Modeling Tidal Hydrodynamics of the Montrose Tidal Inlet System: Ebb Jet and Eddy Formation at a Tidal Inlet with a High-Angle Half-Delta

Montrose Bay’s coastline in Scotland is experiencing the most severe erosions, especially in its southern section, interfacing with the Montrose Tidal Inlet System. This inlet system could induce a distinct ebb tidal jet and eddy when ebbing, influenced by its high-angle half-delta, and the understanding of jet and eddy formation at this type of inlet is still limited. This paper presents the results of a numerical modeling study conducted using Delft3D FM to characterize tidal hydrodynamics at the Montrose Tidal Inlet System, emphasizing the flow features at its seaward side. Acoustic Doppler current profiler measurements captured an asymmetry between peak ebb and flood flow induced by the interaction between the residual of an ebb jet and the alongshore tidal current, which later was successfully replicated by the model, especially after a satellite-derived topography was applied to the Montrose Basin. The observed jet and eddy formation at the Montrose System is unique compared to what has appeared at other inlets with different delta shapes. At spring tides, the jet develops a pair of main and frontal bodies that extend more than 2 km from the inlet and experiences a sharp deflection after interacting with cross current. This jet is accompanied by only one transient eddy with about 1 km diameter at the landward side of the jet frontal. Analysis of residual flow revealed a strong residual going toward the harbor channel at adjacent beaches, which could be contributing to the ongoing sedimentation at the channel.