Debris Flows, Big Slow Movers, and Rocks Slides: Assembling the Geospatial Legacy of Landslides using Lidar, Drones, and Boots on the Ground

Rick Wooten, P.G., North Carolina Geological Survey (ret.), Distinguished AEG/GSA Jahns Lecturer

ABSTRACT: Damaging landslides are a recurring problem in the Blue Ridge Mountains of North Carolina as in other mountainous regions worldwide. Since 1879 landslides in western North Carolina have resulted in at least 84 fatalities and 22 injuries, over 84 destroyed or condemned homes and damage to 60 others, continued damage and threats to regional infrastructure, and have cost well over $53 million since 1990 in direct losses alone. Assembling and maintaining a landslide geodatabase is a multi-year, ongoing effort using data collected from landslide hazard mapping and responses to landslide events. Developing such a geodatabase is a fundamental component of proactive landslide loss reduction.

The NCGS’s landslide geodatabase documents the areal extents prehistorical and historical landslides of various types - key predictors for where landslides may happen in the future. Debris flows, large slow-moving, deep-seated, debris slides and weathered-rock slides (big slow movers); and, rockslides comprise the main types of landslides. Rainfall from landfalling tropical cyclones can trigger hundreds to thousands of debris flows. Rapidly moving debris flows can travel 30 mi/hr (13 m/sec) and have resulted in fatalities and destroyed homes. Mapped debris flows and past debris flow deposits provide the empirical bases for debris flow susceptibility and pathways models – important components of landslide hazard maps. Big slow movers continue to damage and threaten homes, and critical regional transportation and energy infrastructure. Historic reactivation of once-dormant big slow movers typically coincides with extended periods of above normal precipitation, and within composite deposits from past landslides including those modified by human activity. Rockslides and rockfalls pose a significant threat to transportation routes like I-40 and the Blue Ridge Parkway. Direct mitigation costs for a major rockslide can be on the order of $10 million. The resulting extended closures of I-40 and Blue Ridge Parkway can incur $1 million a day in lost revenue, with substantial negative impacts to local and regional economies dependent on these transportation routes.

Archival aerial photography, orthophotography, and satellite imagery are important remote sensing tools used to detect, and optimize field verification of suspected landslide features. The advent of lidar digital elevation models and uncrewed aerial systems (UAS) technology has revolutionized landslide mapping and landslide response capabilities. Integrating geospatial landslide data with historical and meteorological information increases our knowledge of the frequency and magnitude of landslide triggering storms, and sheds light on landslide causes and triggers, and their connections with geology, climate, weather patterns, forests, and land use. The confluence of new technology, the passage of the National Landslide Preparedness Act, and the ongoing impacts of extreme weather patterns linked to climate change present a compelling opportunity for the geoscience community to press forward in a coordinated effort to reduce losses from landslides. An essential part of meeting this challenge is building partnerships within and outside of the scientific community to increase public awareness of geologic hazards.

Speaker Bio

Design & Construction of Two-Mile-Bar Tunnel for Oakdale Irrigation District

Ron Skaggs, PE, GE, Principal Engineer, and Vice President of Engineering - Condor Earth

ABSTRACT: The presentation will describe a case study of the Two Mile Bar 2 tunnel constructed for the Oakdale irrigation District. The review will include the need for a tunnel to replace the historic canal based on geologic hazards, reviewing the geotechnical and geologic investigation of the proposed route, the design of the portals and tunnels, and construction. The construction review will include a detailed review of unanticipated ground conditions which led to change orders which were negotiated between the owner and contractor. Methods within the contract helped define the risk to both parties during the bidding and construction phase and how that played a role in mediating an appropriate cost for the change orders. The project demonstrates a successful process to manage significant changes in the anticipated construction procedures through use of the contract and the willingness of all parties to find an appropriate resolution.

Speaker Bio