Wetted works sill-blocks

A total of 64 sill-blocks have been installed on the bottom of the fast- flowing New Waterway at an average distance of 3.5 centimetres apart. The blocks were delivered by pontoon and positioned with the aid of a floating derrick. Various measuring instruments were used to enable the blocks to be positioned to within one centimetre. A 21-metre-high measuring tower was attached to each block, which remained just poking up above water after the block had been sunk into position.

Since the sills are somewhat curved, the blocks are slightly wedge-shaped. In cross-section the blocks are also flared, thus preventing the tops of the blocks from "rubbing" against each other in such a way as to create a larger crack at the bottom than permitted. Two rubber toes have been fitted on one side of each block, with corresponding notches on the other side.