WRAL WeatherCenter Blog

A New Flood Alert Tool

Posted September 15, 2009

Screen capture from the USGS North Carolina Hydrologic Alert System site showing the interactive map used to select sites and view observations.

Some of you who live in low-lying or otherwise flood-prone locations may be interested in a new service offered up for free by the United States Geological Survey, which has implemented a beta test version of something they call the North Carolina Hydrologic Alert System (NC-HAS), which provides near real-time email or text message alert notifications when user-specified thresholds for water elevation or precipitation amount are met at USGS river and stream gage sites in North Carolina. NC-HAS is a customizable system from which you can receive email or text message notifications when the river stage or streamflow either exceeds or falls below your specified threshold at your site of choice. As you can see from the map in the image, there are lots of stations to choose from, using a zoomable map.

I found the interface to be nicely designed, as you can quickly make your way to a station near your location, and by clicking on it select that station to establish an alert, or just click the "readings" tab on the pop up bubble to see the current stage height and water flow. Of course, to choose a meaningful threshold for an alert, you need to have some idea of how the gage readings correspond to flooding impacts. For those of you near some of the more well-documented sites, there is a National Weather Service page that can help. It's called the Advanced Hydrologic Prediction Service (AHPS). At that site, you can click on a gage location of interest, and you will see a graph of recent water levels. By scrolling down the page, you can also see a list of "flood impacts" that give an idea as to what happens as water climbs to a series of threshold levels. For example, at Crabtree Creek when the water level reaches 14 feet, the lower parking lot at Crabtree Valley Mall is covered with water, while at 23 feet the Hwy 70 bridge floods and travel becomes severely hampered on Glenwood and around the mall.

For those of you interested in making use of this service, I've included links to both the NC-HAS site, and to the AHPS page for our area. Of course, resources like these seem especially valuable as we look back this week on the 10-year anniversary of the tremendous flooding that affected parts of our area during Hurricane Floyd in 1999. You can access a lot of recent and historical infomation on that storm by typing "Floyd" into the search box at the top of this page, and be sure to watch for the special "Focal Point: Floyd" documentary about the storm and its impacts this week on WRAL TV and WRAL.com.

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