Dr. David Rosgen of Wildland Hydrology presented a regional study yesterday, looking at how water, sediment, and debris is predicted to flow along the Waldo Canyon burn scar. It’s called a Watershed Assessment of River Stability and Sediment Supply, or WARSSS. During the presentation, Rosgen said it’ll take the better part of a century for the landscape to return to normal levels.

“The increase in flow is going to last decades, maybe 70-80 years before we get back to pre-fire conditions, because of the …nature of the soils, the precipitation whithin this area, it’s hard to get the site back in terms of mature conifer tree cover. The point is, is the increase in flow is going to be with us. It’s not going to change a lot. The flood peaks [are] a reality for the future. We can do the most by seeing how well the stream channels and the land system can accommodate the increase in flow.”

The WARSSS study identified Camp Creek, Douglas Creek, Fountain Creek and West Monument Creek as the major watersheds impacted by the changed landscape. The study also looked at nearly 90 high-risk sub watersheds, where Colorado Springs officials say $7.2 million in federal Emergency Watershed Protection funds will help mitigation efforts on private property lands.


In today’s Gazette, Bill Vogrin examines the use of sandbags to help minimize flooding damage, and how they’re most effective when used at a neighborhood level.

 

One Response to Flooding: Yes, it Does Matter How you Arrange Those Sandbags

  1. Mark Kissinger says:

    I agree that it is hard to get back to the pre-fire conditions. Realizing this, we need to work with how gravity and the nature of rainfall works, to encourage the succession of native vegetation to repopulate the disturbed fire damaged areas as quickly as possible. The succession of plant species will eventually result in the mature conifer we saw, pre-fire. However, to get there, we must encourage the growth of intermediate native species to take over the flood mitigation duties once performed by the conifer forest ecosystem.

    Rather than using sandbags to funnel water, they should be used along the contour lines of the slope in a series of swales to slow the flow of the water in the first place. Instead of using piles of unsightly sandbags alone to funnel the precipitation, a series of swales, constructed using a combination of cut-in swales and berms heaped over on-site logs, brush and vegetation materials will slow the flow of water, holding it on the slope and making the moisture available for a succession of native plant species to take hold. Consulting experts in native vegetation should provide suggestions for the seeding and planting of the native species most likely to accomplish the flood mitigation goals of the project. Any overflow from each swale should be directed to another series of sales lower on the slope, so that the system effectively slows the water flows to non-destructive levels.

    Many of these species may be considered to be weeds in the urban environment, but they actually are “pioneer species” that specialize in growing in disturbed soil, providing water absorption and soil-holding services until the slower growing trees can become established.

    The idea is to slow the increase in flow, causing the water to be absorbed into the soil, rather than accommodating increases in flow with expensive and ineffective channelization. A well designed system of swales will keep the overflows to a minimum, which can then be accommodated by the established stream beds.

    Some may fear that this system will be too expensive. However, using materials in-situ and coordinating the efforts over an entire watershed, the costs of this method need not be prohibitive. It does require a coordinated planning and design effort up front, but the results will be a showcase for urban fire recovery that will quickly become both visually pleasing and functional. The best part is that natural processes will be doing most of the work. All it takes is a bit of human resolve to direct the mitigation efforts most effectively.

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