Abstract

A field experiment to measure the effects of differing concentrations of pebbles on rate of eoliao sediment transport was carried out on a sand beach on the Northumberland Strait, New Brunswick. Square ceramic tiles (0.15 m × 0.15 m) were used to replicate pebbles. These were deployed in a stratified random array in a rectangular plot 5 m wide and 2 m deep at five different concentrations (surface covers of 19, 24, 29, 34, and 44%) and both singly (two dimensional) and stacked three high (three dimensional). An adjacent plot of similar size was left bare and served as a control. Sediment transport was measured with pairs of vertical traps deployed downwind from each plot and wind speed with three-cup anemometers. Nine data sets totalling 45 runs of 10 min duration each were collected over a total of 4 days. Sediment transport over the tiled plot was normalized against transport over the bare plot. The results show an increase in sediment transport compared with the bare surface for the lowest coverage, followed by a continuous decrease in transport with increasing coverage up to the maximum coverage employed. The rate of decrease was greatest for runs that utilized a three-dimensional form, reflecting an increase in the effective area protected. The results confirm laboratory experiments, which suggest that erosion and transport are initially enhanced by acceleration of flow around pebbles and more efficient transport over the hard surface, but that this is counteracted at higher coverage densities by the increasing area of protected surface.

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