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The Cyclopedia of New Zealand [Otago & Southland Provincial Districts]

Water Supply

Water Supply.

Water was originally supplied in the city by the Dunedin Water Company. The whole of the property of this company, together with the rights and privileges conferred on it under its Act of Incorporation, was acquired by the corporation in 1874, and since then other lands connected with the supply have been purchased for water works purposes. Acting under “The Dunedin Water Supply Extension Act, 1875,” and the Amending Act of 1878, the Council impounded the waters of the Silverstream and its tributaries, and acquired certain lands by purchase and exchange in continguity to these streams. Dunedin is now supplied with water from two sources, known respectively as the northern and southern supply. The northern supply is obtained from a creek named Ross Creek, with a watershed of about 1,000 acres. The works are situated one mile and a quarter from the city boundary, and comprise: a main reservoir (holding 51,000,000 gallons), a settling reservoir (6,000,000 gallons), a stone sterm-water channel (19 chains in length), stone valve tower (with inlet and outlet pipes, screens, etc.), and a keeper's house. The dams are constructed of earthwork, with a puddle trench in the centre. The following figures give some idea of the dimensions of the varius parts of the works: Top length of dam to main reservoir, 363 feet; top width, 12 feet; inside slope, 3 to 1, pitched; outside slope, 2 to 1, turfed; greatest depth of water, 48 feet; bywash of stone, 20 feet wide and 4 feet 6 inches deep; working level of water, 372 feet above the lowest point in the city. The outlet pipes from the valve tower are laid under an embankment of stone pillars. The water is conveyed into Dunedin by 12-inch cast iron pipes track, and also providing convenient access to the reservoir. The pipes will deliver at the town boundary 4,000,000 gallons in the twenty-four hours without pressure. The total cost of the works to the corporation has been £139,350, which was largely increased in consequence of the city having to purchase from a company which had constructed the works. The southern supply is obtained from the Silverstream, and its tributaries, the watershed being about 12,000 acres in extent. The works are situated about three miles from the city boundary, and comprise: a main reservoir (holding 23,000,000 gallons), a cast iron stand pipe for valve (with inlet and outlet pipes, screen, etc.), a storm-water channel, and keeper's house, similar to that at the northern supply, and the dam is constructed of earthwork with a puddle trench. The following are some of the measurements: Top length of dam, 402 feet; top width, 12 feet; inside slope, 3 to 1, pitched; outside slope, 2 to 1, turfed; greatest depth of water, 43 feet; bywash of stone, 8 feet wide and 3 feet deep; working level of water, 422 feet above the lowest part of the city, and 50 feet above the level of the north reservoir (Ross's Creek supply). The reservoir is supplied by an open channel or race about twenty miles long (depth 3 feet bottom; width, 2 feet 6 inches). The fall varies from 4 feet to 2 feet 6 inches per mile. The race is cut in the sides of the hills, and follows their contour with brick tunnels, 5 or 6 chains long, through the short spurs. Along the race there is a level bench 5 feet wide on the outer side, which serves as a means of communication. The creeks are crossed with stone culverts or wood flumings on stone piers, and are intercepted by a dam and inlet gate to a short subsidiary race leading to the main race. At the Silverstream Head there is a concrete dam and inlet gate, the flood waters flowing over the crest of the dam. The water from the reservoir is conveyed for three miles by an 18 inch cast iron pipe under the embankment, cased in concrete. Thence for a distance of about a mile the pipes have a heavy fall, and are 14 inches in diameter. Thence, again, to the city boundary the pipes have a less gradient, and are laid in two branches, supplying different parts of the city and suburbs. The branch for the high levels is 14 inches in diameter, and for the low levels 12 inches in diameter. The two pipes will deliver at the city boundary 5,750,000 gallons in the twenty-four hours without pressure. There being a great variation in the levels of the city, the pressure in the pipes during working hours varies from 10lbs to 130lbs, according to the altitude. The total cost, including purchase of land, and large compensation for water rights and interference with coal mining lands, has been £82,000.

Stafford Street, Dunedin: 1862.

Stafford Street, Dunedin: 1862.