Evolution of Hvar island pocket beaches during the last 200 years (eastern Adriatic coast, Croatia)

Abstract

This study examines the evolution of 30 pocket beaches on the island of Hvar in Croatia over the last ~200 years. The oldest available data was extracted from the Franciscan cadastre and dates back to 1834. The following period was analysed using State Geodetic Administration orthophotos from 1952 and 1958, while the recent period was studied using UAV, GNSS measurements, and photogrammetric techniques, aiming to create high-resolution models. All analyses were carried out using GIS and semi-automatic statistical tools. Our results show that the beaches on Hvar eroded on average 50 % of their total area during the studied period, while the shorelines retreated by 6.5 m. Significant changes in beach areas and shoreline retreat were observed in both periods, without differences in erosion rates (~2.3 m2/yr). Here we showed that rates of shoreline retreat of gravel/pebble beaches revealed to be slower compared to sand beaches (0.04 m/yr and 0.07–0.38 m/yr respectively). Most beaches are formed in alluvial fans and represent therefore part of geomorphic systems which relate beaches to their catchments. Therefore, land cover changes in the catchments, was found to be an important factor affecting beach morphology. Obtained results reveal that 85 % of the analysed catchments exhibited decline in arable land coinciding with obtained trends of beach erosion. We find out that changes in beach size correlates to the changes in shoreline retreat (r2 = 0.7) for 70 % of beaches. However, 30 % of the beaches could be also influenced by other effects, particularly socio-economic activities in the catchment, which could importantly impact on natural variability but could also be associated with errors in Cadastral mapping. This study has shown that there is a trend of beach erosion on Hvar island which is expected to continue in the future. The acquired knowledge can thus contribute to future beach vulnerability assessment.