArcView project file, open it now.

3) Create a 3-D scene. Choose:

View | 3D Scene

4) Set the 3D Scene properties. Select:

3D Scene | Properties. You may wish to experiment with these values later but, for now, set the following values:

ArcView 3D Scene Menu

5) Begin to set up the animation. First:

Highlight ArcView "view" window you have open (the one used to create the 3D scene), then selection:

Animations | Associate View with Scene

Accept the default association "Theme." Next:

Bring up new menu with Animations | Animation Properties

6) Use the Fly-by Animation Builder to create and test animation.

A guide to the settings in this menu can be found here . For your first tests, use the following settings:


ArcView Flyby Animation Menu

When you selection "Draw the Flight Path in View" and press the button, you will be able to trace the flight path like this:

Defining a flightpath

The red highlight will appear AFTER you have finished the tracing. Try to trace a smooth path around the study area. The smoother the curve, the smoother will be the animation.

Use the Flyby Preview in 3D Viewer option to see your animation. Once you are satisfied with the settings, then:

7) Make your MPEG movie.

Once you have tested your animation, then select the Make Movies.. . option on the menu with the following settings:

ArcView Flyby Make Movie Menu

NOTE: When you specify "Make Mpeg Movies" be sure to save the file to the scratch disk on the local computer. Even though your final MPEG file will probably be 1-2 megabytes, the intermediate files (the frames of the animation in JPEG format) will take up much more space. If you try to save these files on your ZIP disk there is a chance you will run out of space!

The process of creating the animation takes some time. The software needs to create each frame of the animation and then put them together as an MPEG animation file. The 145 frames in the menu above can take 10 minutes to create. If you choose to create an animation with more frames, you will need to wait still longer. You will see one or two Windows open as you wait as the program processes the frames. You will receive a message at the very end of the process. Please be patient.

8) Test, save, and cleanup

Once the MPEG file has been created, it can be tested using the Windows Media Player, the RealPlayer player, or Quicktime--whichever of these viewers are found on your computer.

Once you have tested the MPEG file, copy it to your ZIP disk to hand in. Be sure to name the file so that it can be easily identified, something like: "footeanimation1.mpg"

Erase the jpg work files from the local machine to save space for the next person on the computer.

References and Further Reading

Dyhouse, Gary R. 1995. Myths and Misconcptions of the 1993 Flood. URL: http://www.mvs.usace.army.mil/dinfo/pa/fl93info.htm .

McConnell, D. 1998. Mississippi River Flood: 1993. URL: http://enterprise.cc.uakron.edu/geology/natscigeo/Lectures/streams/Miss_Flood.htm .

Pitlick, John. 1997. A Regional Perspective of the Hydrology of the 1993 Mississippi River Basin Floods. Annals of the Association of American Geographers 87 (1): 135-151.

Walker, N. D., L. J. Rouse Jr., G. S. Fargion, and D. C. Biggs. 1994. The Great Flood of Summer 1993: Mississippi River Discharge Studied. Earth in Space 7 (3):11-14. URL: http://www.agu.org/sci_soc/walker.html .

U.S. Army Corps of Engineers. 1998. Corps of Engineers 1993 Flood Data Hompage. URL: http://www.wes.army.mil/el/flood/fl93home.html .

U.S. Geological Survey, Scientific Assessment and Strategy Team (SAST). Fact Sheet on 1993 Flood .

U.S. Geological Survey, Geographic Data Download Page , 1:250,000 scale Digital Elevation Models


Created on 22 November 2000. Last revised 2001.11.26. k.foote@colorado.edu