Water Race System for Waihi Mining

Ohinemuri Regional History Journal 18, June 1974

By ANDREW ROBINSON

We know of the importance of water in alluvial mining when "sluicing" was the only practical way to recover gold but water in one way or another has always been necessary in the recovery of precious metals and minerals even from hard rock. In districts where lode mining was carried on, large quantities continued to be a major requirement. To provide such volumes dams were built and many miles of races were constructed, bearing witness to the ingenuity, hardihood and perseverance of the miners of the era.

THE HAURAKI MINING DISTRICT

The Mines Report of 1886 records the following figures concerning Water Races.

One Sluice Head = 60 cubic ft. per min. or 375 gallons per min.

(In alluvial workings the miners paid so much per sluice head for water used).

THE WAIHI RACE SYSTEM

Water was originally picked up from 3 main sources. Mataura Stream, Ohinemuri River and Waitete Stream. A further source of supply was the Mangatoetoe Stream.

(1) A dam was built across the Mataura near the edge of the bush to contain the water eventually to flow down the race. Naturally only some of it was taken. The race was excavated round the contour of the hills and valleys on an easy grade to terminate on the banks of the Walmsley Creek. There a retaining dam was built and a further race was excavated to conduct the water to the Battery sites. (The first part of the race must have been abandoned early, for though I lived near it and walked and played along its banks as a lad, I cannot recall it carrying any water).

From Walmsley's Creek the race followed contours through the property across to Bulltown and finally to Pipe Lane and the old Waihi Battery on Union Hill. (This is where Mineral Resources N.Z. Ltd. is now operating, treating tailings because prior to Cyanide treatment recovery of values was incomplete). The race ended near Darby Street on the east side of No.6 Shaft, the water then being taken by pipe to the Battery. In the years following W. War 1, the pipes were taken out and a trench opened across Grey Street, spanned by a foot-bridge. The route had been realigned - probably about 1905 - when the Junction Coy. erected their Battery which cut across the race. A tunnel was driven under William St. and connected to the race.

(2) The race from Waitete Stream started behind the dam. It carried the water along on a devious route to finally junction with the race from Walmsley's Creek and went under Bulltown Road by a short tunnel.

(3) A wooden dam was built on the Ohinemuri River near the Rifle Range at the end of Mataura Road. A short length of race was excavated from the Homunga Stream to convey water to the upstream side of this dam and a low level race carried water to Union Hill. Two tail races were dug from the Battery to empty into the Ohinemuri River near the bottom of Clark Street.

A race from Mangatoetoe Stream started from near the old Gas Works and led to the old Battery at the end of Silverton Road and another one downstream from the junction of Waitete River with the Ohinemuri took water to Waikino. (The late Mr. Martin Rohan of Waikino had the contract for building this race in 1895. See Journal 7 - Page 8 [see Journal 7: In Memory of a Pioneer - E])

I came across an 1897 report of Mr. H.P. Barry (a Superintendent of the Waihi Gold-Mining Co. Ltd.) in which he stated:-

"The Company is erecting a new Mill at Waikino, Owharoa. Owing to some little trouble in getting the road bridge across the Ohinemuri River completed, work on the new reduction works was somewhat retarded, but since the bridge was finished and opened for traffic, the various works have been steadily pushed on. The bridge is a strong piece of work 155 feet in length the main truss on trestles built on two concrete piers. Where it was to the Company's advantage, the new works have been let on contract. A.&G. Price, Thames have secured the contract to supply the stamps. A considerable amount of works has been done on the tail race which has been taken out in a large opencut, but it is proposed to tunnel the rest of the distance.

New Water Races.

The necessary motive power will be obtained from a high pressure system of races having a fall of 193 ft. and a low pressure system having a fall of 54. ft. The high pressure system consists of three races - The Mangakara Race and the Stony Creek Race both tributaries of and falling into the Waitekauri River. The Waitekauri Race 6 ft. by 2 ft 6 inches deep and below the junction of its tributaries 7 ft. by 2 ft. 6 inches deep is upwards of 4¾ miles long and commences at a dam a few hundred yards below the Waitekauri Gold Mining Co. Ltd. Mill. This race passes under the old Kauri bush through a tunnel 1530 ft. long. The Waitekauri dam is a substantial wooden structure 16 ft. high with a spill of 68 ft., the total length being 170 feet with wings built of Kauri throughout. The dam on the Mangakara is a permanent piece of stonework upwards of 30 ft. in length and running from 2 ft to 8 ft in height. The Mangakara Race is 5 ft by 18 in. in depth and is upwards of 22 chs. long passing through a tunnel 268 ft. in length. The dam on the Stony Creek will be a wooden structure upwards of 45 ft. in length. The Stony Creek race is nearly ½ mile long 3 ft. wide by 18 in. deep. The pipe line for carrying the water from these races to the mill is of wrought iron 2 ft. 4 in. in diameter and upwards of 1200 ft. long.

The low pressure system consists of the Ohinemuri Water-race 4⅛ miles long 12 ft. by 4½ ft. deep, running for the most part on the South bank of the river but will cross at one point to the North bank by a high trestle flume and recross again to the South side after a distance of about a quarter of a mile. These crossings though expensive were unavoidable owing to the nature of the ground. With the exception of these flumes just referred to, and a wrought iron siphon 5 ft. in diameter and about 475 ft. long, the whole of the race was carried through a ground channel. The dam on the Ohinemuri at the intake of the race will be a strong and solid structure of masonry. It was considered advisable to do this rather than construct in wood, so as to avoid any possible danger in the future through the wood rotting. The water from this race which has a fall of 1 ft. in 2000 will be conducted to two 200 H.P. vortex turbines by a pipe line 4 ft. 6 in. in diameter, branching off into two pipes of 3 ft. 6 in. diameter fitted with equilibrium valves.

The length of the tramway from the mine to the mill is approx. 5¾ miles, 2 ft. 9 in. gauge. The line crosses the Ohinemuri River from the North to the South bank 2¾ miles from the mine by a strong truss bridge upwards of 185 ft. long and 30½ ft. from water to decking. The locomotive has been put together and is now ballasting the line. Twelve of the iron side tipping trucks are on the ground and fifty more are on the way from England."

Note on Wet v Dry Crushing of Ore

It is a popular but erroneous belief that only dry crushing was practised in Waihi in the early days. In 1889 the Waihi Coy. started dry crushing which gave a better return than wet crushing and plate amalgamation. In 1892 the Coy. made another experiment with wet crushing but although stamp duty increased by 30%, bullion extraction dropped by 10%. Consequently wet crushing was abandoned for about 10 years. About 1902 the older 100 head of stamps at Waikino and the 90 head at the Waihi Battery were converted to wet crushing. Thus, after about 14 years dry crushing ceased on the Hauraki Goldfield. (Unfortunately both pan amalgamation associated with dry - crushing and wet crushing with plate amalgamation gave poor returns.)