Effective Monitoring of Permafrost Coast Erosion: Wide-scale Storm Impacts on Outer Islands in the Mackenzie Delta Area

Abstract

Permafrost coasts are extensive in scale and complex in nature, resulting in particular challenges for understanding how they respond to both long-term shifts in climate and short-term extreme weather events. Taking examples from the Canadian Beaufort Sea coastline characterized by extensive areas of massive ground ice within slump and block failure complexes, we conduct a quantitative analysis of the practical performance of helicopter-based photogrammetry. The results demonstrate that large scale (>1 km 2) surface models can be achieved at comparable accuracy to standard unmanned aerial vehicle surveys, but 36 times faster. Large scale models have greater potential for progressive alignment and contrast issues and so breaking down image sequences into coherent chunks has been found the most effective technique for accurate landscape reconstructions. The approach has subsequently been applied in a responsive acquisition immediately before and after a large storm event and during conditions (wind gusts >50 km h −1) that would have prohibited unmanned aerial vehicle data acquisition. Trading lower resolution surface models for large scale coverage and more effective responsive monitoring, the helicopter-based data have been applied to assess storm driven-change across the exposed outer islands of the Mackenzie Delta area for the first time. These data show that the main storm impacts were concentrated on exposed North orientated permafrost cliff sections (particularly low cliffs, >20 m in height) where cliff recession was 43% of annual rates and in places up to 29% of the annual site-wide erosion volume was recorded in this single event. In contrast, the thaw-slump complexes remained relatively unaffected, debris flow fans were generally more resistant to storm erosion than the icerich cliffs, perhaps due to the relatively low amounts of precipitation that occurred. Therefore, the variability of permafrost coast erosion rates is controlled by interactions between both the forcing conditions and local response mechanisms. Helicopter-based photogrammetric surveys have the potential to effectively analyze these controls with greater spatial and temporal consistency across more representative scales and resolutions than has previously been achieved, improving the capacity to adequately constrain and ultimately project future Arctic coast sensitivity.

Multiscale Object-Based Classification and Feature Extraction along Arctic Coasts

“…Figures 4 and 5 presented small differences depending on the classification approach, which is encouraging since very high resolution imagery has become standard for Arctic coastal erosion studies [18,25,48,49]. We see a particularly good fit for our methods to integrate with a novel approach introduced by Lim et al [66] that derives very high resolution imagery through structure-from-motion photogrammetry from imagery capture by Table 3. CNN classifications were generated for the highest resolution images available (0.6 and 1.0 m/pixel) across the eight segmentation scales.…”

“…Figures 4 and 5 presented small differences depending on the classification approach, which is encouraging since very high resolution imagery has become standard for Arctic coastal erosion studies [18,25,48,49]. We see a particularly good fit for our methods to integrate with a novel approach introduced by Lim et al [66] that derives very high resolution imagery through structure-from-motion photogrammetry from imagery capture by helicopter for Arctic coastal reconstruction introduced for measurement of wide-scale storm impacts. Our contribution of identifying multiple coastal features is well suited for modeling complex coastal processes and environmental forcing factors [18,50].…”

Merging Satellite and in situ Data to Assess the Flux of Terrestrial Dissolved Organic Carbon From the Mackenzie River to the Coastal Beaufort Sea

“…Nevertheless, caution should be addressed to local non-deltaic sources of tDOC to the ocean. Offshore the delta, strong winds erode the shoreline permafrost of the Beluga Bay Islands, which may deliver extra carbon to the coastal waters (Lim et al, 2020). These inputs, however, may be limited compared to those originating from the delta (Tanski et al, 2016).…”

The Canadian Federation of Earth Sciences Scientific Statement on Climate Change – Its Impacts in Canada, and the Critical Role of Earth Scientists in Mitigation and Adaptation

“…The effects of sea-level rise will be exacerbated by increased storm damage due to the loss of protective winter ice along shorelines of the Great Lakes, the coasts of eastern Canada, and in the Arctic (Lemmen et al 2016). The longer open water season and greater area of open water increasing storm wave power has already led to more rapid coastal erosion, threatening Arctic settlements such as Hall Beach, NU, and Tuktoyaktuk, NT (Lim et al 2020;Fig. 14).…”