Abstract for the 18th Physics of Estuaries and Coastal Seas Conference, 2016

On the modelling of saltwater intrusion in the – Rhine Canal system with DFlow-FM

Nathanaël Geleynse1, Jos van der Baan2, Gijs van Banning3, Jeroen Adema4

Keywords: salinity, North Sea Canal, stratification, translation wave, DFlow-FM, hydrodynamics.

Abstract The North Sea Canal-Amsterdam Rhine Canal (NSC-ARC) system is a complex canal system in the . Since its completion in 1876, the 21 km long North Sea Canal connects the IJ at Amsterdam to the North Sea at the port of IJmuiden. It is situated in an area of reclaimed land (“IJpolders”). The 72 km long Amsterdam Rhine Canal in turn, connects the North Sea Canal to the rivers Lek and Waal (branches of the river Rhine) in the Dutch hinterland. The coupled canal system receives only less than about 1% of the yearly total Rhine-Meuse discharge at the Dutch border. Together with the New Waterway (entrance to the Rotterdam harbour), it is the most important shipping route of Western Europe. Its navigation locks as well as other impacts, such as pumping of drainage water and extraction of water for industrial purposes, add to the complexity of the system. A major challenge concerns the development of a sound understanding of the hydrodynamics and salt water dynamics of the NSC-ARC system. In particular, it is important to assess whether we can accurately represent today’s salt water intrusion along the Canal. Moreover, it is interesting to investigate future scenarios as well as to assess the effect of control measures. To address this challenge, a proper numerical model is needed, combined with high-quality measurements. The three-dimensional nature of both geometry and (thus) physics inevitably confronts us with extensive computational demands. To address this demand, the newly-developed DFlow-FM software provides a computationally-efficient tool to simulate hydrodynamic and salt water processes in this area. Here, we present findings of our DFlow-FM model of the system. Firstly, we show how we computed the large- scale water balance for the NSC-ARC system based on measurements for the 2014 situation. Subsequently, we present modelled hydrodynamics and salinity (Figure 1 and Figure 2), including a comparison between measured and simulated salinity at several locations along the axis of NSC-ARC (see Figure 3). In addition, we explore the sensitivity of the model system to relevant parameters. We then show the response of the system to future scenarios and measures such as variations of upstream boundary conditions, as apparent from measurements (see Figure 4). Finally, we provide our latest model extensions to further improve our understanding of this weakly-dynamic complex system.

Figure 1 Flow velocity and salinity along a stretch of the North Sea Canal in the vicinity of the ship locks at IJmuiden.

1 ARCADIS, [email protected] 2 ARCADIS, [email protected] 3 ARCADIS, [email protected] 4 ARCADIS, [email protected]

Figure 2 Flow velocity and salinity along a stretch of the IJ, Amsterdam.

Figure 3 Time series of modelled and measured salinity at different depths, at a location in the “Binnenspuikanaal”, IJmuiden.

Figure 4 Upper panel: time series of measured water discharge variations at location ‘Weesp’ along the Amsterdam Rhine Canal. Center and bottom panel: time series of measured chlorine content at location ‘NDSM-pier’ along the IJ, Amsterdam and at location ‘Diemen’ along the Amsterdam-Rhine Canal.