Explore a watershed

In September 2014, a sheriff's deputy in Travis County, Texas, was driving down a small country road during a heavy rainstorm. As she reached a low water crossing at the bottom of a valley, a flooded stream washed her patrol car away, and she lost her life. A better understanding of the surrounding watershed and its hydrology may help prevent similar tragedies in the future.

In this tutorial, you'll perform a basic exploratory analysis of the Bear Creek Watershed, where the incident occurred. In ArcGIS Online, you'll create a feature representing the watershed. Then, you'll add the watershed to a 3D scene along with data about the surrounding terrain. You'll locate the low water crossing where the deputy's car was washed away and create an elevation profile to better understand its changes in elevation. Your exploration will lead to insights that can support future planning and emergency response efforts.

This tutorial was last tested on January 26, 2026.

Requirements

• ArcGIS organizational account with a Publisher, Facilitator, or Administrator role (see options for software access)

Delineate the watershed

First, you'll create a map in Map Viewer and determine the boundaries of the Bear Creek Watershed using an analysis tool. The watershed will represent the area that drains into Bear Creek. Understanding the watershed is important for determining the volume of water flowing into the creek, which can be used to predict where flooding will occur during a storm.

Navigate to the area of interest

You'll start by creating a web map and navigating to the location where the sheriff's deputy's car was washed off the road.

1. Sign in to your ArcGIS organizational account.

   Note:

   If you don't have an organizational account, see options for software access.

2. On the ribbon, click Map.

   

   A new web map opens in Map Viewer. Next, you'll search for and navigate to the area of interest.

3. Click the Search button.

   

4. In the Search window, type Fritz Hughes Park Rd and choose Fritz Hughes Park Rd, Austin, TX, 78732, USA.

   

   The map navigates to Fritz Hughes Park Road in Austin, Texas, near the Colorado River. This road is where the incident occurred, although it did not occur at the exact point indicated on the map.

5. Close the Search result window.
6. On the map, use the scroll wheel on your mouse or the Zoom out button to zoom out until you see Bear Creek north of the road.

   

   Bear Creek is a small tributary of the Colorado River. Fritz Hughes Park Road crosses over it.

7. Zoom out until you can see the lake north of Bear Creek.

   

   This lake is Lake Travis, a reservoir formed by the Mansfield Dam on the Colorado River, just north of Bear Creek.

Create a watershed

Now that you're familiar with the area around Bear Creek, you'll run an analysis tool to identify the watershed that drains into the creek.

1. On the Settings (light) toolbar, click Analysis.

   

   Note:

   The toolbars can be expanded or collapsed. The example images show the expanded toolbars.

2. In the Analysis pane, click Tools.

   

3. In the search bar, type Watershed. In the list of results, click the Create Watersheds tool.

   

   This tool uses worldwide elevation data in ArcGIS Online to determine the watershed area for a specific point. The point used is called a pour point. You don't have a point feature on the map to use as the input layer, so instead you'll sketch a pour point.

   To determine the watershed for a creek, the pour point you use should be the creek's outlet. The outlet is the location where a river, stream, or creek flows into a larger body of water. In this case, the outlet is where Bear Creek flows into the Colorado River.

4. For Input point features, click the Draw input features button.

   

   A sketch layer, Create Watersheds Input Point Features Sketch, is created. By clicking the map, you can add a point to the sketch layer.

5. On the map, click the location where Bear Creek meets the Colorado River.

   Tip:

   The location you click doesn't need to be exact. If necessary, you can zoom in using the mouse scroll wheel.

   

   Note:

   If you accidentally add a point to the wrong location, you can delete it. On the sketch toolbar, click the Select button. On the map, click the point you want to delete to select it. On your keyboard, press the Delete key. You can add another point by clicking the Stamp button on the sketch toolbar.

   The pour point is added to the map. Since you sketched the point, it might be slightly displaced from the creek. You'll add a search distance to find the location of highest flow accumulation (in other words, the creek) near the point.

6. For Pour point settings, for Search distance, type 10. Ensure that Distance units is set to Meters.

   

   A search distance of 10 meters is enough if your pour point seems to be touching Bear Creek on the map. If your pour point is farther off, you may need a larger search distance, or alternatively you may want to sketch a new point.

7. For Output polygon name, type Bear Creek Watershed. Add your name or initials to the end to ensure that your layer name is unique.

   

8. At the bottom of the pane, click Run.

   The tool runs. While it runs, you can check its status by clicking the History button at the top of the pane. The tool may take over a minute to run.

   After the tool finishes, a polygon representing the watershed is added to the map.

   

   Note:

   If your result layer looks significantly different than the example image, you may have placed the pour point incorrectly. Remove the sketch layer from the Input point features tool parameter and sketch a new pour point.

   Water flowing in the area represented by the polygon will flow toward the pour point. During a storm, lots of water may flow at once toward the pour point, causing flooding or dangerous conditions.

9. In the Layers pane, for the Bear Creek Watershed layer, click the Expand button.

   

   The layer is actually a group layer with two sublayers. The WatershedFeatures layer contains the watershed polygon, while the Adjusted Points feature contains the pour point snapped to the location of highest flow accumulation in the search distance you specified.

   The Bear Creek Watershed layer doesn't only exist on this map. When you ran the analysis tool, it was saved to your ArcGIS account. This means that you can add the layer to other maps without needing to create it again.

Style the watershed layer

Before you continue, you'll change the watershed polygon's style to remove the blue fill, so only the outline is shown. This way, you can better view terrain or other features inside the watershed area.

1. In the Layers pane, click the WatershedFeatures sublayer to select it.

   Note:

   Selected layers are highlighted, with a blue bar next to their name.

   

2. On the Settings toolbar, click Styles.

   

3. In the Styles pane, for Types (unique symbols), click Style options.

   

4. Click the Symbol style button.

   

5. In the Symbol style window, for Fill transparency, type 100 percent.

   

6. Close the Symbol style window. In the Style options pane, click Done.

   Now, the watershed is only an outline.

   

   You'll save the layer so this style becomes the default style, meaning it will have this style whenever the layer is added to a new map.

7. In the Layers pane, for WatershedFeatures, click the Options button and choose Save.

   

   The layer is saved.

Add stream data

Knowing the extent of the watershed helps you understand where water flows from, but how much water will flow into the creek during a storm? To answer that, you'll add stream data from the National Water Model (NWM), created by the National Oceanic and Atmospheric Administration (NOAA). This data not only maps streams across the United States but also provides maximum flow forecasts for particular risk levels, indicating how much water might flow through the creek.

The data is hosted with the National Weather Service's reference services. To add it, you'll use the URL to the service.

1. On the Contents (dark) toolbar, click Add.

   

2. Choose Add layer from URL.
3. In the Add Layer window, for URL, copy and paste the following URL:

   https://maps.water.noaa.gov/server/rest/services/reference/static_nwm_flowlines/FeatureServer

4. Confirm that Type is set to ArcGIS Server web service.
5. Click Add to map.

   The Static nwm flowlines layer is added to the map and the Layers pane. This layer contains flowlines (rivers, streams, creeks, and any other flowing water body) throughout the United States.

6. On the map, click the Bear Creek flowline.

   Note:

   The Bear Creek flowline is a thin gray line and may be difficult to see. The example image highlights its location.

   

   The flowline's pop-up appears with more information about Bear Creek.

   

   The pop-up includes five Streamflow rows. These rows provide the amount of water flowing through the stream (in cubic feet per second, or cfs) at particular risk levels, represented by percentages. For instance, 50% Streamflow is the annual maximum discharge whose chance of occurring at least once in any year is 50 percent. Similarly, 2% Streamflow is the annual maximum discharge whose chance of occurring at least once in any year is 2 percent, or during the most extreme storms.

   It takes about 100 cfs to have water overflowing the road at this location, and a flow of 1913 cfs produces an overflow several feet deep on the road, more than sufficient to wash away a vehicle. Developing a forecasting system for this road overflow using the National Water Model can provide warning of these overflow events before a vehicle reaches the low water crossing. This is especially critical when floods occur at night, making it hard to see the water on the road.

7. Close the pop-up.
8. On the Contents toolbar, click Save and open and choose Save as.

   

9. In the Save Map window, for Title, type Bear Creek Watershed. For Summary, type A map showing the Bear Creek Watershed and National Water Model flowlines.
10. Click Save.

So far, you've explored the area of interest and delineated the Bear Creek Watershed as a polygon feature. To learn more about the watershed and why dangerous flooding sometimes occurs here, you'll examine the area in more detail.

View the watershed in 3D

You created your watershed polygon in Map Viewer, which displays data in 2D. But one of the most important parts of hydrology is understanding terrain, especially elevation. To better understand the Bear Creek Watershed, you'll add your watershed polygon to a 3D scene in Scene Viewer, where you'll be able to see vertical changes in the landscape.

In your scene, you'll contextualize the watershed with data about streams, low water crossings, slope, and elevation. Then, you'll create an elevation profile at the low water crossing where the sheriff's deputy's car was washed off the road, allowing you to see the dramatic changes in elevation that made the flooding there so severe.

Create a scene

First, you'll create a scene and add your watershed polygon to it.

1. On the ribbon, next to Untitled map, click the options button.

   

2. Click Scene.
3. If you receive a message asking you to confirm to leave the site, as your changes are not saved, click Leave.

   A new scene opens in Scene Viewer.

4. If a Scene Viewer window appears showing a gallery of featured scenes, close the gallery.

   Next, you'll add your watershed layer to the scene.

5. On the Designer (dark) toolbar, click Add layers.

   Tip:

   Like the toolbars in Map Viewer, the Designer toolbar can be expanded or collapsed by clicking the button at the bottom of the toolbar. The example images show the expanded toolbar.

   

6. Choose Browse layers.

   The Browse layers pane appears, showing layers saved in your account (My content).

7. For your Bear Creek Watershed layer, click Add.

   

   The watershed layer is added to the scene. The scene navigates to the extent of the layer.

8. If necessary, on the scene, use the scroll wheel or the Zoom out button to zoom out until you can see the entire layer.

   

Add contextual data

To better understand the terrain of the watershed, you'll add contextual data from ArcGIS Living Atlas of the World, a curated collection of geographic information.

1. In the Browse layers pane, click My content and choose Living Atlas.

   

   Now, you can add data from ArcGIS Living Atlas.

2. In the Browse layers pane, search for terrain elevation hillshade. In the list of results, for Terrain - Elevation Tinted Hillshade, click Add.

   Note:

   This layer is subscriber content, meaning it can only be viewed by users with an organizational account. If you're using a public account, you won't be able to view the content.

   

   The layer is added to the scene. Before you look at it more closely, you'll also add the slope layer.

3. Clear the search text and search for slope. For Terrain - Slope Map, click Add.

   Note:

   Like the elevation layer, this layer is subscriber content and can only be viewed if you are signed in to an organizational account.

   

4. At the bottom of the Browse layers pane, click Done.

   The Layer Manager pane appears, listing the layers in the map. The terrain layers were added on top of the watershed layer, meaning the watershed is hidden under them. You'll rearrange the layers so you can see the watershed.

5. In the Layer Manager pane, for the Bear Creek Watershed layer, drag the Reposition button above the Terrain - Slope Map layer.

   

   Now, the watershed is displayed on top of the other layers. First, you'll explore the elevation layer, so you'll hide the slope layer.

6. For Terrain - Slope Map, click the Hide button.

   

   The layer is turned off, hiding it on the map. Now, only the watershed and the elevation layer are visible. The elevation layer uses a tinted hillshade effect, which simulates sunlight hitting the layer to depict realistic light and shadow. This effect emphasizes changes in elevation.

7. On the scene, tilt, pan, and zoom to explore how elevation changes throughout the watershed.

   Tip:

   To learn more about the navigation tools available to you, see the Navigate scenes topic.

   

   The elevation layer emphasizes the drainage pattern throughout the watershed, which converges on Bear Creek, the central stream. Even without a layer showing the location of the stream, it's possible to tell where it is because of the deep, narrow trench that winds through the watershed.

   Water flows from high places to low places. During a rainstorm, large amounts of water will flow from all over the watershed into this narrow trench, especially close to the outlet.

8. In the Layer Manager pane, for the Terrain - Slope Map layer, click the Show button to show the layer again.

   The slope layer uses darker colors to show areas where slope is higher (meaning changes in elevation are more dramatic).

   

   The ridges on the sides of Bear Creek are particularly steep. During a storm, water will pour down them rapidly, increasing the chances for deadly floods.

Add low water crossings

You now understand the extent of the Bear Creek Watershed and the changes in elevation within it. Next, you'll look at low water crossings, in particular the crossing where the sheriff deputy's car was swept off the road during a flood. By comparing the low water crossing to the elevation, you'll get a better idea of why the crossing was so dangerous.

The layer of low water crossings you'll use was created by the University of Texas at Austin. You'll search for it among layers hosted on ArcGIS Online.

1. On the Designer toolbar, click Add layers and choose Browse layers.
2. In the Browse layers pane, click My content and choose ArcGIS Online.
3. In the search box, type Low Water Crossings owner:Esri_Tutorials.

   Note:

   The text owner:Esri_Tutorials specifies the owner of the layer.

4. In the list of search results, for Low Water Crossings, click Add.

   

   The layer is added to the scene. The low water crossings are represented by red square symbols.

5. At the bottom of the Browse layers pane, click Done.
6. On the scene, pan, zoom, and tilt until you find the low water crossing upstream of the Bear Creek outlet.

   

   The crossing is at the downstream end of the watershed, not far from the outlet. This area is where most of the runoff will quickly accumulate during a storm event.

   The low water crossing features have additional attribute data, including attached photographs taken of them from the ground. You'll view this data by opening the crossing's pop-up.

7. On the scene, click the low water crossing feature.

   Its pop-up appears.

   

   The pop-up title confirms that this crossing is on Fritz Hughes Park Road. This is where the sheriff's deputy's car was swept off the road by flooding.

8. In the pop-up, click the first photograph.

   A new tab appears, showing the photograph at a larger size. From the photograph, the crossing appears to have three pipes, or culverts, running under it to allow water to pass. During a flood, these culverts might not be sufficient to let all the water through, causing water to build up on the other side until it sweeps over the top of the crossing.

9. Close the tab with the photograph. Scroll through the pop-up and explore the other photographs.
10. When finished with the photographs, scroll to the bottom of the pop-up.

    The bottom of the pop-up contains more information about the low water crossing, including its crossing type, the material it's made of, the number of barrels or pipes allowing water to pass through the culvert, the type of road surface, and more.

    

11. When finished, close the pop-up.

Create an elevation profile

To better understand the elevation at the low water crossing, you'll create an elevation profile. An elevation profile shows the elevation along a line as a graph. You can create an elevation profile by drawing a line across an area of interest.

1. If necessary, zoom in close to the low water crossing.

   

2. On the toolbar, click the Scene tools button.

   

   A window appears with tools you can use to learn more about the scene, such as measuring tools.

3. In the window, click the Elevation Profile button.

   

   The pointer changes. Now, when you click the map, you'll add the vertices of a line to draw an elevation profile.

4. On the scene, click the riverbed upstream of the low water crossing.

   

5. Click points along the creek to create a line. Ensure that your line passes the low water crossing and includes a few points downstream of it.
6. When finished, double-click to add the final point and complete the line.

   

   The elevation profile shows a graph of how the elevation changes along the line you drew.

   Note:

   Depending on the length and position of your line, your elevation profile may look slightly different than the example image. Depending on your organization's settings, your elevation profile may use a different unit of measurement than feet.

   

7. Point to the elevation profile graph to see the elevation at various points along it.

   The large spike in the center of this profile is the road itself. As soon as a vehicle is washed off the road, it drops about 6 feet onto the stream bed below. This drop, in combination with the roughness of the rocky stream bed and the force of the rushing water, makes the vehicle uncontrollable from that point onward.

   From the elevation profile, the story of how flooding might make this crossing particularly dangerous is complete. During a storm, water will rapidly collect in the stream, flowing toward the outlet. The culvert under the crossing might become quickly overwhelmed, causing water to back up behind the crossing. Because the creek is nearly as high as the crossing only about 100 feet (30 meters) back, the water is only backed up for a short period before it sweeps over the crossing, pushing anything on top down a dangerous 6-foot drop into the creek.

8. Close the elevation profile.

   You now have a better understanding of the Bear Creek Watershed. You'll save your scene so you can access it later.

9. On the Designer toolbar, click Save.

   

10. In the Save scene window, for Title, type Bear Creek Elevation. For Summary, type A scene showing the terrain and low water crossings in the Bear Creek Watershed.
11. Click Save.

In this tutorial, you explored a watershed to better understand the circumstances that led to a deadly flooding incident. First, you created a web map in Map Viewer and ran an analysis tool to delineate the Bear Creek Watershed. Then, you added the watershed polygon to a 3D scene in Scene Viewer and contextualized it with information about the terrain and the location of low water crossings. Lastly, you created an elevation profile at the crossing where the incident occurred.

Your exploration helped you understand how water flows throughout the watershed into a narrow stream. The crossing where the incident occurred is close to the outlet, where water will collect in the greatest quantities. The crossing itself has a small culvert that may not be enough to handle such flooding, causing water to back up and eventually sweep over the crossing.

How could an incident like this be prevented in the future? It's possible that installing larger culverts that can handle more water would help. The safest option, however, would be to send warnings during a storm so drivers know to avoid the crossing. The insights from your exploration provide a foundation for advanced analysis, including hydrologic modeling, to support informed decision-making during emergencies and assist with design and planning.

You can find more tutorials in the tutorial gallery.

Acknowledgements

• The Static nwm flowlines service was created by the National Oceanic and Atmospheric Administration (NOAA).
• The Terrain - Elevation Tinted Hillshade and Terrain - Slope Map layers were created by Esri using data from Airbus, USGS, NGA, NASA, CGIAR, NLS, OS, NMA, Geodatastyrelsen, GSA, GSI, and the GIS User Community.
• The Low Water Crossings dataset is used with the permission of Professor David R. Maidment of the University of Texas at Austin.
• Topographic map sources: Esri, TomTom, Garmin, FAO, NOAA, USGS, OpenStreetMap contributors, and the GIS User Community