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.

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

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

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.