Modelling Hydrodynamics and Water Quality in a Brackish Water Lake Under Scarce Data Availability–A Case Study at the Bafa Lake, Türkiye

Abstract Dynamic modelling of brackish water lakes presents significant challenges due to variations in salinity and density over both temporal and spatial scales. These challenges are further exacerbated by anthropogenic activities that disturb the hydrologic regimes of these lakes. This study aims to construct a 3-dimensional (3D) hydrodynamic and water quality model for Bafa Lake, a large, eutrophic, brackish water lake in Türkiye, where the natural hydrologic regime has been significantly altered by artificial inflow and outflow canals. Bafa Lake faces substantial pressure from point and diffuse pollution sources. The water level in the lake is kept at + 2 m by water transfer through an artificial canal, which makes the salinity/density profiles more variable. Delft3D-FLOW and Delft3D-WAQ models were employed for simulating hydrodynamics, salinity/density, and water quality in Bafa Lake. The models were calibrated and validated using a comprehensive hydrologic and water quality data collected over a one-year monitoring campaign. Three management scenarios were developed and tested using the validated model to identify potential solutions for the lake’s eutrophication problem. The scenario analysis revealed that the most effective water quality improvement could be achieved by halting the artificial flow, which provided 5–25% reduction in nutrient concentrations. This finding shows that the alteration of the natural flow regime of the lake has not only affected hydrodynamics but also created problems for lake water quality. Graphical abstract