Vessel-Generated Wake Attenuation by <i>Rhizophora Mangle</i> in Key West, Florida

Abstract

Mangroves have demonstrated the potential to provide engineering services to shorelines through wave attenuation, inland load reduction, and erosion mitigation. However, to confidently leverage these and other natural and nature-based features as coastal protection alternatives, their performance must be quantified over a broad range of environmental conditions that may interact with these systems in nature, ranging from daily stressors to extreme events. This paper examines the attenuation of 236 vessel-generated wakes through red mangroves (Rhizophora mangle) using high-frequency pressure sensors positioned at the fringe (X = 0 m), middle (X = 6.8 m), and sheltered edge (rear, X = 12.6 m) of a narrow mangrove stand near Key West, FL. We observed average characteristic wave height reductions of 38% and 65% at the middle and rear positions, respectively. At the rear of the mangrove stand, wave height attenuation increased with increasing incident relative wave height and increasing incident wave steepness for the range of characteristic wave heights, periods, and water depths observed. A subset of wake events for which water particle velocity measurements were available suggests proportionality between wave height and water particle velocity, which may indicate that transmission coefficients calculated for wave heights may be representative of water particle velocity attenuation as well. This work provides quantitative data to expand the parameter space assessing the performance of natural and nature-based infrastructure in mitigating chronic stressors such as vessel-generated wakes, which may be major drivers of erosion in developed coastal and estuarine regions.