Preprints
https://doi.org/10.5194/egusphere-2022-1350
https://doi.org/10.5194/egusphere-2022-1350
 
12 Jan 2023
12 Jan 2023
Status: this preprint is open for discussion.

Representing the impact of Rhizophora mangroves on flow and sediment transport in a hydrodynamic model (COAWST_rh v1.0): the importance of three-dimensional root system structures

Masaya Yoshikai1, Takashi Nakamura1, Eugene C. Herrera2, Rempei Suwa3, Rene Rollon4, Raghab Ray5, Keita Furukawa6, and Kazuo Nadaoka1 Masaya Yoshikai et al.
  • 1School of Environment and Society, Tokyo Institute of Technology, Tokyo 152-8552, Japan
  • 2Institute of Civil Engineering, University of the Philippines, Diliman, Quezon City 1101, Philippines
  • 3Forestry Division, Japan International Research Center for Agricultural Sciences (JIRCAS), Ibaraki 305-8686, Japan
  • 4Institute of Environmental Science & Meteorology, College of Science, University of the Philippines, Diliman, Quezon City, 1001, Philippines
  • 5Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, 277-8564, Japan
  • 6NPO Association for Shore Environment Creation, Kanagawa, 220-0023, Japan

Abstract. 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 Rhizophora mangroves that have complicated three-dimensional root structures. Here, we present a new model to represent the impacts of Rhizophora 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 Rhizophora 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 Rhizophora mangrove forest. The model further suggested the high efficiency of the three-dimensional root structures of Rhizophora 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 Rhizophora mangrove forests which are linked to mangroves’ vulnerability and ecosystem service.

Masaya Yoshikai et al.

Status: open (until 09 Mar 2023)

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Masaya Yoshikai et al.

Model code and software

Code and data for "Representing the impact of Rhizophora mangroves on flow and sediment transport in a hydrodynamic model: importance of three-dimensional root system structures" Masaya Yoshikai https://zenodo.org/record/7353835#.Y4Rxp-zP3aR

Masaya Yoshikai et al.

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Short summary
Due to complex root system structures, representing the impacts of Rhizophora mangroves on flow and sediment transport in hydrodynamic models has been challenging. This study presents a new drag and turbulence model that leverages an empirical model for root systems. The model can be applied without rigorous measurements of root structures and showed high performance in flow simulations, which may provide a better understanding of sedimentary processes in Rhizophora mangrove forests.