Sediment-Level Oscillations in the Swash Zone of a Mixed Sand and Gravel Beach

Small-Scale Morpho-Sedimentary Dynamics in the Swash Zone of a Megatidal Mixed Sand–Gravel Beach

“…The larger changes-both positive and negativeare loosely approximated by a Gaussian distribution, though with higher kurtosis values (kurtosis of 5.1 and 5.4 for tides 19 and 27, respectively, relative to a value of 3 for a Gaussian distribution). This finding is consistent with similar analyses in the literature [3,7,8,10], which have demonstrated that bed level change over the course of a tidal cycle is the result of the cumulative effect of many instances of small accretion and erosion. The joint probability distributions of the swash height and bed level change associated with each swash event indicate that bed level change and swash height are largely uncorrelated.…”

“…The use of ultrasonic range sensors to obtain remote observations of bed level in the swash zone has provided insight into the dynamics of beach profile change. An important result borne of swash timescale bed level monitoring during the last 15 years is that of the inter-swash timescale of net bed level change, wherein a tendency toward a dynamic equilibrium profile (see [6]) is achieved via a balance between onshore and offshore sediment fluxes over many swash events [3,[7][8][9][10]. This is contrary to the previously prevailing notion that beach face equilibrium is the result of a balance between individual uprush and downrush events (i.e., intra-swash timescales).…”

“…The use of arrays of bed level sensors has allowed for more comprehensive investigations of volume change across the beach profile, including the swash zone, than was previously possible [8,10]. Studies of bed level change at swash or near-swash timescales on MSG beaches are rare: Kulkarni et al [11] used a manual post-and-ruler surveying method to examine bed level change on a MSG beach at time intervals of minutes; Horn and Walton [7] used a similar post-and-ruler method to measure bed level every 10-25 s over a three hour period spanning high tide. They reported increases in bed elevation on the rising tide and decreases on the falling tide, with high frequency (i.e., one time step) bed level variations being nearly as large as the overall bed level change.…”

Coastal Engineering 2008

“…Previous studies of bed-level change in the swash zone have been undertaken, but such measurements are fairly sparse and generally not at sufficiently high frequency to characterise wave-by-wave bed-level change. The methods employed in these studies have included manual measurements of a series of stakes with a graduated rule (Sallenger & Richmond, 1984;Howd & Holman, 1987;Horn & Walton, 2004;Weir et al, 2006), the use of video to measure bed elevations against a series of stakes (Larson et al, 2004) and capacitance probe techniques (Waddell, 1976;Waddell, 1980). These studies suggest that considerable morphological changes can be observed in the swash zone on relatively short timescales.…”