Abstract
The role of bore turbulence for sediment transport in the swash and inner surf zones is investigated using field measurements of (a) cross-shore velocity using an electromagnetic current meter at z=3 cm, (b) turbulent kinetic energy ( TKE) and cross-shore velocity using a 3-dimensional acoustic Döppler velocimeter at z=7.5 cm, (c) water depth using a pressure transducer at z=0, and (d) suspended sediment concentration ( SSC) using seven miniature optical backscatter sensors at z=1–32 cm, on a steep beach in high energy conditions ( H b ≈1.6 m). High SSC and high TKE values were associated with the passing of the bore front while the near-bed flow was undergoing rapid onshore acceleration. Peak TKE values tended to occur whilst the near-bed velocity was still offshore. The SSC peaked only slightly later than the TKE and therefore no evidence exists to support advection of pre-suspended sediment. Correlation tests are performed to assess the predictive capability of (a) a Bagnold-type model based on shear stress, (b) a similar model based on TKE, and (c) a model combining (a) and (b). When the data from the whole time series are used, the combined model improves r 2 values over the shear stress model by up to 9%. If only data within bore events are included, then the improvement increases to over 55%, suggesting a significant effect of TKE on sediment transport across the bore.
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