TY - JOUR
T1 - Observations of near-bed orbital velocities and small-scale bedforms on the Dutch lower shoreface
AU - Van Der Werf, Jebbe J.
AU - Schrijvershof, Reinier A.
AU - Brakenhoff, Laura B.
AU - Grasmeijer, Bart T.
N1 - Funding Information:
This projected was carried out in the context of the KustGenese (Coastal Genesis) 2.0 project funded by Rijkswaterstaat (RWS). RWS is part of the Dutch Ministry of Infrastructure and Water Management and responsible for the design, construction, management and maintenance of the main infrastructure facilities in the Netherlands. We would like to acknowledge RWS, in particular the vessel crew, for carrying out the lower shoreface measurements. We acknowledge the two anonymous reviewers for their constructive comments that helped to improve the paper.
Publisher Copyright:
© 2021
PY - 2022/3/1
Y1 - 2022/3/1
N2 - The lower shoreface, with water depths between about 8 and 20 m, forms the transition between the inner shelf and upper shoreface. Knowledge of the lower shoreface is essential, as it is – in many cases – the sediment source for the upper shoreface and beach. This paper presents new data of near-bed orbital velocities and small-scale bedforms at various depths and locations on the Dutch lower shoreface. Near-bed orbital velocities were beyond 1 m/s during high-energetic wave conditions. They increase with wave height and decrease with water depth, and can be reasonably well described by linear wave theory. Ripple heights range between 0.01−0.03 m and ripple lengths between 0.08−0.20 m. Ripple dimensions are controlled by wave mobility, with lower and shorter ripples for higher waves, and not so much by the currents. The Van Rijn (2007) formula generally overpredicts the ripple heights, and the variation with tidal currents in time. The measurements clearly indicate significant sediment mobility at the lower shoreface under higher wave events. It is yet unclear what this means for the net sand transport. This will depend on the subtle timing of sediment suspension, wave-mean currents and near-bed orbital velocities. It requires detailed modeling to determine lower shoreface net transport rates, and to unravel the controlling sand transport mechanisms.
AB - The lower shoreface, with water depths between about 8 and 20 m, forms the transition between the inner shelf and upper shoreface. Knowledge of the lower shoreface is essential, as it is – in many cases – the sediment source for the upper shoreface and beach. This paper presents new data of near-bed orbital velocities and small-scale bedforms at various depths and locations on the Dutch lower shoreface. Near-bed orbital velocities were beyond 1 m/s during high-energetic wave conditions. They increase with wave height and decrease with water depth, and can be reasonably well described by linear wave theory. Ripple heights range between 0.01−0.03 m and ripple lengths between 0.08−0.20 m. Ripple dimensions are controlled by wave mobility, with lower and shorter ripples for higher waves, and not so much by the currents. The Van Rijn (2007) formula generally overpredicts the ripple heights, and the variation with tidal currents in time. The measurements clearly indicate significant sediment mobility at the lower shoreface under higher wave events. It is yet unclear what this means for the net sand transport. This will depend on the subtle timing of sediment suspension, wave-mean currents and near-bed orbital velocities. It requires detailed modeling to determine lower shoreface net transport rates, and to unravel the controlling sand transport mechanisms.
KW - Field measurements
KW - Lower shoreface
KW - Near-bed orbital velocities
KW - Small-scale bedforms
KW - 22/1 OA procedure
U2 - 10.1016/j.ocecoaman.2021.106012
DO - 10.1016/j.ocecoaman.2021.106012
M3 - Article
SN - 0964-5691
VL - 218
JO - Ocean & coastal management
JF - Ocean & coastal management
M1 - 106012
ER -