Dredging of the canals
Dredging is without doubt the most complex part of the entire project, involving the removal and disposal of 245 000 m3 of sediments.
The challenge is enormous in terms of both engineering and environmental impact.
The sediments will be disposed of on two sites, the PCUK industrial wasteland at Wattrelos (partly on the commune of Leers) and Wasquehal.
Impact studies and risk assessments were conducted under the responsibility of VNF, for the sites at Wasquehal and Leers, while Lille's public land development agency 'Etablissement Public Foncier' is conducting the risk assessment for the former Ugine-Kuhlmann site at Wattrelos. Under a unique and innovative agreement, all the sediment from the Canal de l'Espierre in Belgium will be disposed of on the closest French site at Wattrelos, illustrated here.
On completion of the project, a huge green belt area will be open to the public alongside the Roubaix canal.
This future open space will be managed by Lille Métropole Communauté Urbaine in the context of the policy for metroplolitan green spaces (Espace Naturel Métropolitain).
The choice of dredging techniques is important. Although it is impossible not to disturb the ecosystem of the canal, and in order to minimise the impacts on the wildlife and the flora, VNF is implementing suitable techniques. To preserve as far as possible the banks and their flora (and to accelerate the return to an attractive biodiversity), VNF favoured dredging from the water rather than from the bank (see example below). Moreover, in order to limit the return to suspension of the sediment, dredging uses a ladder dredge on a pontoon rather than a suction dredger.
Dredging on a section of the Wabash & Erie canal in the USA