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 5.6 Campaspe system
Recent conditions
Rainfall in the Coliban River catchment was below the long-term average for every month during 2019–20, except in November and January. Daily maximum temperatures were generally above average, and December 2019 was exceptionally hot. Carryover from the previous year, along with some unregulated inflows in the Coliban River from July to September 2019, facilitated the accumulation of passing flows.
The flow varied along the length of the Coliban River throughout 2019–20. The Coliban River began contracting above Lake Eppalock towards Malmsbury Reservoir from October 2019 onwards, as the flow dried up along the river. Inflows from unregulated tributaries delivered several natural freshes to the whole system between July and September 2019. Passing flows that were accumulated in winter/ spring were used to maintain low flow between Malmsbury Reservoir and Lake Eppalock throughout summer/autumn. Accumulated passing flows were also used to deliver
a fresh to improve water quality for aquatic biota in this section of the river in March 2020.
In 2019–20, the priority pulsed low flow in summer and autumn for maintaining water quality was not required, as there was enough water to maintain a reduced summer/ autumn low flow in the upper sections of the river. However, the water available was insufficient to maintain full connectivity of the river to Lake Eppalock, and the lower reaches contracted to a series of pools in summer.
Scope of environmental watering
Table 5.6.3 describes the potential environmental watering actions in 2020–21, their functional watering objectives (that is, the intended physical or biological effect of the watering action) and the longer-term environmental objectives they support. Each environmental objective relies on one or more potential environmental watering actions and their associated physical or biological functions.
Table 5.6.3 Potential environmental watering actions and objectives for the Coliban River
 Potential environmental watering action
  Functional watering objectives
    Environmental objectives
   Pulsed summer/autumn low flow (five to 15 ML/day for one to 14 days during December to May)
• Maintain water quality including oxygen levels
• Maintain refuge habitat for aquatic animals, including fish and platypus
               Summer/autumn low flow (one to 10 ML/day during December to May)
• Maintain aquatic habitat that support waterbugs, native fish, platypus and fringing vegetation
• Maintain water quality including oxygen levels
                     Summer/autumn freshes (one to two freshes of 25-160 ML/day for one to three days during December to May)
• Maintain the water depth through rifle-run habitats of five to 20 cm for a 25-50 ML/day event to maintain water quality and habitat for waterbugs
• Maintain water depth through rifle-run habitats of 45–55 cm for a 160 ML/ day event to:
• increase water depth to facilitate fish and platypus movement
• clean sediment and biofilms from river substrates
• wet benches and low banks to promote the growth and recruitment of fringing vegetation
                 280 | Victorian Environmental Water Holder | Seasonal Watering Plan 2020–21

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