Hydrodynamic Analysis of a Selected Reach of the Jamuna River under Structural Interventions Using Delft3D

Bangladesh is experiencing severe bank erosion on the Jamuna River, one of the world’s most dynamic and braided rivers. Groynes are widely used in various river training projects to control flow and stabilize banks by lowering velocity and promoting sediment deposition. The function and efficiency of groyne structures in terms of the ideal groyne number and arrangement on the hydrodynamics in the crucial 23-kilometer section of the Jamuna River in Bangladesh are examined in this paper. A popular two-and three-dimensional hydrodynamic model, Delft3D-FLOW, was utilized to assess key parameters, including bed shear stress, water level, and velocity distribution, as well as to simulate flow responses under various intervention scenarios. Water level, discharge, and bathymetry datasets from the Institute of Water Modeling (IWM) for the two-year period of 2021-2022 were processed for model setup. The RGFGRID and QUICKIN modules of Delft3D were utilized to generate the curvilinear grid and bathymetry, ensuring an accurate representation of river morphology. Manning’s n was used as the main tuning parameter for the model’s calibration; n = 0.020 produced the best fit (R² = 0.98) between the simulated and observed water levels at Sariakandi station (SW-15J). Strong model reliability (R² = 0.97) was validated against water level data from 2022, enabling additional simulations of various groyne configurations, such as single, double, triple, and quadruple groynes with spacing-to-length (S/L) ratios of 1.5, 2.0, and 2.5. Groynes significantly changed flow dynamics by rerouting high-velocity currents away from the riverbank, according to simulation results. Erosion control could be improved by increasing the number of groynes and optimizing spacing, which decreases near-bank velocities and bed shear stress. The most balanced results were obtained with configurations featuring four groynes and an S/L ratio of 2.0, which effectively avoided excessive flow concentration between structures while achieving a significant reduction in velocity. On the other hand, redirected flow was able to impinge on downstream banks when S/L ratios exceeded 2.5, which may have increased the risk of erosion. The results highlight Delft3D’s efficacy in assessing structural interventions for riverbank protection and offer guidance on optimizing groyne design for highly braided rivers. This method provides river engineers and planners with a useful framework for creating sustainable interventions that reduce erosion while preserving navigability and the equilibrium of sediment transport. To enhance the resilience of riverbank protection strategies, future research should incorporate morphological modeling to assess long-term changes in the riverbed and investigate climate-induced variations in flow and sediment regimes.