Water

Lakes part of water debate

By Geoff Adams

Standing on an embankment of earth in the middle of a lake system on a sunny autumn day puts me miles away from controversy and debate.

The concrete and steel beneath my feet separates the sea from the fresh water of the Murray River flow.

Water birds are riding a gentle swell, and great lumbering fur seals are playfully clambering over the structure or sunning themselves on the rock embankments while a man from South Australia Water tries to chase them off the engineering. They are not just enjoying the sunny afternoon, but the fish living in the waterways.

Welcome to the lower lakes.

Some of the water given up by northern Victoria irrigators under the Murray-Darling Basin Plan ends up here.

South Australians say the water is needed to maintain the fragile ecosystem of the lower lakes and to prevent incursion of saline sea water into the freshwater lakes and lower Murray River.

Victorian and Riverina farmers and their lobby groups say they have given up enough water and can’t afford to give up any more to preserve the lakes — which were occasionally saline, anyway.

The five barrages, built more than 50 years ago and with a total length of 7km, help keep the sea out of the two major lakes. The biggest of the lakes, Alexandrina, is huge; about 25km long and 10km wide at its widest point, but relatively shallow, which means that it is a major contributor to the 700Gl of evaporation each year.

I climbed down to the water’s edge on the sea side and tasted the water. Definitely salty ... on the other side, I’d call it brackish but not so salty.

Today’s salinity reading puts the Alexandrina side at about 16000 EC units and the Coorong side about 40000, which is close to average for sea water.

The Coorong, where the film Storm Boy was made, is an elongated national park running along the coastline about 80km south-east of Adelaide. For much of its length it comprises two major lagoons separated from the sea by a thin isthmus of land.

The Murray River empties into the lakes and the narrow opening where the water can run into the sea is described as the Murray Mouth.

On the day I visited the barrages with Victorian Nationals leader Peter Walsh and Shadow Water Minister Steph Ryan, they closed and the levels either side were in equilibrium.

The Murray Mouth was only about 100m wide and the ocean swell was pushing into the Coorong.

Next week:

Are the lakes historically salty or freshwater, and what does this mean for Victorian irrigators?

The Murray Mouth

Visitors to the Murray Mouth, who can witness the dredges at work clearing sand from the opening, are told: ‘‘Excessive water extraction, combined with drought conditions, have meant that the barrages have remained closed for long periods to hold water in Lake Alexandrina and Lake Albert for irrigation and other uses.’’