Passive management

Passive management is a way of increasing the values and services of an aquatic ecosystem by allowing the processes and components at the site to reach an equilibrium state without intervention. For example, trees in the riparian zone naturally die or get blown over. Rather than removing the fallen trees they can be allowed to remain in the channel to be moved around by the river flows into a pattern dictated by the channel form. This is not a “do nothing” option, as monitoring is required.

The advantage of passive management is that it requires relatively low investment. However, the cost of monitoring should not be omitted when considering this as an option. It is essential to make sure that objectives are being achieved and that negative impacts are acceptable. If a risk is perceived, such as initial high rates of deposition infilling pools at a site where fish habitat is the objective, then intervention may be required. Risks will only be identified by a comprehensive monitoring program.

The passive management approach can frequently take longer to reach an objective than using intervention. It should not be assumed that leaving the river to adjust without intervention will mean that it will return to its natural state or a desired state. The conditions at the site or in the catchments may have changed, meaning that a return to previous conditions, without further intervention is no longer possible. For example, an upstream reservoir may have been installed and that has altered the sediment and flow regime.

Potential benefits from this intervention:

• Rivers may naturally adjust to changes in their site and catchment conditions, for example after a flood there may be a period of sediment redistribution and vegetation growth to re-establish forms and processes.
• The negative consequences from interventions, such as site disturbance, can be avoided.
• Significant costs associated with works can be avoided.
• The monitoring undertaken to track change can be used to inform other rehabilitation sites.

Potential negative implications from this intervention:

• Time may be required to understand the trajectory of the site, and during this time negative changes may continue to occur.
• Passive management is often perceived as ‘doing nothing’.

Intervention considerations:

• Seek appropriate specialist advice and check legal obligations (e.g. permits).
• The triggers for intervention should be considered and documented.
• The long timeframe needed for passive management mean that institutions need to maintain clear records so that as staff change the site can still be effectively monitored.
• Communication of any changes is essential to maintain landholder and community support.

Additional information

Publications:

Stout, J.C., Rutherfurd, I.D., Grove, J., Webb, A.J., Kitchingman, A., Tonkin, Z. and Lyon, J., 2018. Passive recovery of wood loads in rivers. Water Resources Research, 54(11), pp.8828-8846.

Links:

Australian Government natural resource management monitoring, evaluation, reporting and improvement (MERI) program

Last updated: 10 June 2022