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The Cyclopedia of New Zealand [Canterbury Provincial District]

Drainage

Drainage.

Intimately connected with the question of the water supply is that of drainage, and the inhabitants of Christchurch have gone to great trouble and expense to provide their city with a complete and efficient drainage system. The city is at the highest point only about sixteen feet above high water mark, and the fall from the city to the sea is very gradual. The presence of numerous streams, the nearness of the subterranean water supply to the surface, and the very slight fall in the land, all, at first, combined to render the site of Christchurch distinctly unhealthy. As the town grew, and the houses became comparatively crowded, the vital statistics showed that the city deserved its evil reputation, and it was plain that these disadvantages would be aggravated with its growth. To meet these difficulties, in 1875, a special Act of Parliament constituted the Christchurch Drainage Board. This body proceeded at once to deal with the difficulty in a vigorous and practical manner. Following the recommendation of Mr. W. Clark, C. E., the board has constructed an elaborate system of sewers for surface drainage and sewage proper. Mr. Clark, in his report of 1878, pointed out that the most important feature affecting the public health of Christchurch and its suburbs was its waterlogged site. “Over a large area of the city, especially in winter, water is met with at from four feet to a few inches only below the surface of the ground, and at Waltham the water during the winter time is stagnant on the surface. While, therefore, the present imperfect removal of filth is a growing evil, the exhalation from a very damp soil is abundantly present.” In the year 1875 the population of the city was 10,600, yet there were forty-nine deaths from typhoid and twenty-one from phthisis. The general death-rate (per 1000 births) was 30.4, and the infant death-rate was 184.2. As a proof of the change in health conditions, produced by the drainage system, it is sufficient to quote the vital statistics for 1889. The population had then increased to 16,785, but there were only five deaths from fever, and eight from phthisis, while the general death-rate had fallen from 30.4 to 9.7. The statistics quoted in a previous section show how effective the drainage system has been in protecting and improving the health of the population.

The surface drainage of the city and suburbs is collected in side channels constructed by the various local bodies in the district. These channels discharge storm water into the Avon and its tributaries by means of sewers specially constructed by the board. There are about eleven miles of these sewers, and they cost over £57,000. They are found thoroughly effective in clearing the surface water away. For the removal of sewage proper, Mr. Clark, in his report of 1878, discussed a variety of schemes. He emphatically condemned the suggestion of utilising either the Avon or the Heathcote for sewage channels, and he rejected the plans for discharging sewage into the Sumner Estuary or into the sea. In place of these unsatisfactory methods, Mr. Clark recommended that the sewage should be conveyed to the sandhills, which lie to the east of the city, between it and the sea, and that it should be used there to irrigate and fertilise the soil. The difficulty of fall was got over by pumping, and the liquid sewage is deposited on the sand before it has time to decompose. It is filtered through the sand, and, no longer noxious, is discharged by drains into the estuary. This system has been adopted with unqualified success. The quicksands and the loose nature of the soils caused great trouble in laying the pipes and constructing the sewers, which, with pumping plant, machinery and buildings cost about £127,000. Ample margin was left for a very large increase in the population before further sewers would be required. The sewers are well ventilated, and house connections are made under the board's inspection. In all, the board has nearly fifty miles of covered sewers under its care. The experiment of irrigating the sandhills with the sewage has been highly successful; large tracts of absolutely barren sand have been fertilised, and the Sewage Farm, half way between New page 46 Brighton and Christchurch, is run at a considerable annual profit.

But it must be admitted that much still remains to be done to perfect the drainage system. In 1900 Dr. Frengley made a house-to-house inspection in the city, and his report to the City Council on the subject is very instructive. He examined within the city limits 4116 houses, and found only 468 in a perfectly sanitary condition. There are, the report states, no slums in Christchurch; but, on the other hand, there are nearly 900 premises in the city— nearly one-fourth of the whole—in an unsatisfactory hygienic state. The remedies suggested by Dr. Frengley are: the connection of all houses with the main sewer, and the institution of a high pressure water supply which would ensure the flushing of the drains. The difficulty about the artesian supply is that it is by no means a high pressure supply unless obtained from a great depth. Here, again, the drainage question, naturally involves the water supply; and the possibilities of a high pressure system for Christchurch have often been discussed. The great volume of the Waimakariri suggests that it may be possible to provide the city with a high pressure supply from that source. Careful inspection has, however, convinced many competent critics that the scheme is not feasible. The varying volume of the river, its changes of channel, the expense of laying some forty miles of pipes to supply a large city— these considerations are too important to be lightly dismissed. The alternative scheme is the construction of a reservoir on the Port Hills, to which artesian water could be raised by pumping. The scheme is certainly not beyond the resources of the city, for it has been carried out on a small scale for Lyttelton and Sumner. There is no doubt that in the near future some such provision must be made for the health and comfort of the city. The scheme briefly known as “harnessing the Waimakariri” suggests at least one feasible means for the attainment of the desired end. But in any case, no one who has traced the growth and development of Christchurch believes that its citizens will be content with anything but the best protective sanitary arrangements that their resources will allow.