The Lower Lakes can be compared most closely with the Gippsland Lakes which are open to the sea through a channel which traverses a sea bar, this being constantly dredged to maintain navigability. Any opening to Lake Alexandrina which included navigability would probably have to be at least as wide as the Lakes Entrance Channel (100m?). This width would also be necessary to allow sufficient seawater into and out of the Lakes to maintain a reasonable salinity, otherwise there would be insufficient exchange, and the evaporation may lead to hyper-saline conditions.
The maintenance of such an open channel would be a large scale and expensive operation, and it is likely that it would need to be at least as extensive than at Lakes Entrance, since I would expect that the open ocean at the mouth of the Murray would have similar wave energy.
Another model which could be considered is that used at West Lakes, where the sea is allowed into the Lakes at High tide, and drains out of the other end of the system during falling tide. This maintains the water in the system in a state not too dissimilar to that of fresh sea water, unless there is polluted stormwater coming in from the paved surfaces. If an artificial outlet could be constructed as an exit for seawater, say from Lake Albert through the Coorong, and through the Younghusband peninsula, then a system of maintaining circulation of seawater in the Lakes could be set, thereby preventing the build up of salinity. If navigability were sacrificed, these channels could be much narrower than the one discussed above, perhaps even large pipes. There would presumably also be a much smaller requirement for sand dredging. There would have to be an allowance for the very rare event of flood waters coming down from upstream.
This opens up the possibility of generation of electricity from the water movements though the channels or pipes during the rising and falling tides. The Lakes should be managed with a much wider vision. We can use our technology wisely to maintain our precious environment, and its biodiversity, but we do need to accept that certain changes are inevitable.
If seawater is allowed into the Lower Lakes, it would be necessary to extend the system of mains water pipes around the lakes area for the communities which formerly depended on fresh water from the Lakes, for stock and domestic needs and for irrigation. This could easily be done with the water saved from evaporation in the present condition.
by Elizabeth Gordon-Mills, Phd