Paper No. 3
Presentation Time: 2:00 PM
IMPACT OF OFF-HIGHWAY VEHICLES ON MANCOS SHALE HILLSLOPES: A TERRESTRIAL LIDAR STUDY
GRAUCH, Richard I., US Geological Survey, Denver Federal Center, Denver, CO 80225, KOSOVICH, John J., USGS, Box 25046 Denver Federal Center, Denver, CO 80225-0046 and FRECHETTE, Jedediah D., Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, rgrauch@usgs.gov
Terrestrial lidar (TLS) provides a potentially valuable tool for quantifying hillslope morphology and processes. This ongoing, proof-of-concept study, initiated in fall of 2007, focuses on quantifying the differences between hillslopes that are impacted by off-highway vehicles (disturbed) and those that have minimal
anthropogenic disturbance (undisturbed). Thirteen barren hillslopes (6 undisturbed, 7 disturbed) underlain by Mancos Shale in arid to semi-arid central Utah and western Colorado are being repeatedly scanned at 6 or 12 month intervals. Range accuracy of individual surveys is estimated to be 7 mm (1σ) at 100 m. Seven of the hillslopes have been monumented to assist in the registration of repeat surveys. Distinctive
semi-permanent geomorphic features are utilized for survey registration of the other slopes. Individual scans of each hillslope were registered into a single coordinate system
and then transformed to a local project
coordinate system using PolyWorks IMAlign*
. The resulting point cloud data sets were then tiled, assembled, and clipped for analysis with ArcGIS*. A variety of hillslope metrics are being or will be accumulated for each survey including: slope profiles; rill patterns, densities, depths, and widths; and patterns and magnitude of areas of deposition and erosion.
During one six-month, winter period a disturbed hillslope was dominated by areas of sediment accumulation between 2 and 20 cm, especially high on the slope, mid-slope, and footslope. Sediment loss of similar magnitude occurred in a small area on the backslope and near the crest of the slope. The toeslope has slight to no accumulation. Sediments accumulated high on the slope are interpreted as aeolian. The profile of the upper portion of the slope changed during the same period from concave to convex upward. Net erosion rates for 3 hillslopes determined by TLS will be compared to rates determined on the same hillslopes by rainfall simulations, silt fence containment of sediment, and/or sediment trap. It is anticipated that the TLS rates will better represent the entire hillslope system than will the other methods and will provide reasonable constraints and independent checks for hillslope erosion modeling.
*use of brand names is for information only and does not constitute an endorsement by the USGS
