Art. LIII.—On the Drainage Works at Remuera Swamp.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 2, 1869, Page 219

Art. LIII.—On the Drainage Works at Remuera Swamp. By J. Baber, C. E. (With Illustrations.) [Read before the Auckland Institute, November 15, 1869.] The means for draining the swamp near the Remuera sale-yards, known as Mr. Farmer's swamp, have been provided by laying earthen pipes in a tunnel in a different manner from the ordinary mode. The area of the swamp is twenty acres, in winter it had about three feet of water in the lowest parts. The greatest depth of the drain now laid is twenty-eight feet below the surface of the ridge. The diameter of the pipes used is thirteen inches. In designing the work, care had to be taken, that the pipes, after they were laid, should be secure from accident or displacement, from any slipping of the feet of the upright timbers, and that sufficient room should be left for working, without taking out more earth than was necessary. The strata through which the drive was cut consisted of a red volcanic soil, varying from eight to ten feet in thickness, overlying a bed of white silica and alumina almost destitute of cohesion, falling in from behind the timbers in thick flakes, without warning. The transverse Section 1 (See Plate 13) shows the working: the tunnel being first driven and timbered to a convenient length, a trench two feet wide, and four feet deep, was sunk in the floor of the drive, in this the pipes were laid, and the earth thrown on them as the trench was dug. The floor of the drive was thus raised about nine inches, and the feet of the uprights secured from slipping, while sufficient headway was left above, both for levelling and trucking out the earth from the drive. This plan was continued for about 220 feet, when the white sandy bed became so treacherous, that it was no longer safe to trust to the footing of the uprights, which slipped inwards as soon as the strainers were moved, and the digging the trench commenced. For a short distance Section 2 was used; it was safer, but did not afford the same facilities for keeping the correct gradient, nor for removing the earth. The longitudinal section shows the tunnel from A to B, driven according to Section 1, and its continuance from B to C, according to Section 2, the remainder was laid in an open cutting. The shaft D is permanent, in order to inspect the work at any time without much cost, that at E is a working shaft, filled in at completion. The timber uprights and headers are left in the drive, allowing the earth to fall gradually in upon the earthen pipes. The work was executed in a bad season of the year, in the months of May, June, and July. It cost £222 11s. 6d., or rather more than £1 14s. a yard. The pipes were socket pipes, glazed inside and out, manufactured by Carder, of Henderson's Creek. Like other swamps in the volcanic parts of this district, this one had its summer outlet through the lava, on the south-west side, which dried the swamp in summer, but in winter was insufficient to carry off the water that came from the surrounding land. In the summer of 1868–1869, this outlet was enlarged, in the expectation that it might be rendered more effectual, this, however, did not prove to be the case. The water is now carried under a ridge, and thence to a volcanic cave, where it instantly disappears.