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Abstract: The discontinuous instream plants, which have progressively emerged as potentially advantageous ecomorphologic engineers capable of changing hydraulics, enhancing ecosystem resilience, and influencing sediment deposition, usually grow seasonally. Thus, understanding the feedback of flow fields and sediment deposition to the density and length of vegetation patches is essential in exploring the geomorphic role of vegetation due to its seasonal evolution in natural rivers. In this study, we conducted flume experiments to clarify the interaction mechanisms between the hydraulics and suspended sediment deposition in discontinuous emergent vegetation patches. Results validated with field data demonstrate that discontinuous vegetation patches modify flow velocity and turbulence, significantly influencing sediment deposition along the streamwise direction. Within the vegetation region, represented by Li, the enhanced turbulence and flow velocity induced by emergent vegetation were found to reduce sedimentation, while sediment deposition increased in interval regions. The sediment deposition pattern with the different lengths of patches (Lv) reveals the expansive effects of upstream patch on the downstream interval regions with different vegetation densities. When Li/Lv > 1, the interval is sufficiently long to extend turbulent eddies that originated from upstream dense vegetation patches, which restricts sediment deposition and leads to the decreased deposition of suspended sediment compared to the scenario without vegetation. However, this effect recedes with the increase in interval length. Conversely, the sparse vegetation patch enhances the total deposition magnitude when the velocity in the interval zones is small. When Li/Lv < 1, the decreased sediment deposition is observed in both dense and sparse vegetation scenarios. [ABSTRACT FROM AUTHOR]

We investigate the effects of discontinuous rigid submerged vegetation patches on flow turbulence. Two laboratory flume experiments are performed to validate the large eddy simulation (LES) model. The obtained LES data are in good agreement with the experimental data. They are also highly accurate in capturing the secondary peaks of the mean velocity near the channel bed. The coherent vortices, which are generated by the shear between the slower canopy flow and the faster overlying flow, are associated with the velocity inflection and maximum Reynolds stress around the interface. The mean velocity in the gap regions is evidently slower than that in the canopy regions. A high canopy density and Reynolds number are more conducive for the fully developed flow state of discontinuous vegetation patches. The velocity distinctly increases within the first two patches with a high canopy density. The velocity profile in the large gaps is more stable than that in the small gaps below the vegetation height, whereas the effect of patch distribution is not evident in the overlying flow layer. A spectral analysis shows that two vortex scales, namely, stem-scale and shear-scale vortices, influence the turbulence of flow through discontinuous vegetation patches. The power spectral densities are consistent with Kolmogorov theory for a −5/3 slope when the dominant eddy frequency exceeds 0.04 Hz. [ABSTRACT FROM AUTHOR]