On the ecogeomorphological feedbacks that control tidal channel network evolution in a sandy mangrove setting.
An ecomorphodynamic model was developed to study howAvicennia marinamangroves influence channel network evolution in sandy tidal embayments. The model accounts for the effects of mangrove trees on tidal flow patterns and sediment dynamics. Mangrove growth is in turn controlled by hydrodynamic conditions. The presence of mangroves was found to enhance the initiation and branching of tidal channels, partly because the extra flow resistance in mangrove forests favours flow concentration, and thus sediment erosion in between vegetated areas. The enhanced branching of channels is also the result of a vegetation-induced increase in erosion threshold. On the other hand, this reduction in bed erodibility, together with the soil expansion driven by organic matter production, reduces the landward expansion of channels. The ongoing accretion in mangrove forests ultimately drives a reduction in tidal prism and an overall retreat of the channel network. During sea-level rise, mangroves can potentially enhance the ability of the soil surface to maintain an elevation within the upper portion of the intertidal zone, while hindering both the branching and headward erosion of the landward expanding channels. The modelling results presented here indicate the critical control exerted by ecogeomorphological interactions in driving landscape evolution.
Faculty of Engineering and the Environment , University of Southampton, University Road , Southampton SO17 1BJ, UK.
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van Maanen
School of Environment , The University of Auckland , Private Bag 92019, Auckland, New Zealand.
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Coco
Faculty of Science and Engineering , University of Waikato , Private Bag 3105, Hamilton, New Zealand.
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Bryan
biophysical interactions; mangroves; numerical modelling; tidal channel networks