CLUTHA RIVER GRAVEL.

Otago Daily Times, Issue 20316, 26 January 1928, Page 15

CLUTHA RIVER GRAVEL.

OPERATION OF DRAG LINE. NEW AND ECONOMICAL METHOD. I (From Our Special Rep.:-ter.) GORE, January 24. For the past three weeks a giant apparatus, ungainly in appearance, but most in operation, has been engaged in scooping gravel out of the Clutha River for use or, road formation work near the Clydevale ferry. It is known as a Sauerman drac-hne, and was recently constructed 'by the Public Works Department on the river bank a short distance below the ferry landing. Since it began operations, 4000 cubic yards of gravel have been lifted out of the river by the underwater scoop at a cost that is estimated by the Public Works engineer, to be in the region of Is a yard. The drag-line was examined to-day by the members of the Main Highways Board party, which made a special trip from Balclutha for the purpose of inspecting tne road formation work. It was at once obvious that the greatest benefit of the innovation lies in the fact that a supply of suitable material for road surfacing has been made available within a very few miles of the farthest point at which the construction gangs are working. Although the appartus has not been erected as a permanent structure, 10,000 cubic yards of gravel have yet to be secured, and the drag-line will be kept working for many weeks to come. Near the northern side of the ferry, and at the base of the heavy wooden mast, which acts as the main-stay of the dragline, a large Public Works camp has sprung up, while clusters of workmen’s tents are also to be found at intervals along the re-formed road. A small fleet of heavy lorries is constantly employed in carrying the gravel from the hopper on the_ river bank to the points at which it is required, for the under-water scoop is not slow in action, and since it first plunged into the river, the average “ yield has been as high as 260 cubic yards every eight hours. In devising the Sauerman drag-hne ; full advantage has been taken of a river s natural tendency to deposit material m holes that may be formed in its bed. If the water did not do this, the building oi costly apparatus for scooping at any particular point would be useless, as the supply would soon fail in the workable area within reach. At Clydevale, the bed of the Clutha (or Molyneux as it is known at that point) is largely composed of good road-surfacing gravel, much of which is said to he tailings fro™ mining works in the upper reaches. When the drag-line was installed a plentiful deposit lay waiting for the powerful scoop, and it has been found that the rush of water fills up the holes practically as quickly as the gravel is removed. This was anticipated by the engineers, and to-day they exD •vssed themselves as satisfied that there would be no lack of material within reach of the scoop during the time it was m operation. , . „ The backbone of the Sauerman system a s applied at the Clydevale Ferry consists of a heavilv-stayed and reinforced mast 64ft in height. This has been set m concrete, some 25yds from the river s bank. From the top of the mast a dolphin of three stout wooden piers set in the middle of the river, there stretches a taut steel cable ijin in thickness and 100yds in length. This acts as a track for the toolley wheels on which the scoop is stungj and runs out at a steep grade almost to the water’s level. The scoop is capable of holding one cubic yard of gravel, which is clutched from the river bed by the dragging action of its toothed underside. It is operated on the simplest possible lines, the only attachment being a steel hauling cable passing through a tunning block at the masthead, and leading down to a 45 horsepower winch. In conjunction with this is the automatic tripping gear above the hopper. When a drag is made, the scoop i 3 allowed to run out by force of gravity until it reaches any desired point between the bank of the "river and the dolphin. There ft is allowed to sink under the surface, and when it is resting on the river bod the winch takes in the slack cable and hauls it gradually back towards the bank When the winchraan sees that a full scoop of gravel has been secured, he increases the speed of the hauling drums, and the scoop swings clear of the water and travels up the track cable. In front of it runs the tripping gear, and as this reaches a point immediately above the yawning maw of the hopper the scoop is arrested and upturned. The whole operation takes but a few minutes, and only the winchmen are employed on the actual work of the drag line. It was anticipated that the material secured in this fashion would require screening, and for this purpose special apparatus was installed near the drag line. It has been found, however, that this is not necessary as the gravel is in suitable condition for immediate use. The example set by the Public Works Department at Greenvale is now being followed by the Clutha County Council, and prior to visiting the plant near the ferry the members of the Highways Board inspected the site of a permanent drag line on the river at Balclutha, near the railway station and adjacent to the line. This is being erected out of loan money from the Highways Board, and already much of the initial construction work has been carried out. This drag line differs from the other in that a steel lattice frame mast will be built instead of a wooden pole, and the plant will be operated by electricity. A plentiful and continuous supply of gravel is anticipated, and the council has the advantage of having the drag line beside the railway.