Watering Scenarios

The subsequent scenarios describe a selection of nationally, regionally significant wetlands and other important wetland habitats which may be included for watering as part of the annual watering plan under various climate scenarios. Climate scenarios are hyper-drought, drought, dry, average and wet. Recognition of the inflows to the catchment in the preceding water year are also taken into account. The “wetness” or “dryness” of the catchment gives an indication of the likelihood of wetlands receiving water under predevelopment conditions. The Water Resource Assessment (2005) indicates predevelopment flows for the Lachlan River at Forbes, with maximum annual total flows of 4500 GL, average annual total flows of 1100 GL and minimum annual total flows of <150 GL. Therefore, it is likely that maximum flows would have resulted in floodplain flooding of the lower Lachlan and minimum flows resulting in little, if any, wetland inundation.

Decisions pertaining to when wetlands will receive water are based on:

  • time since last watering;
  • volumes available for watering, i.e. is there sufficient water available to achieve environmental objectives;
  • efficiency of delivery, i.e. can the water reach the target and/or whether other operational flows are also being delivered to the same target; and
  • environmental need, i.e. bird breeding completion or averting fish kills may take precedence over other environmental needs.

Climate Scenarios: Hyper-drought | Drought | Dry | Average | Wet

The order in which scenarios are presented within the tables below does not reflect priority.

Hyper-drought

Hyper-drought scenario: applicable at estimated available licenced environmental water <1733 ML (HS)

(likely under minimum flows at the Lachlan River at Forbes i.e. <150 GL/year)

Target Volume Required Delivery Option Duration of Inundation Outcomes
Burrawang West Lagoon Up to 420 ML Bumbuggan Creek Semi-permanent To protect relocated Purple-spotted Gudgeons; riparian vegetation and resident Brolgas
Curlew Waters ~500 ML Lake Cargelligo inlet Permanent Provide drought refuge for wetland species
Brewster weir pool ~1000 ML Lachlan River Permanent Provide drought refuge for Olive Perchlet and other native fish species

Drought

Drought scenario: applicable at available licenced environmental water  1733 ML to 19,000 ML

(likely at approximately 60%of average flows for the Lachlan River at Forbes i.e. <660 GL/year)

Target Volume Required Delivery Option Duration of Inundation Outcomes
Brewster weir pool ~1000 ML Lachlan River Permanent To protect resident Olive Perchlet
Yarnel Lagoon Up to 360 ML (volume required will be greater if not supplemented by replenishment flows) Wallaroi Creek 4–6 months Water River Red Gums; frog breeding; protect resident Brolgas
Burrawang West Lagoon Up to 420 ML Bumbuggan Creek Semi-permanent To protect relocated Purple-spotted Gudgeon; riparian vegetation and resident Brolgas
Curlew Waters (Lake Cargelligo) ~500 ML (volume dependent on existing volume: used as storage for town water supply) Lake Cargelligo inlet Permanent Provide drought refuge for wetlands species
Lake Brewster inlet wetland 1500 ML (to fill and maintenance flows: Brewster water savings to be used for this purpose Lake Brewster inlet channel >8 months Stimulate wetland plant growth; provide refuge for Olive Perchlet and other wetland species
Lake Cargelligo main lake Up to 5000 ML (fill to 30% capacity dependent on volume of existing dead storage) Lake Cargelligo inlet channel 6–12 months Provide drought refuge for waterbirds and native fish
Eagle Nest Swamp: near Booligal <200 ML Merrimajeel/Muggabah creeks 4–6 months Provide wetland habitat and support bird breeding: note while not listed as regionally significant this wetland has been included due to land management and location considerations
Reed Bed: Great Cumbung Swamp 5000–15 000 ML (greater volume may be required if not piggy-backed on operational or unregulated flows) Lachlan River 4–8 months Maintain reed bed currently in good condition

Dry

Dry scenario: applicable at available licenced environmental water ~20,000 ML to 69,000 ML
(drought and hyper-drought options also considered under the dry scenario)

(likely under less than average flows for the Lachlan River at Forbes i.e. <1100 GL/year)

Target Volume Required Delivery Option Duration of Inundation Outcomes
Lake Merrimajeel/Murrumbidgil Swamp 500–3500 ML (volume required will be greater if not piggy-backed on 9 GL replenishment flows) Merrimajeel Creek >6 months Water River Red Gums; stimulate bird breeding
Lake Cargelligo back wetland area (Management Unit 4: see Lake Cargelligo Community Management Plan) ~10 000 ML (dependent on Lake Cargelligo dead storage being filled previously) Lake Cargelligo inlet >6 months Stimulate bird breeding; support a variety of wetland types
Lake Cargelligo Sheet of Water (Management Unit 2: see Lake Cargelligo Community Management Plan) 4000 ML (dependent on flows being diverted into Lake Cargelligo main lake for other purposes) Lake Cargelligo inlet channel 4–6 months Provide habitat for migratory waders
Lake Ita 6000–14 400 ML VTF (volume required may be greater to reach required CTF) Lachlan River 4–6 months Support River Red Gum forest; Black Box; Lignum and associated habitat within the Kalyarr Conservation Area
Upper Merrowie Creek 6000 ML (volume required will be greater if not piggy-backed on 9 GL replenishment flows) Merrowie Creek 4–6 months Support wetland habitats and colonial bird breeding
Cuba Dam 4000 ML (volume required will be greater if not piggy-backed on 12 GL replenishment flows) Merrowie Creek 4–6 months Support Lignum and bird breeding
Moon Moon Swamp 2520 ML VTF (up to    25 000 ML may be required to fill if not piggy-backed on unregulated or operational flows) Lachlan River 3–6 months River Red Gum watering and to support bird breeding
Willandra Creek 3000 ML (volume required will be greater if not piggy-backed on 12 GL replenishment flows) via Willandra Weir regulator 4–6 months Support a variety of wetland habitats within the National Park
Baconian Swamp 4800 ML VTF (up to     35 000 ML may be required to fill if not piggy-backed on unregulated or operational flows) Lachlan River 4–6 months To support River Red Gum; Black Box; bird and frog breeding
Lake Brewster outflow wetlands 5000–15 000 ML (Brewster water savings to be used for this purpose) Lake Brewster inlet channel 4–6 months Establishing/maintaining wetland vegetation for improved water quality
Water to complete bird breeding events 2–4 months Successful bird breeding event
Mid Lachlan Billabongs Provide diverse floodplain habitat

Average

Average scenario:applicable at available licenced environmental water  ~70,000 ML to         119,000 ML
(previous scenario options also considered)

(likely at average or above flows for the Lachlan River at Forbes i.e. >1100 GL/year)

Target Volume Required Delivery Option Duration of Inundation Outcomes
Great Cumbung Swamp 25 000–50 000 ML (dependent on antecedent conditions) End of system flow 6–12 months Watering River Red Gum community; Reed Bed inundation; bird breeding
Booligal Wetlands 12 000–57 000 ML (dependent on antecedent conditions) Merrimajeel/Muggabah creeks 4–6 months Bird breeding and Lignum support
Lachlan Swamps 20 000 ML Lachlan River 4–12 months Watering semi-permanent wetland vegetation and open lagoons;including watering Lake Ita
Merrowie Creek (Cuba Dam to Chillichil Swamp) 6000 ML (volume required will be greater if not piggy-backed on 9 GL replenishment flows) Merrowie Creek   4–6 months To support River Red Gums; Black Box; Lignum; bird breeding

Wet

Wet scenario:applicable at available licenced environmental water >120 000 ML
(previous scenario options also considered)

(likely at greater than average flows for the Lachlan River at Forbes i.e. >2700 to 4500 GL/year)

* Volumes required are outside the scope of discretionary water and would require translucent flows from Wyangala

Target Volume Required Delivery Option Duration of Inundation Outcomes
Great Cumbung Swamp >50 000 ML* (dependent on antecedent conditions) End of system flow 12 months Watering River Red Gum and Black Box community; Reed Bed inundation; bird breeding
Booligal Wetlands >50 000 ML* (dependent on antecedent conditions) Merrimajeel/Muggabah creeks >6 months Bird breeding and Lignum support
Lachlan Swamps >20 000 ML* Lachlan River 12 months Watering semi-permanent wetland vegetation and open lagoons;including watering Lake Ita
Merrowie Creek (Cuba Dam to Chillichil Swamp) 6000 ML (volume required will be less if supplementing replenishment flows) Merrowie Creek 4–6 months To support River Red Gums; Black Box; Lignum; bird breeding
Lake Brewster outflow wetland 15 000 ML (850 ML = cell 1; 1200 ML = cell 1 & 2; 1200 ML = cell 3); requires maintenance flows Lake Brewster main storage 3–4 months Stimulate plant growth; provide waterbird habitat
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