Parameterization of Mangrove Root Structure of Rhizophora stylosa in Coastal Hydrodynamic Model

Abstract

Mangroves are able to attenuate tsunamis, storm surges, and waves. Their protective function against wave disasters is gaining increasing attention as a typical example of the green infrastructure/Eco-DRR (Ecosystem-based Disaster Risk Reduction) in coastal regions. Hydrodynamic models commonly employed additional friction or a drag forcing term to represent mangrove-induced energy dissipation for simplicity. The well-known Morison-type formula (Morison et al. 1950) has been considered appropriate to model vegetation-induced resistance in which the information of the geometric properties of mangroves, including the root system, is needed. However, idealized vegetation configurations mainly were applied in the existing numerical models, and only a few field observations provided the empirical parameterization of the complex mangrove root structures. In this study, we conducted field surveys on the Iriomote Island of Okinawa, Japan, and Tarawa, Kiribati. We measured the representative parameters for the geometric properties of mangroves, Rhizophora stylosa, and their root system. By analyzing the data, significant correlations for hydrodynamic modeling were found among the key parameters such as the trunk diameter at breast height (DBH), the tree height H, the height of prop roots, and the projected areas of the root system. We also discussed the correlation of these representative factors with the tree age. These empirical relationships are summarized for numerical modeling at the end.

Wave attenuation of coastal mangroves at a near-prototype scale

“…DBH measurements assess the biomass of individual trees and are necessary for estimating mangrove basal area and aboveground biomass. DBH measurements are collected using diameter tape (i.e., fabric measuring tape) at 1.3 m above the soil surface (Tomiczek et al 2020;Mori et al 2022;Figure A-1). If recording the diameter of smaller trees and shrubs, calipers can be used.…”

“…Root diameter is measured to the nearest centimeter using calipers at a predetermined height or distance from the mangrove tree trunk (Ohira et al 2013;Horstman et al 2014;Mori et al 2022;Figure A-5). Although it can vary for a specific project and research goals, previous studies have measured root diameter at a height of 20 cm (Mori et al 2022) or at a distance of 15 cm away from the trunk (Ohira et al 2013).…”

“…Root spread distance measures the distance from the base of the tree trunk to the edge of outermost primary root, which can be measured using a measuring tape, a ruler, or a meter stick (Ohira et al 2013;Mori et al 2022;Figure A-6).…”

State of the practice and engineering framework for using emergent vegetation in coastal infrastructure

“…Stem density and height can be measured through traditional ecological methods (Cintrón and Schaeffer-Novelli, 1984). A variety of methods have been developed to characterize projected area (see Yoshikai et al, 2021 for an overview), including empirical models (e.g., Ohira et al, 2013;Mori et al, 2022), 3D laser scanning (e.g., Chang et al, 2019;Kelty et al, 2022), photogrammetry (e.g., Zhang et al, 2015;Maza et al, 2019), and remote sensing (Figueroa-Alfaro et al, 2022). Eventually, field measurement of engineering morphological parameters could be integrated with ecological field work.…”

Interactive relationship between plant growth and soil chemical properties in a mangrove afforestation stand, Kiribati

“…Tree size and survival rate were measured in 11 of the 19 patches differing in plant age. We used the data of tree height (H, cm) and diameter (D, cm) reported in Mori et al (2022), which were measured in 2019 (Table 1). In each patch, two or three 2 m × 2 m square subplots were randomly chosen, and the number of trees surviving within each subplot was measured.…”