A storm is coming

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Water Resources at center of Arizona's elaborate flood-warning system
June 15, 2016

As Arizonans know, all those stories we tell the relatives and tourists about it being a dry heat is part truth, part myth.

Yes, the summer scorch annually enveloping us this time of year is typically dry. But not always.

The sweltering monsoon season – the time of year that gives lie to those claims about the allegedly tolerable summer temps in our desert regions -- is upon us.

And with it comes the rain – those often-sensational, often-intense, occasionally dangerous summer storms.

It is the season that gives lie to another myth: Those dry washes and riverbeds? They’re not always so dry.

Periodically in the coming months, Arizona’s washes will be awash with water. At times, they will run with astonishing volumes of water, the product of the region’s unpredictable, often scattered summer storms.

Thanks to a complex, multi-agency system including land-based monitors and gauges, as well as radar and satellite imagery, Arizona now has a far more sophisticated capacity for tracking rain levels and the flooding it can produce than it did just a couple of decades ago.

That system, known at the Arizona Flood Warning System, or AFWS, involves government agencies from the federal level, such as the National Weather Service, to county flood-control districts. Generally speaking, it is the mission of those local and federal emergency managers and floodplain administrators to get accurate data about rain and flooding into the public realm as fast as possible.

Jointly, their efforts are coordinated by the AFWS, a duty assigned by statute to the Arizona Department of Water Resources.

Most of the gauges measuring rain and flood-water levels in Arizona are owned and operated by county flood-control districts. Virtually all of the space-age moisture-measuring systems are functions of the feds. That includes satellite-based technology such as the famous Geostationary Operational Environmental Satellite – or GOES – system operated by the U.S. Geological Survey.

In between all those organizations is Arizona’s Water Resources department, mainly in the person of Brian Cosson, the ADWR Flood Warning Coordinator.

“After the 1993 floods, the governor had a task force looking at improving the (flood-warning) system,” said Cosson, who also works with the department’s dam-safety and flood-plain management programs.

“And that’s what happened. The infrastructure was expanded to include (signal) repeaters to send out data, mostly to the National Weather Service and to end-users like emergency managers.”

The ’93 Arizona floods constitute a flood-warning benchmark that captured the attention of citizens and state legislators alike. That was the year raging floodwaters cascading down the Salt River took out the Phoenix-Tempe bridge that was under construction at the time. The spectacular video shot of that event helped spur dramatic changes in how Arizona would monitor the powerful, often dangerous, force of nature that is flooding.

Until then, flood-warning systems were scattershot. Some counties invested substantially in systems of rain gauges and signal repeaters.

Others – mostly rural districts with scarce resources – could invest little to warn residents of impending floods. But it is just as important to Arizonans living on the southern border to know when the Nogales Wash is running fast as it was in 1993 for Tempe and Phoenix residents to know how much water was racing through the Salt.

That spotty system has changed dramatically. Since 1993, 750 rain-and-stream flow gauges have been installed in critical positions around the state. Over 60 signal repeaters, owned by a variety of agencies have been built to assure data gets where it needs to be.

“We are a small player in what’s called the Arizona Flood Warning System,” acknowledges Cosson. “But we help coordinate it all.

“We’re the only agency that is the repository of all that information.”


Listen to flood warning coordinator, Brian Cosson explain Arizona's flood-warning system