Reservoir management encompasses a range of interacting physical, chemical and biological processes, including natural mixing and stratification, artificial mixing, and catchment management to control nutrient inputs.
It also considers the impacts of climate change on reservoir dynamics, downstream oxygenation requirements, and sediment processes under anoxic conditions. Understanding pollutant transport and transformation within reservoirs is also critical for assessing water quality and informing effective management strategies.
From review to reality: the Pindari bubble plume destratification trial
Cold water pollution is a longstanding environmental issue downstream of many large storage dams. During warmer months, reservoirs can stratify into distinct layers, with warm water near the surface and colder, denser water at depth. Where dam outlets draw from these deeper layers, cold water can be released into downstream rivers at the time of year when those rivers would naturally be warm. The resulting temperature suppression can extend for long distances and affect the physiology, behaviour, growth and reproduction of native fish. Reservoir stratification can also contribute to other water quality problems, including low dissolved oxygen, elevated nutrients and soluble metals, and conditions that favour cyanobacterial blooms.
In 2021, the UNSW Water Research Laboratory began consolidating the international evidence on ways to address these impacts. The resulting review of cold water pollution and artificial destratification examined reservoir stratification, its associated water quality effects and the two main engineering approaches available: selective withdrawal and artificial destratification. It also established the next practical questions for the work—where a bubble plume trial could be undertaken, how physical and numerical modelling could support its design, and how renewable energy might make large-scale operation more viable.
Turning the review into published evidence
The original review was subsequently developed into the peer-reviewed journal paper Artificial destratification options for reservoir management, published in Science of the Total Environment in 2025. The research found bubble plumes to be the most effective and scalable artificial destratification option overall, but also highlighted an important gap between scalability in principle and demonstrated success in large reservoirs.
A recurring reason for unsuccessful large-reservoir applications was under-design: the airflow provided was too small relative to the volume of water that needed to be mixed. At the same time, simply increasing airflow creates a practical cost challenge because compressor power requirements and operating costs grow with reservoir size. The review identified renewable energy and optimised variable-flow operation as important parts of making large-scale systems both effective and economically feasible.
Cold water pollution - bubble plume destratification, illustration by Anna Blacka
Learning from the previous NSW strategy
In parallel with the technical development of artificial destratification, WRL assisted NSW DPIRD Fisheries by completing a systematic review of the previous NSW Cold Water Pollution Strategy. The review brought together the actions, outcomes and lessons from the earlier stages of the strategy, helping clarify why cold water pollution remains a significant issue and what should be considered in future management efforts. This work assisted with the subsequent update of the NSW Cold Water Pollution Strategy.
Why Pindari?
The next step was to translate the broader evidence into a practical trial. WRL's preliminary studies for Pindari Dam identified it as the strongest candidate among the large, high-priority NSW dams considered for a cold water pollution mitigation trial. Pindari is challenging because of its large depth when full, but its comparatively smaller storage capacity means less air should be required than at other large reservoirs. Its existing multi-level offtake also provides operational flexibility to mitigate cold water pollution or avoid poor-quality releases if destratification operations to test the reservoir response as part of the trial. Its northern NSW location exposes the reservoir to more extreme heat, providing a demanding test of the technology.
From concept to an installed system
WRL developed the initial concept for the Pindari trial through a series of linked investigations rather than a single design exercise. These included recommendations for the monitoring network required before and during the trial; compressor, diffuser and pipeline design recommendations; and advice on the preferred installation location following a site visit.
Numerical modelling was used to investigate operating procedures and balance the system's power requirements, including questions relevant to renewable-energy procurement and variable-flow operation. WRL also tested diffuser-hole losses using a pressurised chamber with a lab-based physical model. Together, these studies provided a technical basis for progressing the trial from proof of concept through design, while WRL continued providing review and technical direction to NSW DPIRD Fisheries, WaterNSW and the project designers during final design and installation.
Funding, construction and first operation
The evidence developed through the literature review, proof-of-concept assessment and concept-design studies helped demonstrate the potential of a bubble plume trial at Pindari. In September 2025, WaterNSW announced a $26.2 million Australian Government investment in the two-year Pindari Dam Cold Water Pollution project, led by WaterNSW in partnership with NSW DPIRD Fisheries and with funding support from the Commonwealth Government.
Installation of the Pindari destratification system progressed through 2025 and early 2026. While the full installation remained under construction, completion of the distribution pipeline and diffuser created an opportunity to demonstrate the system during the 2025–26 summer.
The system was switched on for its first operational trial on 10 February 2026. It was run at a fixed airflow of 750 L/s and successfully mixed the already stratified reservoir in only four days. This was a demanding initial test: under normal operations, the system would generally be started before strong stratification develops, preventing the distinct warm and cold layers from establishing in the first place. Its ability to break down established stratification provides a strong early demonstration of the system's mixing capability.
What comes next?
The completed system will use a variable-speed-drive compressor, allowing operators to adjust airflow as conditions change. This will create opportunities to minimise operating costs while still supplying enough air to keep the reservoir mixed—a balance identified as critical in the earlier review and modelling work.
WRL will assist with monitoring and reporting during the 2026–27 summer to assess performance under a broader range of reservoir and weather conditions. The trial will therefore test more than whether the system can mix Pindari: it will help establish how a large bubble plume system can be operated responsively and efficiently, and what that could mean for cold water pollution mitigation at other high priority dams.
WRL team
