Coastline Evolution of Large-Scale Artificial Beach Nourishment in the Vicinity of a Newly Built Breakwater: An Empirical Case Study from the South Baltic Coast

Large-scale beach nourishment projects constructed adjacent to port breakwaters may produce spatially contrasting shoreline responses because wave transformation, sediment redistribution, and structural effects act simultaneously. This study presents an empirical analysis of short-term shoreline evolution at a large artificially nourished beach constructed next to the eastern breakwater of the Vistula Spit Channel in the South Baltic Sea. The analysis combines historical orthophotomaps, monthly Real-Time Kinematic Global Positioning System (RTK-GPS) shoreline surveys, drone-based elevation data, hourly wave records, and tide-gauge observations collected between February 2024 and March 2025. The objective was to quantify the spatial and temporal variability of shoreline change and to interpret the observed erosion and accretion in relation to wave conditions, sea-level variability, the presence of the breakwater, and post-nourishment sediment redistribution. Historical shoreline changes were assessed at fixed coastal mileage locations. Monthly shoreline changes were quantified using a polygon-based on Geographic Information System (GIS) procedure, with gross erosion, gross accretion, and net area change calculated for successive survey intervals. Two characteristic 250 m coastal sectors were also compared: the area adjacent to the breakwater and the eastern boundary of the monitored beach. Approximately 55,550 m2 of erosion and 57,851 m2 of accretion were identified during the monitoring period, resulting in a net positive balance of approximately 2301 m2. The small net value masks substantially larger opposing changes in different parts of the study area. The sector adjacent to the breakwater showed a predominantly negative cumulative surface balance, whereas the eastern sector showed a predominantly positive balance. The May–June interval was not uniformly stable, despite generally moderate offshore wave conditions, because a net loss of approximately 9626 m2 was recorded. The results indicate that shoreline evolution was controlled by the combined effects of offshore wave forcing, sea-level variability, wave transformation near the breakwater, initial nourishment geometry, and natural post-nourishment sediment redistribution. Offshore wave parameters were not treated as direct nearshore forcing because refraction, shoaling, diffraction, breaking, and energy dissipation may modify the wave field before it reaches the shoreline. The study provides an empirical description of short-term shoreline adjustment rather than a validated predictive model.