Future scenarios of the coastal front of La Pineda beach

The present study is developed within the framework of the contract "Stabilization and Restoration of La Pineda Beach in the Context of Climate Change and the New Master Plan of the Port of Tarragona," signed between the Port Authority of Tarragona (APT) and the Foundation Institute of Environmental Hydraulics of Cantabria (FIHAC) in April 2021, with the aim of proposing a solution to the problem of stabilization and restoration of La Pineda in accordance with the Sustainable Development Goals (SDGs) and that is compatible with the development plans of the Port and the City.

In the last 18 years, the Port Authority of Tarragona has built protective structures and made annual sand contributions to La Pineda beach as part of the measures established in the environmental impact statement. drying in certain sectors of it, which means that during major storms like the one associated with the Gloria storm (January 2020), the waves erode the beach and even reach the promenade, affecting urban furniture and facilities and services located at the beach level. This problem of sand loss and impact on the coastal front will worsen in the coming years, as an intensification of increasingly frequent storms and a rise in the mean sea level due to climate change are expected.

The main objective of this study is to propose an innovative long-term solution, with a systemic and integrated vision of the coastal front in accordance with the SDGs, that addresses the problem of the stabilization and restoration of La Pineda beach and its surroundings, in the context of global climate change and the development of the new Port Master Plan.
The most recent actions are mainly linked to the development of the Port and the stabilization measures for La Pineda beach included in the environmental impact statement (EIS) on the "extension of the breakwater" project of the Port of Tarragona. These measures include both the construction and extension of protective works, as well as sand contributions and monitoring campaigns. However, the sand contributions since the beginning of the external breakwater's reconstruction (2005-2020) have been around 1,823,053 m³, with an average sediment size D50 ranging from 0.14 to 0.26 mm (about 0.16 mm in recent years). This sand has a size considerably smaller than the native one (0.24 mm, according to previous studies of the area), which has played an important role in the evolution of the beach in recent years, creating a balanced area around the Racó breakwater, a critical erosion area in the central part of the beach, and a zone with significant accretion near the Els Prats breakwater.

Regarding the landscape, the coastal front of La Pineda beach is currently a complex framework constituted by elements of an environmental nature, such as the beach described above, and others of an urban nature. Its scope from a perceptual point of view is captured by the first line of the coastal facade, although from a metabolic point of view it extends much further, linked to ecological connectors and hydrographic corridors.

The expansion of the Port of Tarragona includes the construction of the new contradique dels Prats, which will be developed in two phases as indicated. This will undoubtedly mean a greater visual presence of the port facilities in the overall coastal facade. Similarly, the habitability conditions of the proposed spaces are not clear, as they will undoubtedly be increasingly subjected to the rigors of high summer temperatures and severe storms in autumn-winter. However, it seems appropriate to acknowledge the necessary hybridization and compatibility, whenever possible, of the infrastructures and port works that will be developed with the urban environment.

In this study, an analysis of the dynamics at play in the study area and preliminary future projections of sea level rise has been conducted, which has allowed for an estimation that by the horizon year 2100, the rise in mean sea level is approximately 0.62 m compared to the situation in 2011, considering the scenario in which emissions continue at the same rate (RCP 8.5) as recommended in the fifth IPCC report.

In the coming years, a series of actions are planned to be carried out in the La Pineda area that will transform the coastal front. In particular, regarding the seafront project drafted by the office of Jordi Bellmunt, the expected erosion due to the effects of climate change and the expansion of the Port will cause the practical disappearance of the emerged beach in large areas of the seafront. As a consequence, during episodes of strong storms, the waves will flood the promenade, causing damage to the infrastructure. In relation to the Natura 2000 Network project and the dels Prats breakwater, the expansion of the Port will modify the morphology of the beach, which will experience a substantial increase in the dry beach, making the planned freshwater exchange in the project unfeasible, potentially causing algal blooms, the presence of invasive plants, and resulting hypoxic zones during dry periods if the effects of climate change are not taken into account.

From all of the above, it is concluded that there is a need to incorporate adaptation measures into the actions to be carried out on the coastal front of La Pineda.

The principles on which the proposals presented in this study are based are as follows: reducing climate risks; increasing resilience to the effects of climate change using, whenever possible, nature-based measures; promoting accessibility; diversifying coastal uses; integrating infrastructure into the environment from both a perceptual and metabolic perspective; increasing biological diversity; protecting the Maritime-Terrestrial Public Domain (DPMT); contributing to achieving the SDGs.

Broadly speaking, the adaptation measures proposed in this study are as follows:

-Adaptation measure 1: Protect exposed areas and buildings with a wall
-Adaptation measure 2: Retreat the promenade and demolish the affected buildings
-Adaptation measure 3: Advance the beach with sand or structures

All these adaptation measures include the creation of lagoons in the vicinity of Prats with the following objectives: to reduce the amount of sand needed to be supplied; to improve ecological variability, enhance water quality for the increase of biota (phytoremediation), and increase the quality of ecosystems; to provide the area with new leisure and recreational spaces, as well as various green zones; to improve the environment both from an ecological perspective, from its use value, and from its phenomenology through the landscape integration that the lagoon favors.

Likewise, all adaptation measures entail to a greater or lesser extent the need to rethink the mobility systems of the coastal front, as well as access to the sea. There is no ideal solution; rather, each adaptation measure proposes the necessary modifications to provide universal accessibility, as well as the greatest connectivity of active mobility in order to encourage the use of the entire coastal front. In each case, these mobility/accessibility systems are accompanied by tree and shrub vegetation in order to provide the necessary environmental comfort conditions.