## 4 Results and Discussion
### Shoreline Evolution (Past and Future)
However, as can be seen in Figure 7, the houses of Babilonia Beach act as an artificial barrier (or artificial shoreline), and therefore, there can be no further erosion except for the destruction of the houses themselves. If zone C is analyzed for the entire available time set, it can be observed that the fits are better and that the NSM value amounts to 33.86 m (0.32 m/yr). As in zone B, Figure 4 shows how erosion rates have increased after anthropogenic actions. The effect of erosion on the houses of Babilonia Beach was also analyzed. During the 1930s and up to the 1970s, the built-up area increased, with 8533 m\({}^{2}\) (55 houses) in 1930; 12,277 m\({}^{2}\) (80 houses) in 1946; 17,976 m\({}^{2}\) (117 houses) in 1956; and 19,463 m\({}^{2}\) (126 houses) in 1977. This last value remained stable until 1999. From then on, and as a natural response to the values already discussed, the built-up area has been in continuous decline. Until 2005 the loss of floor area was a mere 131 m\({}^{2}\) (one house). But from 2005 to 2012, the loss increased by 2218 m\({}^{2}\) (14 houses) and has not stopped until 2022 (last data available), with a loss of another 1003 m\({}^{2}\) (6 houses). One should consider the numerous attempts to protect these houses with the use of rock dikes, Hesco barriers filled with rock and sand, etc., that have managed to somewhat slow down the destruction of these houses [49]. Figure 6: Zone B. (**a**,**d**) Shorelines and transects from 1930 to 1989 (background image from 1989). (**b**,**e**) Shorelines and transects from 1997 to 2022 (background image from 2022). (**c**,**f**) Shorelines and transects from 1930 to 2022 (background image from 2022). Having historical erosion data in different transects, it is possible to apply the prediction models explained in Section 3.3. An adequate time horizon, preferably shorter than the available observation period (92 years), should be chosen to consider the data variability and, at the same time, to reduce the impact of data uncertainty on the quality of the results [39]. Therefore, the simulation is extended for 18 years, up to the year 2040 (see Table 3). Uncertainties have been incorporated for each model, including lower/upper bounds, having a surface area that delimits the possible solution (Figure 8). In the Lee-Clark model, uncertainty in the calculation of future erosion (LCe) is incorporated by adding (upper bound) and/or subtracting (lower bound) the LCI to the LRR value for each transect (see Table 2). For the Leatherman model, the limits are introduced using a minimum and maximum estimate of the rate of sea level rise in the future (\(S_{2}\)). According to local estimates, the future rates will be a maximum (upper bound) of 0.5 mm/yr, with a reasonable minimum (lower bound) value of 0.25 mm/yr [25]. As mentioned in Section 2, the historical relative sea level rise (\(S_{1}\)) has been 1.28 mm/yr. As can be seen in Figure 8 and Table 3, the prediction models overlap in most cases. In this situation, it can be said that the shoreline is most likely to be located at some intersection surface of the two models. The Lee and Clark model has a larger difference between the lower and upper limits than the Leatherman. This is probably because the variability in historical erosion rates is greater than the effect of sea level changes for this relatively short simulation period. In the northern part of zone B, the shoreline is predicted to reach the area currently occupied by the cliff dune that, therefore, would also be eroded. In zone C, the houses continue to act as a barrier, although in the northern zone, erosion will increase and the loss of built-up area is likely to increase following the actual trend.