Wetted works - dredging works

In order to install the filter-bed and the bottom-protection, the new Waterway was dredged out from a depth of 14.5 metres below Amsterdam Ordnance Datum (NAP) to a maximum depth of 22.5 metres below NAP. In total 920,000 cubic metres of sand and sludge were dredged up. With the installation of the filter-bed and the concrete sill blocks the bottom was raised to a level of 17 metres below NAP.

Three kinds of dredging vessels were used:

• The tow-hopper for the coarse-dredging of the cunette (trench) in the New Waterway. A backhoe or grab was used to dredge the slopes.
• The dustpan suction-dredger for smoothing the cunette and installing the two bottom filter-layers.
• The inclined stone-tipper for dumping the bottom protection and the other two filter-layers.