Comment on egusphere-2022-1350

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> In hydrodynamic models, vegetation is commonly approximated as an array of vertical cylinders to represent its impacts on flow and sediment transport. However, this simple approximation may not be valid in the case of <em>Rhizophora</em> mangroves that have complicated three-dimensional root structures. Here, we present a new model to represent the impacts of <em>Rhizophora</em> mangroves on flow and sediment transport in hydrodynamic models. The model explicitly accounts for the effects of the three-dimensional root structures on flow and turbulence, as well as the effects of two different length scales of vegetation-generated turbulence characterized by stem diameter and root diameter. The model employs an empirical model for the <em>Rhizophora</em> root structures that can be applied using basic vegetation parameters (mean stem diameter and tree density), without rigorous measurements of the root structures. We showed that compared to the conventional approximation using an array of cylinders, the new model significantly improves the predictability of velocity, turbulent kinetic energy, and bed shear stress measured in a model and a real <em>Rhizophora</em> mangrove forest. The model further suggested the high efficiency of the three-dimensional root structures of <em>Rhizophora</em> mangroves on sedimentation, which allows a relatively high sediment supply to the forest but effectively regulates sediment erosion through reduced bed shear stress, compared to cylinder arrays that exhibit equivalent sediment supply or sediment retention. The presented model could be a fundamental tool to advance our understanding of the sedimentary processes in <em>Rhizophora</em> mangrove forests which are linked to mangroves&rsquo; vulnerability and ecosystem service.