Wetland buffers: numerical modeling of wave dissipation by vegetation

Abstract

The resiliency of coastal communities is imperative because these areas experience risk of damage from coastal storms as well as increasing population pressures and development. The severity of this hazard is compounded by sea level rise and a potential increase in storm intensities due to climate change. The ability of coastal communities to plan for, resist, and quickly and completely recover from severe coastal storm events and flooding is of critical importance. There is a growing interest in applying complementary and redundant approaches to reduce the flood risk of these vulnerable communities, such as incorporating natural and nature‐based features into the project planning process. However, accounting for the benefits of these nature‐based features in coastal design is still challenging. One of the natural features generally acknowledged to offer coastal protection benefits is wetlands. Using laboratory experiments of artificial vegetation as a foundation, the bounds of wave dissipation by vegetation are explored analytically and the effectiveness of wave dissipation by vegetation over large scales is investigated using the spectral wave model STWAVE. Wave heights modeled using a vegetation dissipation formulation are compared to those modeled with the current practice of representing vegetation using bottom friction, particularly the Manning formulation. The vegetation dissipation formulation reduced more wave energy than the Manning bottom friction formulation for submerged wetlands. Because the Manning formulation does not integrate vegetation properties, to achieve consistent results would require varying the Manning n coefficient to account for the spatial and temporal variation in form drag induced by the plants due to changes in plant density, diameter, and degree of plant submergence. Thus, a re‐evaluation of existing methods for assessing wave dissipation by vegetation is recommended for wider application of vegetation dissipation formulations in numerical models. Such models are critical for evaluating coastal resiliency of communities protected by wetland features. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

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

“…The results presented in this study complement the findings from a recent study conducted by Smith et al . [] who quantified the influence of Jamaica Bay's salt marshes on waves generated by southerly winds. Both studies demonstrate the efficacy of present‐day salt marshes in Jamaica Bay for wave mitigation.…”

“…While our results suggest that the salt marshes are able to effectively protect waterfront homes in Broad Channel against eastward waves, the results from Smith et al . [] provide evidence that the salt marshes can also mitigate northward waves and therefore protect the northernmost shorelines of the bay against erosion caused by waves. In the present study, we used a stem density of 200 stems.m −2 , which is based on measurements in Jamaica Bay, whereas Smith et al .…”

“…In the present study, we used a stem density of 200 stems.m −2 , which is based on measurements in Jamaica Bay, whereas Smith et al . [] used a stem density of 400 stems.m −2 , a typical value observed in the Louisiana Coast of Gulf of Mexico [ Jadhav el al ., 2013]. This stem density is larger than the average density of S. alterniflora in Jamaica Bay and, consequently, may overestimate the ability of present‐day salt marshes to reduce wave energy.…”

Biogeomorphology: diverse, integrative and useful

“…In their discussion of intertidal mangrove forests, Balke and Friess (2016) offer a compelling argument for the application of geomorphological knowledge for successful restoration and conservation, and for improving coastal resilience against extreme storms in the tropics. Smith et al (2016) complement laboratory simulations of wave dissipation over wetlands, using numerical modelling, to up-scale over larger areas. Their study further demonstrates how species' morphological traits moderate the nature and efficacy of biogeomorphological processes.…”

“…First, the critical control of organism traits (morphological, physiological and behavioural) on the occurrence, efficacy and dynamics of biogeomorphological processes could be explored in a range of contexts. Smith et al, 2016). Second, more population-and community-level studies are needed to up-scale from individual and single-species impacts.…”