Examinando por Autor "Talavera, Lara"

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Controls on blowout evolution in southern Portugal: A 49-year analysis
(Elsevier, 2024-10-10) Talavera, Lara; Costas, Susana; Ferreira, Óscar
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
UAS & SfM-based approach to Monitor Overwash Dynamics and Beach Evolution in a Sandy Spit
(The Coastal Education and Research Foundation (CERF), 2018-05-01) Talavera, Lara; Del Río, Laura; Benavente, Javier; Barbero, Luis; López-Ramírez, J. Antonio
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 and spatial resolutions (RMS vertical errors spanning from 5 to 8 cm). The morphological changes occurred were detected using Geomorphic Change Detection Software in ArcGIS, and they were correlated with the oceanographic conditions that prevailed during the analysed period. The results obtained provided insight into the response of the system against storm-induced overwash, which caused significant erosion/accretion patterns over a pre-existing washover fan, as well as the landward migration of the system. In addition, this methodology captured the progressive partial recovery of the system, which included onshore transport of sand, fore-beach accretion, and berm reconstruction. Despite the partial recovery observed, spring tides also triggered non-storm overwash in the area during fair-weather conditions, allowing to rethink the actual vulnerability state of the spit against rollover processes.
UAS as tools for rapid detection of storm-induced morphodynamic changes at Camposoto beach, SW Spain
(Taylor & Francis, 2018-05-10) Talavera, Lara; Del Río, Laura; Benavente, Javier; Barbero, Luis; López-Ramírez, J. Antonio
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.
UAS-based High-resolution Record of the Response of a Seminatural Sandy Spit to a Severe Storm
(The Coastal Education and Research Foundation (CERF), 2020-05-26) Talavera, Lara; Del Río, Laura; Benavente, Javier
Human infrastructures in barrier islands restrict the natural storm-induced overwash needed by these systems toevolve, further increasing their vulnerability in the medium and long term. For this reason, accurate overwashmeasurements in coastal environments subject to varying degrees of occupation are needed. In this work, twoUnmanned Aerial System (UAS) flights were performed over two distinct sectors of a sandy spit located inCádiz (SW Spain) prior and after the landfall of storm Emma. This storm was a high-energy event that lasted153 hours,with an average significant wave height of 4 m and a storm peak of 6.81 m., and water levels (tideand 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 beforeand after the storm, and (2) the computation of DEMs of Difference (DoDs), which in turn allowed the analysisof volumetric estimates of erosion/accretion triggered by the significant overwash. The results revealed a non-uniform coastal response between both sectors. The area subject to higher degree of development showed aclear restriction in the onshore delivery of sediment during overwash due to the presence of a channel and aroad, the coalescence of the nine pre-existing washovers into a unique deposit of 77546 m 2, and much higherdamage extents and associated recovery costs. In the natural sector, the overwash processes reactivated thethree 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 suggestthat this spit will likely evolve following different trajectories in the long-term.