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Sonoma County Installs Flood Monitors After Wildfires

Flood risk can be high after wildfires, leading to a secondary disaster. Sonoma County, Calif., installed a flood monitoring solution after the wildfires of 2017 to keep the communities from experiencing dangerous flooding.

Unfortunately for communities that have faced devastating wildfires, the danger to life and property doesn’t end after the fires are extinguished.

Flood risk is high after a fire, and those communities need to be on alert to mitigate against flash flooding, as even modest rainfall can trigger floods with little warning.

That’s why Sonoma County, Calif., and other communities deployed AEM’s post-wildfire flood monitoring solution after the Nuns and Tubbs fires 2017. The solution involves deploying rainfall and flood gauges throughout the area to alert officials when rainfall totals reach a critical point or flooding reaches the point where officials need to respond.

Carlos Diaz, a hydrologist/engineer with the county, noted that after the Nuns and Tubbs wildfires, a response team was convened to identify secondary hazards. The team included members from the United States Geological Survey, Cal Fire and the National Weather Service, which noted the lack of good rainfall gauges in the area.

“We have one at the airport, but they were looking for more granularity in being able to issue their flood watches and warnings,” Diaz said. “One of their recommendations was a network of gauges to be installed with an early warning system.”

The task was made easier because of a neighbor in Napa County, the town of St. Helena, that already had a system and transmitter in place that Sonoma could connect to. “They had some bandwidth and they let us piggyback onto that system,” Diaz said.

Sonoma County installed 12 rain and stream gauges and 10 rain-only gauges across a “pretty sizable chunk of the county,” Diaz said.

He described the system as capturing and transmitting “incredibly small packets of data” that make their way to Sonoma County headquarters in near real time every couple of minutes. Although the alerts are done every two minutes, none of the gauges is transmitting at the same time.

“That was a problem we had with the old system,” Diaz said. “It’s pouring buckets and they’re all trying to send information at the same time, and you’d get data collisions and losses.”

The system allows the administrator to set thresholds for the amount of rainfall over time and the depth of flooding. “The National Weather Service has different thresholds for different rain events," Diaz explained.

Mark Miller, chief commercial officer for AEM, said the company has more than 6,500 hydrological sensors at various critical locations across the country that might be prone to flooding.

“Many of our cities will put up a map with all the water sensors on it out into the community so everybody who lives in the community has the information and can see where hazards might be,” Miller said.

“We help them with modeling. A big part of what we do is take sensing data in and overlay it with inundation maps to get you a clear picture of the area and more of an end-to-end solution.”


Jim McKay is the editor of Emergency Management magazine.