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Jul 17 2013

Ever Changing Landscape

Flooding and mudslides are starting to feel normal in the areas burned by last summers Colorado fires.  I have read in several places that this could be the norm for the next 10 years.  Manitou Springs was hit hard in early July, and Hwy 14 in the Poudre Canyon was closed recently on July 12 due to multiple mudslides blocking the road.

One of these mudslides was one of the larger one in the Poudre Canyon since the fire, and as I looked into the location I was surprised by how small the drainage was that produced this slide.

Here is a radar image of the storm that caused the mudslide.  The historical radar data only includes imagery at every hour so there is not an image of the main system directly over the drainage.  I am not sure of the rain totals but some sites stated rain rates of 1”-2” per hour.

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The rainfall in the area was enough to spike the river at the canyon mouth by about 300 cfs.

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Using the USGS 10m NED data I created an outline of the drainage area that contributed to this slide.  The drainage area is only 1.9 square miles.  It looks like more than 90% of the drainage was burned in the fire.

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All of that created this.  (click the image for more pictures from the Rock Report Blog)

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This is also the first mudslide due to the fire to significantly change a rapid on the Poudre.  This slide happened at a fun rapid known as Three Rocks or Three Way.  Currently there is no way through it, and when the wood gets cleared it appears there will be a new rapid along the left side of the former channel.

Here is a link to some more photos form the Coloradoan.

The big question that lingers is what happens when a much larger drainage area gets an intense rainfall event like this?

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