(3) and (4) Sea water is the only option – what are the implications?
Storage data from upstream indicates that even with an above average catchment intake there will be insufficient freshwater available after other priorities are met, to return levels in the Lower Lakes to the required 0.0AHD within the immediate future.
Sea water is therefore the only available option – it was needed months ago and must be allowed through the barrages to raise lake water levels and cover exposed soils as soon as possible.
These problems are already severe and are escalating as levels fall further but they can’t be addressed with the sea water solution until the Pomanda Island weir is in place and functioning to protect river water supply pump intakes from saline contamination.
Thus, the weir was needed months ago and its completion is now most urgent.
The sea water/fresh water estuarine mix in the lakes would need to be maintained sufficiently below the level of the Pomanda Island weir spillway to prevent wind seiche movement of saline water over the weir from lakes to river in strong southerly winds.
Thus to obtain adequate cover of the exposed lakebed a higher weir spillway height is required(than the 0.1 AHD proposed) to allow for lake levels at or close to 0.0 AHD.