Sand transport under broken waves

Introduction

The surfzone is characterized by breaking waves and bores, which inject large amounts of turbulence into the water column. This turbulence is organized in vortices, that travel downward towards the bed. When these vortices reach the bed, they can entrain sand and hold it in suspension. This contrasts strongly with the situation in deeper water, where the near-bed orbital motion is the main source of sand suspension. Present-day coastal evolution models only include wave orbital motion to calculate sand transport and thus neglect the effect of downward travelling vortices associated with breaking waves and bores. To improve these morphodynamic models, a quantitative understanding of the entrainment mechanism of downward travelling vortices and their effect on sand transport is needed. Improving our understanding of these processes and the development of a practical sand transport formula are the goals of the STW funded research entitled ‘Sand transport beneath broken waves in the surf zone’ , which started in April 2013.

Methods

The measurement rig during the field campaign at Truc Vert Beach, France.
The measurement rig during the field campaign at Truc Vert Beach, France.

To ensure a wide applicability of the sand transport formula in actual coastal-evolution models, this study uses laboratory measurements (BARDEXII) and large field datasets, collected at different beaches and representing a wide range in offshore wave conditions. To extend the available data, also turbulence and sand suspension measurements will be collected during the international and multidisciplinary field campaign MegaPEX (MEGA Perturbation EXperiment) at the Sand Motor during a 4 to 6 week period in the fall of 2014.

 

More information: Joost Brinkkemper or Gerben Ruessink