Waldo Canyon flooding, and last week's near-miss 

One of the biggest factors in flooding is how fast rain falls on vulnerable terrain

Last Thursday's storm looked like the big one.

In Manitou Springs, site of mass destruction during a flood two weeks before, police blocked roadways. A siren wailed. Fountain Creek rose with muddy water.

But thankfully the Aug. 22 storm turned out to be anticlimactic.

The next morning, the creek was high, but everything was pretty much back to normal. In fact, Independent handyman George Davis, who lives in the mouth of Williams Canyon and saw his garden wall and cars float away Aug. 9, says Williams creek only had "a little water" during the worst part of the storm.

But here's what's weird: The Aug. 9 storm was largely limited to Williams and Waldo Canyon watersheds within the Waldo Canyon Fire burn scar. By comparison, National Oceanic and Atmospheric Administration Warning Coordination Meteorologist Tom Magnuson estimates that the Aug. 22 storm covered most of the burn scar. And upstream from there, the Woodland Park area saw 2 to 4 inches of rain.

So why didn't Manitou flood last week? There were two keys, according to Magnuson.

First, the inch of rain on the burn scar took about two hours to fall, giving that water a chance to soak into the ground. On Aug. 9, that much rain fell in just 15 minutes in Williams and Waldo.

Second, the huge amount of water coming down from Woodland Park didn't just shoot quickly through Fountain Creek, as some feared would happen; the creek, with all its twists and turns, did manage to slow it somewhat.

A major lesson to take from this: One of the biggest factors in flooding is how fast rain falls on vulnerable terrain. And the Aug. 9 storm was much more severe in that regard, with rain quickly pounding the ash-covered ground.

In fact, Magnuson now estimates that small swaths of that earlier storm were so severe that they could be considered a 25-year event. It was just lucky that only a small portion of the burn scar bore the brunt of it.

"If it would have hit Sand Gulch and Wellington Gulch, and a couple gulches up from Cascade," he says, "it would have been much worse."

— J. Adrian Stanley

When the mud returns ...


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