Applications of the Unstable Slope Management Program for Federal Land Management Agencies: Colorado National Monument

Abstract:

Rockfall is a prevalent mechanism of sediment transport and a universal geohazard in terrestrial canyons across the globe. The Unstable Slope Management Program (USMP) for Federal Land Management Agencies (FLMAs) was developed in 2019 to help FLMAs proactively manage rockfall and landslide hazards along transportation corridors. This field-focused study applies the USMP to Colorado National Monument, a National Park Service unit that encompasses a network of canyons on Colorado’s Western Slope. One of the park’s main attractions is Rim Rock Drive, an historic road along the outer rim of the canyon network. Small rockfalls occur daily along Rim Rock Drive and park trails, and severe rockfalls have caused major damage to park infrastructure in the last 20 years. The USMP provides a systematic approach to assessing slope-related hazard and risk on public lands; data collected using USMP methodology is used to inform management decisions related to geotechnical assets. In this study, we apply the USMP’s methodology to over 200 rock and talus slopes along over 40 miles of road and trail in Colorado National Monument. We quantify slope activity using USMP Slope Hazard score, and total risk with Total USMP Score, and use these data to identify problematic slopes. Throughout the park, slope issues are related to geologic conditions (i.e. weak rock units, undercutting relationships, tectonic deformation) and infrastructure conditions (i.e. sight distance, traffic, speed limit). Each section of the park is susceptible to a unique combination of slope-related issues. We discuss these quantitative data in the context of park concerns and propose proactive management recommendations to park administration. This study represents another step toward proactive geotechnical asset management across all public lands. Our findings and the obstacles we encountered while administering the USMP at Colorado National Monument are relevant to other FLMAs moving toward proactive geotechnical asset management practices.