Comparison of Implicit and Explicit Vegetation Representations in SWAN Hindcasting Wave Dissipation by Coastal Wetlands in Chesapeake Bay

Abstract

Assessing the accuracy of nearshore numerical models—such as SWAN—is important to ensure their effectiveness in representing physical processes and predicting flood hazards. In particular, for application to coastal wetlands, it is important that the model accurately represents wave attenuation by vegetation. In SWAN, vegetation might be implemented either implicitly, using an enhanced bottom friction; or explicitly represented as drag on an immersed body. While previous studies suggest that the implicit representation underestimates dissipation, field data has only recently been used to assess fully submerged vegetation. Therefore, the present study investigates the performance of both the implicit and explicit representations of vegetation in SWAN in simulating wave attenuation over a natural emergent marsh. The wave and flow modules within Delft3D are used to create an open-ocean model to simulate offshore wave conditions. The domain is then decomposed to simulate nearshore processes and provide the boundary conditions necessary to run a standalone SWAN model. Here, the implicit and explicit representations of vegetation are finally assessed. Results show that treating vegetation simply as enhanced bottom roughness (implicitly) under-represents the complexity of wave-vegetation interaction and, consequently, underestimates wave energy dissipation (error > 30%). The explicit vegetation representation, however, shows good agreement with field data (error < 20%).

Quantifying Seasonal Seagrass Effects on Flow and Sediment Dynamics in a Back‐Barrier Bay

“…) into the wave action density spectrum balance equation. Recent studies (e.g., Baron-Hyppolite et al, 2018;Wu et al, 2016) have shown that this explicit vegetation representation in the SWAN model can produce reasonable simulation results that were in good agreement with field data and flume experiments.…”

“…This approach adds a vegetation dissipation term which depends on vegetation height (), stem diameter (), shoot density ( N ), and vegetation wave drag coefficient () into the wave action density spectrum balance equation. Recent studies (e.g., Baron‐Hyppolite et al., 2018; Wu et al., 2016) have shown that this explicit vegetation representation in the SWAN model can produce reasonable simulation results that were in good agreement with field data and flume experiments.…”

Development of damage curves for buildings near La Rochelle during storm Xynthia based on insurance claims and hydrodynamic simulations

“…Unfortunately, no more meteorological information is available. If we again compare the indices from Table 2 to those found in the literature such as Baron-Hyppolite et al (2019), we find comparable goodness of fit between modelled and measured waves.…”

Monitoring Impact of Salt-Marsh Vegetation Characteristics on Sedimentation: an Outlook for Nature-Based Flood Protection

“…The XBeach model can adequately predict wave attenuation after calibration of the bulk drag coefficient (van Rooijen et al 2016;Garzon et al 2019aGarzon et al , 2019b. The formulation by Mendez and Losada (2004) is also implemented in the SWAN model by Suzuki et al (2012) and several studies (e.g., Vuik et al 2016;Baron-Hyppolite et al 2019) have demonstrated that after calibration this extended SWAN model can adequately predict wave attenuation across a salt marsh.…”