The influence of roughness coefficient on hydrodynamic simulations: A case study at the Co Chien estuary, Mekong delta

Abstract

Erosion in the Mekong Delta in general and the coastal area of Tra Vinh province in particular is still happening. One of the direct causes of erosion is due to hydrodynamic factors. Numerical modeling is important in studying and analyzing hydrodynamic regimes in coastal and estuarine areas. The reliability of simulation results heavily depends on the accurate determination of input parameters, among which the roughness coefficient is a crucial parameter. In coastal and estuarine areas, determining the value of the roughness coefficient is challenging due to the complex topography and hydrodynamic factors influenced by the combined effects of waves, currents, and tides. This study aims to assess the impact of the roughness coefficient (Manning's M - inverse of Manning's n ) on simulation results using the MIKE 21/3 Coupled Model FM at the Co Chien Estuary - one of the main branches of the Mekong River. The results show that as the Manning number (M) increases, water level range and current speed rise, with M impact diminishing from the river mouth toward the sea. M notably affects spring tides more than neap tides, especially at tidal troughs and peak velocities. A Manning value of 40 – 50 provides reliable results. This study initially identifies a suitable range of Manning's M values for the study area, contributing to improving the reliability of numerical models.