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Estuarine Sand Dunes as a Nature-Based Solution Against Salt Intrusion : An idealised morphostatic model approach

Geerts, S.J. (2023) Estuarine Sand Dunes as a Nature-Based Solution Against Salt Intrusion : An idealised morphostatic model approach.

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Abstract:Saltwater intrusion in estuaries can pose a critical issue with significant implications for human activities. The intensity of salinity intrusion and the salt intrusion length are influenced by various factors, of which freshwater river flushing and the amount of vertical transport are key predictors. This study investigates the impact of estuarine bedforms on the salt intrusion length within estuaries. Estuarine sand dunes potentially increase the net vertical flux and, as such, reduce the salt intrusion length. We investigate the complex dynamics of estuarine salt transport and determine the potential of estuarine sand dunes as a nature-based solution against salt intrusion. This is investigated using an idealised hydrostatic model with 2DV geometry with model settings based on the Rotterdam Waterway (RWW), the Netherlands, during low river flow velocities. We show that the presence of estuarine sand dunes does not qualitatively change the dominant transport mechanisms and degree of stratification in the estuary, although quantitatively a different salt intrusion length may form by a changing balance of transport components. Changes in dune geometry and characteristics impact the salt intrusion length, which is most sensitive to a change in dune height. An increase in dune height enhances vertical advective transport, bringing more saline water upwards through the water column and thus reducing stratification. Similarly, a decrease in dune length increases the dune slope and enhances the vertical exchange. Dune asymmetry has a negligible influence on our model results. Manipulation of an existing sand dune field by dredging or dumping of sediment affects the salt intrusion length. The reduction in salt intrusion length is roughly proportional to the total volume of sediment used. Dredging of artificial sand dunes in a flat bed can serve as a mitigation tool against salt intrusion. If dredged sufficiently deep, dredged dunes generate sufficient vertical mixing to counteract the adverse effects of deepening the channel, maintaining estuary navigability while enhancing vertical mixing with local topography. In this way, estuarine sand dunes can serve as a nature-based solution against salt intrusion without changing accessibility to seaports.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:31 mathematics
Programme:Applied Mathematics MSc (60348)
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