Quantitative Analysis of the Seasonal Growth of Myricaria laxiflora on Flow Structure

Previous studies on vegetation–flow interactions have underestimated the morpho-biomechanical complexity of riparian plants. By integrating mechanical testing and flume experiments, the study deciphered the morpho-mechanical adaptations of Myricaria laxiflora (a Three Gorges riparian shrub) across its dormant period, early growth period, and growth boom period, while analysing the flow structure responses in the wake area. Biomechanically, stem stiffness showed minimal variation between the dormant and early growth periods, but the bending modulus increased twelvefold during the growth boom period. Aquatic morphological changes were jointly determined by frontal area and mechanical properties: Under maximum flow rates, the greatest bending occurred during the early growth period, followed by the dormant period and then the growth boom period. From the dormant to growth boom periods, the vertical frontal area expansion zone shifted from regions distal to the bed to areas adjacent to the bed, causing a corresponding descent in velocity inflection points within downstream mean velocity profiles. During early growth and growth boom periods, the development of small leaves and lateral branches enhanced frontal area, but elevated flow rates triggered vegetation reconfiguration, thereby weakening overall flow resistance. Turbulence analysis revealed spatially expanded sweep dominance during the growth boom period, intensified ejections and vortices at shear boundary layers lateral to vegetation, amplified inward/outward interactions linked to lateral branch growth, small and dense leaf morphology promoting turbulence dissipation, flexible stems homogenising wake flow and stabilising vortical structures.