Deformation of Spartina patens and Spartina alterniflora stems under irregular wave action

ABSTRACT Physical modeling studies have endeavored to quantify the influence of plant biophysical parameters and hydrodynamics on wave-vegetation interactions and coastal protection. The accuracy with which such studies have characterized stem motion is limited by the predominant use of plant surrogates, and the few saltmarsh species considered in live vegetation studies. To address this, prototype-scale experiments were conducted in the outdoor Large Wave Canal of the Institut National de la Recherche Scientifique, Québec, in collaboration with the University of Ottawa and the National Research Council Canada, allowing novel characterization of live vegetation deformation under wave action. Two saltmarsh species were investigated (Spartina alterniflora, Spartina patens) under various irregular wave conditions (0.03 m< H s <0.28 m, T s 2.5, 10 s). Stem deformation was characterized using submerged cameras and bending angle tracking, coupled with wave height and velocity measurements. Significant differences in stem flexibility were observed between species, with S. alterniflora exhibiting more rigid stems (EI alterniflora =0.051 Nm2) than S. patens (EI patens =0.0015 Nm2; t-test; p<0.05). The two species consequexhibited different bending angles under similar hydrodynamic conditions, expected to influence their relative coastal protection capacity.    These findings provide critical insight into the design of marsh construction or restoration for coastal protection.