Paper No. 4
Presentation Time: 8:00 AM-6:00 PM
ROAD-INDUCED GULLY EROSION ALONG PIKES PEAK HIGHWAY, COLORADO, USA
The Pikes Peak Highway is a partially paved road between Cascade, CO and the summit of Pikes Peak. Significant gully erosion is occurring on the hillslopes due to the concentration of surface runoff, the rearrangement of drainage pathways along the road surface and adjacent drainage ditches, and the high erodibility of weathered Pikes Peak granite that underlies the area. As a result, large quantities of sediment are transported to the surrounding valley stream networks causing significant damage to water quality and aquatic, wetland, and riparian ecosystems. This study establishes the slope/drainage area threshold for gullying along the Pikes Peak Highway and a sediment budget highlighting rates of gully erosion and subsequent valley deposition for a small headwater basin. The study area encompasses a 5.2 km segment of the road at an elevation range of 2600 m - 3000 m. Slope and drainage area for individual gullies was calculated with a high-resolution elevation dataset in a GIS, topographic maps, and field observations. Gullies were surveyed and all sites were mapped using GPS. Cesium-137 analysis was used to estimate deposition rates in the North Fork Crystal Creek basin. The threshold for gullying along the road is Scr = 0.21A-0.45 and the road surface reduces the critical slope requirement for gullying compared to natural drainages in the area. Total gully volume for the twenty gullies along the road is estimated at 5974 m3, with an erosion rate of 64 m3 y-1 to 101 m3 y-1. Net valley deposition is estimated at 180 m3 y-1 with 114 m3 y-1 to 138 m3 y-1 unaccounted for by gullying. The hillslope-channel interface is decoupled with minimal sediment transport downstream due to insufficient discharge causing the system to become choked with coarse-grained sediment.