Wave Dissipation by Vegetation

Abstract

PURPOSE:This Coastal and Hydraulics Engineering Technical Note (CHETN) provides a literature review of 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.

Nature-based flood protection: The efficiency of vegetated foreshores for reducing wave loads on coastal dikes

“…These instruments are mainly based on measurements carried out during low-energy conditions (Anderson et al, 2011), which leads to uncertainties when applying them to storm conditions. This is reflected by the large variability in formulations that describe the drag coefficient as a function of wave properties and vegetation characteristics (Table 2).…”

The influence of species, density, and diversity of macroalgal aggregations on microphytobenthic settlement

“…For example, macrophytes with district morphological characteristics reduce wave heights differentially (Anderson et al. , Ysebaert et al. ).…”

Modeling wave attenuation by salt marshes in Jamaica Bay, New York, using a new rapid wave model

“…The method of Mendez and Losada [], which is based on linear wave theory and the Morison equation [ Morison et al ., ], has been a practical physics‐based method to describe wave energy dissipation due to the drag force exerted on vegetation elements. For example, the phase‐averaged wave models such as SWAN [ Suzuki et al ., ], STWAVE [ Anderson and Smith , ], and MDO presented here, adopt this method to simulate wave attenuation due to vegetation. This method was developed for waves only and the effect of currents is usually taken into account through the vegetation bulk drag coefficient C D,v .…”

“…In recent years, some of the existing phase‐averaged wave models such as SWAN [ Suzuki et al ., ] and STWAVE [ Anderson and Smith , ] have been improved to simulate wave‐vegetation interactions through a physics‐based approach, i.e., the theories of Dalrymple et al . [] and Mendez and Losada [].…”