Mean currents and sediment transport in a rip channel

Temporal observations of rip current circulation on a macro-tidal beach

“…Aagaard et al, 1997;Brander, 1999;Brander andShort, 2000, 2001;MacMahan et al, 2005MacMahan et al, , 2006Bruneau et al, 2009). This modulation has been linked to temporal changes in the expression of the morphology causing: (1) spatial and temporal variation in the pattern of wave dissipation; and (2) morphological flow constriction.…”

Far-infragravity and infragravity “pulses” in a rip current

“… at shorter time scales (~17 minutes) both the spectra and co-spectra were dominated by the incident swell (0.082 Hz; ~12 s) and wind waves generated by a sea breeze (0.167 Hz; ~6 s); these higher frequency waves together with the mean current were the dominant transport at short time scales (Greenwood et al [22]). Neither the consistency of the low frequency pulses through time, nor their origin(s), can be discussed in detail here, although a number of possible forcing mechanisms should be mentioned: (a) inherent modulations of the landward mass transport by Stokes drift or wave rollers over the segmented bar (Aagaard et al [2]), which is the fundamental driver of the rip cell; (b) standing farinfragravity and infragravity waves within the rip neck itself produced by wave grouping (MacMahan et al [6]; Bruneau et al [7]); and (c) current shear instabilities (Smith and Largier [16]) and (d) the expulsion of vortices from the surf zone induced by wave-group forcing of large scale Lagrangian structures (MacMahan et al [19]; Reniers et al [30,32]). …”

“…More recently, Aagaard et al [2] showed that infragravity oscillations were important to the net flux of suspended sediment in rip current systems at least at certain stages of the tide (low tide); furthermore, Greenwood et al [22] demonstrated that infragravity oscillations do influence the net transport of suspended sediment at least in the rip neck under low to moderate energy conditions, and may in fact control the direction of the suspended sediment flux at certain stages of the tide. In this paper, we document very low frequency motions ("pulses") in a rip channel under swell conditions and demonstrate their potential to transport suspended sediment offshore.…”

“…Frequently, "rips" form an integral part of a cellular water and sediment circulation in both marine and lacustrine surf zones; the classic circulation model is a net flux of water landward across the bar under the breaking waves followed by an alongshore and seaward flux through the feeder channel and rip neck respectively (Komar [1]). This flux is often modulated by the tide, even under micro-tidal conditions (Aagaard et al [2]; Brander [3,4]; MacMahan et al [5,6]; Bruneau et al [7]). Since the early work of Shepard [8], Shepard et al [9], McKenzie [10], Reimnitz [11], Reimnitz et al [12], Cook [13] and Greenwood and Davidson-Arnott [14,15] and more recently Smith and Largier [16] and Thornton et al [17], the assumption has been that rips play an important role in maintaining both the water and sediment balance on the upper shoreface, and are a large constraint on topographic change.…”

A Field and Numerical Study Into Rip Currents in Wind-Sea Dominated Environments

“…Together with the onshore mass transport over the sand bar the rip current system fulfils the requirements of mass continuity. (Aagaard et al, 1997;Brander, 1999;Callaghan et al, 2004;Dette et al, 1995;MacMahan et al, 2005). Current meters deployed in cross shore or longshore transects provide Eulerian flow measurements and give insight in the temporal variations of rip currents.…”