remote sensing Review Remote Sensing Applications for Landslide Monitoring and Investigation in Western Canada Renato Macciotta * and Michael T. Hendry Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB T6G 2R3, Canada; [email protected] * Correspondence: [email protected] Abstract: Transportation infrastructure in mountainous terrain and through river valleys is exposed to a variety of landslide phenomena. This is particularly the case for highway and railway corridors in Western Canada that connect towns and industries through prairie valleys and the Canadian cordillera. The fluidity of these corridors is important for the economy of the country and the safety of workers, and users of this infrastructure is paramount. Stabilization of all active slopes is financially challenging given the extensive area where landslides are a possibility, and monitoring and minimization of slope failure consequences becomes an attractive risk management strategy. In this regard, remote sensing techniques provide a means for enhancing the monitoring toolbox of the geotechnical engineer. This includes an improved identification of active landslides in large areas, robust complement to in-place instrumentation for enhanced landslide investigation, and an improved definition of landslide extents and deformation mechanisms. This paper builds upon the extensive literature on the application of remote sensing techniques and discusses practical insights gained from a suite of case studies from the authors’ experience in Western Canada. The review of the case studies presents a variety of landslide mechanisms and remote sensing technologies. The aim of the paper is to transfer some of the insights gained through these case studies to the reader. Keywords: remote sensing; landslide monitoring; geotechnical investigation; risk management Citation: Macciotta, R.; Hendry, M.T. Remote Sensing Applications for Landslide Monitoring and Investigation in Western Canada. 1. Introduction Remote Sens. 2021, 13, 366. https://doi.org/10.3390/rs13030366 The integrity of the transportation network in Western Canada for securing uninter- rupted fluidity of goods and people through the network are essential for the economy of Received: 16 December 2020 the region. Transportation corridors through the Canadian Cordillera and through river Accepted: 19 January 2021 valleys in the prairies are exposed to natural slope instabilities and steep cuts required to ac- Published: 21 January 2021 commodate railroads and highways, where slope-related hazards are common. Landslide types in these regions include rock falls, rock slides and topples, earth flows, deep seated Publisher’s Note: MDPI stays neutral rotational and translational soil landslides, and compound landslides [1–6]. In this regard, with regard to jurisdictional claims in a robust approach to manage the risks associated with landslides in natural and cut slopes published maps and institutional affil- becomes essential. iations. The risk management framework for landslides in natural and cut slopes has been previously discussed elsewhere [7–11]. After defining the scope of analysis, the framework requires characterizing the magnitude and likelihood of the slope failure, as well as the magnitude and likelihood of the potential consequences, which become the basis for esti- Copyright: © 2021 by the authors. mating risk (combination of likelihood and consequence for each failure scenario analyzed). Licensee MDPI, Basel, Switzerland. The level of risk calculated in this risk analysis (qualitative or quantitative) is evaluated This article is an open access article against some adopted criteria to define its tolerability (risk assessment). The outcome of distributed under the terms and the risk assessment informs decision-making regarding the requirement for risk mitigation conditions of the Creative Commons and control strategies (e.g., protection, stabilization, early warning), as well as the need Attribution (CC BY) license (https:// for increased knowledge of the slope physical characteristics (e.g., geology, groundwater), creativecommons.org/licenses/by/ failure mechanisms and potential triggers; and monitoring requirements for managing 4.0/). Remote Sens. 2021, 13, 366. https://doi.org/10.3390/rs13030366 https://www.mdpi.com/journal/remotesensing Remote Sens. 2021, 13, x FOR PEER REVIEW 2 of 22 Remote Sens. 2021, 13, 366 2 of 23 warning), as well as the need for increased knowledge of the slope physical characteristics (e.g., geology, groundwater), failure mechanisms and potential triggers; and monitoring requirements for managing residual risks. This is where remote sensing techniques residual risks. This is where remote sensing techniques become provide increased benefit to become provide increased benefit to in-place instrumentation, particularly given the more in-place instrumentation, particularly given the more frequent adoption of quantitative risk frequent adoption of quantitative risk analyses since the late 1990s and early 2000’s [12– analyses since the late 1990s and early 2000’s [12–15]. This risk management framework is 15]. This risk management framework is illustrated in Figure 1 [11]. illustrated in Figure1[11]. FigureFigure 1. 1.General General risk risk management management framework framework for for landslides landslides in in natural natural and and cut cut slopes. slopes. After After [ 11[11].]. WithinWithin the the risk risk management management framework framework in in Figure Figure1, 1, monitoring monitoring plays plays a fundamentala fundamental role.role. NotNot onlyonly is is robust robust monitoring monitoring the the cornerstone cornerstone of of effective effective early early warning, warning, but but also also fundamentalfundamental for for increased increased understanding understanding of of the the landslide landslide mechanisms, mechanisms, kinematics kinematics and and triggers.triggers. InIn thisthis regard,regard, remoteremote sensingsensing technologies technologies havehave continued continued to to develop develop to to the the pointpoint where where they they are are becoming becoming routine routine practice practice for for landslide landslide monitoring monitoring and and for for landslide landslide investigation as part of the hazard analysis in Figure1[ 16]. These include ground-based investigation as part of the hazard analysis in Figure 1 [16]. These include ground-based and airborne (from manned and unmanned aircrafts) photogrammetry, laser scanning, and airborne (from manned and unmanned aircrafts) photogrammetry, laser scanning, and satellite and ground-based radar interferometry [17–28]. and satellite and ground-based radar interferometry [17–28]. This paper presents a review of six case studies in Western Canada from the au- This paper presents a review of six case studies in Western Canada from the authors’ thors’ experience; where remote sensing was used in combination with other site inves- experience; where remote sensing was used in combination with other site investigation tigation and monitoring technologies to gain understanding of the slope deformation and monitoring technologies to gain understanding of the slope deformation mechanisms mechanisms and develop early warning systems. A brief description of the geologic and develop early warning systems. A brief description of the geologic context, landslide context, landslide extents and deformation patterns are followed by a description of the extents and deformation patterns are followed by a description of the instrumentation and instrumentation and remote sensing techniques deployed and the insights gained. It is remote sensing techniques deployed and the insights gained. It is noted that the work noted that the work presented here reflects the methods that were considered most suited forpresented the case here studies reflects discussed, the methods which that may were vary considered in other contexts most suited and for the other case jurisdic- studies tions.discussed, This workwhich is may not anvary exhaustive in other contexts literature and review for other of remote jurisdictions. sensing This techniques work is for not landslidean exhaustive investigation; literature however, review of it remote presents sensing valuable techniques examples for for landslide how the investigation; information capturedhowever, from it presents remote sensingvaluable techniques examples enhance for how the the implementation information captured of the landslide from remote risk managementsensing techniques framework. enhance the implementation of the landslide risk management framework. 2. Chin Coulee Landslide 2.1.2. Chin Location Coulee and GeologyLandslide 2.1. TheLocation Chin and Coulee Geology landslide is located near the town of Taber in southern Alberta, Canada.The TheChin landslide Coulee islandslide within ais broadlocated valley near thatthe wastown dammed of Taber to in develop southern the Alberta, Chin CouleeCanada. water The reservoir.landslide Theis within landslide a broad was likelyvalley triggered that was by dammed a combination to develop of the the works Chin requiredCoulee water to relocate reservoir. Highway The landslide 36 from was near likely the toe triggered of the slope by a combination to the crest ofof thethe slopeworks (whichrequired required to relocate fill placementHighway 36 in from the upper near the part toe of of the the slope) slope and to the filling crest of of the the reser- slope voir(which[29– required31]. The locationfill