Future Plans for Lake Wyangan

Lake Wyangan Sustainable Water Supply and Quality, Agricultural Growth and Recreation Project Plan

The current project plan aims to manage water quality (nutrients and salinity) to sustain the environmental and recreational values of North Lake and improve water availability to irrigators via South Lake (both potential and current). It is anticipated that this plan will evolve over time and the concept may improve as further research and community feedback are received.

The objective of the current project is to achieve sustainable water supply and quality by the North and South Lakes working in unison to reduce salinity and manage nutrient levels that cause blue green algae outbreaks. The North Lake will be the 'recreation lake', and the South Lake will be a 'working lake' that stores and mixes irrigation water, reclamation, stormwater, and North Lake water to supply blended irrigation water to landowners to increase agriculture output. The North and South Lake Wyangan are considered two water bodies separated by Jones Road. No water would be transferred to North Lake after the start of the project.

Through this project, Lake Wyangan will be converted from a terminal lake into a flow-through system. North Lake will flow to South Lake, and water will be mixed in the South Lake, and blended water will be delivered through pipe infrastructure to irrigate agriculture. Over time, the water extraction from Lake Wyangan will lower salinity, and accompanied by nutrients management, the water quality of the lake will improve. Sustainable water quality and supply will enhance the ecosystem and support recreation activities at the North Lake, such as swimming, fishing, boating and passive recreation.


 

Scope of proposed works:

Stage 1: Delivery of treated reclamation water to South Lake
Stage 2: Delivery of blended irrigation water to Landowners for agriculture
Stage 3: North Lake Water Quality Improvement
Stage 4: Sediment and nutrient management of inflow water to North Lake
Stage 5: North lake amenity improvement

 

Lake Wyangan Project Plan - Infrastructure - Water Input and Output - Video

 

What would be the project's effect (Intervention Scenario) on North Lake?

North Lake General Salinity Thresholds – Freshwater Biota

The preliminary water salinity modelling indicates two different destinations for North Lake water under two scenarios of "No Intervention" and "Intervention". The "Intervention" scenario is based on implementing the Lake Wyangan concept plan and using South Lake as a reservoir to deliver water to irrigate agricultural lands. North Lake water will flow to South Lake, and it will be replaced with freshwater. By taking such an action, "Intervention" scenario, the salinity level of North Lake water in 2035 will remains at the current state (2500 – 2700 EC). However, by doing "No Intervention", the salinity level of North Lake water will rise dramatically to around 6000 EC in 2035. And this is in spite of maintaining the water level in the lake.

The salinity level of the lake water would potentially impact the function of the aquatic ecosystem in the long-term. A salinity level of more than 3000 EC would have lethal and adverse effects on freshwater Microinvertebrates and the majority of Macroinvertebrates. Juvenile fish survivorship and their growth rate would be impacted at 3000 to 7300 EC (Dunlop et al., 2005). This means that under the "No Intervention" scenario, the high salinity level of the North Lake by 2035 can adversely affect native fish reproduction and growth.





A threshold-based model for monitoring, regulatory action, and management of salinisation in a freshwater ecosystem is adapted from Schuler et al., 2019. This indicates that by the increase of salinity, the impacts on the exosystem will gradually shift from reversible to irreversible status. At point A), water salinity is low, and our aquatic ecosystem is functioning satisfactorily. By the increase of salinity from point A) to B), the ecosystem can adapt itself to the condition. At point B), the economic and social costs of taking action (Intervention) are reasonable, and salinisation effects are still irreversible (green shaded area).

The salinity increase from point B) to C) would have dramatic effects on the ecosystem function. At point C), extensive management can assist in mitigating some harmful effects of salinisation on the ecosystem; however, some effects are probably irreversible (red shaded area). At this point, the economic and social costs of an intervention are higher than point B). It can be presumed that the salinity level of North lake water is currently at point B) where the ecosystem is still functioning, and the cost of taking action at this salinity level is reasonable. However, under “No Intervention” scenario, water salinity will surge overtime to a level similar to point C) at which the cost and effectiveness of taking action is higher than before.


 

Year 2035

References:
^{Dunlop, J., McGregor, G., & Horrigan, N. (2005). Potential impacts of salinity and turbidity in riverine ecosystems. National Action Plan for Salinity and Water Quality. State of Queenslands.
Schuler, M. S., Cañedo-Argüelles, M., Hintz, W. D., Dyack, B., Birk, S., & Relyea, R. A. (2019). Regulations are needed to protect freshwater ecosystems from salinization. Philosophical Transactions of the Royal Society B, 374(1764), 20180019.
Krause, C., Dunn, B., Bishop-Taylor, R., Adams, C., Burton, C., Alger, M., Chua, S., Phillips, C., Newey, V., Kouzoubov, K., Leith, A., Ayers, D., Hicks, A., DEA Notebooks contributors 2021. Digital Earth Australia notebooks and tools repository. Geoscience Australia, Canberra. https://doi.org/10.26186/145234
Baldwin DS, (2020) Sediment quality in Lake Wyangan and the implications for the on-going management of the lake. A report prepared for Griffith City Council. 15 pp.}