Assessing dredging impacts on channel morphodynamics and erosion–deposition in the Mai Thanh Inland Port reach of the Gianh River using the MIKE 21 FM model

Abstract

This study evaluates the impact of dredging on the hydraulic regime and channel morphodynamics—erosion and deposition—along the Gianh River reach near the Mai Thanh inland port using the MIKE modeling suite. A linked modeling chain was established: MIKE NAM (rainfall–runoff) to estimate catchment inflows, MIKE 11 HD (1D hydraulics) for routing and for providing boundary conditions to MIKE 21 FM (HD+ST) for 2D hydrodynamic and sediment-transport simulations. Model parameters were calibrated and validated against representative flood events (2013, 2016), showing high agreement (Nash–Sutcliffe ≈94–96%; mean absolute water-level error ≈0.34–0.45 m), ensuring confidence in scenario simulations. Under adverse flood-season conditions (September–November 2016), comparison of “pre-dredging” and “post-dredging” scenarios shows: (i) a slight increase in mean velocity (~0.6 cm/s), (ii) a reduction in peak flood water level of about 0.15 m, (iii) an increase in unit discharge at the outlet (e.g., at the 15 October flood peak: from 39.58 to 42.97 m³/s/m), and (iv) localized channel-bed changes, with the dredged area tending to infill rapidly after the flood season and maximum bed variations reaching ~2 m. The results imply that dredging can enhance conveyance capacity but entails localized erosion–deposition risks; adherence to approved dredging extents and techniques, together with annual monitoring of channel evolution, is necessary to inform protective measures against bank erosion and to maintain channel stability.