Beach Response to a Shoreface Nourishment (Aveiro, Portugal)

Abstract

In Aveiro (NW coast of Portugal), a coastal monitoring programme was carried out in sequence of a shoreface nourishment intervention (over than 2 M m3) 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.

Morphological Development and Behaviour of a Shoreface Nourishment in the Portuguese Western Coast

“…The magnitude of beachface seaward translation, represented by changes in beach width (Figure 6) measured between July 2020 and April 2021 is 76 m; the same estimate using October 2020 and January 2021 surveys is 60 m. These figures are in close agreement with the maximum seaward displacement (60 m) of the +3.05 m CD contour line observed between June 2020 and January 2021 in a nearby profile [20]. Moreover, our data suggest that beachface progradation slowed down or ceased after March 2021 (cf.…”

“…The study relies upon high resolution monitoring following the largest shoreface nourishment undertaken in Portugal, encompassing the downdrift domain potentially affected by short-term sediment redistribution. This work extends and complements previous study on the same field area [20], but it differs by introducing a sediment budget approach that allowed the understanding of post-nourishment sediment dispersion. In addition, we investigate the time scale required for the beach to acquire a condition of equilibrium replicating the equilibrium beach profile of Bruun's, following the imposition of a significant sand volume.…”

“…Herein, we describe the impacts of a high-magnitude shoreface nourishment in the morphological evolution and behaviour of a wave-dominated, high-energy beach-dune system. We add a sediment budget approach to previous work targeting the same area [20]. This has improved the understanding of the processes governing post-nourishment sediment dispersion within the survey domain.…”

Wave Impact Analysis on a Beach-Dune System to Support Coastal Management and Nourishment Works: The Showcase of Mira, Portugal

“…On P1 and P2, the DC height was re-established at 11 m (Figure 7), an elevation sufficient to prevent overwash events and thus dune erosion. Further monitoring of the Mira beach-dune system evolution will be necessary to support future coastal management (Silva et al, 2020;Mendes et al, 2021;Pinto et al, 2022) and dune vulnerability maps to wave forecast and predicted sea level rise (e.g., Vousdoukas et al, 2012;Mickey et al, 2018;Cunha et al, 2021). Besides this, research works point towards a significant increase in overwash frequency and magnitude by 2055 and further aggravation by 2100, particularly at the central part of a barrier (Ferreira et al, 2021).…”

Multi-Decadal Seawall-Induced Topo-Bathymetric Perturbations along a Highly Energetic Coast

“…The relation between the magnitude of the perturbation and seawall length was investigated in the bibliography, but the laboratory and field data show no consistent results [14], and for long seawalls, no correlation is physically plausible [22]. This is in contrast to other management solutions for which direct relations are observed; see Reference [59], for example. At the Lacanau seaside resort, a local retreat of approximately 5-10 m along 400 m is observable in 2011 at the southern end of the seawall (Figures 6b) relative to the longshore average position of the shoreline.…”