Future scenarios and climate change adaptation of the coastal strip of La Manga del Mar Menor

The Region of Murcia is a coastal region that has a vast and rich coastline, with numerous ecosystems and spectacular landscapes. Moreover, its economy depends largely on its coast as it hosts activities ranging from very traditional ones like fishing to others such as mass sun and beach tourism or maritime transport, as well as infrastructures and urban centers of great importance for the region. The past has taught us that the coastal strip and the shoreline are highly dynamic and exhibit significant natural variability.

Unfortunately, the economic development model implemented, especially in the second half of the 20th century, and the extensive exploitation of coastal resources have posed a great threat to the coastline, increasing its exposure and vulnerability in many areas due to urban pressure and the degradation suffered. As part of this development, urbanization has modified and rigidified the coast, conditioning its natural variability.
The construction of buildings and roads on dunes and coastal ridges; the draining of marshes and coastal lagoons, and the construction of dikes and groins have contributed to this coastal rigidification.

To these anthropogenic pressures, the threat of climate change must be added. Changes in the atmospheric temperature and precipitation regime, the increase in the frequency of extreme weather and climate events are, today, some of the most well-known risk-inducing factors on the coast. However, in the coastal realm, other marine-origin factors such as the rise in mean sea level, the increase in sea surface temperature and associated marine heatwaves, changes in extreme sea levels or in the direction and intensity of waves, or acidification, are crucial when addressing the risks of flooding, erosion, or other types of impacts on marine ecosystems.

Within the Region of Murcia, La Manga del Mar Menor is an important coastal strip that is about 20 kilometers long, with a width ranging from 100 to 1200 meters, extending from Cape Palos to the Salinas and Arenales of San Pedro del Pinatar.

La Manga is responsible for the formation of the Mar Menor, the largest coastal lagoon in Spain. La Manga and the Mar Menor form a unique geomorphological and ecological element, pressured by urban development and tourism-related activities. Therefore, it is configured as a highly exposed element to coastal impacts of erosion and flooding derived from climate change.

The definition of a coastal adaptation plan in response to the effects of climate change requires the definition of strategies to reduce risk. To achieve this, it is necessary to act individually or collectively on the components of that risk: the hazard and impacts, exposure, or vulnerability. The possible strategies to reduce the risk of erosion and flooding range from controlled abandonment, protection, and accommodation, to advancement or progression towards the sea.
In order to reduce the risk of erosion and flooding in La Manga del Mar Menor, an adaptation plan is proposed that combines controlled retreat and coastal protection through four measures consisting of implementing: sediment containment elements, coastal defense elements, restoration of ecosystem services, and instruments for reducing exposure.

Within this adaptation plan, a high-resolution analysis and adaptation proposals have been made for three specific locations: Mojón Beach, Pudrimel Cove, and Estacio Beach.

Mojón Beach is located on a coastal stretch bordered to the north by the port of Torre Horadada in Alicante and the port of San Pedro del Pinatar in the Region of Murcia to the south. The dominant marine dynamics generate a southward transport of sediments, and the beach is reinforced by a promenade that protects houses built very close to the shoreline. Currently, the longshore currents generated by the waves sweep the sediment from the northern section of the promenade to the south, undermining its foundation, leaving adjacent houses unprotected, and reducing the area of dry beach.

The first measure is the reduction of exposure by recovering the Maritime Terrestrial Domain invaded by a set of buildings constructed on the dune and without protection from the promenade.
The second measure consists of sediment containment through the construction of a support dam in front of Avenida el Saladero, 120 meters in length, which promotes the stabilization of the coastline along the entire maritime front of Mojón.

The third measure is based on the restoration of ecosystem services through dynamic regeneration supported by the dike, which is carried out when the minimum beach width is less than 10 meters through actions that provide the beach with at least 30 meters of width.

The Pudrimel cove is a coastal stretch bordered to the north by Pudrimel beach and to the south by Esparto beach. It is an enclosed system whose balanced plan shape corresponds to the fit between the rocky points of Pudrimel and Cocedor. The marine dynamics are mild due to the sheltering effect of the rocky outcrops, especially at the ends of the cove, which has facilitated extensive urban development with invasions of the beach-dune system. Currently, the system is in equilibrium, but the available beach width is very limited in the northern area of Pudrimel and the southern area of Playa del Cocedor, reaching less than 10 meters in some points.

The first measure consists of reducing exposure by reclaiming the Maritime Terrestrial Public Domain invaded by a set of buildings constructed on the dune and completely unprotected against wave action in the central and southern sections of the cove.

Additionally, a second measure is proposed to contain the sediment through two 120-meter-long dikes, in front of the Punta del Cormorán urbanization on Pudrimel beach and in front of Oasis street on Esparto beach. Given the static equilibrium in which the cove is situated, the construction of these perpendicular dikes aims to zone the northern and southern sections and prevent the fill dumped in that area from dispersing throughout the bay due to dynamic actions.

The third measure involves the restoration of ecosystem services through dynamic regeneration, which begins with a current discharge of 20,000 m³ in the northern zone and 60,000 m³ in the southern zone, ensuring a minimum beach width of 15 meters.

The stretch located between Estacio and Levante beaches is formed by two coastal segments separated by the Calnegre point but with similar behavior. The first segment, located to the north, includes the beaches of Estacio, Punta Seca, Las Gaviotas, El Arenal, Pedrucho, Eurovosa, and Banco del Tabal. To the south of the Punta de Calnegre, you will find the beaches of Galúa, Barco Perdido, Las Amoladeras, and Levante. It is a coastal stretch where the longitudinal transport of sediments is practically non-existent, and the shape of the beach is conditioned by a rocky slab that runs almost parallel to the shoreline, at a distance varying between 200 and 400 meters, and functions as a submerged dam, limiting the energy of the incoming waves and stabilizing the shoreline.

The first measure consists of reclaiming the invasions of the Maritime Terrestrial Public Domain, thus reducing the exposed elements. The second measure focuses on stabilizing the coastline through an artificial reconstruction of the gaps present in the rocky slab in order to mimic its hydrodynamic and morphological behavior, without forgetting its environmental benefits linked to the fixation of flora and fauna. In the case of the continuity of the slab, the return currents that sweep the sediment from the beach front to the sea disappear. In order to recover the ecosystem benefits of the beaches after erosion due to the rise in mean sea level, the third measure consists of dynamic regeneration that ensures the minimum width of the section does not fall below 10 meters.