Influence of Mangrove Trees on the Storm Surge Simulation Induced by Tropical Cyclone

Mangroves can reduce flood and erosion risk by attenuating wave and storm surge impacts, trapping allochthonous sediments. The effectiveness of flood reduction by mangroves is controlled primarily by the drag force associated with the cross-sectional tree area perpendicular to the water flow. The cross-sectional area at a specific location that is related to the vertical distribution of roots, trunks, and crowns of mangrove trees determines local reduction effectiveness, while the extent of mangrove zones with distinct tree size and density distributions determines overall flood reduction effect.

In this study, the Coast and Estuarine Storm Tide (CEST) model is modified based on pseudo-porosity, in order to implement the proposed numerical solution of. The methodology is to maintain grid cells that are large relative to mangrove stem diameter, but include a method that resolves the mangroves at a sub-grid cell scale. The basic principle of the pseudo-porosity approach is to assume that the fraction of area open to flow between mangrove trees can be represented by a pseudo-porosity term denoted by P where P smaller than 1. The parameter P is defined as the ratio of the volume of water versus the total volume of water and mangrove trees on the same area.

The South Florida Basin developed by Florida Public Hurricane Loss Model (FPHLM) is used to verify and calibrate the storm surge component of hydrodynamic models using historical hurricanes including Wilma (2005) and Irma (2017). The result indicate that the maximum surge patterns on land are different from the case without mangrove effect. With the new developed pseudo-porosity module, the landward inundation extents of Wilma and Irma are decreased roughly 15 to 30 percent, and the inundation volume also decrease 20 percent. It indicates that this approach is suited to model the effect of the vegetative resistance offered by mangroves in most storm surge models. This approach that lends itself to this type of parametrization is the use of a pseudo-porosity term to augment the standard, 2D, water depth-averaged, non–linear shallow water (NLSW), or long wave, equations that are typically used for storm surge and tide modeling.