Investigating an unexpected event

​​​​​​When investigating an unexpected event related to water/sediment quality you will typically aim to:

  • identify the causes
  • understand the consequences
  • mitigate the impacts
  • ensure that management systems are in place to minimise such events in the future.​

Unexpected events may arise naturally, or may be associated with human disturbance (including accidents).These events may be associated with small-scale discharges or large-scale diffuse disturbances (e.g. catchment wide).

Extreme or unusual climatic conditions often lead to unexpected events and can exacerbate impacts for existing developments.

If you need to undertake remedial management as a consequence of an unexpected event, use the Water Quality Management Framework to determine the nature and extent of that remediation work​.

Unexpected events typically require rapid response, possibly with no or little existing information on the particular waterway.

Obvious candidate causes are investigated in the first instance, before invoking the need for a detailed investigation. Often the cause may be transient and not easily linked to the subsequent impact.

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If an unexpected event occurs, current understanding of key waterway processes should be used to develop or refine a conceptual model of the nature of the event and its potential causes. This process would typically be led by the relevant management authority (or regulator) for the waterway, with assistance from any relevant operators, industry bodies and researchers (stakeholder involvement).

In many instances, particularly after significant weather events, there is precedent for similar events so you can quickly evaluate common pressures and stressors (e.g. fresh water inputs to marine systems, anoxic events associated with inputs of large amounts of organic matter, acidic pulses).

Concurrently, use other information (including monitoring data) that provides background to the nature of the waterway and the event (and similar waterways and events) to develop a series of hypotheses for why the event occurred. Include all hypotheses regardless of their probability.

The resulting conceptual models will help you to identify the potential causes (pressures), their associated stressors and the key ecosystem receptors, including those for which effects have already been observed.

Response to an unexpected event will need to be rapid so updating or developing conceptual models needs to occur quickly.

Effort spent to improve the understanding of the waterway and development of hypotheses for the cause(s) of the event will lead to better-targeted event response and clearer assessment of the consequences of the event.

Response to the event will be guided by the community values and associated management goals.

The event could potentially affect any number of community values, so these and associated management goals (including levels of protection) will need to be defined by the relevant management authority (or regulator) if they do not already exist.

Step 2 will normally occur in parallel with the development or refinement of conceptual models at Step 1, particularly for acute events, and require stakeholder involvement.

If early evidence shows that the unexpected event could be associated with a licensed or unlicensed discharge, then community values and more specific management goals may have already been set by the regulator during assessment of the waste discharge.

Key concepts:

Development or refinement of conceptual models, community values and management goals at Steps 1 and 2 form the basis for indicator selection.

Select a mix of indicators for the pressures, stressors and ecosystem receptors, consistent with using multiple lines of evidence in a weight of evidence process for assessing and managing water/sediment quality.

Selection of lines of evidence and their associated indicators for an unexpected event can be difficult. We provide use-specific quality of evidence tables to assist.

For some events, you can use nationally and internationally developed standard procedures as guides. For example, the Australian Government National Investigation and Reporting Protocol for Fish Kills.

Use general advice in the absence of specific guidance for the unexpected event, which may provide guidance on indicators that otherwise might not be considered.

Where the cause of the event is clearly identified, indicators may still need to be selected, collected and assessed for confirmation or evidence (monitoring).

An existing event-response management plan may recommend lines of evidence and specific indicators but you should tailor the final selection to the event.

Often, there will be a need to rapidly mobilise sampling. This may impose limitations on the types of data that can be collected at first, depending on equipment and skill sets that can be deployed for the initial response.

Key concepts:

Suitable water/sediment quality guideline values for each of the relevant biological, chemical and physical indicators will be based on the desired level of protection (if applicable) for the management goals set for the relevant waterways.

The water/sediment quality guideline values need to be relevant to the event.

Suitable water/sediment quality guideline values may already exist from current water quality management plans (e.g. catchment or regional scale) or discharge license agreements.

Depending on the nature of the event, the default guideline values (DGVs) for water/sediment quality may not be applicable.

For example, if the event is a fish kill, water/sediment quality guideline values for toxicants might need to be considered at levels of acute toxicity rather than chronic toxicity, and chronic toxicity is the basis of the toxicant DGVs.

While it is desirable to derive site-specific guideline values through monitoring or laboratory or field studies, the transient nature of many of these events may not allow sufficient time to develop them.

Key concepts:

To define the draft water quality objectives (or sediment quality objectives) for the event response, select the guideline values and/or narrative statements at Step 4 for each indicator selected at Step 3 that should ensure the protection of all identified community values and their management goals (Step 2). Choose the most stringent of the guideline values for the water/sediment quality objectives (W/SQOs).

W/SQOs may already exist from current water quality management plans or discharge licence agreements. For licence agreements, draft W/SQOs are typically proposed as draft compliance limits.

At this stage, these are aspirational objectives that have not yet accounted for economic and social considerations (Step 8).

Key concept:

After comparing relevant water/sediment quality monitoring data with the water/sediment quality objectives (W/SQOs), together with the evidence from any additional lines of evidence, use the results to:

  • assess water/sediment quality and spatial extent of the event
  • identify the cause of the event.

It may take time to acquire ambient toxicant data (requiring laboratory analysis). For the initial assessment you may use field-measured values for useful physical and chemical (PC) stressors, including dissolved oxygen, pH, electrical conductivity and ammonia.

Use a weight-of-evidence process to evaluate the various lines of evidence. This process assesses results from multiple lines of evidence across the pressures, stressors and ecosystem receptors. It is the key process by which the protection of community values is assessed. Using a weight-of-evidence process for an unexpected event will help to identify its cause.

Multiple potential outcomes are possible from a weight-of-evidence evaluation. We provide use​-specific evaluation tables to assist with interpretation.

The W/SQOs are deemed to be met when:

  • those lines of evidence considered as essential for informing acceptable water/sediment quality are met
  • results for other supporting lines of evidence are consistent with no compromise to current or future water/sediment quality.

If the W/SQOs are met, and if determining the cause of the event is not a priority, then management should focus on maintaining or improving that quality. This will require a check of any possible improvements to management strategies at Step 8, and then implementation at Step 10.

Where a weight-of-evidence process is used to determine the cause of the event, meeting the W/SQOs or other criteria across all lines of evidence may be interpreted as an inconclusive result.

For example, a stressor causing impact may be transient in the waterway so that by the time the investigation is underway and completed, the system has recovered with no evidence of the cause remaining, based on the data collected.

You have 3 options available if the weight-of-evidence evaluation concludes that:

  • W/SQOs are not met
  • adverse trends are evident
  • result is inconclusive (e.g. stressor was transient in the system), or
  • there is conflicting evidence from separate lines of evidence.

If W/SQOs are not met clearly, you have 3 options:

  • formulate, assess and prioritise management strategies to improve water/sediment quality (Steps 8 to 10), or
  • reassess the appropriateness of the water/sediment quality guideline values (Step 7), and/or
  • consider selection of additional or alternative indicators or lines of evidence (Step 7).

Key concepts:

You may want to refine the water/sediment quality objectives (W/SQOs ) if the assessment at Step 6 indicates:

  • draft or existing W/SQOs have not been met, or
  • assessment is equivocal (e.g. uncertainty that draft or existing W/SQOs can be met in the future).

Use the better-quality system data gathered throughout the process (Steps 3 to 6) or specific ecological-effects studies to make any refinements.

Alternatively — or in addition — you could include additional relevant lines of evidence and associated indicators (via Step 3) if the weight-of-evidence evaluation at Step 6 showed:

  • insufficient lines of evidence to make an evaluation of suitable quality, or
  • one or more of the selected indicators proved impractical to implement or failed to provide evidence of sufficient certainty or sensitivity.

Studies required to refine W/SQOs or include additional lines of evidence at this step may not necessarily be lengthy, and may include:

  • implementing additional monitoring
  • continuation or refinement of existing monitoring
  • dedicated ecotoxicological studies, to establish more relevant indicators or water quality guideline values.

If the assessment from Step 6 sufficiently explains the causes and consequences of the event, proceed to Step 8 to consider management actions. If further lines of evidence are warranted, return to Step 3.

In practice, Steps 7 and 8 are likely to be conducted in parallel. Depending on the nature of the unexpected event, both steps would usually involve or be undertaken by a management authority, an industry body or an operator. The work would be presented to the relevant management authority (including regulator) and other stakeholders for consideration.

Key concepts:

You may consider revising or strengthening the water quality management systems via this step and continue management and monitoring at Step 10 if:

  • water/sediment quality is assessed to be acceptable
  • the cause is demonstrated to have been an unusual natural event
  • the risk has generally been well managed.

If the water/sediment quality is assessed as inadequate, to have potentially or actually caused harm to community values, or has potential to re-occur, you may need to consider alternative management strategies or remediation to reduce the risk of further events and improve the water/sediment quality of the waterway after the event.

In some circumstances, the mere occurrence of an unexpected event may prompt a review of the management systems in parallel with Steps 1 to 7.

Any alternative management strategies or improved system management that is developed at this step may be adopted at Step 10. Or the alternatives may first be shared with the management authority (potentially for approval) or for wider consideration through stakeholder involvement.

If the water/sediment quality objectives were met, before progressing to Step 10 you can consider options for:

  • maintenance of the management system outcomes
  • continual improvement of water/sediment quality.

If the water/sediment quality objectives have not been met, evaluate the effectiveness of current management strategies to address the identified water/sediment quality issues and recommend possible improvements.

Formulate, assess and prioritise improved and/or alternative management strategies (e.g. point source discharge mitigation, catchment remediation measures, industry practice changes) on the basis of cultural, economic, environmental and social considerations (quadruple bottom line).

Agreement on​ final management strategies will require robust stakeholder involvement. This is supported by relevant monitoring, modelling (predictive models), cultural, economic and social studies and, where possible, multiple objective decision support tools.

Supportive monitoring programs include those that evaluate the effectiveness of various management practice options, as well as those that improve the skill of the predictive models (e.g. better calibration and validation data).

Predictive models (e.g. catchment and receiving water models) assist you to:

  • quantify water/sediment quality improvements from alternative management strategies
  • assess if water/sediment quality guideline values are met.

Key concepts:

Assessment of whether or not the water/sediment quality objectives (WSQOs) are achievable is based on the information gained from Steps 6 to 8.

If the preferred management strategies will meet or are expected to meet the WSQOs (assessed at Step 8), and are culturally, economically and socially acceptable, then go to Step 10.

In the case of:

  • draft WSQOs set for a catchment plan or specific license discharge, these can be finalised.
  • existing WSQOs for an existing plan or waste discharge licence, this would indicate compliance.

If the WSQOs are not achievable (e.g. costs/impacts associated with the necessary improvements to meet the water/sediment quality objectives are not acceptable), then you have 2 options:

  • Iterate back through the framework to refine the components of the relevant steps. For example:
  • at Step 1, improve the current understanding based on knowledge gained from monitoring and the assessments made at Steps 7 and 8
  • at Step 2, reconsider the management goals (including level of protection) in consultation with the management authority and some stakeholder involvement. At Step 5, this would result in a set of incremental or stepped WSQOs that are focused on improvement towards meeting the original management goals in the longer term.
  • Where a point or diffuse waste discharge was identified as the cause of the unexplained result (at Step 6), it may be assessed to have unacceptable water/sediment quality consequences when considering the potential for similar events in the future. In this case, either:
  • regulatory action may be required (for a discharger), or
  • the pressure under consideration may be assessed to have unacceptable water/sediment quality consequences, and the management strategies could include rejection of a development application, or closure and/or remediation strategies for an existing development.

If you have reached this step because of an assessment of increased risk to community values — either as a legacy of the event or because of an increased risk of repeated events — and improved management to reduce this risk is not considered possible, then a revision of the water quality management goals may be required via Step 2.

Usually this will not be the case, and it will be concluded that the event resulted from sufficiently rare circumstances that the existing management systems are considered to remain adequate. Or alternative management systems will be required to reduce the harm from the current event or the risk of future events to acceptable levels, and the focus will move to Step 10.

Key concept:

You have reached Step 10 because acceptable water/sediment quality has or can be achieved.
To better predict similar events in the future and mitigate against their effects (to the extent that management goals are achievable), continual improvement of both management and monitoring should be undertaken at this step, regardless of how you reached Step 10.

The process of recovery from the event or alternative management actions from Step 8 need to be incorporated into the management systems.

Implement an agreed adaptive management strategy that will include:

  • action plans to implement agreed ma​​nagement strategies
  • monitoring programs to establish baselines and track improvements in management practices
  • monitoring programs to track improvements towards meeting the water/sediment quality objectives (for all indicators or lines of evidence).

You will need to establish appropriate arrangements for stakeholder involvement and reporting.

Ongoing monitoring and management then leads to continued cycling through the Water Quality Management Framework with improvements incorporated at all relevant steps based on knowledge gained along the way.

Key concepts: