# The Influence of Hard Protection Structures on Shoreline Evolution in Riohacha, Colombia
## 4 Results and Discussion
### Zone 3: Cliff Area  
Table 6 shows a mean NSM of \(-\)37 m in Zone 3, with an average LRR of \(-\)2.3 m/yr, indicating significant cliff-top recession. The LRR variability is moderate (mean LCI: 0.66 m/yr), and the confidence in these estimates (LR2) averages 0.9 across all transects. Transects T22 and T23 exhibit lower erosion due to the cliff's orientation against predominant waves and currents from the west (Figure 8A). Unlike Zone 2, the cliffs in Zone 3 increase in height westward, making them more geotechnically unstable and likely contributing to higher recession rates. However, recent data (Figure 8A) suggest a slowdown  
Figure 6: (**A**) Historical shorelines and transects, Zone 2 beach. (**B**) Historical shorelines and transects, Zone 2 cliff. in retreat. The absence of a protective beach intensifies erosion [67], likely due to sediment retention by groins in Zone 1. The lack of pre-2003 images for Zone 3 complicates assessing the groins' impact on their natural dynamics. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Transect**} & \multicolumn{4}{c}{**DSAS Years 2003–2022**} & \multicolumn{4}{c}{**HTA**} & \multicolumn{2}{c}{**EHD**} & \multicolumn{2}{c}{**KFB**} \\ \cline{2-10}  & **NSM** & **LRR** & **LCI** & **LR2** & **Lower** & **Upper** & **Lower** & **Upper** & **Lower** & **Upper** \\  & **(m)** & **(m/yr)** & **(m/yr)** & **LR2** & **Bound** & **Bound** & **Bound** & **Bound** & **Bound** & **Bound** \\ \hline T21 & \(-45.8\) & \(-2.9\) & \(0.6\) & \(0.94\) & \(-97.7\) & \(-105.9\) & \(-52.9\) & \(-81.4\) & \(-51.3\) & \(-86.0\) \\ T22 & \(-27.9\) & \(-1.5\) & \(0.4\) & \(0.91\) & \(-49.2\) & \(-53.3\) & \(-25.1\) & \(-42.6\) & \(-16.1\) & \(-46.2\) \\ T23 & \(-18.9\) & \(-0.8\) & \(0.6\) & \(0.51\) & \(-26.4\) & \(-28.6\) & \(-3.7\) & \(-32.7\) & \(3.9\) & \(-31.0\) \\ T24 & \(-49.4\) & \(-3.1\) & \(0.7\) & \(0.94\) & \(-103.0\) & \(-111.7\) & \(-55.7\) & \(-86.0\) & \(-54.4\) & \(-89.8\) \\ T25 & \(-45.9\) & \(-2.9\) & \(0.6\) & \(0.94\) & \(-96.0\) & \(-104.0\) & \(-52.7\) & \(-79.4\) & \(-50.1\) & \(-84.1\) \\ T26 & \(-41.5\) & \(-2.6\) & \(0.4\) & \(0.97\) & \(-87.7\) & \(-95.0\) & \(-51.8\) & \(-68.8\) & \(-44.0\) & \(-73.9\) \\ T27 & \(-38.4\) & \(-2.3\) & \(0.5\) & \(0.94\) & \(-76.3\) & \(-82.7\) & \(-41.6\) & \(-63.3\) & \(-36.6\) & \(-68.5\) \\ T28 & \(-38.5\) & \(-2.5\) & \(0.4\) & \(0.96\) & \(-84.3\) & \(-91.4\) & \(-48.8\) & \(-67.2\) & \(-43.0\) & \(-73.4\) \\ T29 & \(-37.7\) & \(-2.3\) & \(0.3\) & \(0.98\) & \(-78.0\) & \(-84.4\) & \(-47.6\) & \(-59.6\) & \(-38.3\) & \(-66.1\) \\ T30 & \(-27.8\) & \(-1.7\) & \(0.4\) & \(0.93\) & \(-58.2\) & \(-63.1\) & \(-31.3\) & \(-48.8\) & \(-23.7\) & \(-53.8\) \\ T31 & \(-37.3\) & \(-2.3\) & \(0.3\) & \(0.97\) & \(-76.3\) & \(-82.7\) & \(-45.1\) & \(-59.8\) & \(-36.2\) & \(-65.1\) \\ T32 & \(-34.3\) & \(-2.1\) & \(0.3\) & \(0.96\) & \(-68.6\) & \(-74.3\) & \(-39.6\) & \(-54.7\) & \(-32.3\) & \(-61.4\) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Displacement rates of the coastline extracted from DSAS in Zone 3 and results of the prediction models. Figure 7: Zone 2—cliff, future projections up to 2045. Transects T11, T16, and T17 have not been calculated. Between 2014 and 2018, urban development advanced into this area despite evident cliff recession (Figure 9). By 2021, urbanization peaked, but in 2022, some buildings near the cliff were removed (red box in Figure 9). This city expansion highlights the absence of a coastal geomorphodynamics study like this one. The three prediction models estimate a significant recession by 2045 (Figure 8B, Table 5). At T23, the lower bound of the KFB model suggests cliff accretion, which is unrealistic without human intervention and should be disregarded. The HTA model predicts the highest recession rates but with lower variability, while the EHD and KFB models provide similar estimates, though the latter shows greater dispersion. The EHD model's prediction band falls within the KFB model's range, reinforcing their consistency (Figure 8B).