In Aveiro (NW coast of Portugal), a coastal monitoring programme was carried out in sequence of a shoreface nourishment intervention (over than 2 M m${}^3$) performed in 2020. In this programme, almost one year of biweekly subaerial topographies and quarterly bathymetric surveys have been collected along a 10 km coastal stretch between June 2020 and June 2021. In this study, topographic and bathymetric surveys were analysed to assess the expectation that if the shoreface nourishment is located in sufficiently shallow water depths, its landward movement will feed adjacent beaches and, consequently, increase the subaerial beach volume. Results show that the subaerial beach volume is well correlated with the 1.05 m (above MSL) isoline displacement through time. While the seaward limit of the shoreface nourishment moved landwards about 200 m, the shoreline proxy (isoline of 1.05 m) displayed a maximum seaward displacement of 60 m. The displacement of the shoreline proxy was highly variable in space, along the 10 km coastal stretch, and also in time, during storm events. During such events, both landward and seawards displacement of the shoreline proxy took place, depending on the spatial position. Moreover, while beaches close to the initial shoreface nourishment intervention displayed faster accretion patterns than those located farther away, the well-defined onshore movement of the shoreface nourishment did not result in a considerable beach volume increase. The achieved results were also compared against case studies of shoreface nourishments with similar volumes performed worldwide.

Current coastal protection strategy in Portugal defines beach and shoreface nourishment as a valid measure to mitigate coastal erosion in some erosional hot-spots, being considered as an adaptation measure under the present climate change scenario, including the impacts of sea level rise. However, scant objective data on shoreface nourishments are available to evaluate performance of this type of intervention in mitigating beach erosion and managing coast risk. We present the first monitoring results of a ≈2.4 × 10⁶ m³ shoreface nourishment on the Aveiro coast (Costa Nova—Ílhavo), the largest until now in Portugal, focusing on its morphological development, impacts on adjacent beaches due to alongshore spreading and cross-shore redistribution, and contribution to the sediment budget of the nourished sediment cell. The analyses are based on high-resolution coastal monitoring data, provided by the Portuguese COaStal MOnitoring Program (COSMO). A Multiple Monitoring Cell (MMC) approach was used to evaluate local and feeder efficiency of the nourishment, sediment budget exchanges within both the placement and wider survey domains (≈1 km² and 12 km², respectively). Results show rapid (ca. 6 months) morphological change over the placement area, with a decrease of about 40% of the initial volume. Fast onshore sediment redistribution explains part of this change, placed sand having merged with the pre-existing bar system increased the volume of the shallower nearshore. Longshore transport is reflected by increasing the robustness of the bar downdrift of the placement area and also explains the negative sediment budget (0.75 × 10⁶ m³) of the survey domain, which corresponds to losses through its southern boundary. Sediment spreading also induced accretion of the subaerial section of Costa Nova beaches in front of the placement area, reversing their long-term erosive trend. In contrast, this trend persisted at downdrift beaches. This suggests that the time lag of the subaerial beach response to this intervention increases with the distance to the placement area, and reversal of the erosive trend will only be noticeable in the following years. This study provides new insights on the time scales of beach response to high-magnitude shoreface interventions in high-energy wave-dominated sandy coasts, which will support decision making regarding similar operations designed to manage erosional hot-spots elsewhere.

Coastal erosion impact on low-lying sandy shorelines represents a worldwide problem, which is particularly felt in various segments of the Portuguese coast where this geomorphological type represents 42% of its total length. Beach nourishment is a viable engineering alternative for shore protection and the assessment of offshore sources of beach-fill material is an essential aspect when implementing this mitigation strategy. The CHIMERA project carried out a multidisciplinary inspection on four segments of the west Portuguese coast to assess their potential as offshore borrow areas for beach nourishment. Altogether, these segments covered an area of c . 35 km ² , at water depths between 20 and 42 m. They were surveyed using multibeam, sub-bottom profiler, ultra-high resolution multichannel seismics and a set of 126 surface samples and 72 vibrocores (with 3 m long each). To comply with the Portuguese legislation, sand types were assessed by granulometric and chemical analyses for evaluating the quality of sediments in terms of contamination. High-resolution magnetic surveys were conducted to find potential archaeological artefacts. The adopted methodology proved to be adequate to quantify and describe the spatial distribution of useful sediment volumes, supporting the ongoing Integrated Coastal Sediment Strategy for mainland Portugal.

This paper describes a feasibility study of large scale, sand bypassing solutions at Aveiro and Figueira da Foz tidal inlets, undertaken for the Portuguese Environment Agency (APA). Aveiro and Figueira da Foz are existing river ports where breakwaters constructed to maintain navigable entrances have resulted in excess updrift accretion and severe downdrift erosion. These entrances require ongoing dredging and cause dangerous navigation conditions, especially for smaller vessels. The study showed that large-scale sand bypassing systems can restore the stability of shorelines on high-energy coastlines, based on the success of fixed sand bypassing systems, such as in East Australia.

The concept of depth of closure (DoC) plays a pivotal role in coastal morphodynamics and engineering, serving as a key parameter for estimating sediment budgets, designing beach nourishment projects, and modeling shoreline changes. Despite its significance, field measurements of DoC remain limited due to the logistical, operational, and financial challenges of systematic topo-bathymetric data collection. This study provides a field-based evaluation of DoC along the mainland Portuguese coast, encompassing diverse wave energy conditions, geomorphological characteristics and exposure. 64 nearshore-beach profile surveys conducted across 14 locations between 2018 and 2021, under the Portuguese Coastal Monitoring Program (COSMO), were analyzed. To define DoC, the study introduces the Relative Morphological Variability (RMV) criterion, setting a critical threshold of 1.2 local measurement uncertainty. DoC results indicate significant regional variability: on the high-energy western coast, ranges from 7.8 m to 14.1 m (MSL); on the lower-energy southern coast, values are shallower, from 4.1 m to 7.2 m (MSL), reflecting not only the lower wave energy environment but also seasonal data acquisition limitations. Empirical estimations using Hallermeier’s and Birkemeier’s formulas were compared with field data. While Hallermeier’s method consistently overestimates the DoC, Birkemeier’s approach aligns more closely with observed values, particularly along the western coast. These findings highlight Birkemeier’s formula as the preferred empirical method for estimating DoC along the Portuguese coast when field data is scarce or unavailable. This work underscores the importance of precise field measurements and validated empirical approaches, providing new insights for coastal management and engineering applications.

The CHIMERA project, contracted by the Portuguese Environment Agency (APA) and co-funded by the EuropeanUnion Cohesion Fund (Portugal 2020 | POSEUR) intended to characterize the sedimentary record of three 10km2 areas and one 5 km2 area in the Portuguese inner shelf. Multibeam bathymetry and backscatter, parametricecho-sounder, ultra-high resolution multichannel seismics and magnetic data were acquired along high resolutionorthogonal grids. The main aim of the project was to evaluate potential borrow areas for high-magnitude beachnourishments in long term eroding stretches of the Portuguese western coast. The diversity, the large density andthe high quality of geophysical data allow for a multidisciplinary geological interpretation of the datasets.In this presentation we focus on magnetic data and its interpretation combined with acoustic data. We applieda detailed processing scheme to acquired magnetic data, which allowed retrieving several components of themagnetic spectrum and estimating some source depths. We then analyzed the geological significance of theanomalies by studying their correspondence to seismostratigraphic units mapped from seismic data. Fit betweenmagnetic signature and geologic structure was found for most of the cases, although magnetic anomalies withinthe same wavenumber spectrum may express different geological units for each study area. A correspondence wastypically found for the basement, and for recent sedimentary structures such as paleo-channels and paleo-coastalbarriers. In other cases, low wavenumber anomalies may express intra-basement geology, too deep to be observedby our high-resolution seismics. For individual anomalies we check for a relation with shallow features, eventuallyarcheological artifacts.Publication supported by FCT- project UID/GEO/50019/2019 - Instituto Dom Luiz.