Hydrodynamics and Sediment Transport in Shallow Lakes and Implications for Water Quality

Shallow lakes are considered very important but highly dynamic aquatic environments wherein hydrodynamics play an important role in controlling sediment resuspension, nutrient cycles, and the overall quality of water. In the current study the combined influence of wind-driven currents, tidal exchanges, and storm turbulence on sediment transport dynamics and resulting water quality changes in Lake Chilika, the largest coastal lagoon in India. Three-dimensional hydrodynamic-sediment-nutrient modeling (3D-HSNM) is conducted to simulate seasonal variations in flow velocities, bed shear stress, suspended sediment concentration (SSC), and nutrient transport rates in the three different sub-zones. Field surveys were carried out for 24 months (2022-2024) to obtain the field data for water levels, turbidity, total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP), and dissolved oxygen (DO) values. Model results are in excellent agreement for all variables considered (R² ≥ 0.83; Nash-Sutcliffe Efficiency ≥ 0.79). Monsoonal winds greater than 7.8 m/s resulted in bed shear stress up to 0.34 ± 0.11 N/m² that caused resuspension events with SSC as high as 168 ± 42 mg/L and SRP fluxes from bottom sediments of 8.4 ± 2.6 mg/m²/d. The existence of strong positive correlations (r > 0.86, p < 0.01) among wind speed, bed shear stress, SSC, and nutrient loads indicates that the primary mechanism of water quality deterioration at times of high-energy events is through hydrodynamic internal loading processes. The results of this study provide a physically based approach to managing eutrophication and turbidity in such environments.