Quantifying Sediment Transport Across a Rapidly Eroding Berm
Abstract
Accurate field and laboratory measurements are needed for reliable computations and model validation of intra-storm beach evolution. Yet, the quantification of near-bed hydro-sedimentary dynamics is daunting due to the paucity of sensors capable of partitioning the different sediment transport modes and the inherent limitations of in situ data collection in extreme wave conditions. We performed a near-prototype physical model study (1:2.5) to investigate the sediment transport processes during erosion of a berm. We constructed a steep berm with 0.21 mm natural sand from the Oregon coast. Water levels and wave characteristics during a segment of Hurricane Sandy were simulated, and high-resolution spatial and temporal sampling was carried out at three stations across the berm (seaward slope, crest, lee side). Instantaneous near-bed sediment concentrations and flow velocities were recorded with conductivity concentration profilers (f = 8 Hz) and acoustic Doppler profiler velocimeters (f = 100 Hz) respectively at a range of 29 mm. The suspended sediment concentrations were collected with turbidity sensors at 3 and 8 cm above the bed. The sediment fluxes were calculated as the product of concentrations and the streamwise flow velocity components. Cross-shore net sediment transport was collocated with the bed level variations and sand volume losses estimated from the profile changes that were recorded with a terrestrial laser scanner system. We present the relative contribution of the sheet flow and suspended sediment transport to the total load and associate the transport with wave run-up and wave overtopping discharges. We found that for sediment transport, the suspended load was more dominant than the sheet flow in the inner surf zone, but that sheet flow was more important in the swash zone (exceeding 90% of the suspended load at times). The results also show unexpected and initial accretion at the lee side of the berm prior to the erosion of the full berm profile, despite the continuous erosive wave conditions and rising water levels.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMEP0610024P
- Keywords:
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- 1625 Geomorphology and weathering;
- GLOBAL CHANGE;
- 3020 Littoral processes;
- MARINE GEOLOGY AND GEOPHYSICS;
- 4315 Monitoring;
- forecasting;
- prediction;
- NATURAL HAZARDS;
- 4217 Coastal processes;
- OCEANOGRAPHY: GENERAL