Modeling wave impact on salt marsh boundaries

Abstract

[1] Wind-wave attack is the fundamental cause of erosion of salt marsh boundaries. Tidal forcing acts as a proxy determining at which elevation waves pound against the marsh edge and conditioning the propagation and transformation of wave trains as they move toward these boundaries. The objective of the present work is to evaluate, through analysis of the results of a numerical model, the effect of wave action on marsh boundaries as a function of tidal elevation and wave height for different edge configurations. In order to link numerical simulations to field conditions, the model inputs are based on topographical and hydrodynamical surveys conducted at a study site at the Virginia Coast Reserve (VCR), VA. Model results show that the wave thrust on the marsh scarp strongly depends on tidal level. The thrust increases with tidal elevation until the marsh is submerged and then rapidly decreases. The wave thrust is maximum for a vertical scarp and minimum for a terraced scarp. Similarly, wave energy dissipation is maximized just above the marsh platform elevation, when wave reflection is reduced and wave breaking occurs at the marsh edge.

A Field Study of How Wind Waves and Currents May Contribute to the Deterioration of Saltmarsh Fringe

“…Using this concept, wave radiation stress gradients can be connected with the forces acting on the current to calculate the wave-driven current over the reef (e.g., Symonds et al 1995;Gourlay 1996;Hearn 1999;Tartinville and Rancher 2000;Symonds and Black 2001;Gourlay and Colleter 2005;Monismith 2007). Similar to coral reefs, typical coastal wetlands have steep scarps of various heights, and wave breaking and current generation inland of a marsh edge have been reported in the literature (e.g., Tonelli et al 2010;Truong et al 2014). Considering the geometric and physical similarities, the same concept can be applied to the margin of inundated saltmarshes where wave radiation stress gradients drive the current in the marsh fringe under storm conditions.…”

“…An increased fetch as a result of wetlands converting to open water over the last century has produced higher wind waves breaking on the marsh edge (e.g., Tonelli et al 2010;Prahalad et al 2014) causing considerable erosion of wetlands Marani et al 2011;Fagherazzi et al 2013;McLoughlin et al 2014). This process of wetland loss has been less well documented in deltaic landscapes where large extensive wetland landscapes have been slowly replaced by shallow bays and estuaries.…”

Fluxes of water, sediments, and biogeochemical compounds in salt marshes

“…Salt marsh formation and persistence are dependent on the net flux of suspended sediment onto the marsh platform (Kirwan et al 2010;Fagherazzi et al 2012) and loss of salt marsh during storms Tonelli et al 2010). Interactions between tidal flows and marsh vegetation promote deposition of sediment delivered to the marsh platform during flooding tides.…”

Salt-marsh evolution at Northwick and Aust warths, Severn Estuary, UK: a case of constrained autocyclicity.

“…The strongly empirical, time-stepping model described by Gao and Collins (1997) is for a particular marsh coupled with a sandflat. Depending on the relative vertical accretion rate between the sandflat and the marsh, the effect of breaking waves on the increasingly steep, sloping zone that develops between the two environments was shown to lead to scarp formation and retreat (see also Tonelli et al 2010). Gao and Collins (1997) suggested, but did not model, how a new marsh could develop on the sandflat below the cliff.…”