Riverbanks fail when the toe is washed out. Once the base of the bank goes, the slope above collapses into the river, and the next flood carries it away. Roads, embankments, bridges and farmland along the bank go with it.
Rock bags protect the toe and the slope. They can be laid as a single row at the toe, stepped up the bank, or combined with gabions or vegetation, depending on the river and what sits above it.
Common layouts
- Slope revetment: bags laid on the bank face from the bed up to the design flood level
- Stepped revetment: bags placed in tiers on a steeper bank
- Bank toe with gabions: rock bags at the toe, where scour is worst, with gabions or other protection higher up
- Bank and river bottom protection: bags along the toe and onto the bed, so scour at the edge cannot undermine the bank
Why a flexible toe matters
Most bank failures start at the toe, below water, where scour is strongest and inspection is hardest. A rigid toe that is undermined cracks or tips. A rock bag toe settles with the bed and keeps covering it.
Bags are placed in the wet by crane or excavator, so work on the toe does not need the river diverted. Grouped bags interlock and resist higher velocities than single bags (see the size guide).
Bioengineering
Rock bags can be used on their own or as the hard toe of a bioengineering design, with vegetation on the bank above water level. Fine sediment collects between the rocks, plants root into it, and invertebrates use the gaps as habitat. Many river authorities now ask for this kind of design.
What to send for a quote
- Length and height of bank to protect
- Design flood velocity and water levels
- Bed and bank material, and photos
- Access along the bank for lifting equipment
Questions
- How far up the bank should rock bags go?
- Usually from the toe up to the design flood level, with vegetation or lighter protection above. The designer sets the exact level from the hydraulic study.
- Can rock bags be combined with gabions?
- Yes. A common layout puts rock bags at the toe, where flexibility matters most, and gabions higher up the bank.
- Do I need to divert the river to place rock bags?
- Usually not. Bags are lifted by the ring and placed in flowing water.
Published by EVOSNT Trading FZCO, manufacturer of EVO Rock Bags. Product figures are from our technical specifications. General guidance only; the project engineer is responsible for the final design.
