Abstract:Post-fire rehabilitation treatments are commonly implemented after high-severity wildfires, but few data are available about the efficacy of these treatments. This study assessed post-fire erosion rates and the effectiveness of seeding, straw mulching, and contour felling in reducing erosion after a June 2000 wildfire northwest of Loveland, Colorado. Site characteristics and sediment yields were measured on 12 burned and untreated control plots and 22 burned and treated plots from 2000 to 2003. The size of the hillslope plots ranged from 0Ð015 to 0Ð86 ha.Sediment yields varied significantly by treatment and were most closely correlated with the amount of ground cover. On the control plots the mean sediment yield declined from 6-10 Mg ha 1 in the first two years after burning to 1Ð2 Mg ha 1 in 2002 and 0Ð7 Mg ha 1 in 2003. Natural regrowth caused the amount of ground cover on the control plots to increase progressively from 33% in fall 2000 to 88% in fall 2003. Seeding had no effect on either the amount of ground cover or sediment yields. Mulching reduced sediment yields by at least 95% relative to the control plots in 2001, 2002, and 2003, and the lower sediment yields are attributed to an immediate increase in the amount of ground cover in the mulched plots. The contour-felling treatments varied considerably in the quality of installation, and sediment storage capacities ranged from 7 to 32 m 3 ha 1 . The initial contour-felling treatment did not reduce sediment yields when subjected to a very large storm event, but sediment yields were significantly reduced by a contour-felling treatment installed after this large storm. The results indicate that contour felling may be able to store much of the sediment generated in an average year, but will not reduce sediment yields from larger storms.

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Post‐fire sediment yields can be up to three orders of magnitude greater than sediment yields in unburned forests. Much of the research on post‐fire erosion rates has been at small scales (100 m2 or less), and post‐fire sediment delivery rates across spatial scales have not been quantified in detail. We developed relationships for post‐fire bedload sediment delivery rates for spatial scales up to 117 ha using sediment yield data from six published studies and two recently established study sites. Sediment yields and sediment delivery ratios (SDRs; sediment delivered at the catchment scale divided by the sediment delivered from a plot nested within the catchment) were related to site factors including rainfall characteristics, area, length, and ground cover. Unit‐area sediment yields significantly decreased with increasing area in five of the six sites. The annual SDRs ranged from 0.0089 to 1.15 and these were more closely related to the ratio of the plot lengths than the ratio of plot areas. The developed statistical relationships will help quantify post‐fire sediment delivery rates across spatial scales in the interior western United States and develop process‐based scaling relationships. Published in 2013. This article is a U.S. Government work and is in the public domain in the USA.

[1] Rill erosion can be a large portion of the total erosion in disturbed forests, but measurements of the runoff and erosion at the rill scale are uncommon. Simulated rill erosion experiments were conducted in two forested areas in the northwestern United States on slopes ranging from 18 to 79%. We compared runoff rates, runoff velocities, and sediment flux rates from natural (undisturbed) forests and in forests either burned at low soil burn severity (10 months or 2 weeks post-fire), high soil burn severity, or subject to skidding of felled logs. The runoff rates and velocities in the natural sites (2.7 L min −1 and 0.016 m s −1 , respectively) were lower than those in all the disturbed sites (12 to 21 L min −1 and 0.19 to 0.31 m s −1 , respectively), except for the 10-month old low soil burn severity site where the velocity (0.073 m s −1 ) was indistinguishable from the natural sites. The mean sediment flux rate in the natural sites also was very small (1.3 × 10 −5 kg s −1 ) as compared to the rates in the disturbed areas (2.5 × 10 −4 to 0.011 kg s −1 ). The hillslope gradient did not affect the runoff or sediment responses. The sediment flux rates generally were greater in the initial stage of each inflow period than in the steady state condition, but there was no corresponding transient effect in runoff rates. Rill erosion modeling implications based on these data are presented in part 2 of this study.

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Between 1998 and 2002, six sites were established immediately after large wildfires in the western United States to determine the effectiveness of contour-felled log erosion barriers in mitigating post-wildfire runoff and erosion. In each pair of matched, burned, and small watersheds (1–13 ha), one was treated with contour-felled log erosion barriers and one was left untreated as a control. For 4 to 6 post-fire years, runoff and sediment yields were measured and correlated with rain properties. High-intensity rainfall produced most of the measured runoff and sediment yields except in the southern California site, where long-duration rain events produced most of the runoff and erosion. For small rain events (less than the 2-year return period for the 10-min duration), the runoff, peak flows, and sediment yields were lower in the treated watersheds than in the control watersheds, but there was no treatment effect for rain events with larger return periods. Improper installation and degradation over time reduced the effectiveness of contour-felled log erosion barriers. Rainfall characteristics and installation procedures should be carefully considered before choosing contour-felled log erosion barriers for post-fire hillslope stabilisation.