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Arrays of real mangrove pneumatophores (i.e. aboveground pencil roots) and artificial dowel mimics were constructed in a laboratory flume to examine differences in canopy flow dynamics. Compared to the uniform-height dowel canopy, the non-uniform height of the pneumatophores significantly reduced the intensity of the canopy shear, and shifted the turbulence maxima observed directly above the dowels upwards by approximately the standard deviation of the pneumatophore heights. Consequently, bed shear stresses were up to two times greater in the uniform-height dowel canopy than in a pneumatophore canopy of similar density. At the same time, ratios of the within-canopy velocity to the free-stream velocity above the canopies were not significantly altered by the heterogeneous height, shape and spatial distribution of the pneumatophores. Our results emphasize that uniform dowels are poor proxies of real pneumatophore canopies and may lead to underestimations of sediment-trapping efficiency. [ABSTRACT FROM AUTHOR]

This introduction to the special issue entitled, “Sediment- and hydro-dynamics of the Mekong Delta: from tidal river to continental shelf”, describes the setting and program design of collaborative studies with integrated field and modeling experiments in 2014–2015, along with associated research in the region. The Mekong River is among the largest on Earth in terms of water discharge, and much of the sediment delivered from the Tibetan Plateau has accumulated in the subaerial and subaqueous components of the Mekong Delta. As a group, the papers in this special issue describe the portion of the system where the sediment source signal is altered along the tidally influenced river and is delivered to the shorelines and continental shelf. The linked studies provide a holistic view of the system, and emphasize the interactions between hydrodynamics and sediment transport processes in sub-environments as sediment makes its way along the path from source to sink. [ABSTRACT FROM AUTHOR]