On the assessment of channel deepening impacts in micro-meso tidal estuaries: A systematic analysis

Abstract

The need for efficient maritime transportation in estuaries has led to the development of diverse dredging strategies to accommodate vessels with deep drafts. Most recent studies assessing the environmental impacts of channel deepening use advanced, tailored models to simulate the long-term response to historical bathymetric changes in estuaries worldwide. However, these models are often time-consuming and highly specific to local conditions, limiting the broader applicability of their results. In addition, a common limitation is the significant time gap between the bathymetric data used, often exceeding 100 years. This makes it challenging to quantify the effects of isolated deepening operations, which is essential for understanding the influence of human intervention on estuarine dynamics. To overcome this limitation while ensuring efficient and adaptable modelling, this paper presents a three-dimensional idealised model (Delft3D) to quantify the short-term, e.g., weeks, hydrodynamic and salinity response to dredging operations in micro-meso tidal, well-mixed estuaries. Implications on channel operativity are also discussed. The numerical experiments examine variations in both channel depth and dredging length. Key findings suggest that dredging length is critical in the estuarine response. Specifically, dredging length has a greater influence on tidal amplification than channel depth. Changes in the flow structure are primarily driven by changes in the barotropic pressure gradient and bed shear forces, which vary spatially along the estuary, defining three distinct regions of behaviour. In addition, salt intrusion increases linearly with channel depth and becomes particularly sensitive to dredging length in shorter operations. Regarding basin management, results reveal that landward operativity is compromised by dredging in the lower river.