Page 57 - VEWH Seasonal Watering Plan 2020-21
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Table 2.2.3 Potential environmental watering actions and objectives for the lower Latrobe wetlands (continued)
2.2. Latrobe system
 Potential environmental watering action
 Functional watering objectives
 Environmental objectives
  Heart Morass
        Partial fill (during August to December, with top-ups as required to maintain water level above -0.3 m AHD5)
    • Maintain water levels above -0.3 m AHD year-round to avoid exposing acid sulfate soils
• Provide seasonal variation in water depth throughout the wetland to support the growth and flowering of semi-aquatic plants
• Provide appropriate wetland fringing habitat for frogs and turtles
• Provide conditions that support waterbug communities and food resources for frogs, turtles and waterbirds
• Stimulate bird breeding by providing nesting habitat via inundating reed beds and deep water next to reedbeds
                Partial wetland flush (during June to November)
 • Fill wetland to 0.5m AHD and allow water to flush through the wetland to export accumulated salts and sulfates
• Allow the import and export of nutrients, dissolved organic carbon and seed dispersal between the Latrobe River and Heart Morass
        Trigger-based fill or partial fill to respond to acid sulfate soil exposure or control salinity (any time)3
• Respond to decreasing pH from the rewetting of exposed acid sulfate soils (most likely during high-wind events)
• Dilute salt concentrations within the wetland that may be caused by king tides from Lake Wellington or other sources. This watering action is likely to be triggered6 if wetland overtopping appears likely; based on rising water levels at Lake Wellington (reaching or exceeding +0.5m AHD)
     Top-up (anytime, following bird breeding event if required)
  • Prolong wetting of reed beds to maintain habitat for waterbirds and protect chicks from predators, following an observed breeding event
       1 While a full fill is the target, if salinity in the Latrobe River is too high a partial fill may be provided instead, helping to achieve some of the listed functional watering actions. This is most likely to eventuate under drought conditions.
2 Timing of this flow changes depending on the scenario. An extended partial fill may be required under a drought scenario, however under dry to wet scenarios, partial fills either side of the full fill over late winter and spring are preferred. Top-ups over summer are unlikely under a drought scenario, as reduced flow in the Latrobe River is likely to increase salinity levels beyond a tolerable limit for wetland filling.
3 Trigger-based events may override other planned watering actions if required, to maintain conditions at the site.
4 If salinity level in the Latrobe River exceeds 15,000 μS/cm, a fill or partial fill will not be provided.
5 Maintaining the water level above -0.3m AHD is a high priority, to avoid exposing acid sulfate soils.
6 If the salinity level in the Latrobe River exceeds 10,000 μS/cm, a fill or partial fill will not be provided.
 Victorian Environmental Water Holder | Seasonal Watering Plan 2020–21 | 55

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