Large wood placement

The placement of large wood (at least 0.1 metre in diameter and 1 metre in length) involves placing large native timber into a river, typically to deflect flow away from the bank. This action can improve habitat, increase hydraulic roughness, and increase geomorphic complexity and diversity at a faster rate than would naturally occur. It is preferential to use native hardwood logs with root balls.

The specific arrangement and orientation of placed large wood will be dependent on the project objectives, river type, riverbed load and river energy. Large wood arrangements can vary from single logs to entire trees or engineered timber structures.

Depending on the stream power and bed load, stabilisation of the wood may be required to manage the risks involved with the large wood moving and causing damage rather than improving the ecological value. Vertically driven timber piles or ballast blocks can be an effective method of stabilising large wood.

Potential benefits from this intervention:

• Promotes local scouring and erosion which improves geomorphic diversity and complexity providing greater habitat areas.
• Provides habitat for biota of all levels of the food chain.
• Potentially increases the hydraulic roughness of a reach which will reduce flow velocities and stream power.
• Modifies surface water/ground water exchange and enhances water quality.

Potential negative implications from this intervention:

• Introduced large wood can be less complex than natural sources which can result in a loss of important habitat niches.
• Can move during flood events and damage infrastructure such as bridges and culverts.
• Depending on the arrangement, location and method of stabilisation, large wood can pose a safety risk to river users.

Intervention considerations:

• Seek appropriate specialist advice and check legal obligations (e.g. permits).
• Clarify the objectives of large wood placement.
• Determine if a sustainable source of suitable timber is available.
• Plan the arrangement of the timber to best achieve the objectives of the project while limiting the risks associated with large wood.
• Consider if the large wood needs to be stabilised, and if so, how.
• Ensure that that damage to the riparian zone is minimised during the placement of large wood.
• Safety of volunteers and employees including seasonal exposures (e.g. heat) and high risk areas (e.g. crocodile presence in waterways or areas with soil contaminant risks).

Additional information

Publications:

Brooks, A. 2006. Design guideline for the reintroduction of wood into Australian streams. Land & Water Australia. Canberra.

Price, P. and Lovett, S. 1999. Riparian Land Management Technical Guidelines. LWRRDC. Canberra.

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.

Zhang, N. and Rutherfurd, I.D., 2020. The effect of instream logs on river-bank erosion: Field measurements of hydraulics and erosion rates. Earth Surface Processes and Landforms, 45(7), pp.1677-1690.

Last updated: 22 June 2022