Characterization of salt wedge intrusion process in a geographically complex microtidal deltaic estuarine system

Abstract

Deltas are strategic systems of high ecological and economic importance since they provide various environmental resources and fertile alluvial soils. Different types of hydrodynamic processes occur in deltas, including saline intrusion. We implemented a three-dimensional numerical modeling system using the EFDC + Explorer Modeling System to analyze the characteristics of saline intrusion in the Sinú River delta, Colombia. We configured the model with field data from two measurement campaigns in February and November 2021, dry and wet seasons, respectively, and with secondary information. Several climatic conditions to cover a wide range of variability in the main forcing factors were simulated, specifically river discharge and tides: (1) without the influence of the El Niño Southern Oscillation (ENSO) climatic phenomena; (2) under critically low conditions of flow discharge; and (3) with sea level rise forecasts. The model was calibrated using in-situ water velocity data and salinity profiles. We obtained Index of Agreement (d) values between 0.67 and 0.99 for salinity and higher than 0.9 for water velocity. The numerical simulation provides valuable information about this stratified salt wedge system's dynamic nature, mainly due to changes in river discharge. The simulation demonstrated that river discharges above 319 m3/s were sufficient to prevent salt wedge intrusion, which are typical values registered annually between May and November. The scenarios under critical low discharge conditions and sea level rise projections showed a maximum reach of the salt wedge intrusion of 7.40 km. The model proved efficient in evaluating the saline intrusion process in the Sinú River delta, obtaining practical results that describe the dynamics of this process. It was shown that by simulating physical processes, such as salinity stratification, numerical models provide useful information on how these estuarine systems respond to different environmental stress factors associated with current climate variability, such as long drought periods or El Niño South Oscilation (ENSO), since salinity gradients play an important role in deltas' aquatic life, since they influence the distribution of phytoplankton, which is a key player for primary productivity.