Century-scale dataset of bathymetry and shoreline position for Tagus ebb-tidal delta, Portugal.

Understanding long-term coastal changes requires comprehensive records of morphological data spanning extended periods, ideally over multiple decades. Nevertheless, significant challenges arise from the restricted availability and accessibility of reliable data, especially in the case of complex coastal systems dominated by wave-current dynamics, such as ebb-tidal deltas (ETDs). This study introduces a new dataset for Tagus ETD in central Portugal, from 1845 to 1985 based on historic nautical charts available for the area. The data includes: (1) high-resolution bathymetric surfaces of ETD configuration for years 1845, 1879, 1893, 1929, 1939, 1960 and 1985; (2) shoreline position of three different indicators (Low-Water Line, High-Water Line and foredune dune seaward limit) at the adjacent coast for the same years; (3) rates-of-change for shoreline position of the High-Water Line indicator. Data also includes an uncertainty assessment for hydrographical and shoreline position information estimated from historic nautical charts. These data provide a valuable resource for describing, understanding, and modelling the long-term behaviour of ETDs not covered by other currently available datasets.

Embayed beach configuration explained by wave sheltering.

Embayed beaches, characterized by their distinctive planform curvature, are a common feature along coastlines worldwide. This study introduces a novel approach to describe bay shape that extends our understanding about the processes that control embayed beach development. The novel approach was thoroughly tested against one-line models and applied to real-world cases covering a wide range of spatial scales, wave climate conditions and geomorphological settings. Here we show that the equilibrium curvature of embayed beaches can be correctly described and explained by considering headland-provided offshore wave sheltering alone, without explicitly accounting for wave shoaling, refraction, diffraction, or longshore transport. This holds true as long as the offshore wave climate is accurately characterized, including complete information regarding the mean and the spread of the incoming wave direction. For narrow-banded dominant swell wave regimes, the inclusion of background wind sea components has been identified as crucial for predicting curvature in the more sheltered embayed domain. The presented model significantly contributes to the understanding of how waves shape embayed beaches.

The future of insular beaches: Insights from a past-to-future sediment budget approach.

Sustainable management of insular beaches, that are critical to tourism-based economies, depends on sound understanding of coastal evolution drivers. However, interconnections among geological, oceanographical, biological and human key-drivers of coastal change, operating at relevant spatial and temporal scales, remains poorly understood. This work aims at understanding and quantifying the main drivers of insular beaches evolution using a past-to-future sediment budget approach, and to address future coastal impacts raised by anthropogenic interventions and climate change. This approach was developed in Porto Santo's beach from the early 20th century to the middle 21st century. Results show that anthropic activities undertaken during the late 20th century perturbed the existing long-term (natural) coastal stability. They caused significant reduction of the main sediment source (river sediment yield) and increased sediment sinks (e.g. sediment extraction from beach, harbour sedimentation). Altogether, this resulted in the onset of an erosive trend that persists until present. Projecting patterns of coastal change into the forthcoming decades strongly depends on sediment management strategies. We show that the adoption of a neutral strategy (i.e. compensating for anthropogenic-induced losses with beach nourishment) will not be enough to cease beach erosion, given the negative impacts related to acceleration of future sea level rise. Still, maintenance of the socioeconomic values of Porto Santo's beach can be achieved by triggering positive anthropic influences on its sediment budget. The past-to-future sediment budget approach proposed herein provided a unified perspective on the evolution of the main drivers of coastal change and simultaneously offers foundations for adaptations strategies aiming at increasing sustainability of insular beaches.