Key points from the Murray River Barrages Environmental Flows Report produced for the Murray-Darling Basin Commission in 2000. It's purpose was to provide guidance to the Commission from a panel of scientists to better manage the river for the benefit of the environment. A few key points below are from the report and clearly acknowledge that the Lower Lakes were once part of a much larger estuary that included the Coorong.
From page 10, Key Issues:
"The Scientific panel identified four key issues driving the serious degradation of environmental values in the Lower Lakes and Coorong. These are:
• the reduced area of the estuary
• changed water regimes of the lakes and river
• freshening of brackish and saline habitats
• reduced habitat for aquatic plants
The first two issues are the most significant in terms of their impact and their influence in driving the other key issues."
From page 43:
"The reduction in the size of the estuary has reduced the size of the tidal prism by around 90% of its original pre-barrage size. In 1914 the lake area affected by tides was 97.3 km2 (75 000 hectares), with a spring tidal prism of 20 000 ML (Walker 1990). These figures indicate that the original tidal prism produced a twice-daily exchange of similar magnitude to the flows of 20 000 ML/day for a month or more which would now be required to substantially clear the mouth of accumulated deposition (Harvey 1988)."
From: page 44, Opportunities for Improvement:
Options for rehabilitation measures to address the key geomorphological issues - Long Term
"Enlarge the diversity of habitat in the estuary by increasing the size of the tidal prism and the flushing effects of tides at the mouth. An option for management is to relocate the barrage system to Wellington or to Pt Sturt–Pt McLeay."
From page 62, Ecological Needs:
"The changes in water regime and the presence of the barrages have both led to a reduced extent of the estuarine system, now approximately 11% of the former area (Bourman ibid). Along with the changes, there has been an increase in the extent of the freshwater environment behind the barrages and an increase in the spatial and temporal occurrence of hypermarine conditions in the Southern Lagoon. There has been the establishment of unvarying marine salinities for long periods in the remnant estuary when the barrages are closed. Clearly, management of the region needs to enhance the environment for estuarine macro-invertebrates and for estuarine-marine fish."
From page 64, Long-term Changes:
"Consider removal of present barrages and investigate options for new structures at Wellington or Pt Sturt. This would greatly enlarge the estuary and return it to its historical form. More information on hydrology, geomorphology and biology of the system is needed before this major change could be implemented."