Modeling Attenuation of Storm Surge over Deformable Vegetation: Parametric Study

Abstract

This paper presents a parametric study on storm-surge reduction by flexible vegetation in coastal wetlands under idealized prototype conditions. A vegetation-induced flow resistance model that considers flow depth, flow velocity, and vegetation properties has been developed and verified using laboratory data. The model computes the drag resulting from deformable vegetation under both emergent and submerged conditions. Numerical experiments were conducted to reveal the potential of wetlands in reducing storm surge, and to examine the role of the vegetation field in obstructing surge water. Although a constant Manning’s coefficient is used commonly in hydrodynamic models simulating storm surge over coastal wetlands, the current study reveals the extraordinary temporal variation in the Manning’s coefficient. The dynamic Manning’s coefficient felt by the flow is not only a function of vegetation properties, such as stiffness, diameter, vegetation height and population density, but also varies with the water depth and flow velocity. Before vegetation becomes submerged during a storm event, the dynamic Manning’s coefficient increases with a rising water level; once the plants become submerged the coefficient decreases. The dynamic variation is attributed to the interaction between flow conditions and vegetation stiffness. Both the storm dynamics and vegetation biomechanical properties need to be taken into account for the parameterization of vegetation-induced drag and the assessment of flood risk reduction by coastal wetlands.