COORONG, LOWER LAKES AND MURRAY MOUTH REGION

In reply to Mr WILLIAMS (MacKillop) (26 June 2012) (Estimates Committee B).

The Hon. L.W.K. BIGNELL (Mawson—Minister for Tourism, Minister for Recreation and Sport): The Minister for Water and the River Murray has received this advice:

Narrung Bund

The Narrung bund was constructed using steel sheet piles, concrete blocks, steel ties and approximately 40,000 cubic metres of imported sand. Phase 1 of the project removed the sheet piles, concrete and steel and a combined total of approximately 29,000 cubic metres of imported sand. It is estimated that approximately 1,000 to 2,000 cubic metres of sand was lost from the site during construction and removal through scouring and transport by currents. The remaining material is heavily mixed with acid sulfate bed sediments and, for environmental reasons, is not able to be removed to land disposal.

Phase two work at Narrung was completed on 18 October 2012. Phase two required a dredge to remove peaks that were identified as having the potential to have implications for normal navigation and to ensure there would be no significant impacts on water exchange between Lake Alexandrina and Lake Albert.

Goolwa Channel Regulator at Clayton (Clayton Regulator)

The Clayton Regulator was constructed using approximately 165,000 cubic metres of imported sand.

Pre-removal surveys determined that some imported material was covered by, or mixed with, acid sulfate sediments. In order to reduce the risk of acid sulfate soils being removed, the contract for regulator removal specified the removal of 80,000 cubic metres of imported material. During the removal process it became evident that the extent of mixed material was greater than expected. This, in conjunction with some difficulties experienced in excavating rocky material, resulted in a total volume of approximately 38,000 cubic metres of clean material being removed to land.

Currency Creek Regulator

The Currency Creek regulator was constructed using approximately 71,000 cubic metres of sand, 3,500 cubic metres of crushed rock and small quantities of geotextile and plastic geogrid.

On-ground works commenced in April 2013 and stages one and two have been completed. Stage one involved the removal of the mixed material from either side of the sand core of the regulator, exposing the sand core to ensure as much as possible can be removed. This material was disposed of in an underwater disposal site located one kilometre from the regulator site. Stage two involved the removal of an estimated 28,000 cubic metres of clean sand to an on-land disposal site. This is the total volume of sand that could be removed to ensure that no acid sulfate soils were removed to land.

All work to remove the Currency Creek regulator was completed in August 2013, the spreading of the stage two disposal location on private property is not yet completed and the rock is currently stockpiled on site. These items have been delayed due to wet weather resulting in the contractors unable to continue working. These tasks will be completed once site conditions improve around November 2013.