• Rocky Mountain Research Station
• 240 West Prospect
• Fort Collins, CO 80526
• (970) 498-1100

A New Approach to Estimating Soil Erosion and Mitigation Effectiveness Following Wildfire

To address this shortfall in information and tools, a series of major studies were initiated that were funded by numerous Joint Fire Science Program projects, the National Fire Plan, NFS regions, the WO NFS Fire and Aviation Staff, and the Rocky Mountain Research Station in collaboration with the USDA-ARS. The studies had two main emphases. The first was a field component measuring soil erosion rates following wildfire at plot, hillslope, and small watershed scales in forests and on rangelands. The second was to develop a management tool to incorporate variability into soil erosion prediction. A major finding from the field studies was that erosion mitigation treatments work for some, but not all rainstorms. One of the most widely used mitigation methods during the 1990s, cutting fire-killed trees and installing them on the contour of burned hillslopes, is moderately effective for smaller storms, but not for high intensity thunderstorms. Historically, broadcast seeding is the most common post-wildfire treatment with the expectation that immediate new growth will provide rapid vegetative cover on burned hillslopes. Since seeds generally do not germinate until the spring following the fire (and only then when enough moisture is available), the vegetative cover is rarely dense enough to effectively reduce erosion the first year after the fire when the greatest erosion is likely to occur. Appling straw mulch to provide 60 to 70 percent ground cover has been shown to afford significant erosion reduction. Other findings from studies following over a dozen wildfires emphasized the variability of fire severity across a burned hillslope (a mosaic of high and low burn severity as well as unburned patches), variability of fire effects on soil, and as always, the variability of weather.

The same time as these field studies were carried out, a new approach to predicting soil erosion and mitigation effectiveness was undertaken which would accommodate the variability in climate, soil and burn severity distribution. RMRS and ARS scientists and computer specialists developed an online interface to predict postfire erosion called the Erosion Risk Management Tool, or ERMiT. ERMiT not only incorporates variability into predicting erosion, but also allows users to estimate the effectiveness of seeding, of applying different amounts of mulch, and of installing logs on the contour from a single run. The erosion estimates are not average values, but rather are the values associated with a certain risk of occurrence. In other words, a manager may be concerned about a very sensitive watershed and want to predict how much erosion would likely be exceeded one year in ten. In a watershed with fewer resources at risk, the manager may be interested in predicting a lower erosion rate that is likely to be exceeded more often. These risk-based predictions are more realistic postfire erosion evaluations than were the average values generated by other erosion models.

Risk-based soil erosion modeling is on the cutting edge of erosion prediction, and has been quickly embraced by public land managers. Over 200 public and private specialists have been trained to apply the ERMiT technology in workshops sponsored by the Forest Service and the Bureau of Land Management. Thus far in 2006, the ERMiT model has been run over 1600 times. In the first three weeks of August alone users from 9 different states on at least 20 fires used ERMiT to support over 150 wildfire impact analyses.

Reference

Web Site