Coastal erosion, which is the gradual loss of sediment over time, poses a significant threat to South Africa’s coastline. The monitoring and detection of coastal erosion is essential for the effective management of coastal environments and can be quantified by the delineation of coastal boundaries. Remote sensing techniques such as Synthetic Aperture Radar (SAR) offer an unique opportunity to extract shoreline positions over large areas of the coast. In this study, C-band SAR data was used to derive backscatter coefficients for three different areas of interest in the Eastern Cape province in South Africa over a ten year period. Thresholding and edge detection techniques were used to delineate shoreline positions. The coastal erosion and accretion trends were calculated and the results indicated that the Linear Regression Rate (LRR) for the three different study areas showed various coastal erosion seasonality trends. The shoreline LLR ranged between −0.01 and −3.28 m/year for the Cape Recife area and 0.17 and −4.78 m/year for the Nelson Mandela Bay beach front. The overall pattern was erosion during the winter months and accretion during the summer months. In contrast, for the Kings Beach area, there was a consistent accretion trend where the LRR values ranged between 0.94 and 1.68 m/year. The findings of this study suggest that SAR remote sensing and thresholding-based methods could be a suitable technique for detecting and monitoring coastal erosion seasonality patterns.