Evaluation of vegetated shoreline capacity using CSHORE-VEG

Abstract

A versatile vegetation module has been implemented into the Cross-Shore model (CSHORE) to evaluate the capacity of coastal and marine wetlands with respect to wave-height attenuation and wave-runup reduction. This extended model, Cross-Shore-Vegetation (CSHORE-VEG), is capable of simulating the effects of rigid and flexible vegetation with spatially varying biomechanical properties. To accurately estimate the vegetation-induced energy dissipation rate, a drag coefficient formula that is independent of the vegetation flexibility was developed based on field data collected in salt marshes in Terrebonne Bay, Louisiana, during a tropical storm. This universal drag coefficient formula along with other existing drag coefficient formulas have been implemented into CSHORE-VEG to meet different needs. CSHORE-VEG has been validated against four independent datasets involving different vegetation properties for wave attenuation and mean water level change. After achieving good agreement in model-data comparisons, CSHORE-VEG was employed to quantify the capacity of two representative salt marshes composed of Spartina alterniflora and Elymus athericus for wave attenuation. As a result, two ineffective vegetated shoreline scenarios were identified. Furthermore, a procedure for determining the percentage of broken vegetation stems and modeling the corresponding wave-height reduction was applied to evaluate the wave-height reduction under realistic field conditions.

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