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Water transfer slows

Monday, 12th April, 2010

* Water being released into Lake Menindee * Water being released into Lake Menindee

Lakes Wetherell and Pamamaroo continued to fall last week as water was transferred to Lakes Menindee and Cawndilla in anticipation of inflows in May and June.

The NSW Office of Water has advised that the falling levels in Lake Pamamaroo and the associated reduced head caused flow at the Menindee inlet to fall to a maximum of about 14 GL/d. Inflows to the lakes are now increasing, and the rate of transfer will steadily increase.

Releases to the lower Darling River through Weir 32 are currently being reduced to 200 ML/d, as the combination of the current volumes in Lake Victoria and the flows from the upper Murray means there is no requirement for additional water from Menindee Lakes. It is expected that the volume in storage will increase in the weeks ahead as the anticipated Darling River flows arrive.

When the volume in storage reaches 640 GL, the management of releases from the Menindee Lakes moves from the NSW Government to the Murray-Darling Basin Authority. This volume is likely to be reached in mid to late April. Control of the water will remain with the Authority until the volume in storage next falls below 480 GL.

In its fourth information paper on the current floods in the Barwon-Darling river system, the NSW Office of Water noted the large volume of inflow between Brewarrina and Bourke from the Culgoa River system and the large inflows between Bourke and Wilcannia from inflows from the Warrego and Paroo Rivers. Flows from the Paroo catchment are likely to sustain flows in the Barwon-Darling River above Wilcannia at relatively low rates for an extended period of time.

Satellite imagery showed that by April 5 the bulk of floodwater had reached the lower reaches of the Paroo River, where there are extensive systems of channels, flood-runners and billabongs which the flood has replenished. The complex network of streams in this area is providing significant storage for the floodwaters and slowing down the water and spreading it out across the floodplain.

The Warrego River peaked at Fords Bridge last week and is now receding. This water will enter the Darling River at Toorale Station, between Bourke and Louth. So far in April 180 GL has passed Fords Bridge. A total of about 220 GL is expected to pass this point by the end of the flood event. Peak flows throughout the Culgoa system were generally lower than first expected. Floodwaters are now in the lower reaches and are flowing into the Barwon-Darling River.

The next milestone in this flood event is when the peak arrives at Bourke. The Bureau of Meteorology has forecast minor flooding for Bourke with a peak around April 13. Flow from the Culgoa system is now reaching Bourke. It will be possible to better estimate the likely volume and timing of flows at Wilcannia, and the volumes that will reach the Menindee Lakes, after the hydrograph for Bourke is confirmed and the Paroo inflows quantified.

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