Conditions for plug formation in oscillatory flow

Suspended and Bedload Transport in the Surf Zone: Implications for Sand Transport Models

“…Apparently, effects of wave breaking turbulence and of strong horizontal pressure gradients (c.f. Sleath, 1999) near the bar crest do not produce thicker phaseaveraged sheet flow layers compared to previous non-breaking wave and tunnel observations of oscillatory sheet flow. This suggests that existing models for sheet flow (bedload) transport, that have been developed for non-breaking wave conditions, may also be used for surf zone conditions.…”

Observations and modeling of wave-acceleration-induced sediment transport in the surfzone

“…Theory [Madsen, 1974], numerical models [Drake and Calantoni, 2001], laboratory measurements [Sleath, 1999], and field observations [Foster et al, 2002] suggest that horizontal pressure gradients can cause a sand bed to become fluidized such that resistance to stress is greatly reduced, thus mobilizing sediment. Sediments in unsteady flows respond to forces associated with flow-induced drag, particle stress (either via collisions for coarse grains or via vicosity of interstitial fluid for concentrated fine grains), and horizontal pressure gradients (caused by accelerating flows).…”

“…The sawtooth-like shape of nearly breaking and broken waves is associated with large fluid accelerations and decelerations during the passage of the steep wave faces, followed by relatively smaller decelerations during the passage of the gently sloping rear of the wave, producing a skewed acceleration profile. Field observations [Hanes and Huntley, 1986, Elgar et al, 2001, Foster et al, 2002, laboratory experiments [Madsen, 1974, Cox et al, 1991, King, 1991, Sleath, 1999, and numerical simulations [Drake and Calantoni, 2001, Hsu and Hanes, in preparation] suggest that fluid accelerations may have a significant effect on sediment transport. Two-phase sheet flow simulations [Hsu and Hanes, in preparation] corroborate previous field observations [Madsen, 1974, Foster et al, 2002 that indicate severe bed failure under the large flow accelerations, or horizontal pressure gradients, that precede maximum onshore velocities of near-broken waves in the surfzone.…”

Sheetflow Sediment Transport Under Asymmetric Waves and Strong Currents

“…Dohmen-Janssen et al (2002) and O'Donoghue and Wright (2004b) have found that under the same flow conditions, sheetflow layer thickness for very fine sand (d 50 = 0.13 -0.15 mm) approximately doubled that of coarser sand (d 50 0.2 mm). There is no available appropriate explanation and it might indicate the different transport for very fine sand, i.e., plug flow may easily occur with fine sand (Sleath 1999). This is not accounted in the new model and therefore may lead to its larger error.…”