# The Influence of Hard Protection Structures on Shoreline Evolution in Riohacha, Colombia
## 1 Introduction  
The shoreline serves as the boundary between land and sea, subject to alterations from both natural processes and anthropogenic factors. Natural processes can be associated with the usual coastal dynamics (e.g., waves, tides, sediment transport), more extreme phenomena (such as storms or floods), and factors related to the terrestrial part (such as vegetation, geology, cliff profile, etc.). In addition, these natural processes are being modified in many cases by the effects of climate change (i.e., sea level change or extreme events), especially in the last 40/50 years [1]. These factors have altered natural coastal dynamics, leading to localized erosion and deposition processes that have transformed the original state of certain areas [2]. Anthropogenic factors can also determine or condition coastal evolution with the construction of coastal engineering infrastructures, sand extraction, land use, etc. All these phenomena, together or separately, can modify the erosion ofcliffs and beaches [3; 4]. The problems associated with erosional phenomena range from increased exposure of the population to natural hazards such as tsunamis or floods, to the degradation of ecosystems, or economic losses due to the destruction of houses, the decline in tourism, or the loss of land itself [5; 6]. In contrast, accretion zones are generally less vulnerable to natural hazards by moving the coastline further offshore; in addition, tourism and economic activity tend to increase [7]. Latin America's coastal zones face growing climate challenges, including erosion, rising vulnerability, and ecosystem degradation. With over 600 million inhabitants, many countries--such as Brazil, Colombia, and Venezuela--have more than 30% of their population in Low-Elevation Coastal Zones (LECZs), areas below 10 m above sea level [8]. These regions are particularly vulnerable to flooding, sea level rise, tsunamis (and the resulting inundation), and other extreme weather events [1; 9; 10]. Additionally, Latin America is projected to experience the second-largest population growth globally, with an 80% increase in LECZ residents over the next century [11]. Colombia's coastal regions, particularly the Caribbean coast, are renowned for their diverse marine ecosystems and pristine beaches, which support a thriving tourism industry and play a key role in the national economy [12]. However, these areas are undergoing profound transformations due to coastal erosion, sedimentation, and human interventions such as dam construction, inadequate coastal infrastructure, and mangrove deforestation. Increased tourism has further intensified these pressures. Currently, approximately 50% of the Colombian Caribbean coastline is affected by erosion, leading to the displacement of some coastal communities [13]. Studies report varying erosion rates from the 1950s to the early 2010s across different regions: from 0.62 m/yr to 3.3 m/yr in the Department of Cordoba, up to 5.3 m/yr in Magdalena, and around 3 m/yr in La Guajira [14; 15; 16]. The study of shoreline evolution is essential for assessing coastal risks and informing sustainable management strategies [17]. To accurately measure shoreline changes, various remote sensing techniques and analytical tools are employed, including aerial photographs, satellite imagery, historical maps, and airborne LiDAR surveys. These, combined with Geographic Information Systems (GIS), enable the reconstruction of coastline evolution across different temporal scales [18]. Such datasets provide critical insights into both long-term (>60 years) and medium-term (10-60 years) shoreline movements and transformations [19]. Recent studies demonstrate the effectiveness of these methodologies. In a broader historical approach, [PERSON] et al. [20] analyzed Holderness Coast (U.K.) cliffs through map data (1852-1929), aerial photos (1952-1996), and LiDAR-GPS data (2011), reporting an average recession rate of 1.25 m/yr. Similarly, [PERSON] et al.