Report on the continued growth of private dams in the Moorabool Catchment

The issue of the high number of private dams in the Moorabool Catchment and their impact on flows within the river has been recognised for many years. The 2004 Sinclair Knight Mertz study Moorabool River Water Resource Assessment identified that one the "Key Issues in the Catchment" was the "Impact of farm dams on flows". https://www.ccmaknowledgebase.vic.gov.au/resources/R05_Final_report_d1.pdf

Modelling done in the report produced the following table of supply demands:

Newer modelling has allowed for more refined figures, although studies to determine the impact of private dams over different climate scenarios are ongoing.

Figures from the annual Victoria Water Accounts have been alarming. Private dam volumes in the Moorabool Basin compared to inflows are the second highest in the state. The stated figure of 20,236ML in 2017-18 was equivalent to the capacity of Barwon Water's West Barwon Reservoir.

A graphic from a 2020 study titled Investigation of trends in farm dam development over time. (Department of Environment, Land, Water and Planning - Jordan, P., Shepherd, D., & Race, G. (2020)) is illustrative of how large the impact of private dam development is within the Moorabool Catchment. It compared subcatchments in 3 different basins. Franklin Creek in Gippsland, Love Creek near the Otways, and Woollen Creek in the Moorabool catchment which feeds into Lal Lal Reservoir. The volume of private dams compared to km2 of Woollen Creek was 8 to 10 times that of the other subcatchments:

In the recent Central and Gippsland Regional Sustainable Water Strategy completed last year, both the Moorabool and Maribynong catchments were acknowledged as private dam hotspots and an action adopted which committed to: 

Action 4-13:
Review of water resource risks in small, dry, peri-urban catchments

Southern Rural Water will lead a project over two years to review resource risk and share evidence and reporting to build a shared understanding with communities on the risks, consequences and mitigation options we can use to address the increasing effects of small catchment dams. This project will focus on the upper Maribyrnong and upper Moorabool catchments (including tributaries) as identified hotspots, but recommendations from this review may be relevant to other catchments.

However the rationale was based on the belief that the issue was mainly due to "land uses are changing between agriculture and urbanisation". This was not what PALM supporters were observing on the ground. Downstream irrigators and farmers who are reliant on the river for stock and domestic needs had expressed concerns that large private dams were being developed in the upper catchment.

The group resolved to do its own study of where private dam development was occurring, and to see if it exceeded the growth rates described by DEECA. We were assisted by anonimised data from SRW showing licenced dams within the catchment.

Google Earth and its capacity to compare historical satellite imagery was used to note new and enlarged private dams developed, particularly over the last decade. It allowed an approximation of volumes based on a recognised formula for Victorian dams. In total this ultimately involved over 200 dams the majority from 2012 onwards, and many hours of volunteer time and effort.

PALM's report titled The Dammed Future of the Moorabool River - Testing arguments over the trajectory of private dam construction in the Moorabool River Catchment was sent to the Water Minister, Southern Rural Water and other relevant agencies in March 2023. PALM acknowledges within the document that:

This is a community driven and created discussion paper. While every reasonable endeavour was made to be as accurate as our limited resources permit, the report is presented as a basis for a policy review of how private dam development is managed within Victoria.

PALM does not imply, and no reader should infer, that any landowner within any areas covered by this investigation has enlarged or constructed a dam in breach of the rules applicable at the time of enlargement or construction.

From PALM's perspective there were a number of key points.

• It appears the annual increase in new private dam volumes over the last 10 years was triple that predicted by DEECA studies.
• Quite a number of the recent dam installations of significance appeared to coincide with either windfarm development or plantation harvesting. 
• A concerning number of dams were constructed on watercourses as defined by the government dataset (https://discover.data.vic.gov.au/dataset/vicmap-hydro-1-250002)

It is the last point which is most troubling to PALM. A landholder digging a small dam in the corner of a paddock to provide stock needs is unlikely to impact the river. However in a narrow catchment such as the Moorabool virtually all watercourses contribute flows to the Moorabool River. The placement of new and enlarged dams on those watercourses will likely have a direct impact. The Water Act specifies that such dams should be licenced by the responsible authority. Southern Rural Water has since indicated to PALM that there are currently a number of dams of concern and that investigations are being conducted.

Monitoring and compliance is of course a factor in the proper management of water resources, but this does not address the inherent ambiguities within the current licencing system. As stated PALM's primary objective has been for the report to provide a "basis for a policy review of how private dam development is managed within Victoria". Part of that review must include addressing the fragmented approach to the authorising of new and enlarged private dams. Currently a landholder seeking to install a catchment dam in the system may have to approach 3 different authorities; Southern Rural Water, Moorabool Shire and the Corangamite Catchment Management Authority. This needs to be reformed.

Next, the ambiguities around what constitutes a watercourse need to be resolved. While the Water Act appears to be clear on what it considers a watercourse, and these appear on maps used on Victorian Government planning portals, they remain open to interpretation by regulatory staff. This amplifies confusion for landholders, and for other interested parties, and needs to be addressed in a manner which will protect the Moorabool. 

Finally the education of landholders regarding their obligations and the potential impacts of certain activities, especially those who may not be aware of how flow stressed the Moorabool system is, must be the responsibility of those managing the system, particularly Southern Rural Water.

PALM considers that there must be a moratorium on new private dams in the system until these issues are resolved. We all need to face up to the fact that the catchment’s water has been massively over extracted for years and we are killing the river. It may well mean urban water users have to accept they will have to pay a bit more for water to be sourced elsewhere. It may also mean that landholders consolidate dams on their properties and construct reticulated systems to get water over their holdings just as some are already doing. PALM would fully support government initiatives to restructure the way water is used in the catchment such as assisting with  reticulation costs.

If the government, the agencies, and the community get on the same page then this river just may have a fighting chance.

Update

ABC have published a story on the report. It can be accessed here.