What is an extreme event?
Extreme events are defined under the NSW Water Management Act 2000 and the Commonwealth Water Act 2007. They are:
- Prolonged dry periods,
- water quality events that risk not satisfying local uses and values, or
- any other event which has led to a management plan being suspended in the past 50 years.
The NSW Government has developed an extreme events policy (PDF, 974.16 KB) and incident response guides for all surface and groundwaters in the Murray Darling Basin. The guides are included in each of the water resource plans as they are placed on public exhibition.
The policy establishes the principles by which all water resources within the NSW Murray-Darling Basin will be managed during an extreme event. It aims to ensure critical human water needs are met. It also gives effect to the water sharing priorities under Section 60 of the Water Management Act 2000.
The policy framework establishes a staged approach and provides a range of measures for water managers to deploy as conditions deteriorate.
In the case of a drought event, the management response involves progressively introducing more stringent measures to support the highest priority needs as the event becomes more critical. For water quality events, management responses will be guided by the type of event.
The incident response guides provide further detail on possible actions during drought and water quality events. The IRGs have been developed as part of the water resource planning process.
For drought or water shortage extreme events the stages are:
| Intent of responses
| Surface water
Can deliver all account water under normal river operations practices.
Groundwater levels remain within acceptable ranges, with annual recovery as expected given rainfall/recharge events.
Provide certainty for water use planning.
Long term water security and emergency/drought contingency planning.
Emerging drought / water shortage
Unable to deliver 100% of high priority account water and maximum expected use of general security under normal river operations practices.
Unacceptable groundwater level and or pressure declines potentially or actually impacting on groundwater availability to high priority groundwater dependent ecosystems, basic landholder rights and local water utilities.
Drawdown to levels that could lead to aquifer subsidence.
Operational measures in the current water year to reduce transmission losses and prevent potential future failure to supply water in accounts (surface water).
Limit potential impacts in local areas via dealings restrictions and potential local area access restrictions (groundwater).
Drought response readiness - local water utilities.
Severe drought / water shortage
Only able to deliver restricted high priority demands and restricted remaining general security account water.
Continuing unacceptable groundwater level or pressure declines.
Unacceptable drawdown impacts on ‘efficiently constructed’ basic landholder right bores (i.e. levels below the pump or deeper than the bore).
Evidence of aquifer compaction.
Restricting access to account water, restricting trade and suspending some water sharing plan rules in addition to increased operational measures to prevent potential future failure to supply water in accounts (surface water).
Restrict access from bores in all affected areas.
Drought management/ restrictions - local water utilities.
Critical drought / water shortage
Only able to deliver restricted town water supply, stock and domestic and other restricted high priority demands.
Water level declines pose a risk to long term availability of the groundwater resources - subsidence, and/or mobilisation and induced flow of poorer water quality.
Access by ‘efficiently constructed’ BLR bores significantly impacted.
Suspension of some water sharing plan rules.
Severe restrictions required to prioritise remaining supplies for critical human water needs (surface water and groundwater).
Avoidance of permanent damage to aquifers (compaction or salinization).
Emergency drought management measures/restrictions - local water utilities.
In addition, Critical Water Advisory Panels will be established when the criticality level of an extreme event is declared at Stage 2 or above for surface water, and stage 3 or above for groundwater.
The key role for the Panels is to provide advice to the department on appropriate response measures and criticality levels and to provide input on local views.
Further information can be found in the Critical Water Advisory Panels fact sheet (PDF, 278.98 KB).
The current stage is included in the individual valley water allocation statements and the summary of allocations on the department’s website.