Watering Requirements

The watering requirements and watering history of the nationally and regionally significant wetlands are summarised below. This summary helps the decision-making process by matching available environmental water with the requirements of each wetland and time since last appropriate watering.

Note: Lake Brewster and Lake Cargelligo have not been included in this table due to the complexities of water use and management required for these two wetlands.

Nationally Significant Wetlands
Wetland Guage no. Gauge height (m) Discharge (ML/d) Date; Duation of last inundation Volume required (ML) Condition Delivery constraints
Cumbung: Reed Bed 412005 0.5–0.67; 1.1 for significant response 275–661; 713 for significant response 2010/11;  >6 months 5000 to 30 000 Poor Levees
Cumbung: Lignum Lake 412005 1.1 713 2010/11 25 000 to 30 000 Unknown
Cumbung: Marrool Lake 412005 1.1 713 2010/11 25 000 to 30 000 Unknown
Lake Cowal 412036 7.2 14 500 2010/11 Moderate–good Large volumes required; delivery difficult
Booligal Wetlands 412005 2.1 (BB); 0.47(CTF) 2500 (BB); 236 (CTF) 2010/11;    ~6 months 12 000 to 57 000 Moderate–good Delivery between Dec–March inefficient
Lake Merrimajeel 412005 1570 2010/11;    >6 months 500 Moderate Delivery between Dec–March inefficient
Murrumbidgil Swamp 412005 1560 2010/11;    >6 months 3500 Poor–moderate Delivery between Dec–March inefficient
Cuba Dam 412039 1.07 1500 (with Gonowlia Weir open) 2010/11;    >6 months 4000 Moderate Delivery between Dec–March inefficient
Merrowie Creek (Cuba Dam to Chillichil) 412039 1.07 (3.1 required at Willandra Weir) 1500 (with Gonowlia Weir open) 2010/11;    >6 months 6000 Moderate Delivery between Dec–March inefficient
Lachlan Swamp 412005 850 2010 up to     20 000 Moderate Delivery between Dec–March inefficient

Guage no. and name: 412005=Booligal Weir, 412036=Jemalong Weir, 412039=Hillston Weir

CTF=Commence-to-flow; BB=Block Bank

Regionally Significant Wetlands
Wetland Guage no. Gauge height (m) Discharge (ML/d) Date; Duation of last inundation Volume required (ML) Condition Delivery constraints
Baconian Swamp 412045 1.46 600 2010 4800 Poor–moderate Piggy-backing EW best option for delivery
Burrawang West Lagoon Bumbuggan Creek 340 2010/11; semi-permanent 420 to fill system Good Some drying required to increase environmental value
Horseshoe Lagoon Unknown Unknown
Lake Ita 412005 600 2011 (partial filling); weeks 6000 to        14 400 Moderate Specific release to Ita is not an option due to high CTF
Moon Moon Swamp 412005 0.85 2000 2010; 2 months 1980 Moderate Significant losses occur to Willandra Crk; Middle Crk; and Merrowie Crk
Upper Merrowie Creek 412039 1.07 1500 (with Gonowlia Weir open) 2010; 4 months 3000 Moderate Delivery between Dec–March inefficient
Wilga Lagoon 412004 3.14 (wet); 3.82–4.085 (dry) 12 983 (wet);        17 211 (dry) 2010 Moderate–good Unknown
Willandra Creek 412038 1.17 (with regulator closed) 2400 2010/11;      4–6 months 3000 (regulated section); 9000 (downstream of Willandra NP) Moderate Currently lower CTF than under natural conditions
Yarnel Lagoon Wallaroi Creek 2010; 4 months 360 to fill Good Yarnel Management Plan to be taken into account

Guage no. and name: 412004=Cottons Weir, 412005=Booligal Weir, 412038=Willandra Weir, 412039=Hillston Weir, 412045=Corrong Weir

CTF=Commence-to-flow; Willandra NP=Willandra National Park, EW=environmental water

Fish Passage

 Native fish need a variety of habitat types to complete their life cycle and therefore rely on free movement or passage within rivers.  Key native species such as Murray cod, golden perch and silver perch are known to travel long distance through inland waterways, often migrating hundreds of kilometres. Impeding fish passage through the construction of dams, weirs, floodgates and waterway crossings can negatively impact native fish by:

  • Interrupting spawning or seasonal migrations;
  • Restricting access to preferred habitat, available food resources and breeding partners;
  • Reducing genetic flow between populations;
  • Increasing susceptibility to predation and disease through aggregation below barriers;
  • Fragmenting previously continuous communities; and
  • Disrupting downstream movement of adults and impeding larval drift through the creation of still water (lentic) environments.

Natural flow regimes are essential in maintaining connectivity between upstream and downstream reaches and adjacent riparian and floodplain habitats. Instream structures that span the whole channel can impede natural flows, acting as physical and hydrological barriers to fish movement and isolating upstream and downstream habitats. The delivery of environmental water may also provide an opportunity to drown out these instream structures, in particular, instream weirs. The Lachlan River has many fixed crested weirs along it length which prevent fish from travelling up and down the river except when larger flows submerge these weirs and allow fish to cross (NSW DPI 2006). The pulsing of environmental flows or the piggy-backing of environmental flows on operational or unregulated flows can be used to drown out some weirs, while also ensuring that property and infrastructure are not damaged. Drown-out is most effective during spring–summer when native fish are more likely to migrate and should occur for a number of days or weeks if possible.

Weir Drown Out Volumes

The daily volumes required to drown out some instream weirs on the Lachlan River are listed below.

Weir Discharge Volume
Cottons Weir (Forbes) 9250 ML/d
Condobolin Weir 3800 ML/d
West Condobolin Weir 3800 ML/d
Willandra Weir 8500 ML/d
Hillston Weir 4750 ML/d
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