# The Influence of Hard Protection Structures on Shoreline Evolution in Riohacha, Colombia
## 4 Results and Discussion
### Zone 3: Cliff Area
Agreement between models enhances confidence in predictions, narrowing probable outcomes and improving risk assessments for land management [68]. By 2045, cliff retreat is projected to impact buildings at T21, T24, T25, and T26, highlighting the need for the Municipality of Riohacha to integrate these findings into land-use planning, particularly considering the overlapping EHD-KFB model area. Figure 8: (**A**) Historical cliff-top evolution in Zone 3, cliff area south of Riohacha. (**B**) Future predictions based on HTA, EHD, and KFB models. Table 7 presents the rate of change in eroded material in Zone 3, showing fluctuations over different periods based on available imagery. Annual surface loss varies significantly, with extreme erosion events primarily linked to severe marine conditions caused by hurricanes and cold fronts, often associated with El Nino Southern Oscillation (ENSO) [1; 15]. Between 2003 and 2022, Colombia's Caribbean region experienced variable storm activity, with particularly active periods in 2005-2010, 2013, and 2016-2019, aligning with the most intense erosion phases. These peaks in hurricane activity were often driven by La Nina or ENSO-neutral conditions. In addition to storm activity, the erosion in Zone 3 may also be influenced by sediment retention caused by the groins built between 2006 and 2009. This period coincides with a phase of intense erosion in Zone 3, suggesting a possible connection. From 2009 to 2018, sediment retention was substantial (see Figure 5), aligning with the highest cliff recession rates in this area. However, since 2019-2020, with most groins nearly filled, erosion appears to have slowed (last column in Table 7). This trend suggests that once sediment retention reaches capacity, some equilibrium may be reestablished, potentially reducing erosion rates. As has been shown in other work [53], while groins promote sand accumulation, they can also induce significant alterations in adjacent areas, particularly downstream of their location. The possible link between groin-induced sediment trapping and increased erosion in Zone 3 requires further investigation to better understand the long-term coastal dynamics and improve future shoreline management strategies. It should also be noted that the intensification of extreme climate events under climate change could potentially enhance the influence of ENSO on coastal erosion processes in this region. ENSO phases are known to modulate storm frequency, wave energy, and precipitation patterns in the Caribbean, leading to variations in sediment transport and shoreline stability [1]. For instance, El Nino conditions often reduce tropical cyclone activity but can intensify dry seasons, potentially lowering sediment supply from riverine inputs, while La Nina tends to increase the precipitation patterns. Figure 9: Evolution of the urbanized area of Riohacha in Zone 3.  
to promote more frequent and intense storms that can accelerate coastal erosion. In the context of Riohacha, such shifts could exacerbate localized erosion hotspots, particularly near infrastructure-like groins, by altering nearshore currents and sediment dynamics. However, quantifying these impacts remains challenging due to the lack of high-resolution temporal and spatial data linking ENSO indices with coastal morphological changes in the study area. Future studies should integrate regional climate data, hydrodynamic modeling, and long-term shoreline monitoring to better understand and predict the compounded effects of ENSO variability and climate change on shoreline evolution.