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Research provides more accurate understanding of coastal zones

Tuesday, 14 August 2018

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CMER's recent publication 'The impact of flexibility on flow, turbulence and vertical mixing in coastal canopies' is the third to be published from Maryam Abdolahpour's PhD research with co-authors Dr Kathryn McMahon and Professor Paul Lavery. In it, we describe the outcomes of a number of laboratory flume experiments where Maryam assessed the influence of flexible canopies (in this case a Posidonia australis canopy) on the hydrodynamics within and above the canopy.

While a lot of research has examined the effects of canopies on hydrodynamics, it has overwhelmingly focused on rigid canopies, and their relevance to flexible canopies, such as seagrasses, was questionable. A laboratory investigation compared rigid canopies and flexible, buoyant model plants that mimicked the seagrass P. australis.

We demonstrated that embedding realism in model vegetation, in the form of buoyancy and flexibility, can profoundly impact the flow and mixing in wave-dominated conditions. In flexible canopies, the movement of the leaves resulted in less drag, so that the reduction in water velocity in the canopy was up to 65% less than rigid canopies. The flexible canopy also had far more turbulence near the sediment surface. Finally, the vertical turbulent diffusivity was about 35% less in the flexible canopies. All of these effects have significant implications for the transport of materials into and out of canopies and the many important ecological processes that depend on this movement of materials. While the use of appropriate flexible vegetation adds complexity to modelling efforts, it is a critical step toward a more accurate understanding of flow and mixing in coastal environments.

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