No abstract

Abstract:Postfire runoff and erosion are a concern, and more data are needed on the effects of wildfire at the watershed-scale, especially in the Colorado Front Range. The goal of this study was to characterize and compare the streamflow and suspended sediment yield response of two watersheds (Bobcat Gulch and Jug Gulch) after the 2000 Bobcat fire. Bobcat Gulch had several erosion control treatments applied after the fire, including aerial seeding, contour log felling, mulching, and straw wattles. Jug Gulch was partially seeded. Study objectives were to: (1) measure precipitation, streamflow, and sediment yields; (2) assess the effect of rainfall intensity on peak discharges, storm runoff, and sediment yields; (3) evaluate short-term hydrologic recovery.Two months after the fire, a storm with a maximum 30 min rainfall intensity I 30 of 42 mm h 1 generated a peak discharge of 3900 l s 1 km 2 in Bobcat Gulch. The same storm produced less than 5 l s 1 km 2 in Jug Gulch, due to less rainfall and the low watershed response. In the second summer, storms with, I 30 of 23 mm h 1 and 32 mm h 1 generated peak discharges of 1100 l s 1 km 2 and 1700 l s 1 km 2 in the treated and untreated watersheds respectively. Maximum water yield efficiencies were 10% and 17% respectively, but 18 of the 23 storms returned Ä2% of the rainfall as runoff, effectively obscuring interpretation of the erosion control treatments. I 30 explained 86% of the variability in peak discharges, 74% of the variability in storm runoff, and >80% of the variability in sediment yields. Maximum single-storm sediment yields in the second summer were 370 kg ha 1 in the treated watershed and 950 kg ha 1 in the untreated watershed.