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Probabilistic soil erosion modeling using the Erosion Risk Management Tool (ERMiT) after wildfires.
Robichaud, P.R.; Elliot, W.J.; Wagenbrenner, J.W. 2011.
Probabilistic soil erosion modeling using the Erosion Risk Management Tool (ERMiT) after wildfires.
ISELE Paper Number 11039.
International Symposium on Erosion and Landscape Evolution.
18-21 September 2011, Anchorage, Alaska.
ASABE Publication Number 711P0311cd. 9 p.
Keywords: ERMiT, Wildfire, Erosion, WEPP, Postfire, Validation
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Abstract:
The decision of whether or not to apply post-fire hillslope erosion mitigation treatments, and if so,
where these treatments are most needed, is a multi-step process. Land managers must assess the risk of
damaging runoff and sediment delivery events occurring on the unrecovered burned hillslope. We
developed the Erosion Risk Management Tool (ERMiT) to address this need. ERMiT is a web-based
application that uses the Water Erosion Prediction Project (WEPP) technology to estimate sediment
delivery, in probabilistic terms, on burned and recovering forest, range, and chaparral lands with and
without the application of mitigation treatments. User inputs are processed by ERMiT to combine rain
event variability with spatial and temporal variability of soil burn severity and soil properties, which
are then used as WEPP input parameter values. Based on 20 to 40 individual WEPP runs, ERMiT
produces a distribution of single sediment delivery rates with a probability of occurrence for each of
five postfire years. In addition, sediment delivery rate distributions are generated for postfire hillslopes
that have been treated with seeding, straw mulch, and erosion barriers such as contour-felled logs or
straw wattles. Using postfire sediment data from 21 small instrumented watersheds (< 14 ha), we
compared each storm.s measured sediment delivery to the ERMiT-predicted delivery. Observed
delivery rates were within the predicted range of values 77 percent of the time, with 14 percent of the
observed values being greater than the estimated range, and 9 percent being less than the predicted
range. Most of the under predictions were associated with studies in the Colorado Front Range. The
ERMiT tool tended to over predict sediment delivery in the Northern Rockies and in California. Only 3
percent of the observed delivery events were associated with snow melt processes, whereas 36 percent
of the predicted values were influenced by snow melt. Based on these results, we are considering
improvements such as incorporating erodibility values for more forest soil types, adjusting the weather
characteristics in the climate generator, and reducing the occurrence of snow melt erosion response.
Postfire assessment teams are actively using the ERMiT model for making hillslope mitigation
treatment decisions based on the probability of damaging sediment delivery occurring after a wildfire.
Moscow FSL publication no. 2011h
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