Causes of the different behaviour of the shoreline on beaches with similar characteristics. Study case of the San Juan and Guardamar del Segura beaches, Spain

Abstract

Storms can alter the beach shape, relocating large volumes of sediments and generating drastic changes in the coastline. In the last 60years, beaches shoreline behaviour has been different even though the energy of the waves was similar. Therefore, it is necessary to understand the factors that affect the sandy coasts for better future management. In this research, two beaches, with different erosion rate, located in the southeast of Spain (separated by only 40km of distance) have been studied. The beaches: i) have similar orientations, ii) are open to waves with similar sand lengths of 9.8km and 6.6km, and iii) have similar median sediment size (D). For its study, shoreline evolution has been analysed from 1956 to 2017. From the results obtained, it can be seen that: i) Between 1992 and 2017, San Juan just lost 3% of its surface, while in the previous period (1956-1990) it was 50%, and ii) Guardamar surface lost in 1992-2017 was 18%, and in the previous period it was 14%. For the analysis of the agents involved in both beaches, cross-shore profiles (volume), marine climate, biocenosis and sedimentology studies were carried out. The results showed that the energy on both beaches was very similar. The biocenosis had not changed and, however, the morphology of Guardamar seabed had increased to 1m deep in some places, which had caused part of the beach berm erosion. Furthermore, important differences were found from the sedimentological study, concluding that the content of calcites and the degree of homogeneity of the particles are the real factors that caused these two beaches to behave differently against erosion.

3-D Morphological Change Analysis of a Beach with Seagrass Berm Using a Terrestrial Laser Scanner

“…This coast experiences a severe pressure of tourist inflow, and several beaches are subject to erosion (example study cases are References [53][54][55][56][57]). Artificial nourishment of beaches is common in this region, notably between 1985 and 1999 [58].…”

Experiences with beach nourishments on the coast of Alicante, Spain

“…The placement of sand on the beach is considered the most acceptable form of coastal stabilization [5,8]. However, it is important to be aware of the effects of the anthropic actions carried out in the past to project future coastal works [1,2,4,17,22,23].…”

Relationship between shoreline evolution and sediment wear

“…Therefore, sediments are an important part of understanding coastal processes [12]. Many authors relate shoreline changes to sediment movements, specifically between the shoreline and the depth of closure [10,13,37], while others indicate that sediment wear is an important factor in shoreline evolution [8,32,33].…”

“…Therefore, it is clear that the mineralogical composition of the sediment is an important factor to consider in wear [34]. However, according to several authors, the most influential factors in sediment wear are the morphology and fatigue of the material [21,32]. Fatigue is understood as the breakage of the material when it is submitted to long-duration dynamic efforts, or the tendency to fail due to cyclic loads [4,5].…”

“…Therefore, it is known that the sediment is worn by breakage when the particles collide with each other, by the dissolution of the mineral elements that compose it and by the fractures and micro-fissures of the particles [20,21,32]. However, the degree of influence that sediment wear has on beach erosion is not known.…”