Laying soil and scour protection

Bow thrusters, main propellers and river current move more material than most asset owners expect. In front of a busy berth, a single winter of manoeuvring can pull a metre of bed material away from the toe of the wall; around a bridge pier, current does the same job more slowly but just as effectively. Once the bed drops below design level, the structure loses passive support exactly where it needs it most.

We start with a pre-placement survey: soundings or multibeam data combined with a diver or ROV inspection of the toe, so the volume that has actually been lost is known before material is ordered. Protection is then built up to the design profile — graded rock, gravel filter layers, geotextile or concrete mattresses — placed from a pontoon or crane under diver guidance, in layers that will not damage the structure they protect.

The job is only finished when coverage is proven. A post-placement survey compares the achieved profile with the specification, and the difference plot goes into the asset file. For berths with heavy thruster loads we usually advise a repeat sounding after the first season — protection that is monitored lasts years longer than protection that is placed and forgotten.