THE WELLINGTON WATER SUPPLY.

New Zealand Times, Volume XXXIII, Issue 5309, 1 April 1878, Page 3

THE WELLINGTON WATER SUPPLY.

TO THE EDITOR Of THE NEW ZEALAND TIMES. Sib, —I venture to make: the following remarks with reference to the supply of water from the present waterworks of the city. The only source of supply, as you are aware, is the rainfall upon the catchwater basin lying above the main clam in the Upper Kaiwarra stream. The area of this basin is about 520 acres, the hills on each side of the valley rising to an altitude of about 800 feet above sea level. The rainfall in the neighborhood of Wellington is about 42 inches per annum, ascertained by taking the average of ten or twelve years. But this is the quantity as ascertained at or near sea level, and it is well known that the quantity of rainfall diminishes rapidly with increasing elevation. Now, assuming that the diminution on this ground, the Upper Kaiwarra hills, is. four inches, we hare thirty-eight inches left as available for the supply of the basin. If all this were available for the supply of the town, little need be said for years to come, but this is not the case. The total supply is reduced by many causes, such as percolation through the oround, plant absorption, and (which is by far the most important cause of loss) by evaporation, In countries in which these causes have much less influence than ought to be attributed to them here the loss arising from them is estimated at fully one-half of the total rainfall. Here I think the loss would be greater; but even assuming it not to be so, we are left with about eighteen inches of available rainfall over the area of five hundred and twenty acres, or about nine and a-half gallons to the square foot. Reducing the area to feet, and multiplying by 94, we obtain about two hundred and fifteen millions of gallons of water per annum as available for the supply of the city from this source, or about six hundred thousand gallons per diem. Now, the question arises what would be a fair supply of water for ordinary domestic purposes in this city. Upon this I can offer no very decided opinion; but reference to what is considered reasonable in other places may help to determine the question. The present population is nearly —2'OTUOO, and although as yet not more than one-third of the town is supplied, the water is failing. But assuming that the supply were available for the whole city, and that twentyfive gallons per head per diem would be sufficient for ordinary purposes, we would only have a margin of a hundred thousand gallons per diem for all other puposes—such as waste, fires, supply to shipping, supply for manufacturing purposes, machinery, street watering, and the many other claims upon the water which must ordinarily arise. That the margin, even in present circumstances, is insufficient, is however palpable, and we must remember that the population of the city and the claims for water supply will increase. It is doubtful, moreover, whether 25 gallons per bead can be considered as a sufficient supply for ordinary purposes. For my part I think it too little ; and if I am correct in this, the total quantity which the present waterworks are calculated to yield is not more than sufficient to give a reasonable ordinary supply for domestic purposes to the present population, without maldng any allowance whatever for waste, fires, manufacturing purposes, &c., as above. I ventured long ago to point all this out, and suggested that the permanent supply of the city should be derived from the Hutt River, just above its junction with the Mungaroa. Ido not think the latter stream would be fit, and it would be simply absurd to go to the Paikakariki. Of one thing I feel quite assured, namely, that no time should be lost in adopting some scheme which will place this city in a position of perfect security as regards its water supply.—l am, &c., Wm. Thos. Locke Travers. March 30.