Wave-mud interaction over the muddy Atchafalaya subaqueous clinoform, Louisiana, United States: Wave processes

Abstract

[1] Observations of wave and sediment processes collected at two locations on the Atchafalaya inner shelf show that wave dissipation in shallow, muddy environments is strongly coupled to bed-sediment reworking by waves. During an energetic wave event (2 m significant wave height in 5 m water depth), acoustic backscatter records suggest that sediment in the surficial bed layer evolves from consolidated mud through liquefaction, fluid mud formation, and hindered settling to gelled, under-consolidated mud. Net swell dissipation increases steadily during the storm from negligible prestorm values, consistent with bed softening, but shows no correlation with detectable fluid mud layers. Remarkably, the maximum dissipation rate occurs poststorm, when no fluid mud layers are present. In the waning stage of the storm, the contribution of different wave-forcing processes to wave dissipation is analyzed using an inverse modeling approach based on a nonlinear three-wave interaction model. Although wave-mud interaction dominates dissipative processes, nonlinear three-wave interactions control the shape of the frequency distribution of the dissipation rate. In the wake of the storm, the viscosity values predicted by the inverse modeling converge toward measured values characteristic for gelled mud in a trend that is consistent with a fluid mud entering dewatering and consolidation stages.

Wave evolution across the Louisiana shelf

“…The same trend is observed during relatively weak wind forcing, suggesting that observed bottom-induced dissipation is stronger than predicted by the model, consistent with observations from previous studies (Sheremet and Stone, 2003;Sheremet et al 2005;Elgar and Raubenheimer, 2008;Trainor, 2009, Sheremet et al 2011). …”

“…Sediment deposition extends to about 92.55° W and is restricted to approximately shoreward of the 10 m isobath (Allison et al, 2000). The presence of mud on the Louisiana shelf is known to dampen wave energy near the coast (Sheremet and Stone, 2003;Sheremet et al 2005;Kineke et al, 2006;Elgar and Raubenheimer, 2008;Trainor, 2009, Sheremet et al 2011, and has been linked to the progradation of the eastern Chenier Plain (figure 1a) along a coast where most of the shoreline is retreating (Wells and Kemp, 1981;Roberts et al, 1989;Draut et al, 2005a).…”

“…For instance, on with those dates in figure 2b) suggests that wave energy is lost during onshore propagation (further analyzed below). The loss in wave energy could be caused by bottom friction, wave breaking, or the interaction between waves and the seafloor mud layer in this area (Sheremet and Stone, 2003;Sheremet et al 2005;Elgar and Raubenheimer, 2008;Trainor, 2009;Sheremet et al 2011). It is known that dissipation can be enhanced in muddy regions through wave-mud interaction (Gade, 1958;Dalrymple & Liu, 1978;Ng, 2000;Sheremet and Stone, 2003;Sheremet et al 2005;Elgar and Raubenheimer, 2008;Trainor, 2009;Sheremet et al 2011), but it is difficult to separate the effects of seafloor rheology from other processes affecting the wave evolution, in particular because little is known about the mutual interaction between waves, currents, and mud, and the corresponding effects on wave damping across the shelf.…”

“…However, field observations show that short waves, which do not interact strongly with the seafloor, also lose energy while traversing muddy areas (Sheremet and Stone, 2003;Sheremet et. al, 2005;Elgar and Raubenheimer, 2008;Sheremet et. al, 2011), and that generation of high-frequency waves by wind during fetch-limited conditions can be suppressed (Trainor 2009).…”

Clinoforms and clinoform systems: Review and dynamic classification scheme for shorelines, subaqueous deltas, shelf edges and continental margins

“…sediment motion threshold, leading to the thick foreset deposition ( Fig. 6b; Kuehl et al, 1986Kuehl et al, , 1997Driscoll and Karner, 1999;Hernández-Molina et al, 2000a;Walsh et al, 2004;Swenson et al, 2005;Puig et al, 2007;Jaramillo et al, 2009;Sheremet et al, 2011;Mitchell, 2012;Mitchell et al, 2012;Qiu et al, 2014).…”