UAS Identify and Monitor Unusual Small-Scale Rhythmic Features in the Bay of Cádiz (Spain)

Abstract

Unusual shore-normal and barred-like rhythmic features were found in Camposoto Beach (Bay of Cádiz, SW Spain) during a monitoring program using unmanned aerial systems (UAS). They appeared in the backshore and persisted for 6 months (October 2017–March 2018). Their characteristics and possible formation mechanism were investigated analyzing: (1) UAS-derived high-resolution digital elevation models (DEMs), (2) hydrodynamic conditions, and (3) sediment samples. The results revealed that the features did not migrate spatially, that their wavelength was well predicted by the edge wave theory, and that they shared characteristics with both small-scale low-energy finger bars (e.g., geometry/appearance and amplitude) and swash cusps (e.g., wavelength, seaward circulation pattern, and finer and better sorted material in the runnels with respect to the crests). Our findings pinpoint to highly organized swash able to reach the backshore during spring tides under low-energy and accretionary conditions as well as backwash enhanced by conditions of water-saturated sediment. This study demonstrates that rhythmic features can appear under different modalities and beach locations than the ones observed up to date, and that their unusual nature may be attributed to the low spatiotemporal resolution of the traditional coastal surveying methods in comparison with novel technologies such as UAS.

High-Resolution Interannual Evolution of the Dune Toe at a Mesotidal Barrier (Camposoto Beach, SW Spain)

“…Camposoto Beach is located on the southwest (Atlantic) coast of the Iberian Peninsula in the province of Cadiz. The area is part of the northern section of the Sancti Petri sand spit (San Fernando municipality) (Figure 1) extended along 5 km in a NNW-SSE direction as a consequence of the littoral drift that flows in a SE direction [23,34].…”

“…Camposoto is a sandy beach backed by a low dune ridge with an average height between 4 and 6 m; it is sparsely vegetated and interrupted by various washover fans, which is part of Natural Park Bahía de Cádiz due to its ecosystemic diversity and landscapes [34,35]. According to the Habitats Directive (Council Directive 92/43/EEC), the Camposoto dunes are included in the dune system of 'El Chato-Sancti Petri', which includes several Habitats of Community Interest, such as embryonic shifting dunes (HCI 2110), shifting dunes along the shoreline-'white dunes' (HCI 2120)-and humid dune slacks (HCI 2190).…”

“…A rollover process has been identified for the Sancti Petri spit with retreat rates of around 1 m per year [35,[43][44][45]. As a result, the migration of the sand spit has occurred landwards as sea storms have activated the overwash processes and deposited the eroded material behind the dunes [34,39]. Evidence of this rollover process that has been recorded during the last decade encompasses the recession of the dune toe quantified by del Río et al [29] between 1956 and 2008, the fragmentation of the foredune ridge and the outcropping of ancient salt marsh depositions observed by Talavera et al [46] in the intertidal zone of the beach after storm events.…”

“…In addition, various removable infrastructure elements are installed during the summer season at the upper part of the beach to serve visitors. This generates significant anthropic pressure, which often translates into the trampling of the dunes in the areas close to the beach accesses [23,34,45]. The impacts of the front beach erosion and the damage generated over this infrastructure led to various beach nourishment projects in 1998 (737,000 m 3 ), 2010 (102,200 m 3 ), 2015 (105,200 m 3 ) and 2018 (150,000 m 3 ) [47,48].…”

Quantitative Characterization of Coastal Cliff Retreat and Landslide Processes at Portonovo–Trave Cliffs (Conero, Ancona, Italy) Using Multi-Source Remote Sensing Data

“…"Agisoft Metashape" (version 1.5.1 https://www.agisoft.com (accessed on 24 July 2023)) was used to manage and process UAV data and GCP coordinates. Using the procedure suggested by different authors [41,[65][66][67][68], it was possible to create the DSM and orthophoto of the surveyed area.…”