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Discrete log jam structures

Discrete log jams structures are an engineered arrangement of logs that are typically held in place with vertically driven piles. Generally, the aim of log jams is to temporarily modify the near-bank hydraulics of a specific site by providing an artificial form of flow resistance that naturally would have been provided by large woody debris. If used to manage bank erosion, a series of log jams may be required to sufficiently reduce the flow velocity and erosion. Log jams will generally improve fish habitat and cause some localised scour and deposition that will contribute to improving the geomorphic diversity of the reach. These structures are used in cases where there is either a lack of supply of large wood, or the conditions mean it is buried or transported quickly making it ineffective, or both. The long-term goal should be to address any underlying issues in large wood supply or transport/burial.

Cross-channel log jam, constructed to slow anabranch development. Photo by B. Berry

Potential benefits from this intervention:

  • Indirectly address bank erosion while providing habitat for fish.
  • Encourage local scour and deposition of sediments and organic matter, which improves the geomorphic diversity of the river.
  • Use natural biodegradable materials.
  • Increase overall hydraulic roughness and reduce stream power.

Potential negative implications from this intervention:

  • Log jams have a limited life span of approximately 10-15 years.
  • There is potential for high disturbance during construction including vegetation removal and heavy machinery within rivers.
  • Log jams do not provide immediate bank stabilisation and may lead to ongoing bank movement.
  • Log jams may not be conducive to recreational activities.
  • Log jams may accumulate debris and be a barrier to fish passage (dependent on location and design).

Intervention considerations:

  • Seek appropriate specialist advice and check legal obligations (e.g. permits).
  • Assess if the erosion processes are the result of high velocity flows directed at the riverbank.
  • Assess whether rock armouring is needed to manage excessive bank erosion and the risk of outflanking.
  • Evaluate the direction and rate of channel migration to see if it lends itself to redirection of flow.
  • Consider if the log jams may provide habitat for target species.
  • Determine if suitable and sustainably sourced timber is available.
  • Consider the design life required from the structural component.
  • 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.

Daley, J. and Brooks, A.P. 2013. A performance evaluation of Engineered Log Jams in the Hunter Valley. Griffith University, 53 pp. ISBN 978-1-922216-23-6.

Last updated: 10 June 2022

This page should be cited as:

Department of Environment, Science and Innovation, Queensland (2022) Discrete log jam structures, WetlandInfo website, accessed 30 August 2024. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/management/rehabilitation/rehab-process/step-4/intervention-options/discrete-log-jam-structures-mod.html

Queensland Government
WetlandInfo   —   Department of Environment, Science and Innovation