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Flowing on the northern side of the Great Dividing Range, the Broken River and its main tributary, Hollands Creek, rise in the Merrijig, Strathbogie and Wombat Ranges. The catchment area is 7,724 square kilometres and its highest point rests more than 900 metres above sea level.
Lake Mokoan and Lake Nillahcootie are currently the two main storages on the system, that allow water to be held for release on demand from water users.
Irrigators in the Broken System hold 25,297 megalitres in irrigation entitlements and an additional 7,487 megalitres is reserved for stock and domestic entitlements
Water is allocated each year based on the amount of water available in storages minus the losses that occur during storage and delivery (e.g. evaporation).
The Mokoan Project has produced a number of Fact Sheets, which provide more detail on the Broken System, its flows, storages, current allocations, management and reliability.
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Lake Mokoan Pipeline Tender Drawings
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 Decommissioning Lake Mokoan will provide average annual water savings of 44,000 ML/year. These savings arise from 48,000 Ml/yr in evaporation losses from the current lake, minus 13,000 ML/yr in evaporation loss from the rehabilitation Winton Wetland, plus 9,000 ML/yr from reliability water savings.
The 44,000 ML/yr savings was derived using the Goulburn-Broken System water resource allocation computer model REALM. The model has been utilised by Goulburn-Murray Water for determining bulk entitlements for both the Goulburn and Broken River basins and is being used for auditing the MDBC Cap in accordance with Murray-Darling Basin Commission requirements.
The model applies operating rules to the systems storages and waterways, and simulates the last 112 years of climate conditions to predict what will happen when Lake Mokoan is taken from the system. |
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Removing Lake Mokoan from the system without other actions will reduce the reliability of supply to existing Broken System irrigators. Reinstatement of supply reliability will be achieved by a package of "offset measures. The offsets effectively provide the required reliability of supply to irrigators through reduced water losses or by transfer of demand to the adjoining Goulburn system.
The REALM model has determined that approximately 9,000 ML/year in reduced water losses and transfers are required to ensure the existing reliability of supply is maintained after Lake Mokoan is decommissioned.
The reduced water losses and transfers achieved by offset measures have a dual function of maintaining existing reliability of supply and providing environmental flows. This is because of the difference in the timing of these two outcomes. During wet and normal years, these savings/transfers will spill from Lake Nillahcootie to become environmental flows when these flows are most needed. It is only during dry years, that the water savings will be stored in Lake Nillahcootie and become available, again when required, for irrigation. Hence, overall, the offset water savings/transfer will meet both the environmental flow needs and ensure that reliability of supply to existing users is maintained.
More efficient operation of the Broken System to reduce water losses has been the subject of extensive studies as part of this Project.
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Investigation of various offsets relies on a scorecard based evaluation. The scorecard has been developed to allow the comparison of a broad range of reliability offset measures. Factors used in the scorecard include cost, reliability benefit, impact on end of valley flows, project risks, environmental and social impacts and community acceptance. An updated scorecard extract will be available on this website in coming weeks to provide more detail on the range of offset measures investigated.
Possible offset measures that maintain the reliability of supply to Broken system irrigators have been released by Goulburn-Murray Water. These Offsets follow 18 months of investigations and further consultation will be undertaken with Broken system and other water users on a number of Offset Package options.
Investigations have narrowed down the extensive range of individual options into four Offset Packages. The packages detail a range of potential infrastructure, efficiency improvement and water purchase options, including:
 Remote control and monitoring of supply structures and stream flow stations
Dynamic real time monitoring of irrigation diversion flow meters
Supply into Broken River downstream of the East Goulburn Main Pump station and pipelines to supply areas upstream of the East Goulburn Main Pipelining of part of the Major Creek system
Re-regulation storages on Lake Mokoan Inlet Channel and adjacent to Broken Creek
Water entitlement purchase
Operational improvement options
To view publications on the above topics, follow the links below.
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