On the importance of nearshore mesh discretisation for modelling the evolution of managed shorelines

Hybrid two-dimensional (2D)/one-line shoreline models provide a more computationally efficient process for modelling shoreline change over both the micro (<10 years) and meso (10 - 100 years) timescales. An important aspect of this shoreline modelling approach is to ensure that the outputs are mesh independent (i.e., predictions are due to the underlying physics being solved, and not due to mesh resolution), which is achieved through identifying an optimal mesh discretisation for the area of interest. In this paper, we apply the MIKE 21 hybrid 2D/one-line model to examine the influence of mesh discretisation on the simulation of shoreline change in individual cross-shore coastal profiles at equal intervals alongshore, with focus on a sandy coastline along Absecon Island, New Jersey. Our findings suggest that while the optimal mesh discretisation varies based on the nature of the coastal environment under investigation, there are limitations in the applicability of hybrid models to managed shorelines. Based on these outcomes, the recommendation is that researchers would need to have more dynamic modelling capabilities to better discretise coastal environments for modelling shoreline positions, particularly since active coastal management affects model calibration and therefore reliability of model outputs. These results have important implications for optimising mesh generation to facilitate more robust applications of hybrid 2D/one-line shoreline models along sandy coastlines to better inform coastal risk management decisions.