Abstract
AbstractAn experimental study of unidirectional flow through a model mangrove forest measured both velocity and forces on individual trees. The individual trees were 1/12th scale models of mature Rhizophora, including 24 prop roots distributed in a three‐dimensional layout. Thirty‐two model trees were distributed in a staggered array producing a 2.5 m long forest. The velocity evolved from a boundary layer profile at the forest leading edge to a vertical profile determined by the vertical distribution of frontal area, with significantly higher velocity above the prop roots. Fully developed conditions were reached at the fifth tree row from the leading edge. Within the root zone the velocity was reduced by up to 50% and the TKE was increased by as much as fivefold, relative to the upstream conditions. TKE in the root zone was mainly produced by root and trunk wakes, and it agreed in magnitude with the estimation obtained using the Tanino and Nepf (2008) formulation. Maximum TKE occurred at the top of the roots, where a strong shear region was associated with the change in frontal area. The drag measured on individual trees decreased from the leading edge and reached a constant value at the fifth row and beyond, i.e., in the fully developed region. The drag exhibited a quadratic dependence on velocity, which justified the definition of a quadratic drag coefficient. Once the correct drag length‐scale was defined, the measured drag coefficients collapsed to a single function of Reynolds number.
Highlights
In coastal regions around the world, continuous socioeconomic development, sea level rise, and increasing storm intensity are leading to an increased risk of environmental and socioeconomic damages
For water depth h 5 25 cm (Figure 7a), which was higher than the root zone (HRmax 5 16.8 cm), the velocity was diminished in the root zone (Z/HRmax < 1), where the frontal area was highest, and the velocity was enhanced above the root zone, where the frontal area was lowest
A mangrove forest model based on the Rhizophora morphology was built at 1/12th scale
Summary
In coastal regions around the world, continuous socioeconomic development, sea level rise, and increasing storm intensity are leading to an increased risk of environmental and socioeconomic damages. Strusinska-Correia et al (2013) studied tsunami damping by mangroves using tree models with cylinders distributed in different layers to account for the prop roots, considering values of root density of a 5 year old Rhizophora mangrove They measured solitary wave free surface evolution along the forest and forces exerted on different individual trees, showing a high decay of the force after the first three rows. A better understanding of the flow adjustment and hydrodynamic drag within the complex mangrove geometry will enable a better quantification of coastal protection provided by these ecosystems This information is required to accurately evaluate the services provided by mangrove forests, which can facilitate coastal management decisions.
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