Quantifying the high coastal dynamics of tropical mesotidal barrier island-spit systems: case study in Northeast Brazil

This study aimed to quantify the morphological variations of the tropical mesotidal barrier-spit systems (MBs) in Northeast Brazil to understand their evolution. Therefore, Landsat 5 TM and Landsat 8 OLI images were used to construct two multitemporal analyses: one in 4-year intervals (low frequency) and another in 1-year intervals (high frequency). The results revealed that the coastal dynamic was so intense that only high-frequency analysis could represent its evolutionary behavior. Low-frequency analysis, on the other hand, could lead to the misinterpretation of the data. Despite the strong coastal dynamic, there was a long-term equilibrium in the areas occupied by the MBs. Furthermore, regarding evolutionary behavior, there were two different types of MBs: migrant and stationary. Migrant MB movement resulted from the joint actions of the meteo-oceanographic forcings that generally push the whole barrier westward, conserving its shape. The migration rate can reach 100 m per year. This process represents the visible and massive movement of sediment along the shore. The changes observed in most MBs, whether migrant or stationary, reflect their ephemeral nature and must serve as a warning for human interventions.