Aspects of the salt wedge and containment structures: Lock-Dam and the São Gonçalo Channel

Abstract

The São Gonçalo Channel connects the Patos Lagoon to the Mirim Lagoon, constituting a highly significant water body in southernmost Brazil. Its waters are used for multiple purposes, including public supply, irrigation, navigation, and recreation. To maintain freshwater conditions and prevent saltwater intrusion from the Atlantic Ocean, the São Gonçalo Channel Lock-Dam (SGCLD) was built in 1977. After nearly fifty years of continuous operation without revitalization or modernization interventions, this study aimed to evaluate the effectiveness of the SGCLD in containing saltwater intrusion in the southern portion of the channel and in the Mirim Lagoon. To this end, water quality data from the Development Agency for the Mirim Lagoon were analysed, along with data collected during a field campaign conducted in 2023 using a Conductivity-Temperature-Depth (CTD) profiler under conditions of saltwater intrusion. The measurements were carried out across two cross-sections downstream and upstream of the dam, allowing for an assessment of its efficiency. The data used correspond to depth and conductivity, which were subsequently converted into salinity. Processing was performed in Python using specific scripts. The results indicate that the SGCLD achieves over 90% efficiency in preventing the upstream advancement of salinity, ensuring the maintenance of multiple water uses, and contributing to water security and the region’s socioeconomic development.