Flexible 3D-printed models of salt marsh vegetation to investigate unidirectional and oscillatory flow dynamics

The assessment of ecosystem services of salt marsh vegetation requires accurate replication of their biomechanical properties, particularly stem width and flexural stiffness, for example, with surrogate stems in flume experiments. Based on the versatility of three-dimensional (3D) printing, this study utilizes flexible filament to achieve in situ measured biomechanical stem properties from field campaigns. The stems are tested in unidirectional and oscillatory flow conditions to investigate the near-stem alteration of the surrounding flow field. Statistical evaluation based on a multivariate version of the two one-sided tests confirms that the surrogate stems replicate biomechanical stem properties of the tested salt marsh species. The area of extent of the influence of the stem is quantified through an enstrophy threshold of 3×10−4 s−2 for unidirectional and 5×10−6 s−2 for oscillatory flow conditions. That area of extent is shown to be a useful indicator for quantifying the influence of the stem on the surrounding oscillatory flow. The correlation between the Cauchy number and the stem position resulting from the fluid–structure interaction in both unidirectional (R2 = 0.62) and oscillatory (R2 = 0.78) flow conditions is presented. Furthermore, the fluid–structure interaction and the resulting changes in the surrounding flow field vary depending on the salt marsh vegetation species that the surrogate stems are replicating. Overall, 3D printing with flexible filaments is confirmed as a novel approach compared to previously utilized surrogate materials to replicate the biomechanical properties of live vegetation in flume experiments, paving the way for future studies to address more complex geometries or varying material properties found in live vegetation in salt marshes or other ecosystems.