Managing landslides along road corridors using remote sensing

Maintaining roads is an optimization problem. Local officials must balance limited and sometimes shrinking budgets with the needs of their communities to have safe and reliable transportation systems. Unfortunately, the importance of a particular maintenance issue is often judged based on anecdotal information and complaints from the public rather than hard data. This approach is inefficient in terms of both cost and value; fixing the “squeaky wheel” might be more expensive and have a lower net-positive impact on the communities that we serve. Of course, there is a chance that the optimal maintenance decision is made. Most road maintenance groups are seasoned at making these tough decisions, but the question remains—is there a better way?

Remote sensing technologies such as lidar, radar, and high-resolution digital photography and photogrammetry can be used to make millimeter-scale distance, volume and area measurements more efficiently than using traditional physical inspection methods. Moreover, when multiple remote sensing datasets are collected, accurate measurements of changes over time can be made. Yet, despite their favorable cost-benefit ratio, remote sensing tools are not commonly used for roadway asset management at the city and county level and are used even more rarely for managing landslides along road corridors.

The reason remote sensing tools are rarely used for landslide management is multi-faceted. There is a common misconception that remote sensing tools are prohibitively expensive. There is also a common misconception that the data requires complex or difficult-to-perform analyses to be useful. And, perhaps most importantly, there is an understandable tendency of roadway managers to have a narrow and intense focus on only what is within their rights-of-way, even though most landslides initiate or have precursor indicators outside rights-of-way. The good news is that this paradigm is shifting, and as the price of drone-based remote sensing tools and services continue to drop, the availability and reliability of remote sensing data for managing landslides that affect city and county roads is increasing.

Drone-based lidar and photogrammetry tools and services are now well within the reach of city and county highway departments. For as little as a few thousand dollars of initial investment, road managers can obtain reliable drones with high-resolution cameras that can be used to create 3-D point-cloud models of roads and surrounding slopes that are prone to landslides. The same drones can be used for automated or manual photographic inspection flights that can be used for cataloging and quantifying assets like road signs and guardrails and for identifying maintenance issues like clogged culverts, erosion, and pavement or concrete cracking. And the best part is that most of this can be done with a small direct investment in equipment and training, utilizing existing staff. There are also many drone services companies and engineering and survey firms that have drone lidar and photogrammetry capabilities. Such companies can usually provide high-end change detection and other analysis services that may be needed.

High-quality lidar, photography and photogrammetry data can be used to measure changes over time and perform intermittent slope monitoring for a fraction of what it might cost to repair or stabilize a slope. And if this approach is taken for a longer corridor of landslide-prone terrain (i.e., miles or tens of miles), otherwise incipient slope failures can be found and mitigated long before they affect the road. There is also a wealth of publicly available lidar data from fixed-wing manned aircraft data collections. The publicly available data can serve as baseline datasets for change detection and monitoring purposes. As is often the case, these datasets can be used for corridor-scale landslide hazard mapping and susceptibility mapping.

The availability and accessibility of remote sensing data has made managing landslide hazards at the local-road scale easier than ever. City and county officials are now able to inspect their built assets and surrounding natural slopes for a fraction of the cost of traditional methods, track slope movement over time, and develop realistic landslide susceptibility models based on high-resolution data. Optimized decision-making with respect to landslide hazard management can now be made based on complex data rather than on subjective observations and anecdotal information, ultimately resulting in fewer and lower-cost landslide-related repairs, fewer and shorter road closures, and a safer and happier traveling public.

Cody Stopka, M.S., Geohazard Asset Management and Monitoring Group, GeoStabilization International, supports efforts to drive customer awareness and project development for the remote sensing, instrumentations, and monitoring business market. He is a geologist with extensive experience in landslide and rockfall monitoring, assessment and mitigation. (307) 461-1431. To learn more about what city and county officials are doing to monitor and manage their landslide hazards using remote sensing by visiting www.geostabilization.com/services or by calling (855) 579-0536.