Sand moving along the beach under the influence of wind and waves is pushed into the Murray mouth by onshore water movement. The mouth itself is kept open by the flow of sea-water in and out but incoming sea-water is carrying sand in suspension which settles when the water slows in the sheltered estuarine water. This sand blocks the channels inside the entrance unless water flowing from the river can scour away the sand and take it back out to sea.
In 1981 the mouth of the Murray River was closed for the first time in recorded history by natural sand movement accompanied by a low flow of water from the river. Engineering attempts to re-open the river failed completely and the mouth only re-opened in a subsequent flood. In 2002 the river mouth again seemed likely to close as the flow from the river declined. Previous experience indicated that, once it had closed, the Murray mouth could not be re-opened by dredging and with a closed mouth sea water would not reach the Coorong which relied on a mix of salt and fresh water to maintain its complex environment. Without regular sea-water the Coorong would be unacceptably altered.
Sand dredging began in 2002 to stop the river closing and ensuring that the Coorong remained healthy. Handling the watery-sand environment was challenging and some large earth-moving equipment sank before appropriate equipment was adopted.
Now sand is sucked up from the bed of the two channels (the Goolwa and the Cooyong) for twenty-four hours a day and pumped through large flexible piping to be dumped on the ocean beach. The project, begun in 2002, is still in full swing in 2006 and is likely to continue until the river flow increases. The logic of taking so much water upstream that the downstream flow is reduced to the extent that major engineering works are needed to compensate for the reduced flow downstream seems weird and indicates a lack of co-ordination.