RIVER IMPROVEMENTS.

Hauraki Plains Gazette, Volume XXXX, Issue 5471, 6 September 1929, Page 4

RIVER IMPROVEMENTS.

NEW MACHINE ON PIAKO RIVER A TRIUMPH FOR DESIGNERS. Since the beginning of settlement on the Hauraki Plains the Lands Drainage Department has been criticised by settlers for not improving the channel of the lower reaches of the Piako River. The critics pointed out that drains and canals were being made to run water as quickly as pcs. sible into the river, and that improvements were constantly being made to the channel in the upper reaches and in the tributaries, resulting in floodwaters being brought down in a rush within a few days instead of steadily over 1 a period of weeks, as formerly. The critics overlooked the fact that this work progressed slowly, and that the increased flow of water and the churning by propellors caused scouring in the lower’ reaches, so that the river became of greater capacity as a greater capacity was required Old settlers will remember that the river was fordable at many places, and that the launches had to work with the tides.

The improvement. to the river is demonstrated by the fact that only on rare occasions, and in exceptional circumstances, has flooding occurred, and that the assertion that floodwater from the upper reaches would cause the river in the lower reaches to remain high for so long as to impair efficient flood-gate action has not been borne out. The additional capacity given by the dredging and stop-bank-ing which was done a few years ago has enabled floods of record height to pass unnoticed within the past two winters.

As the department’s work on the Hauraki Plains is drawing to a close, and the end is in sight, the tir>e has come to put the main outlet in such a state as to ensure a wide margin of safety for all time, and thus the river channel from Hobahia to Kaihere is now receiving further attention. To obtain the greatest capacity for the river it has to be widened and deepened by dredging the bottom an.l placing the stop-banks well back from the water’s edge at normal times. This undertaking, while similar to the dredge work which has been done on the Plains is of such magnitude that none of the department’s huge plant was capable of doing it except by numerous costly handlings. The expenditure of £lO,OOO or so on a special machine for this job alone was unwarranted, so the department set about constructing a dredge at the least possible cost. The machine commenced working last week-end, and anyone who cares to walk half a mile or so down the stop-bank from Horahia Road and examine it will find that it is a veritable triumph for the skill of the officers of the Lands Drainage Department. .

The object was to make a machine which would lift spoil from the middle of the river and deposit it up to two chains back from the water’s edge, and to do this by utilising materials on hand as much as possible. As a basis an old Michigan walking drag-line machine was taken and reconstructed to a larger scale. It is still known as No. 19, but no one would recognise it in the machine which, when on loan to the Public Works Department a few years ago, constructed the outlet which crosses Puke road. That machine had a 48ft boom and a two-cylinder engine. The new machine has a four-cylinder engine and a boom which projects out for 100 ft—almost the width of two roads.

The calculation of the weights required to balance this boom with its yard bucket and ton of spoil,' in all positions ; the size to make the supports so that the machine would not capsize, and the power required to swing the boom through about 160 degrees, and possible up-hill, as when the machine is not level, and to take into account the materials which were available, made a stupendous task. One factor was so dependent on another’ that months of work must have been undertaken before any of the fitters at the department’s depot were given a single job. Very difficult must have been the task of calculating the power required for the various opera tions, such as, for instance, the lifting of the machine in the process of walking, and in starting the movement of the boom from a position near a right angle to the line of progress.. The machine is of the familiar drag-line type in that it fills its bucket by dropping it from the end of the boom and dragging it in, but it is able to swing the bucket out so that it can actually pick up and empty 20ft or so beyond the end of the boom. More interesting, however, is the method of moving or walking. Alongside the body of the dredge are two long “feet.” When it is desired to move the dredge forward these “feet” are pushed ahead. Long levers working on rollers on the “feet” lift the front or we machine, which is then moved forward and lowered. The movement may be likened to a seal walking or a man rowing a boat. The crew of the dredge comprises three men, and the dredgemaster has an array of eleven clutch or gear levers to actuate.