Abstract

Measurements of cross-shore velocity (u) at z = 3 cm and suspended sediment concentration (SSC) at z = 1–33 cm were collected from the swash zones of gently sloping (Perranporth, UK) and steep (Sennen, UK) beaches, during morphodynamic conditions ranging from highly dissipative to almost reflective and breaker heights ranging from 0.8 to 2.2 m. Nine swash-zone data collection runs were used to compare the performance of simplified versions of Bagnold-type energetics sediment transport models on the two different beaches. Models originally designed for suspended load, where the sediment transport (I) is approximately proportional to u4, showed no apparent improvement over those intended for bedload, where Iu3. It is suggested that the lowest SSC sensors could be measuring high concentrations in the sheet-flow layer, where previous laboratory results suggest a u3 model is most appropriate. The overall performance of the model is better (average r2 = 76%) on the gently sloping beach than on the steep beach (average r2 = 49%). Modifications to account for processes, such as bore turbulence, may improve the model's performance, particularly on steep reflective beaches.

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