Abstract:
The riverbanks of the Inner Mongolia section of the Yellow River, located in a typical seasonal permafrost region, are subject to persistent risks of deformation and collapse due to the combined effects of freeze-thaw cycles, water flow erosion, and groundwater level fluctuations. Riverbank collapse not only threatens the stability of river channels but also endangers the lives and property of residents along the banks. Monitoring riverbank deformation and investigating its patterns and influencing factors are essential for the prevention and mitigation of riverbank collapse disasters. This study utilized 153 Sentinel-1A images acquired between April 2018 and April 2024, applying SBAS-InSAR (Small Baseline Subsets-Interferometric Synthetic Aperture Radar) technology to derive the spatiotemporal distribution characteristics of riverbank deformation in two typical meander bends, Shisifenzi and Wenbuhao. Given the challenges posed by low coherence and vegetation-covered soil surfaces in seasonal permafrost regions, a 120-day temporal baseline was adopted to effectively capture seasonal deformation during freeze-thaw periods and flood seasons, ensuring the precision and continuity of monitoring results. Goldstein filtering and the Minimum Cost Flow (MCF) phase unwrapping method were employed to enhance accuracy. Sentinel-2 optical imagery was integrated with the InSAR monitoring results, along with land use types, topographical features, and Normalized Difference Vegetation Index (NDVI) values, to comprehensively analyze the location and causes of deformation. NDVI values calculated from vegetated flood season images and sparsely vegetated winter images were compared with InSAR coherence maps to assess the impact of vegetation coverage on monitoring accuracy. The results reveal that the SBAS-InSAR monitoring data exhibit a significant linear correlation with leveling measurement data, with a root mean square error (RMSE) of 1.11 mm and a coefficient of determination (R²) of 0.754, confirming the high consistency and reliability of the SBAS-InSAR method for monitoring riverbank deformation under freeze-thaw conditions and in complex geomorphological settings. In the Shisifenzi area, the annual average deformation rate ranged from -20 to 25 mm/year. Two significant uplift regions were observed, showing a tendency to merge into a contiguous area. The most pronounced subsidence occurred in farmland areas of Shisifenzi Village, with a rate of 18.5 mm/year. Two subsidence zones were identified along the embankments at the apex of the Shisifenzi meander and the right riverbank near Guanniuju Village, where seasonal deformation exceeded 6 mm. In the Wenbuhao area, the annual average deformation rate ranged from -18 to 20 mm/year. Uplift regions were sporadically distributed, with an average deformation rate of 16.7 mm/year, while subsidence zones were concentrated along the eastern riverbank, with a maximum rate of 14.9 mm/year and seasonal deformation between 8 mm and 14 mm. Overall, riverbank deformation exhibited a pattern of slight general uplift interspersed with localized subsidence. Significant deformation areas were influenced by factors such as soil structure, agricultural activities, freeze-thaw cycles, and water flow erosion during flood seasons. Deformation demonstrated pronounced seasonal characteristics and spatial heterogeneity. Meander bends were particularly affected by water flow erosion, leading to reduced embankment stability and notable subsidence. Furthermore, groundwater levels, river water levels, and soil temperature and moisture showed strong correlations with riverbank deformation, making them critical factors. Precipitation, however, displayed weaker correlations due to the region’s arid and low-precipitation climate. This study demonstrates that SBAS-InSAR technology is effective in monitoring riverbank deformation in complex environmental conditions, providing reliable technical support for disaster prevention and mitigation in seasonal permafrost regions.