The site itself has no hydrographical network. Not one stream flows down the gentle slope. However, water is close at hand in the nearby Flemish lowlands which have a characteristic watergang drainage system, as indicated by the place names, which often end with the “ingues” suffix signalling the presence of water.
In the dale, at the bottom end of the “Longues Pièces” zone, flows a brook once renowned for its crystal clear water and the presence of watercress. Today, it is blocked by the railway lines of the Channel Tunnel terminal and disappears entirely after that.
