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

This 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 (h(r)), the ratio between wave height (H-S) and water depth, and current directions impact the wave height decay. Further, we present empirical representations of the bulk drag coefficient (C-d) as a function of the Keulegan-Carpenter (KC) and Reynolds (Re) numbers, and the h(r) ratio(.) When applying the distinction between current directions, this representation exhibits better agreement when using the Re (rho(2) = 54%) and h(r) (rho(2) = 77%) than with the KC (rho(2) = 39%). Furthermore, we show that the representation of C-d can be improved by using a h(r)-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 H-S computed within the marsh results in a root-mean-square error of 0.014 m, overestimating the largest H-S (0.22 m) by 18%. Finally, these expressions are applied to several hypothetical sea conditions. Under similar vegetation characteristics, H-S 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.