After the 1953 and 1976 North Sea floods, a flood defense plan, called the Sigma Plan, was conceived to protect the Flemish part of the Scheldt estuary against future storm surges.
The plan is governed by Waterwegen en Zeekanaal NV (W&Z), a Flemish government agency and since 2005 aims to combine flood defense with strengthening the river’s ecology through the creation of flood control areas.
Maintaining the navigability of inland waterways is also a key task of W&Z, whereby a huge amount of sediments are produced. W&Z set up a pilot project in Dendermonde, involving the construction of a compartment dyke of a flood control area using dredged material from the River Scheldt without intermediate storage between the dredging and the construction process.
Jan De Nul Group and its environmental subsidiary Envisan set out an extensive testing campaign to develop engineered sediments for use in the construction phase. This involved the testing of specific additives on the geotechnical characteristics of the dredged material.
Based on the results of the geotechnical dyke model and an economical appraisal, a specific combination was identified for large-scale use. After being mechanically dredged and transported by barges to a location near the flood defence works, the sediments are pumped ashore to the mixing plant.
The dredged material is delivered to a pontoon equipped with screens and a set of piston pumps able to push the relatively dry sediment approximately 600 m to the mixing plant.
To ensure that the dyke exhibits the performance as intended in the design calculations a Quality Assurance / Quality Control (QA/QC) program is installed. Multiple field tests are executed during construction to determine strength and permeability of the engineered sediments in the dyke body.