The planned Seine Scheldt West canal will provide a viable inland waterway connection of the Port of Zeebruges with the Seine-Scheldt liaison and the (Western) European waterway network. An extensive feasibility study was carried out, showing that from cost-benefit and technical point of view, a connection along the existing Derivation canal of the Lys is the most feasible route. The Lys itself, the most important affluent of the Scheldt, is the backbone of the Seine Scheldt liaison in the Scheldt Basin. This paper is only dealing with the aspects of salt intrusion, which is a consequence of connecting the canal to the Zeebruges Port.
Different mathematical models were used to describe the effects of constructing this canal, allowing stretched Vb convoys on the water system, including the effect of salt intrusion.
Salt flux to the canal was calculated on the basis of a measurement campaign, and used as input to calibrate diffusion and dispersion parameters for a scenario model of the new canal. Assuming reduced fluxes for a Dunkirk type lock, average canal salinity was calculated, which on its turn was used as a boundary condition for a density dependent groundwater model. The surface water model shows that with limited discharges the saline front can be stopped in the polder area where actually already saline groundwater occurs. The groundwater model shows that in the connection area of the Port, where a new canal must be constructed with a much higher canal head than the head of the surrounding groundwater, the deeper saline groundwater levels are mobilized and drained by the hydrographic network. This results in an increase of saline water concentrations near the new canal, while along the existing canal effects are fairly limited.
Measures against salt intrusion imply a certain amount of fresh water use. As the own catchment is limited in size, in periods of drought additional water resources must be addressed in order to supply the necessary fresh water.
Theoretically, these resources can be created and filled up with fresh water of flood events which would normally be diverted through the canal. In fact the canal was built in the second half of the 19th century to relieve the area of Ghent from floodings. Through the widening and deepening this function of the canal will even improve. Mathematical models were used to quantify the reduction of risk for flooding, which was included as a benefit in the cost-benefit analysis.
Although the discharges required to prevent saline intrusion are rather limited (in the order of 1 m³/s) and hardly matter on the whole of transfers, the claims on the water resources in the densely populated Scheldt basin are high and still increasing. In the context of the expected dryer summers due to global warming, there is a need to fit any new project in a global water resources management strategy on basin scale, in order to make it socially acceptable.