Measuring effectiveness of three postfire hillslope erosion barrier treatments, western Montana, USA

摘要

After the Valley Complex Fire burned 86000 ha in western Montana in 2000, two studies were conducted to determine the effectiveness of contour-felled log, straw wattle, and hand-dug contour trench erosion barriers in mitigating postfire runoff and erosion. Sixteen plots were located across a steep, severely burned slope, with a single barrier installed in 12 plots (four per treatment) and four plots left untreated as controls. In a rainfall-plus-inflow simulation, 26 mm h~(-1) rainfall was applied to each plot for 1 h and 48 L min~(-1) of overland flow was added for the last 15 min. Total runoff from the contour-felled log (0·58 mm) and straw wattle (0-40 mm) plots was significantly less than from the control plots (2·0 mm), but the contour trench plots (1·3 mm) showed no difference. The total sediment yield from the straw wattle plots (0·21 Mg ha~(-1)) was significantly less than the control plots (2·2 Mg ha~(-1)); the sediment yields in the contour-felled log plots (0·58 Mg ha~(-1)) and the contour trench plots (2·5 Mg ha~(-1)) were not significantly different. After the simulations, sediment fences were installed to trap sediment eroded by natural rainfall. During the subsequent 3 years, sediment yields from individual events increased significantly with increasing 10 min maximum intensity and rainfall amounts. High-intensity rainfall occurred early in the study and the erosion barriers were filled with sediment. There were no significant differences in event or annual sediment yields among treated and control plots. In 2001, the overall mean annual sediment yield was 21 Mg ha~(-1); this value declined significantly to 0·6 Mg ha~(-1) in 2002 and 0·2 Mg ha~(-1) in 2003. The erosion barrier sediment storage used was less than the total available storage capacity; runoff and sediment were observed going over the top and around the ends of the barriers even when the barriers were less than half filled.