Rubble islands are dynamic sedimentary features present on reef platforms that evolve under a variety of morphodynamic processes and controlling mechanisms. They provide valuable inhabitable land for small island nations, critical habitat for numerous species, and are threatened by climate change. Aiming to investigate the controlling mechanisms dictating the evolution of One Tree Island (OTI), a rubble island in the Southern Great Barrier Reef, we combined different remotely-sensed data across varying timescales with wave data extracted from satellite altimetry and cyclone activity. Our findings show that (1) OTI had expanded by 7% between 1978 and 2019, (2) significant gross planform decadal adjustments were governed by the amount, intensity, proximity, and relative position of cyclones as well as El Niño Southern Oscillation (ENSO) phases, and (3) the mechanisms of island growth involve rubble spits delivering and redistributing rubble to the island through alongshore sediment transport and wave overtopping. Frequent short-term monitoring of the island and further research coupling variations in the different factors driving island change (i.e., sediment availability, reef-wave interactions, and extreme events) are needed to shed light on the future trajectory of OTI and other rubble islands under a climate change scenario.

The increasing pressures and hazards derived from human action and climate change make the implementation of coastal monitoring plans a requirement for assessing coastal responses and evolution. For this reason, this work aims to use unmanned aerial systems (UAS) in combination with Structure from Motion algorithms for detecting morphodynamic changes caused by a storm in Camposoto beach (SW Spain). This approach provided pre- and post-storm digital elevation models of the study area with root mean square vertical errors of 6.89 and 5.54 cm, respectively, that allowed the identification of storm-induced gain and loss of sediment using Geomorphic Change Detection software. Furthermore, it also captured the response of the system against the action of specific marine processes such as storm-induced swash, collision, and overwash. The results obtained highlight the importance of an optimum flight plan design (e.g. the use of 85–75% front and side image overlap, respectively) and enhance the suitability of the UAS technology to satisfy the demands and needs in coastal monitoring studies in comparison with the traditional techniques, namely aerial photogrammetry, satellite imagery, and/or light detection and ranging.

Talavera, L.; del Río, L.; and Benavente, J., 2020. UAS-based high-resolution record of the response of a seminatural sandy spit to a severe storm. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 679-683. Coconut Creek (Florida), ISSN 0749-0208.Human infrastructures in barrier islands restrict the natural storm-induced overwash needed by these systems to evolve, further increasing their vulnerability in the medium and long term. For this reason, accurate overwash measurements in coastal environments subject to varying degrees of occupation are needed. In this work, two Unmanned Aerial System (UAS) flights were performed over two distinct sectors of a sandy spit located in Cádiz (SW Spain) prior and after the landfall of storm Emma. This storm was a high-energy event that lasted 153 hours,with an average significant wave height of 4 m and a storm peak of 6.81 m., and water levels (tide and surge) of up to 4 m. The images derived from the UAS flights were processed with Structure From Motion (SfM) algorithms using Pix4D software, resulting in high-resolution mosaics and Digital Elevation Models (DEMs) of the study area. These allowed (1) the digitization of the washover deposits in both sectors before and after the storm, and (2) the computation of DEMs of Difference (DoDs), which in turn allowed the analysis of volumetric estimates of erosion/accretion triggered by the significant overwash. The results revealed a nonuniform coastal response between both sectors. The area subject to higher degree of development showed a clear restriction in the onshore delivery of sediment during overwash due to the presence of a channel and a road, the coalescence of the nine pre-existing washovers into a unique deposit of 77546 m2, and much higher damage extents and associated recovery costs. In the natural sector, the overwash processes reactivated the three pre-existing washovers (which enlarged their areas up to 200%) with no significant damages reported. These findings serve as examples of coastal responses to future similar hydrodynamic conditions, and suggest that this spit will likely evolve following different trajectories in the long-term.

Talavera, L.; Del Río, L.; Benavente, J.; Barbero, L., and López-Ramírez, J.A., 2018. UAS & SfM-based approach to Monitor Overwash Dynamics and Beach Evolution in a Sandy Spit. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 221–225. Coconut Creek (Florida), ISSN 0749-0208. The role of overwash processes is of great relevance in the long-term evolution of sandy barriers, and it can also affect coastal infrastructures in the short term. In this work, a 10-month monitoring program based on the use of Unmanned Aerial Systems (UAS) in combination with Structure from Motion (SfM) algorithms was performed in order to monitor morphological changes and ulterior evolution at Camposoto beach, an overwash-prone coastal spit located in SW Spain. This UAS&SfM approach allowed the reconstruction of 6 Digital Elevation Models (DEMs) of the area with high temporal an...

Coastal lagoons are highly productive transitional water bodies threatened by human factors and vulnerable to global climate change effects. Monitoring biophysical parameters in these ecosystems is crucial for their preservation. In this work, we used Sentinel-2 and Landsat imagery combined with in situ data to (1) develop preliminary algorithms for retrieving the Chl-a concentration and water surface temperature of six lagoons located in the Ebro Delta (NE Mediterranean Sea, Spain), and to (2) compute maps and trend lines for analysing their spatiotemporal evolution from 2015 to 2022. Our findings showed that the algorithms’ accuracy ranged from 72% to 78% and had limited potential under high Chl-a concentration regimes. Even so, they revealed the lagoons’ trophic status, usual fluctuations, and deviations of both parameters attributed to seasonal (i.e., light and temperature) and short-term physical (i.e., winds) forcing, as well as valuable spatial patterns potentially useful for conservation efforts and land use planning. Future work will focus on the acquisition of a larger in situ data sample under a range of environmental conditions to improve the algorithms’ robustness, which in turn will allow the investigation of natural and human factors controlling the dynamics of the two investigated parameters.

Blowouts are wind-formed depressions that help maintain the sediment budget and enhance biodiversity in coastal dunes. However, the drivers controlling their evolution and the temporal scales associated to their genesis, development and decay phases remain unclear. To address this, the morphometric characteristics of a series of blowouts on the Ancão Peninsula (South Portugal) were digitized using imagery from 1972 to 2021, and used to analyse changes in the number of blowouts, total area, morphometric characteristics (width, length, orientation), and elongation rate over time. These data were compared with metocean time series and human activities, allowing the identification of blowout phases, drivers, and associated temporal scales. This work revealed that the blowout genesis phase primarily arised from the impact of physical external factors (e.g., non-storm low-to-moderate winds blowing out sand from dune scarp irregularities formerly created by extreme wave events), creating incisions across the foredune crest, and lasted 1 or 2 years. The blowout development phase, still ongoing, was characterized mainly by blowout expansion and rotation of large blowouts from North-northeast (NNE) to the East-northeast (ENE) controlled by external physical forces at specific times (e.g., low-to-moderate winds) and blowout internal factors (e.g., size and orientation). Complete blowout decay phases were not observed, except the complete artificial sealing of some blowouts due to fencing, which lasted 4 years. These findings suggest that a complete and natural blowout genesis-development-decay cycle could likely take more than five decades, with complex and spatiotemporally variable ecogeomorphic feedbacks driving their evolution. The only phase reversal documented was the reactivation of the artificially sealed blowouts, due to storm impacts. Allowing the dune and blowouts to evolve naturally appears to be the current best approach for the dune management at the studied area.