The RocLoc Stabilisation System (RLSS) was developed by intuitively addressing the specific challenges of the Oaky Creek Diversion.

The basic problem was to ensure the integrity of the cascade steps, while allowing for settlement. The unstable substrate precluded the use of a solid-faced structure, yet the use of rock armouring (which is ideally suited to these situations) still relied upon finding a way to form up the actual cascade steps.

Water Solutions considered that these challenges could be met by forming the cascade steps from interlocking concrete crib-wall type blocks, with rock fill behind. These modular blocks would ensure the consistency of the vertical faces of the steps, maximising long-term energy dissipation and could be designed to articulate in response to settlement without compromising the integrity of the cascade structure.

Relatively small rock could be used to protect the base of each cascade step from erosion. Although small rocks could be easily moved by the waterfall flow, they could be kept in place by placing an open grid of concrete beams over them. The grid of beams would effectively act as a hydraulic lid, holding the rock beneath in place. Water flowing over the cascade would impart a downward thrust on the beams, while being deflected laterally.

The combined effect of the physical presence of the grid beams and the deflected jets of water would then prevent the displacement of exposed rock within the open grid pattern. If the rocks are not displaced then structural integrity of the system is assured. The grids could be easily tied back into the cascade crib wall.

After much consideration and trial, three basic block types – the Anchor Block, Baffle Block and Weir Block were developed to provide a complete system for cascade step stabilisation. Together, the blocks were expected to:

  • Ensure the required vertical drop is maintained
  • Retain upstream rockfill material
  • Retain rockfill material at the base of the drop
  • Adapt to settling of bed materials


The blocks would be made of pre-cast, reinforced concrete and could be readily lifted into place from within the waterway itself. Rock fill material would subsequently be placed about the blocks to complete the structure.