A negative sediment budget (SB) drives short-term shoreline dynamics, while long-term processes like mean sea level (MSL) rise dominate changes over decades to centuries. Estimating drivers like SB is crucial for projecting long-term coastal changes under a quasi-stable sea level (∼7 ka). This study estimates the SB for three coastal cells, each representing a stretch of coastline with distinct shoreline behaviors over different time scales along the middle littoral of Rio Grande do Sul, Brazil, in order to simulate responses to mean sea-level (MSL) rise for the years 2039, 2049, 2074, and 2124. Medium- and short-term shoreline variations were analyzed using satellite images (2009–2022) and orthomosaics (2022–2023). Deterministic SB values were calculated using inverse modeling and integrated into coastal response simulations via the Random Shoreface Translation Model. Despite all calculated SB values being negative, shoreline projections showed an inversion in historical depositional patterns. Cell 1, historically in a relatively stable area, showed a rate decrease until 2074 (–5.5 m/yr), increasing by 2124 (–6.4 m/yr). Cell 2, previously characterized by severe erosion, displayed a similar pattern, decreasing until 2074 (–5.1 m/yr) and rising by 2124 (–5.3 m/yr). Cell 3, with less erosive SB values, showed a consistent erosion rate across all timeframes (–2.6 m/yr). Minor variations in erosion rates over short-term scales (2039–2074) highlight the influence of the calculated SB, derived from historical trends when MSL rose slowly. In long-term shoreline projections (2124), shoreface geometry increasingly influences coastal retreat, with longer and gentler shoreface profiles linked to higher retreat rates. • Integration of remote sensing, field surveys, and modeling improved coastal projections. • Sediment budget controls present to short-term shoreline behavior. • In the future coastal sectors may shift in behavior. • Sea level rise rules future shoreline position in the long-term. • Gentle slope shoreface profiles are more prone to erosion in the long-term.
Carvalho et al. (Sun,) studied this question.