|Wave-induced sand re-suspension at dredged gravel pits based upon hydrodynamic measurements (Tromper Wiek, Baltic Sea)|
Garel, E.; Lefebvre, A. (2010). Wave-induced sand re-suspension at dredged gravel pits based upon hydrodynamic measurements (Tromper Wiek, Baltic Sea). J. Coast. Res. SI 51: 195-204
In: Journal of Coastal Research. Coastal Education and Research Foundation: Fort Lauderdale. ISSN 0749-0208, more
dredging; suspended sediment concentration
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Gravel pits created by anchor hopper dredging may affect regional sediment transport patterns by trapping sediments. In turn, this may cause -or enhance- erosion at the adjacent coastline. Reliable assessment of such impacts requires a good understanding of the hydro-sediment dynamic processes acting at dredged pits. This paper examines the processes for sand re-suspension from pressure, current and turbidity data collected inside and outside a single dredged pit, in a non-tidal environment (Tromper Wiek, Baltic Sea). The data confirm the generally weak sediment dynamics in the area, with waves being the main hydrodynamic agent for sediment re-mobilization. Comparisons with historical data indicate a small number of sediment re-suspension events (<15%), over a 37 months-long period, without significant difference inside and outside the pit. Suspended sediment concentration profiles are predicted inside the studied pit by a simplistic model, tuned to over-estimate sediment re-suspension. The results suggest that the depth of the excavation should be very shallow (<1 m) for the bed material to be frequently extracted out by waves, and redistributed over the area. With pits up to 7 m-deep within the extraction zone, we conclude that a significant fraction of sediment is trapped over the long-term period (years).