Multi-month sedimentological characterization of the backshore of an artificial coarse-clastic beach in Italy

Abstract

In this paper, a sedimentologic characterization of an artificial coarse-clastic beach at Marina di Pisa (Tuscany, Italy) is carried out within a 5 month timespan (October 2018–February 2019). The beach was built in 2007 as a form of coastal protection due to severe erosion processes occurred along this sector of the coast in the past 150 years. The grain-size characterization was performed using pyDGS, a digital grain-size analysis software developed by Buscombe (2013). It is an open-source Python framework that uses a continuous wavelet transform method to calculate grain-size parameters (e.g., mean grain size, sorting) from images. By matching grain-size data with the topographic evolution of the beach provided by DGPS surveys of the backshore, we pointed out a seaward shift of coarser pebbles after medium-energy events (max significant wave height about 3 m). This trend suggests that wave reflection processes onto the seawall are generated during those events, producing a significant cross-shore transport of pebbles along the backshore. Such reflection processes had already been reported in the scientific literature during higher energy wave states though, which means that the artificial beach had decreased the protection level over time. These observations might be useful for coastal managers to optimize future coarse-clastic beach fill interventions. Digital grain-size analysis proved to be reliable and less time-consuming compared to traditional techniques, such as dry-sieving grain-size analysis and caliper measurements. Further improvements are still required specially to extend the survey in the underwater environment.