EROSION FROM WATERSHEDS AFTER WILDFIRE: AN EVALUATION OF LOG EROSION BARRIERS

Log erosion barriers (also known as contour felled logs) are used increasingly to control runoff and erosion after wildfires, yet their effectiveness at different scales is poorly understood. Following the June 2000 Hi Meadow Fire near Bailey, Colorado, I examined erosion from 4 adjacent, severely burned watersheds (1 to 17 ha) to determine the effect of log erosion barriers (LEBs). Two watersheds were treated with LEBs, and two were not. I instrumented the watersheds with a total of twelve rainfall gages, 4 check dams at the bottom of the watersheds, and eight 10-meter long sediment traps on the hillslopes. I measured cross sectional area of rills on hillslopes above sediment traps and throughout the basins. The study period, June to October 2001, provided 117 mm of precipitation with a maximum intensity of 5.5 mm in 10 minutes. Six storms produced runoff. The resulting sediment yields approximated 910 and 700 g m^-2 in the untreated watersheds and 630 and 120 g m^-2 in the treated watersheds. One of the treated watersheds had significantly less sediment yield than the untreated watersheds; the other did not (a = 0.05, paired t-test, d.f. = 5). Sediment yields estimated from the hillslope traps averaged 283 (sd = 358) and 46 (sd = 52) g m^-2 in the untreated and treated watersheds, respectively. More than 60% of sediment yield from the watersheds came from channels. The difference in mean sediment yield between treated and untreated hillslopes was not significant (p = 0.17, paired t-test, d.f. = 3). Rills, which were strongly correlated with sediment yield from hillslopes (r² = 0.82), were also similar in the treated and untreated watersheds. The results indicate that LEBs are not effective in reducing erosion from hillslopes. At the watershed scale, LEBs may reduce sediment yield; however, irrespective of treatment, most sediment came from channel erosion rather than hillslopes. This study can help guide future studies on runoff and erosion mitigation as well as cost-benefit analysis of post-fire rehabilitation.