Lock 3 is undergoing maintenance for the next several weeks, and the attached video makes interesting viewing of the draining procedure in preparation for this. It is fascinating to note that the foundations at Lock 3 were different from those at other locks built by South Australia.
The foundation at Lock 3 is better than at any other site in South Australia. It consists of a bluish clay underlying the river sand at a depth from six feet to 14 feet below low water level. On top for about one foot, this clay resembles a rock which has to be gadded-out, but underneath is much softer and is readily broken with a pick. It is a solid, regular and almost watertight material.[i]
But the preparation for the floor work was difficult nonetheless. Robert Barclay, a labourer, spoke of the ‘back-breaking’ work: ‘With the solid riverbed, footings had to be chiselled out from it instead of making a pile foundation. After removing the sand from the river floor, we had to dig about eight feet into the stone to secure a hold, so the force of the water would not push the lock and weir away. It was terrible hard digging, just like cement that had gone hard in a bag, got wet and set hard.’[ii]
This riverbed had other interesting aspects. Assistant engineer George Mudie found a collection of fossils including a shark’s tooth of the genus charadon which lived millions of years ago, a palatal tooth of another extinct fish and a cluster of whale bones.[iii] Other workers found fossils too.
[ii] Helen Stagg, Harnessing the River Murray, Stories of the people who built Locks 1 to 9, 1915-1935, p. 108.