Tuesday, July 18, 2017

Water Wheel: Deadly Flash-Flood in Arizona (VIDEO)

At the Water Wheel swimming hole, about an hour-and-a-half north of Phoenix.

At the Arizona Republic, "The Payson flash flood: How did this happen?":

It happened in a flash.

A wall of black water mixed with fallen trees, ash and debris swept away 14 people Saturday, killing nine, at a swimming hole at Cold Springs near Payson.

The search for another person, Hector Miguel Garnica, continued with no success Monday and was to resume Tuesday.

Sgt. Dave Hornung of the Gila County Sheriff's Office said finding Garnica alive would be a "miracle."

As searchers and investigators worked through the day, questions persisted, beginning with, "How did this happen? And could it have been avoided?"

Officials said they are not sure exactly what led to the flood, but attention turned to an area upslope of the flood site, where a wildfire blackened 7,198 acres in June along the Highline Trail.

“We’re actually still trying to evaluate whether damage from Highline Fire contributed,” said Carrie Templin, a spokeswoman for Tonto National Forest.

After a wildfire

Wildfires leave scars. Some of the scars are obvious — blackened stumps, charred hillsides, fallen trees — but others remain hidden from view.

One such scar is the sudden inability of the forest to absorb rain and runoff.

A summer monsoon storm can trigger flash floods such as the one that swept through Ellison Creek on Saturday. Ordinarily, vegetation, both dead and alive, mitigates the effects of heavy rain. The forest floor, full of trees, brush, grass, roots and duff, absorbs water, so that it moves downhill slowly.

Wildfire strips away brush and branches. Trees can be reduced to ash. Not only does that raindrop flow downhill without interference, it picks up speed.

“After fires, there’s nothing to stop that raindrop," Youberg said. "There’s nothing to slow down that velocity.

“There’s nothing there that breaks the fall.”

The result can be what happened on Ellison Creek — a deadly wall of water filled with mud, ash, rocks and trees, the flotsam of nature swept downstream.

Flash floods can develop miles away and come with no warning — it’s possible to be hit by rushing water under clear skies. The wall of water that struck Saturday was said to have been 40 feet wide and 6 feet tall...

Also, "Arizona swimming hole flash flood: What we know now."