Fels Glacier Valley Slope Deformation Analysis and Geohazard Assessment for the Trans Alaska Pipeline System (TAPS)

Abstract Alyeska Pipeline Service Company (Alyeska) conducts ongoing pipeline integrity monitoring of the Trans Alaska Pipeline System (TAPS), including sites prone to slope instability and potential future landslides. Fels Glacier valley, an eastern tributary of the upper Delta River valley in the glaciated, rugged east-central Alaska Range, is a site of active slope movement on the valley’s south-facing slope. Located about three miles east of the Richardson Highway and the TAPS pipeline, Fels Glacier valley is drained by Lower Miller Creek, which is crossed by the TAPS pipeline. Several university researchers have postulated that a long-runout rock avalanche or a sequence of events involving catastrophic failure of the deforming slope, damming of the drainage from Fels Glacier, and subsequent outburst flooding, could severely impact the TAPS oil pipeline. However, this conclusion was reached without a structured geohazard assessment to estimate the probability of occurrence of these scenarios and vulnerability of the TAPS pipeline to their occurrence. In 2016, Alyeska initiated a geohazard assessment of Fels Glacier valley to assess the potential risk exposure of TAPS. In addition to several field reconnaissance surveys and review of satellite and ground-based radar monitoring conducted by others, desktop analysis of LiDAR data using a novel image analysis technique to estimate 3D displacement vectors was conducted to establish the pattern of ground displacement and develop a geologic model. This paper provides an overview of the geohazard assessment and details of the LiDAR image analysis. The findings illustrate the utility of comparative image analysis using repeat LiDAR surveys and orthophotos to estimate a true 3D displacement field as part of quantitative geohazard assessment of pipelines.