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If you haven't had a chance to look at the flood summary page, please do
when you get a chance:
http://bcn.boulder.co.us/basin/forum/flood.html
We've just added a photo of the debris flow that came down Black Tiger
Gulch after the fire in 1989 and also links to some websites about
debris flows. Because wildfires can coat soils with oil from the
vegetation that make the soil hydrophobic, runoff and erosion following
a wildfire can trigger flashflooding and/or debris flows.
At a recent Watershed Forum, Deborah Martin of the USGS gave a talk on
flooding after the Buffalo Creek fire, and mentioned that their research
indicates that there are roughly 100 year cycles of fires and flooding
going back many centuries in the Buffalo Creek area, which has similar
terrain and vegetation to the foothills west of Boulder. (I've heard the
1894 flood down Boulder Creek-- the so-called 100 year flood, was mainly
caused by water coming down Four Mile Canyon, which had been largely
deforested by fires in prior years.)
Obviously many of the canyons along the front range are ripe for flash
floods even without fires. (Check out some of the historical accounts of
floods compiled by Elizabeth Black through the BASIN flood page).
Boulder Creek and tributaries like Goose Creek, Four Mile Canyon Creek
and South Boulder Creek are all major flood hazard areas with studies or
mitigation efforts currently going on.
Mark McCaffrey
See http://basin.org/forum/fire-flood.html for more information on this list.