ArcGIS Online

Map in a minute: Map floods using ArcGIS Online and ArcGIS Living Atlas

At certain times of the year, the news can be dominated by images of massive flooding in coastal areas. In September 2020, Alabama and the Florida Panhandle were in the news as Hurricane Sally made landfall in Gulf Shores with high winds and torrential rains.

Hurricane Sally shortly after landfall as seen on radar
Source: National Weather Service (public domain)

Heavy rains and flooding often accompany hurricanes and other storm events. According to NOAA, flooding is the major threat for inland populations. Flash flooding can occur in the blink of an eye due to intense rainfall, often accumulating from some distance away. Flooding along rivers and streams can last for many days after a storm has passed.

 

Make a flood map

ArcGIS Living Atlas of the World includes authoritative live feeds and other content that helps you learn more about current and predicted flood conditions. Follow these steps to make your own flood map in a minute (or less) using Living Atlas content.

Step 1 — Sign in to your ArcGIS account and open Map Viewer. There are two ways to add layers from the Content (dark) toolbar:

(1) Click Add, then Browse layers.

Add>Browse layers

or (2) Click Layers, then Add layer.

Add layer

Step 2 — Choose Living Atlas from the Add layer drop-down.

Living Atlas search

Step 3 — Enter “flood” in search to locate matching layers from the Living Atlas. Scroll down to locate the Live Stream Gauges layer and click (+) to add it to the map. You can also enter “stream gauges” to narrow down the search results.

Add layer

Tip: To learn more about any layer, click the layer title to View item details.

View item details

From the Live Stream Gauges item overview we learn that the layer shows near real-time stream gauge readings compiled from a variety of sources. The layer is updated hourly. Once added to the map, the legend shows the current flood status.

Legend

To simplify the map and focus on stream gauges showing flood conditions, a filter can be applied.

Step 4 — Click Filter in the Settings (light) toolbar on the right. Note there is an existing expression that filters for gauges with recent updates.

Click Add expression.

Add expression

Step 5 — Construct a filter expression as follows:

a – Select Status as the attribute from the list.

b – Select includes as the operator from the dropdown list.

c – Choose the desired values from the dropdown list.

Expression

Step 6 — Click Done, then Save, when finished.

Save filter

The map shown below is the result of applying the following expression:

Status includes Minor Flood, Major Flood, Moderate Flood.

Stream gauges

Click a gauge to view its pop-up for more information.

Stream gauge pop-up

Step 7 — Return to search using “water forecast” and scroll down to locate the National Water Model (Hourly Forecast) layer. Click (+) to add it to the map.

Add from Living Atlas

From the National Water Model (Hourly Forecast) item details we learn that the layer presents a time-enabled model from the National Weather Service that forecasts streamflow volume and velocity for the entire United States. The model predicts the flow in every river reach of the National Hydrography Dataset.

Note that the layer is time enabled, so a time slider appears that you can use to explore the hourly forecasts.

Step 8 — Adjust the layer order to draw the gauges on top of the streams. In Layers, grab the Live Stream Gauges layer and  drag and drop it above the National Water Model layer.

Order layers

 

The flood map

In a minute or so, with just a few clicks, a map showing current flood conditions and hourly stream forecasts has been authored.

Flood map
View larger image

Since the National Water Model (Hourly Forecast) layer is time-enabled, a time slider appears at the bottom of the map. Using the time slider you can (a) play or pause the animation, (b) adjust the time slider interval, (c) step forwards or backwards in time intervals, or (d) open Time slider options to adjust time settings to set the playback speed, time span, and time display.

Time slider

Click a stream to identify it and view forecast flow and deviation from normal flow for the time period selected using the time slider.

National Water Model pop-up

Click a stream gauge to learn more about the current flow and status. Click More info in the pop-up to view details about the gauging station.

Stream gauge pop-up

 

Improve your map

Experiment with different basemaps to see which you like best. You can alter layer transparency and symbols to emphasize the content you want. Add other related layers from Living Atlas to add additional context.

The map shown below uses the following:

For more information, see Use effects.

Flood map
View larger image

 

More information

For more information, see the following:

 

This blog article was originally published on September 17, 2020, and has been updated.

About the author

Corporate technology evangelist and advocate at Esri, focusing on ways to broaden access to geographic information and helping customers succeed with the ArcGIS system. On a good day I'm making a map, on a great day I'm on one. Follow @bernszukalski or email bszukalski@esri.com

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