Monday, July 25, 2011

Fire and water - floods, muds, and flows

The monsoon rains coming on top of the worst wildfire season in Arizona's modern history are producing floods, mudslides, and debris flows. [right, Horseshoe 2 fire. Credit,]

A flash flood and possible mudslide took out the main water line for the town of Tombstone, which for more than 100 years carried water by gravity feed from Miller Canyon in the Huachuca's, an area severely impacted by the Monument fire. [note: I initially mistakenly said it is in the Chiricahu's]

A home in nearby Hereford was also hit with flooding and reported mudslide, but Phil Pearthree, Chief of the AZGS Environmental Geology Section which handles natural hazards, cautions that the first floods after fires are notoriously full of ash, and people generally have no idea how much suspended sediment is carried by floods in our region.

The AZ Dept. of Transportation reopened a section of highway 191, one of the few paved roads in the White Mountains, after it had been closed for a week due to a likely debris flow.

Residents in the Wallow fire area are preparing for floods, mudslides, and debris flows as well. The good news is the National Weather Service has worked pretty hard to incorporate the greatly increased possibility of mass movements in the post-fire regime into their flood warnings.

Phil noted that these stories and others really illustrate the fact that there is very little time to develop any mitigation measures between fire and the onset of the monsoon. So, counties and cities, let's try to plan ahead and anticipate areas that may be affected by fires and flooding in the coming years. Some of them seem to be getting that message now. Coconino County has confronted that reality since last year's Schultz fire and subsequent flooding and rising concerns over debris flows.

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