Unmanned Aerial System (UAS) orthoimagery based on Structure-from-Motion (SfM) has recently gained popular demand in environmental and agricultural studies for its high-spatial resolution and cost-effectiveness. The accuracy of the UAS terrestrial surveys is achieved by direct georeferencing with GPS correction technology (e.g., Post-Processed Kinematic, PPK) and further improved when coupled with ground control points (GCPs). However, the installation of GCPs on-site limits the effectiveness in both time and human resources. This study proposes a new positional correction method that overlays multiple surveys of UAS orthomaps to estimate temporal shoreline changes of wetlands using image cross-correlation, as implemented in common Particle Image Velocimetry (PIV) software. PIV provides spatially variable imaged displacement information needed to optimally match image regions between two subsequent surveys.