Please note the posted coordinates are a starting point only, they will have you close, because the flow fluctuates you will need to walk down and be within 1-2 meters of the water’s edge.
The Murray-Darling Basin is about 250,000 square kilometres and is bounded by the Great Dividing Range to the east, and the Mount Lofty Ranges to the west. In the north it's separated from the Great Artesian Basin by an impermeable division. Today the area of the Murray-Darling Basin consists largely of flat plains country in which Quaternary and Tertiary sediments rest on a hard impervious basement of rocks - predominantly of the Paleozoic Age (about 250 million years old). A major feature which occurred during this long evolution was a great incursion of the sea during the Tertiary period. The seas flowed in, over what is now the south eastern coast of South Australia and at the time of maximum inflow created the Murravian Gulf reaching as far inland as present day Balranald and Swan Hill.
As conditions on earth changed over the long 100-million-year development of the Murray-Darling Basin so did the geological and biological processes, and it is all there, recorded in the layers of the sediments–limestone from marine organisms, brown coal from ages of lush plant growth, silts carried down from the mountains by the river to form the great flat sea of search that is now the Hay-Balranald plain.
As the sea commenced its great retreat, it left behind in the sediments and in the soil enormous quantities of salt, particularly in the Mallee region of north-west Victoria and the adjacent part of South Australia. Today that same salt is a major problem due to clearing, irrigation and improper management.
While the slow subsidence of the floor of the Murray-Darling Basin was taking place, an outcropping of rock was pushing up around the margins of the basin to form the surrounding highlands. Even within the basin all was not completely quiescent, and in recent geological times faults have occurred. The most significant of these is the Cadell Tilt Block between Echuca in Victoria and Deniliquin in New South Wales which is one of the most spectacular examples in the world of faulting altering the course of a river. Along the fault line which lay squarely across the path of the River Murray a massive block reared up at a faster rate than the river could cut down through it. Finally, about thirty thousand years ago the flow in the Murray west of the fault was blocked off altogether and the river was diverted north and south to find paths around the giant obstruction.
Another movement forced the river to cut completely new channels for itself. In the more westerly section of the Murray-Darling Basin another uplift, the Pinnaroo Block–profoundly affected the character of the river by damming it off to form a giant fresh-water lake called Lake Bungunnia. The Lake extended from near the site proposed for the Chowilla Dam, close to the South Australian-Victorian border, back as far as Robinvale in Victoria. Later, the Pinnaroo Block Dam was breached by a stream flowing on the seaward side of the Block which had cut back into it until a channel had formed - releasing the water of Lake Bungunnia once again to flow out to the sea, this caused the river in South Australia became rejuvenated, flowing in a narrow valley, cutting down sharply to form many miles of the beautifully golden calcareous cliffs which are a feature of the Murray in that state.
Where we have you standing today is the Murray Mouth is the point at which the River Murray meets the Southern Ocean. The Murray Mouth's location is changeable. Historical records show that the channel out to sea moves along the sand dunes over time. At times of greater river flow and rough seas, the two bodies of water would erode the sand dunes to create a new channel leaving the old one to silt and disappear.
The mouth is an opening in the coastal dune system which separates the river system from the ocean, and which extends from near Goolwa in a south-easterly direction along the continental coastline for about 145 kilometres. The mouth divides the dune system into two peninsulas. The peninsula on the west side is Sir Richard Peninsula which terminates at the mouth with a point named Pullen Spit. The peninsula on the east side is Younghusband Peninsula which terminates at the mouth with a point known in some sources as Sleepy Hollow.
Water flows throughout the mouth from two directions. Firstly, the flow from the west passes along a passage known as the Goolwa Channel which is bounded by Hindmarsh Island to its north side. Secondly, the flow from the east passes along a passage known as the Coorong Channel. The Coorong Channel itself is fed by the Mundoo Channel which passes between Hindmarsh Island and Mundoo Island to the north, and by the Tauwitchere Channel to the east.
River Murray water is used by farmers for irrigation in four of Australia's states, as well as supplying water to most towns along the river, and many further away through various pipelines. It has been widely accepted that too much water is being extracted; however business and political concerns make it difficult to remedy the problem. A visible symptom of the over-extraction of river water is the closing of the Murray Mouth.
From October 2002 until 2010 dredging machines operated at the Murray Mouth. Between 2002 and 2006, two machines operated moving sand from the channel to maintain a minimal flow from the sea and into the Coorong's lagoon system. Without the 24-hour dredging, the mouth was at risk of becoming silted and closing, cutting the supply of fresh seawater into the Coorong, which would then warm up, stagnate and die. Dredging continues at a cost between $3m to $6m annually.
To log this Earth Cache, we require you to visit the Murray Mouth, the posted coordinates will have you close, because the flow fluctuates you will need to walk down and be within 1-2 meters of the water's edge to make some observations, consider the information given, then message us with the following answers to the best of your ability.
1. While standing within 1-2 meters of the River, describe what are you standing on? Describe colour texture and speculate where this has come from.
2. Dig down 10-15cm (you should be able to do this with your hands), can you see any difference, explain why or why not and what has caused this difference?
3.When facing the Southern Ocean look to your South East, what do you see, can you name this landform. Can you see any geological processes in action?
4. Hypothesise about which direction Murray’s mouth currently moving and why?
5. A photo of your team or GPS with the Murray’s Mouth or one of the Dredges the background, upload as many photos as you like!
You are welcome to log your find straight away to keep your TB's and Stats in order but please message us with your answers within a couple of days. Cachers who do not fulfil this Earth Cache requirement will have their logs deleted without notice.
Source: Murrayriver.com.au, Wikipedia.