Observations of surf beat forcing and dissipation

Abstract

[1] We used a simple energy balance equation, and estimates of the cross-shore energy flux carried by progressive surf beat, to calculate the rate of net surf beat forcing (or dissipation) on a beach near Duck, North Carolina. Far inside the surf zone, surf beat dissipation exceeded forcing. Outside the surf zone, surf beat forcing exceeded dissipation. When incident waves were large, surf beat dissipation inside the surf zone and forcing just outside the surf zone were both very strong (the surf beat energy dissipated in the surf zone in a single beat period was of the same order as the total amount of surf beat energy stored in the surf zone). During storms, shoreward propagation of surf beat maintained surf beat energy in the surf zone. Net surf beat dissipation in the surf zone scaled as predicted by a simple bottom stress parameterization. The inferred dissipation factor for surf beat was 0.08, within the range of wave dissipation factors usually observed in the field and 27-80 times larger than drag coefficients appropriate for the mean longshore current. The observed rapid forcing, rapid dissipation, and shoreward propagation of surf beat are not simulated by existing models of surf beat dynamics.

Infragravity waves over topography : generation, dissipation, and reflection

“…In water depths less than about 1 m, φ > 0 and infragravity energy is lost to higher Although tidal modulations were absent, previous studies on the North Carolina coast [Henderson and Bowen, 2002] identified similar cross-shore regions and rates of net infragravity gain and loss, and suggested that bottom drag may account for the observed losses, even though the drag coefficient necessary to explain the observations was an order of magnitude larger than estimates from other published studies of the nearshore region. Equation (2.2) neglects bottom drag, and instead demonstrates that nonlinear energy exchanges between infragravity waves and higher frequencies (swell and wind waves) explain most of the infragravity losses, similar to a concurrent study on the North Carolina coast [Henderson et al, submitted, 2006].…”

“…Previous studies have attributed infragravity energy loss to bottom drag [Raubenheimer et al, 1995, Henderson andBowen, 2002] and to breaking .…”

Reynolds averaged Navier–Stokes modelling of long waves induced by a transient wave group on a beach

“…The amplitude of the reflected negative pulse is smaller than that of the incident bound wave trough in the inner surf zone. The process of reduction of the negative pulse appears to be linked to the superposition of long waves generated within the surf and the swash zone (Baldock 2006) rather than to the dissipation owing to bottom friction (Henderson & Bowen 2002). Therefore, the presence of the outgoing positive pulse which propagates from the shoreline at t ≈ 115 s can be explained as a low-frequency wave generated within the surf and swash zone.…”

Cross‐ripple patterns and wave directional spectra

“…The flowmeters were sampled at a rate of 2 Hz in half hour intervals continuously. Further details on the instrumentation are given by Henderson and Bowen [2002] and Hay and Mudge [2005].…”