Weekly-scale shoreline monitoring using low-cost UAV photogrammetry: A case study from a highly dynamic beach in Sri Lanka

Abstract. Coastal areas worldwide are experiencing rapid changes due to erosion and sediment movement, yet monitoring these changes frequently remains economically challenging, especially in developing countries. This study presents an affordable approach to track shoreline changes over short time periods using widely available UAV (Unmanned Aerial Vehicle) technology and smartphone-based positioning systems. We monitored Red Beach in Sri Lanka weekly for one month, conducting aerial surveys at both high and low tides to capture how the beach changed day-to-day and throughout tidal cycles. The analysis performed using the digital shoreline analysis system in ArcGIS environment. Our findings revealed that the beach behaves as a complex, compartmentalized system where different sections respond differently to coastal processes. Although the beach showed overall sand accumulation during the study period, statistical analysis confirmed this growth occurred only in specific areas while other sections remained stable. The maximum zone of active change extended well beyond measurement uncertainties, indicating genuine coastal dynamics. Comparing high and low tide shorelines also revealed rapid, short-term shifts in active swash zone. This research demonstrates that affordable UAV-based mapping can effectively detect meaningful coastal changes, offering a practical solution for coastal management in regions with limited financial resources. Future work should explore integrating more accurate positioning devices at reasonable costs and extending monitoring over longer periods to capture seasonal patterns of erosion and accretion.