Lance,

If there were no barrages (no sea dykes), during periods of prolonged drought the Lower Lakes would be mostly full of seawater. So during drought the evaporation would be more-or-less 100% of seawater.

During the recent Millennium drought, water levels in Lake Alexandrina fell precipitously from 0.85 metres above sea level to -1.10 metres below. There was simply not enough water in upstream dams to keep both Lake Alexandrina and the adjacent Lake Albert supplied with adequate fresh water notwithstanding the Snowy diversions and strictly limited allocations for irrigation during the drought.

The South Australian government could have opened the 593 gates within the five sea dykes to let the Southern Ocean in, but instead kept the gates shut tight. This was not reported in the national media, instead, during the drought, television cameras focused on either the receding lake waters or the sand dredge working to keep the Murray's mouth open, conveniently avoiding images of the massive sea dykes in between.

As soon as the floodwaters arrived in the spring of 2010, the government opened the gates to let excess freshwater out.

And Jennifer, only parts of the lake were saltier, not sea salty (50,000EC), during minimal flow periods. Your continued implication that these piddly little two foot tides, when they are there at all, could change the composition of the entire lake do you no credit at all.

Nor does you continued debasing of terminology to the point where you claim a concrete wall with no contact with wave action is a "sea dyke". Any water barrier is defined by the task it performs and for 99% of the time this wall holds fresh water at a level 50cm above AHD. It only holds back sea water during the peaks of storm surges and the very rare times when river flows have ceased long enough for over 500mm of evaporation to take place.

In the Australian context, the only "sea dykes" we have is when the good ladies of Glebe spend the afternoon at Bronte Beach.

Lance

The word 'barrage', according, to the Macquarie dictionary (Macquarie Australian encyclopedic dictionary 2006), is a military term.

The dykes are known locally, and within Murray Darling Basin Authority publications, as the barrages, however, the correct term for an embankment restraining the waters of a river or the sea is a dyke.

The dykes hold back the Southern Ocean and created a freshwater reservoir with a storage capacity of 1,974 GL. The dykes are variously built of earthen embankment, concrete sluices, concrete piers and stop-logs. The Goolwa and Tauwitchere dykes include a lock.

There are five dykes stretching a distance of 7.6 kilometres and they have dammed and damned the Murray River's estuary.

That Peter Smith should say “the natural environment CANNOT be restored…” not only says he acknowledges that the original environment of the Lower Lakes was estuarine, but assumes he has the right to tell the rest of us that we are stuck.

Locks and weirs along a river are one thing, but weirs across a tidal estuary are quite another. Even in 1903 engineers knew that the barrages would cause ‘harm’ to the Lakes, especially during drought. In 1903, “A Report by Experts”, about the feasibility of the barrages warned,

“Supposing the barrage to have been erected, if the supply of fresh water is not sufficient to provide for evaporation, the surface level of the lake will fall below that which is now maintained by the influx of the sea, large areas of the foreshore may be left dry, and the remaining submerged areas become little better than salt swamps. If the supply of water from the upper reaches of the river is not sufficient to keep the lakes reasonably full, the effect of the erection of the barrage as described above would be serious injury to the condition of the lakes instead of being an improvement.”

That ‘serious injury’ included acid suphate soils being exposed in 2009 when the Lower Lakes were allowed to dry down to one metre below sea level because the barrages were kept closed. Sea water at sea level would have kept those soils covered and also would have left enough water in the Lower Lakes for recreational uses to continue through the milenium drought.

It is not too late to restore the estuary should the nation decide the environmental merits are worthy.

http://nla.gov.au/nla.news-article4987833

Taswegian,
I am sorry but your lack of understanding the Lower River Murray is abvious from your post.

Lance,
Thank you for your posts bur as I have found disagreeing with Jennifer is a no – no!