ERDC/CHL CHETN-I-82 "Wave Dissipation by Vegetation"

INTRODUCTION: Flooding resulting from hurricanes and other extreme storm events is a prominent risk along the coasts. These coastal areas are typically of low elevation and relief, making land and infrastructure highly susceptible to inundation by storm surge and waves. The severity of this threat is exacerbated by sea level rise and a possible increase in storm frequency and strength due to climate change. Although hard protection structures such as levees and floodwalls reduce flood risk, these structures may fail when storm conditions exceed the design threshold. There is a general consensus that wetlands, which often serve as transition zones between open water and dry land, could act as buffers and reduce storm surge and propagating waves substantially before they encounter coastal development. Unfortunately, the capability of wetlands to serve as protection during extreme storms is not understood fully or well documented; furthermore, water level and wave height reductions by vegetation are studied only in low-energy environments. Nonetheless, these studies present methods to quantify vegetationinduced wave attenuation for both modeling and design. This technical note focuses on the damping of propagating water waves by vegetation, but also discusses surge reduction briefly. Although waves may be encountered in freshwater environments (e.g., boat wakes, lake fetch, flood waves, etc.), this review focuses on coastal vegetation and resultant effects on flood and storm damage reduction.