An improved estimation of surficial velocities obtained by MT-TOPSAR interferometry: a case study of Oldman River Dam, Alberta, Canada

Numerous dams in North America are constructed on foundations and/or abutments consisting of unstable weak materials or low-friction pre-sheared surfaces such as the Oldman River Dam (ORD), in southern Alberta, Canada. The objective of this paper is to examine the performance of Interferometric Synthetic Aperture Radar (InSAR) on the slow-moving ORD site by comparing the mapped velocities obtained through InSAR analysis in 2015–2022 with velocities from previous investigations. Additionally, the study aims to determine the precision of estimated velocities by analyzing InSAR temporal decorrelation and incorporating the error of simplifying the assumption necessary to decompose line-of-sight velocities. The results indicate the spillway, covering an area of ~ 26 × 10 3 m 2 , has been moving at an average total velocity of 1.26 mm/year. On the slope of the embankment, measuring ~ 160 × 10 3 m 2 , an active area next to the left abutment is also experiencing a higher average velocity of 8.29 mm/year (both rates in millimeters per year). An analysis of the precision of the estimations showed an accuracy of 0.72 and 2.78 mm/year for the spillway and embankment, respectively. Overall, the spillway velocities have not deviated much from 1 mm/year in the study period but the embankment’s active area decelerated from > 20 to 5 mm/year toward the end of 2022. Eventually, a lagged spillway displacement in response to seasonal variation of the reservoir level was also observed.