Rock armouring

Rock armouring (also known as rock rip rap, rock revetment or rock beaching) involves the placement of quarried, angular rock against a riverbank to prevent further erosion of the bank. Rock armouring is commonly used in the protection of infrastructure such as bridges and culverts. The design of the rock armouring requires hydraulic calculations to determine an appropriate rock size to ensure that the rock will not be washed away. The rock is graded and placed to a design thickness to ensure that it forms an interlocking mass.

Often this intervention is combined with vegetation establishment to stabilise the bank, eventually making the engineered structure redundant.

Potential benefits from this intervention:

• Allows for rapid stabilisation of bank and associated reduction in sediment inputs.
• Typically involves less design and maintenance requirements compared to other bank erosion management options.
• Can stop multiple bank erosion processes.

Potential negative implications from this intervention:

• High disturbance during construction including vegetation removal and heavy machinery within rivers.
• Rock armouring does not necessarily address the cause of erosion and often contributes to erosion elsewhere within the river system as a consequence of excess energy.
• Rock armouring is incompatible with the evolution of meandering river patterns.
• Rock armouring can limit habitat availability for both terrestrial and aquatic fauna. The changed substrate and increased water velocities in the armoured section can reduce habitat values for some aquatic species.
• May not be conducive to recreational activities.

Intervention considerations:

• Seek appropriate specialist advice and check legal obligations (e.g. permits).
• The emphasis of the rock armouring works is to protect the bank toe from fluvial entrainment.
• If mass failure (i.e. bank slumping) is active at the site, other interventions may be required prior to or alongside rock armouring.
• The disturbance and cost associated with rock armouring may not justify physical intervention.
• Determine if other infrastructure is threatened and whether it could more efficiently be moved rather than protected.
• Consider the design life required from the structural component and whether vegetation can establish adequately in this timeframe.
• Safety of employees including seasonal exposures (e.g. heat) and high risk areas (e.g. crocodile presence in waterways).

Additional information

Publications:

Department of Sustainability and Environment (DSE). 2007. Technical Guidelines for Waterway Management, Department of Sustainability and Environment, Victoria.

Rutherfurd, I.D., Jerie, K. and Marsh, N. 2000. A Rehabilitation Manual for Australian Streams, Volumes 1 and 2. CRC for Catchment Hydrology and LWRRDC. Canberra.

Links:

Aggregates and rock for engineering purposes - Guidelines for the specification of armourstone

eWater RIPRAP toolkit - a spreadsheet program for the design of rock lining (rip-rap) for bank protection.

Last updated: 14 December 2021