Wave Attenuation by Spartina Saltmarshes in the Chesapeake Bay Under Storm Surge Conditions

Juan L Garzon,M Maza,J L Lara,C M Ferreira,I J Losada

doi:10.1029/2018jc014865

Abstract

AbstractThis study investigates the capacity of a Spartina alterniflora meadow to attenuate waves during storm events based on field observations in the Chesapeake Bay. These observations reveal that environmental conditions including the ratio between water depth and plant height (hr), the ratio between wave height (HS) and water depth, and current directions impact the wave height decay. Further, we present empirical representations of the bulk drag coefficient (Cd) as a function of the Keulegan‐Carpenter (KC) and Reynolds (Re) numbers, and the hr ratio. When applying the distinction between current directions, this representation exhibits better agreement when using the Re (ρ2 = 54%) and hr (ρ2 = 77%) than with the KC (ρ2 = 39%). Furthermore, we show that the representation of Cd can be improved by using a hr‐based modified Re and KC formulation, yielding correlations of 76% (modified Re) and 78% (modified KC). The proposed expressions are validated during another storm and predicted HS computed within the marsh results in a root‐mean‐square error of 0.014 m, overestimating the largest HS (0.22 m) by 18%. Finally, these expressions are applied to several hypothetical sea conditions. Under similar vegetation characteristics, HS of 1.55 and 0.8 m (close to a 10,000‐ and 100‐year recurrence interval storm) are attenuated by 50% and 70%, respectively, at 250 m from the marsh edge. This study provides evidence that validates the saltmarsh wave attenuation capacity during storms, quantifies this attenuation, and supports the transferability of the existing formulas in the literature across similar coastal marshes.

Highlights

The use of green infrastructure to protect coastal communities has gained popularity during the last decade, especially under the threat of rising sea levels and changes in global and regional climate patterns
This study investigates the capacity of a Spartina alterniflora meadow to attenuate waves during storm events based on field observations in the Chesapeake Bay
This study investigated the wave attenuation capacity of a S. alterniflora saltmarsh along a cross‐shore transect at a natural preserve area of the Chesapeake Bay

Summary

Introduction

The use of green infrastructure to protect coastal communities has gained popularity during the last decade, especially under the threat of rising sea levels and changes in global and regional climate patterns. Several studies have already demonstrated the ability of these natural solutions to efficiently attenuate storm surge, wave energy, and current velocities (Costanza et al, 2008; Garzon et al, 2019; Glass et al, 2017; Maza et al, 2015; Mendez & Losada, 2004; Möller et al, 2014; Möller & Spencer, 2002; Nepf, 2004; Resio & Westerink, 2008) These ecosystems continuously provide ( during storm events) many cobenefits in addition to wave protection services, including water quality improvements, sediment budget, carbon sequestration and storage, fishery habitat, and opportunities for tourism, recreation, education, and research (Barbier et al, 2011; Castagno et al, 2018; Donatelli et al, 2018; Sutton‐Grier et al, 2015). Several laboratory and field experiments have led to a better understanding of the coastal protection

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