Assessment of the hydrodynamic and salinity behaviour of Gatun lake, Panama

Gatun Lake serves as the primary freshwater reservoir for Panama Canal operations, and it is a major source of municipal water supply for Panama City. Since the opening of the Neo-Panamax locks in 2016, Gatun Lake’s average salinity has increased significantly. Drought and lock operations have acted on the lake simultaneously, so the observed record cannot separate their contributions, and the main drivers for salinity transport within the lake remain poorly understood. For this study a three-dimensional Delft3D-FLOW model was developed and applied to examine salinity dynamics between 2016 and 2023. Salt loads through the Neo-Panamax locks were held constant while the model was forced with observed hydrology, which isolates the lake's hydrodynamic response from variability in lock operations. Under salt loads of 4500 and 6000 metric tonnes per day, salinization intensifies during dry seasons, with concentrations in the central and southern basins ranging between 0.35 and 0.50 PSU and approaching 0.60 PSU near the locks. Salt transport in the northeastern part of the lake is restricted by the railway embankment, which limits salinity exposure of the Monte Esperanza and Sabanitas drinking-water intakes. While wind-driven circulation contributes to the lake-wide distribution of saline water, its influence is secondary to the assumed magnitude of saltwater intrusion through the locks. Under the scenarios examined, the railway embankment and the magnitude of salt load through the locks emerge as the dominant controls on where salt accumulates in the lake. These results can help inform management decisions aimed at protecting Panama’s freshwater supply.