THE WATER SUPPLY.

New Zealand Times, Volume XXXIV, Issue 5658, 19 May 1879, Page 3

THE WATER SUPPLY.

TO THE EDITOR OF THE NEW ZEALAND TIMES.

Sib,—Being neither doctor, lawyer, nor learned man, nor using the water, it may seem somewhat presumptuous that I should advance anything oh so momentous a subject as the Wellington water supply. Be that as it may, from experience and observation I have gained some knowledge not generally known, which I think may be useful in estimating—lst. The rate at which the reservoir will fill up ; 2nd. a way to investigate that evil, believing that the principle that has been efficient in a small way will be equally effective in a large, with one exception, ic , the prevailing winds acting on a large surface of water will have the tendency to wash and wear down the steep sides of the reservoir. On a small stream running through my garden (having a watershed of about a square mile of grassed land), about 20 years ago I formed a pond 100 ft. x 50ft., and 2-Jffc. deep ; three years after I let the water off in order to clean it out. I found about a foot of sediment all over it. An agriculturist, on seeing the fcetid deposit, said ; if would be a source of great gain to me—so I then thought. - But after cleaning it out a few times I found the gain would not pay the labor, so it was abandoned. On filling up the pond I formed two small ones, leaving an open course between, and supplying them from a higher point of the stream. Now theflood water goes clear off, and carries the sediment with it. This principle could be applied on the Kaiwarra stream; when the upper basin is formed if a flood-channel were carried round the south side of. the present one and the water shut off in times of heavy rain, little sediment would be deposited In the lower one, this channel would also intercept the storm water coming down from the hill and gullies. There would be less need tor a flood-channel on the north side as it is mostly covered with bush, so the water would come down more slowly and less polluted. The upper basin would require to be cleaned out perhaps once in seven years. In order to facilitate that object it might be divided longitudinally, so one aide could be cleaned whilst the other was full.—l am, &c„ Robt. Donald,