The Fate of Mud Nourishment in Response to Short-Term Wind Forcing
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The Fate of Mud Nourishment in Response to Short-Term Wind Forcing Kirstin Schulz1
· Knut Klingbeil2 · Claudia Morys3 · Theo Gerkema4
Received: 25 March 2019 / Revised: 14 May 2020 / Accepted: 20 May 2020 © Coastal and Estuarine Research Federation 2020
Abstract In this study, results from a realistic 3D hydrodynamic and sediment transport model, applied to a channel in the Dutch Wadden Sea, are analyzed in order to assess the effect of short-term wind forcing, the impact of fresh water effects, and the variability induced by the spring-neap cycle on the transport of suspended sediment. In the investigated region, a pilot study for sediment nourishment, the so-called Mud Motor, is executed. This project aims for the beneficial re-use of dredged harbor sediments through the disposal of these sediments at a location where natural currents are expected to transport them toward a nearby salt marsh area. The model results presented in this study advance the understanding of the driving forces that determine sediment transport in shallow, near-coastal zones, and can help to improve the design of the Mud Motor. In the investigated channel, which is oriented parallel to the coastline, tidal asymmetries generally drive a transport of sediment in flood direction. It was found that already moderate winds along the channel axis reverse (wind in ebb direction), or greatly enhance this transport, up to an export of sediment over the adjacent water shed (wind in flood direction). The most beneficial wind conditions (moderate westerly winds) can cause an accumulation of more than 90% of the initial 200 tons sediment pool on the intertidal area; during less favorable conditions (northeasterly winds), less than a third of the dumped sediment is transported onto the mudflat. On-shore winds induce a transport toward the coast. Surprisingly, sediment pathways are only sensitive to the exact disposal location in the channel during wind conditions that counteract the tidally driven transport, and freshwater effects play no significant role for the dispersal of sediment. Keywords Mud motor · Wadden sea · Numerical model · Sediment transport
Introduction Coastal wetlands, such as salt marshes, provide unique habitats for numerous species and protect the shore from erosion Communicated by Stephen G. Monismith Kirstin Schulz
[email protected] 1
Alfred-Wegener-Institut Helmholtz-Zentrum f¨ur Polar - und Meeresforschung, Bremerhaven, Germany
2
Department of Physical Oceanography and Instrumentation, Leibniz Institute for Baltic Sea Research Warnnem¨unde, (IOW), Seestraße 15, 18119 Warnem¨unde, Germany
3
Faculty of Science, Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
4
NIOZ Netherlands Institute for Sea Research, Department of Estuarine and Delta Systems, and Utrecht University, P.O. Box 140, 4400 AC Yerseke, The Netherlands
by dampening wave energy. As their existence is closely linked to the tidal inundation, the rising sea levels will likely result in an extensiv
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