Securing a water future for the Gympie region

Developing the Water Security Strategy was grounded in collaboration. Gympie Regional Council worked closely with GHD, Seqwater and the Department of Local Government, Water and Volunteers, combining technical knowledge, policy alignment and shared regional goals. Regular workshops and reviews helped drive consistent decision-making and coordination.

This approach consolidated data on hydrology, infrastructure condition, network performance and demand. Each water treatment plant was assessed for reliability, quality and capacity. Reservoirs and network hydraulics informed upgrade priorities, while climate modelling highlighted drought and saline intrusion risks for coastal bores. The analysis showed the need for interconnection and diversified sources to build regional resilience. 

A key outcome was defining measurable levels of service objectives. These set expectations for reliability, restriction frequency, essential supply during drought, water quality and recovery from outages. For instance, the strategy targets a probability of supply shortfall below 0.1 percent (a 1-in-1,000-year event), medium restrictions less than five percent of the time and a minimum essential supply of 100 litres per person per day during drought.

By defining success clearly, the framework supports proactive investment and operations, creating a consistent baseline across all schemes and linking upgrades directly to community outcomes. 

The strategy is built on robust modelling that tests current and future supply reliability under many scenarios. Using synthetic rainfall and demand sequences spanning 10,000 years, stochastic hydrological modelling identified storage volumes needed to meet service targets. Results showed that existing run-of-river schemes, such as those serving Gympie, Imbil and Amamoor, cannot meet reliability goals without additional off-stream storage or interconnection to the Borumba Dam system.

Population is projected to grow from about 29,000 in 2023 to 36,400 by 2050, with non-residential demand, including industry and standpipes, making up roughly a quarter of total use. The strategy targets a 10 percent reduction in demand through improved management and leakage control, delaying costly upgrades and supporting sustainable investment. 

To support flexible decision-making, the strategy developed four potential pathways, each tested against drought performance, resilience and cost:

• Pathway 0: Maintains existing decentralised systems
• Pathway 1: Combines local schemes
• Pathway 2: Centralises Mary Valley supply via Gympie
• Pathway 3: Creates a fully integrated regional system

Adaptive Pathways Planning guides transitions based on triggers such as population growth, restriction frequency and asset condition. This preserves flexibility, allowing the region to adapt without locking into a single solution. The preferred approach is hybrid — centralising Mary Valley supply at Gympie while maintaining existing systems elsewhere until integration is needed.

Investigations revealed key vulnerabilities. The Gympie Water Treatment Plant, more than a century old, lacks redundancy and poses a high risk of interruption. Mary Valley schemes experience frequent trihalomethane and manganese exceedances. Cooloola Cove needs more capacity and raw water transfer redundancy, while western schemes face source losses and limited storage.

Despite these challenges, the region has strong opportunities to build resilience. The Mary Basin Plan allocates 4,000 ML per year of strategic reserve to Council, supporting long-term planning. The Borumba Pumped Hydro Project and Seqwater’s Lake Macdonald upgrades offer coordination opportunities and temporary water supply options. Improved demand management and reduced non-revenue water can delay major capital works, while partnerships and shared funding can strengthen regional planning. 

Each pathway was assessed through a multi-criteria analysis aligned with Council’s Corporate Plan. Pathway 0 offers low capital cost but carries higher ongoing risk. Pathway 1 provides moderate improvement, Pathway 2 delivers high reliability at reasonable cost and Pathway 3 offers the greatest resilience but at prohibitive expense.

Meeting service targets requires 1,100 to 3,300 ML of storage depending on the pathway. Centralised storage and treatment, as in Pathway 2, improve reliability and reduce long-term costs. The preferred hybrid pathway balances cost and resilience, delivering consistent service levels and better water quality. 

The roadmap spans three phases. From 2025 to 2030, the focus is on feasibility and design for a new Gympie Water Treatment Plant and Mary Valley transfer pipeline, interim upgrades at Imbil, Goomeri and Kilkivan, and region-wide demand management. Negotiations with state agencies will secure access to strategic reserve allocations.

Between 2030 and 2040, construction of the new plant and pipeline will proceed, with redundant small plants decommissioned and storage expanded. From 2040 to 2050, the focus will shift to optimisation, asset renewal and ongoing review of triggers and performance. The program aims to reduce restriction frequency below five percent by 2035, achieve full water quality compliance by 2030 and deliver major cost and reliability improvements by 2050. 

The Gympie Regional Water Security Strategy provides a flexible framework for managing long-term supply risks. Through integrated modelling, adaptive planning and strong collaboration, Gympie Regional Council now has a roadmap to guide investment and operations. This approach transforms uncertainty into structured, evidence-based action and serves as a model for other regional councils.

The preferred hybrid pathway, centralising Mary Valley supply while optimising local systems, balances cost and resilience. Implementation is already underway through the Gympie Water Resilience and Augmentation Program, positioning the region to meet future challenges with confidence. 

The journey to water security in Gympie is one of collaboration, innovation and adaptability. By bringing stakeholders together, consolidating data and planning for uncertainty, the strategy sets a new benchmark for regional water management making the region ready for whatever the future may bring.

As communities across Australia face similar challenges, Gympie’s experience offers valuable insights into building resilient and sustainable water systems. Our commitment to proactive planning, partnership and continuous improvement will help safeguard water resources for generations to come. 

This article was written in collaboration with Emma Fisher, Gympie Regional Council. Contributions have been made by OD Hydrology.