Find areas at risk from aquifer depletion

Explore the data

You've been provided with three datasets, representing three factors affecting the Ogallala Aquifer: urban areas, irrigation data at the county level, and average precipitation data. First, you'll explore these layers.

  1. Download the Groundwater project package.
  2. Locate the downloaded Groundwater.ppkx file on your computer. Double-click the file to open it in ArcGIS Pro. If prompted, sign in to your ArcGIS account.

    If you don't have ArcGIS Pro or an ArcGIS account, you can sign up for an ArcGIS free trial.

    This lesson was most recently tested for ArcGIS Pro 2.8. If you're using a different version of ArcGIS Pro, you may encounter different functionality and results.

    Map of the United States showing urban areas in black and counties ranging in color from beige to pink to purple

    A map of the United States appears. The black areas are urban areas. The counties are symbolized based on the percentage of land that receives irrigation, with darker colors corresponding to more irrigation.

  3. In the Contents pane, turn off Irrigation and turn on Precipitation.

    Map of the United States with the East and South colored blue, changing gradually to yellow in the West, and the Northwest Coast in dark blue

    This layer displays average annual precipitation between the years 1990 and 2009.

  4. On the ribbon, on the Map tab, in the Navigate group, click the Explore button to activate it.

    The Explore button on the ribbon has a blue background when it is activated.

  5. Click anywhere on the Precipitation layer on the map.

    A pop-up appears, listing the attributes of the identified feature. The GRIDCODE attribute refers to the mean annual precipitation value in inches.

    Pop-up for a precipitation feature in the middle of the nation with a GRIDCODE value of 20

  6. Close the pop-up.

    Agricultural irrigation and urban areas are both heavy water consumers. They help you understand where the greatest amounts of water are being withdrawn from the Ogallala Aquifer. The Precipitation layer can help you understand where the aquifer is being replenished.

Download aquifer data

While most of the data for this lesson has been provided, you'll need to access aquifer data from the United States Geological Survey (USGS) and prepare it for your map.

  1. In a browser, open the USGS site Aquifers: Map of the Principal Aquifers of the United States.
  2. Scroll down the page to find the Data heading under Principal Aquifers of the United States.
  3. Click the first download link, aquifrp025_nt00003.tar.gz [7.6MB GZ].

    If you cannot locate the file, you can also download it from ArcGIS Online.

    The file has the extension .tar.gz, which is a type of file that has been compressed twice instead of once. You'll need to unzip the contents twice to view the images.

  4. Locate and unzip the downloaded .tar.gz file from within the aquifrp025_nt0003.tar folder.
  5. Unzip aquifrp025.tar.

    Four files are extracted. The .txt file contains metadata. The other three files make a shapefile of aquifer polygons.

    The three files in Windows Explorer that make up the shapefile: aquifrp025.dbf, aquifrp025.shp, and aquifrp025.shx

  6. In ArcGIS Pro, on the Map tab, in the Layer group, click Add Data.

    Add Data button on the Map tab of the ribbon

    The Add Data window appears.

  7. Browse to and choose aquifrp025.shp. Click OK.

    A new layer is added to the Contents pane, but nothing appears to have been added to the map.

  8. In the Contents pane, right-click aquifrp025 and choose Zoom To Layer.

    You navigate to the full extent of the aquifrp025 layer.

  9. Zoom out until you can see the United States.

    The data is not drawing in the correct location. This problem is caused by an unknown or incorrectly defined coordinate system.

Define the coordinate system

Next, you'll find out the coordinate system of the aquifer layer. A coordinate system defines positions and measurement values of geographic features on a map. If the wrong coordinate system is defined for a layer, it can lead to that layer not being displayed correctly on the map, like your aquifer layer.

  1. In the Contents pane, double-click aquifrp025.

    The Layer Properties window appears.

  2. Click the Source tab and expand Spatial Reference.

    Spatial Reference defined as Unknown Coordinate System in the Layer Properties window

    This layer has an unknown coordinate system. Until the coordinate system is known, the map will not know where to draw the data. You'll search the layer's metadata for spatial reference information and use the Define Projection tool to assign it to the data.

  3. Click Cancel.
  4. Open aquifrp025.txt in any text editor.

    In the aquifrp025 folder, right click the text-file to open it with a text editor supported by your system.

  5. Using the text editor's Find tool, search for datum.

    The document has a section named Spatial_Reference_Information, which lists the Horizontal_Datum_Name as North American Datum of 1983. This coordinate system is also known as NAD 1983.

  6. In ArcGIS Pro, on the ribbon, click the Analysis tab. In the Geoprocessing group, click Tools.

    Tools button on Analysis tab of the ribbon

    The Geoprocessing pane appears.

  7. In the Geoprocessing pane, search for and open the Define Projection tool.
  8. For Input Dataset or Feature Class, choose aquifrp025.
  9. For Coordinate System, click the Select coordinate system button.

    Select coordinate system button next to the Coordinate System parameter

    The Coordinate System window appears. It contains a searchable list of coordinate systems.

  10. Search for NAD 1983.
  11. Expand Geographic coordinate system, North America, and USA and territories. Choose NAD 1983.

    NAD 1983 selected in the Coordinate System window

  12. Click OK.
  13. In the Geoprocessing pane, click Run.

    The coordinate system is defined and the aquifer polygon data appears on the map in the correct location.

    Map of principal aquifers in the United States


    The default symbology of the aquifer layer is random. Your symbology may differ from the example images.

Display the Ogallala Aquifer

Next, you'll filter this layer to show only the Ogallala Aquifer. You can filter the layer by creating a definition query. A definition query is an expression that you create using values and fields within a layer's data to filter the layer to show only specific features. For instance, if you wanted to display only the Ogallala Aquifer, you'd create a query that said AQ_NAME (the field for aquifer names) is equal to High Plains aquifer (another name for the Ogallala Aquifer).

  1. Double-click aquifrp025. In the Layer Properties window, click the Definition Query tab.
  2. Click New definition query.
  3. Use the drop-down menus to construct the clause Where AQ_NAME is equal to High Plains aquifer.

    Clause constructed in the definition query window

  4. Click Apply and click OK.

    Now, only the Ogallala Aquifer is displayed on the map.

    Map showing only the Ogallala Aquifer

    Next, you'll change the name of the layer to better reflect its content.

  5. In the Contents pane, click aquifrp025 to select it. Click the layer name a second time to make it editable and change the name to Ogallala Aquifer.

    You'll also change the layer's default symbology and make it transparent so that you can see the precipitation data under it.

  6. Under the Ogallala Aquifer layer name, right-click the color patch and choose Moorea Blue.

    Moorea Blue selected in the color picker window

  7. On the ribbon, click the Appearance tab. In the Effects group, change Layer Transparency to 50.0 %.

    Layer Transparency slider on the Appearance tab of the ribbon

    The layer symbology updates on the map.

    Map of the Ogallala Aquifer in the middle of the United States

Filter layers

The Ogallala Aquifer covers a significant portion of the United States. Irrigation from the aquifer has allowed this relatively arid region to become a highly productive agricultural area. But the livestock and grains raised in the high plains use aquifer water faster than it is replenished from rainfall. It does not contain many urban areas, but it does contain many farms. Next, you'll filter the Irrigation and Precipitation layers to show areas that irrigate a lot of land and receive little rain.

  1. In the Contents pane, double-click the Precipitation layer.
  2. If necessary, in the Layer Properties window, click the Definition Query tab.

    In the Precipitation layer, the GRIDCODE field refers to the mean annual precipitation in inches. You'll display areas that receive 20 or fewer inches of rain.

  3. Click New definition query and create a definition query that reads Where GRIDCODE is less than or equal to 20. Click Apply.

    GRIDCODE <= 20 set as the active definition query in the Layer Properties window

  4. Click OK.

    Map with only the yellow parts of the Precipitation layer, covering most of the western United States

    Most of the western half of the United States receives low amounts of rainfall, meaning aquifer recharge in these areas is slower. The eastern edge of this arid zone passes almost directly through the Ogallala Aquifer.

    Next, you'll filter the Irrigation layer to show areas with a large amount of irrigated land.

  5. Turn on the Irrigation layer and open its Layer Properties window.
  6. Apply a new definition query that reads Where Irrigated Land (Percent) is greater than or equal to 20. Click OK.

    Map with the Irrigation layer filtered to only counties with the highest irrigation rates

    Some of the most irrigated counties in the United States are located on the Ogallala Aquifer. Other irrigated areas include California's Central Valley, the Arkansas Delta, and the Mississippi Delta.

Find urban areas at risk of water scarcity

You've now collected your three spatial criteria: urban areas, arid areas, and highly irrigated areas. Next, you'll find the areas where all three criteria combine to pose the heaviest burden on the Ogallala Aquifer.

  1. In the Contents pane, click the UrbanAreas layer to select it.
  2. On the ribbon, click the Map tab. In the Selection group, click Select By Location.

    Select By Location button on the Map tab of the ribbon

    The Geoprocessing pane opens to the Select Layer By Location tool.

  3. In the tool, set the following parameters:
    • For Relationship, choose Within a distance geodesic.
    • For Selecting Features, choose Ogallala Aquifer.
    • For Search Distance, type 150 and choose Miles.

    Parameters for the Select Layer By Location tool

  4. Click Apply and click OK.

    A total of 407 features are selected on the map.

    Map with all urban areas within 150 miles of the Ogallala Aquifer selected

    Next, you'll narrow the selection to urban areas that are in areas with lots of irrigation and not a lot of rain.

  5. In the Select By Location window, change Relationship to Intersect.
  6. Change Selecting Features to Precipitation.
  7. Clear the Search Distance parameter.
  8. Change Selection type to Select subset from the current selection.

    Select Layer By Location tool with updated parameters

  9. Click Apply, then click OK.

    Now, only 141 features are selected on the map.

  10. In the Select By Location window, change Selecting Features to Irrigation and click Apply. and then OK.

    There are 16 urban areas selected. The largest is Lubbock, Texas.

    Final selected urban areas on the map

  11. In the Contents pane, right-click UrbanAreas, point to Selection, and choose Make Layer From Selected Features.

    The UrbanAreas selection layer is added to the Contents pane.

  12. Rename the new layer Urban Areas at Risk. Turn off UrbanAreas.
  13. On the Quick Access Toolbar, click Save.

    Save button on Quick Access Toolbar

    The project is saved.

The 16 selected urban areas are those which place a particularly high burden on the Ogallala Aquifer, but also those most at risk from aquifer depletion because they are particularly reliant on groundwater. Farmers in the high plains region are working to test and adapt new methods for reducing irrigation, but the rate of extraction is still higher than the rate of recharge. Much of the food consumed in the United States is grown with water from the Ogallala Aquifer, and running out of this resource will impact not only towns like Lubbock, but the entire country.

In this lesson, you downloaded aquifer data and defined its coordinate system. You filtered irrigation and precipitation data to arid lands and highly irrigated counties. Finally, you selected urban areas that intersected with these two factors over the Ogallala Aquifer.

There are more factors that impact recharge rates for aquifers. More porous or permeable soils allow a faster recharge. High winds cause rainwater to evaporate before it seeps into the ground. How could these models be incorporated into your analysis?

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