HR: 0830h
AN: H51D-1106    [PDF]
TI: Hillslope Erosion Processes after High Severity Wildfires, Colorado Front Range
AU: * Pietraszek, J H
EM: jpietrzk@cnr.colostate.edu
AU: MacDonald, L H
EM: leemac@cnr.colostate.edu
AB: High severity forest fires can increase soil erosion rates by two or more orders of magnitude, with potentially severe consequences to downstream water resources. The objectives of this study were to contrast hillslope and rill erosion in severely burned areas, and quantify the effects of different controlling variables. Sediment yields are being monitored from 34 sites that burned at high severity in early summer 2002 in the central Colorado Front Range. Twenty-three of these sites are in topographically convergent swales with contributing areas of 100 to 7000 m$^{2}$. The other 11 sites are on planar hillslopes with contributing areas ranging from 30 to 150 m$^{2}$. Rill formation is being measured at 117 cross-sections in 14 of the 23 swales. Tipping bucket rain gages are measuring rainfall intensities within 0.5 km of each site. For individual storms the sediment yields per unit area vary by an order of magnitude, and this is largely due to the spatial variability in the amounts and intensity of rainfall. In the swales storm sediment yields can exceed 1.0 kg m$^{-2}$, and on average the swales produce approximately 2-3 times more sediment per unit area than the planar hillslopes. The greater topographic convergence in the swales results in more concentrated overland flow, and this is evidenced by the rapid rill incision in the swale axes. The cross-sectional area of these rills ranges up to 0.05 m$^{2}$, and the cross-sectional area of these rills has been increasing in the second summer after burning despite the gradual increase in ground cover. Data from a storm of 8 mm shows that rill erosion in the swale axes can account for nearly 80% of the measured sediment yields. A better understanding of rill erosion is needed to accurately predict post-fire erosion rates and design effective rehabilitation treatments.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting