Page 101 - VEWH Seasonal Watering Plan 2020-21
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Recent conditions
The Tarago River catchment received below-average rainfall in winter 2019 but above-average rainfall in spring 2019 and summer 2020. Most of the rain fell downstream of the Tarago Reservoir, so although it provided natural flow in the river it did not translate to significant inflows into the storage.
Winter/spring high flows, winter/spring freshes, spring high flow and autumn high flow requirements and most of the recommended summer/autumn freshes were met from natural flows. Summer/autumn freshes were the highest- priority potential watering actions for all scenarios in 2019– 20; they play a critical role in providing habitat for native fish species (such as short-finned eels and common galaxias) and maintaining water quality throughout the system.
A volume of 1,000 ML of water for the environment will be carried over to help meet critical priorities in 2020–21.
Scope of environmental watering
Table 3.3.1 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 objective(s) they support. Each environmental objective relies on one or more potential environmental watering actions and their associated physical or biological functions.
Table 3.3.1 Potential environmental watering actions and objectives for the Tarago River
3.3 Tarago system
  Potential environmental watering action
  Functional watering objectives
  Environmental objectives
   Summer/autumn fresh (one to five freshes of
75 ML/day for two days during December to May)
   • Scour sediment from holes and around large woody debris to maintain habitat for native fish in low-flow periods
• Allow the localised movement of native fish
• Prevent terrestrial vegetation growth on sandbars
• Maintain water quality by aeration in times of low flow
             Autumn high flow (one fresh with a peak of 100 ML/day for two days in a minimum seven-day duration during April to May)
 • Form and maintain scour holes around large wood
• Cue spawning for diadromous fish (e.g. Australian grayling)
• Allow the downstream movement of Australian grayling
• Assist the dispersal of juvenile platypus
          Spring high flow (two to three high flows with a peak of 200–300 ML/day for two days in a seven-to-10 day duration during September to October)
  • Form and maintain scour holes around large wood
• Prevent the encroachment of terrestrial vegetation into the channel
• Cue the upstream migration of juvenile diadromous fish (such as Australian grayling) from the sea or estuary into the river
• Wet higher benches to maintain the fringing aquatic vegetation and ensure vertical zonation of the fringing vegetation
• Provide a cue for platypus to select nesting burrows above high water level
             Winter/spring fresh (one to two freshes with a peak of 100–200 ML/day for two days during June to September)
 • Prevent sediment build-up and remove biofilm from large woody debris to maintain habitat for macroinvertebrates and fish including river blackfish
• Maintain access to habitats by ensuring sufficient depth through riffles to allow fish movement between pools and reaches
• Cue the downstream migration of species such as eel and tupong
• Wet the banks, wetting the lower benches to maintain the fringing aquatic vegetation
         Winter/spring low flow
(75 ML/day [or natural] during June to November)
• Prevent the encroachment of terrestrial vegetation in the channel
• Wet the banks to promote streamside vegetation growth
• Maintain an adequate depth through riffles to allow access to habitats for fish and platypus
• Maintain water quality through increased low flows to flush the system and wet additional habitat for fish and macroinvertebrates
• Maintain foraging habitat for platypus
            Victorian Environmental Water Holder | Seasonal Watering Plan 2020–21 | 99

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