Lower Broken and Nine Mile creeks have been regulated for over a century. Before regulation, the creeks would have had most of their flow in winter and spring and then contracted to isolated pools or dried out during summer and autumn. The adjacent floodplain would have also flooded regularly. The creeks now have numerous weirs that maintain a relatively constant flow from mid-August until mid-May to support irrigated agriculture. These modifications have changed the way native animals use the creek. Previously, native fish would have moved into the creek when it was flowing and returned to the River Murray as it dried. Both creeks now provide year-round habitat for native fish, and fish passage structures allow fish to move between weir pools. Water for the environment is used to support these permanent fish habitats, by providing flows to trigger fish movement and support fish passage, control water quality and flush azolla as necessary.
The lower Broken Creek is operated separately to the upper Broken Creek and the Broken River, because regulated water is delivered to the lower Broken Creek from the Goulburn and Murray systems via the irrigation channel network.
Water for the environment can be provided to the lower Broken Creek from the Goulburn system through the East Goulburn Main Channel and from the Murray system through the Yarrawonga Main Channel. Water is released into the lower Broken Creek from several irrigation area regulators along the length of the lower Broken Creek. The main priority for environmental watering in the lower Broken Creek system is to maintain minimum flows throughout
the year. Particular attention is given to reaches 1 and 2 during the non-irrigation season, when flow can stop. The next priority is to deliver freshes in winter and spring to trigger fish movement and spawning, maintain water quality and manage azolla blooms in reaches 3 and 4. The measurement point for environmental flows in the lower Broken Creek is at Rices Weir.
Some of the environmental flow targets for the lower Broken Creek are partly or wholly met by operational water releases (inter-valley transfers [from the Goulburn to the Murray] or choke bypass flows [when bypassing the Barmah choke in the Murray]) that are delivered to meet downstream demands. These operational deliveries mainly occur during peak irrigation demand between spring and autumn. Water for the environment may be used to supplement these operational releases and to deliver recommended flow components that are not met by the operational releases.