Fire, Erosion, and Floods

Some folks say forest managers need to focus on thinning in and around communities to protect homes from wildfire. This article reminds us that wildfire effects an be much more widespead than the burned area itself, and shows why active forest management aimed at reducing fire severity may be appropriate in the backcountry.

“Concerns rise about flooding, debris flows in Lake Christine Fire burn scar”

“Local emergency managers are particularly concerned about flood and flow risks from the Lake Christine Fire burn scar.”

“Wildfires result in a loss of vegetation and leave the ground charred and unable to absorb water,” said a statement from a consortium of emergency management agencies in the Roaring Fork Valley. “This creates conditions for flooding. Even areas that are not traditionally flood-prone are at risk of flooding for up to several years after a wildfire.”

“The soils that experienced the greatest burn severity are shedding the water rather than absorbing it, Thompson said. Water was flowing off hillsides in sheets and eroding the road between the main parking lot and the Mill Creek Trailhead, he said.”

Here’s a Debris Flow Probability Map of the 12,500-acre Lake Christine Fire area and surrounding communities in Colorado.

5 thoughts on “Fire, Erosion, and Floods”

  1. What is interesting to me about this is that it is pretty much unassailable in Colorado and New Mexico that there are serious watershed impacts (and flooding) post-fire.
    Yet in California, Oregon, and Montana this does not seem as common. Perhaps different soils? Different amounts of slope? Or just social fingerprints of the historic timber wars? (fuel treatments = logging= bad)? It’s interesting to consider.

    • The timber wars have had a great and long-lasting influence, but that seems to be changing as the residents of rural towns see what has happened in Paradise, the Napa Valley, etc. If a fire burns in the Hetch Hetchy Valley and the reservoir that supplies San Francisco and other Bay Area cities is clogged with sediment, the urban public’s sentiment may change rapidly. Of course, the reservoir is in a national park, so forest management options are limited.

      The situation is a bit different in the coastal mountains of So. Calif., where severe mudslides often occur after intense wildfires, but the vegetative cover is different — lots of chaparral.

  2. Sharon – may I suggest John McPhee’s book Control of Nature, which includes a section on the fire/erosion/debris flow cycle in southern California. SoCal knows well that erosion/debris flows and dry ravel follow fires, and the LA County Dept. of Public Works is as on top of the situation as is possible – they really do have their act together. I worked with them on post-fire issues in 1993. We toured the string of debris basins along the western edge of the San Gabriels. They had dump trucks running 24 hours/day for two weeks after the first storm (about 0.5″) to empty some of the debris basins, which filled quickly after the first postfire storm. It was extremely fortunate that there was not another storm at that time. This cycle is relatively new to Colorado, which is catching up rapidly.

  3. “Some folks say forest managers need to focus on thinning in and around communities to protect homes from wildfire.” I’m one of those. “… active forest management aimed at reducing fire severity may be appropriate in the backcountry.” I also don’t disagree with that (emphasis on the “may”). I just think the Forest Service needs to keep its funding priorities straight – that remote infrastructure is less important than residences and lives.

    • Jon, I have no reason to believe that those aren’t FS priorities as well. However, folks like Denver Water have different priorities. It’s interesting that that idea (that the FS should take the $ it uses for watershed fuels projects in partnership with Denver Water and others, and use it for areas around communities) I don’t think has been raised in Colorado. We generally seem to think it’s a good idea to work together and to protect water supplies.


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