TAILINGS AND THEIR EFFECTS.

Mount Ida Chronicle, Volume II, Issue 67, 13 May 1870, Page 3

TAILINGS AND THEIR EFFECTS.

Mr. J. T. Thomson, in a letter to the Secretary for Land and Works, on the floods in the Taieri Plains, makes the following remarks on the tailings question, which at this time will be read with interest :—■

" In estimating the probable effects of the diggings, I have not, for upwards of three years, had an opportunity of examining the tailings of the principal seats of operations, viz., at Hyde*Hamilton, and Naseby, yet I then observed that ineach case they were rapidly extending their length down to the Taieri river. At that time the light sediment alone was carried into it, but i the time did not appear long distant when the heavier portions, such as sand, gravel, and shingle, would also be so borne on, more so especially durin» floods. This fact was pretty apparent even then, that with the extension and * prosperity' of the diggings the Taieri river would have the greater burden to carry seawards ; and when we examine the Goldfields map of the Province, compiled by Mr. Vincent Pyke, which shows gold bearing valleys round all the Rock and Pillar mountrins, Lam merlaw ranges, Mount Ida, and Hio-h----lay, we cannot avoid the conclusion that the Taieri river will, in that future extension :*nd prosperity, become the great sludge channel of a very important ininiug district., Now, when the sediment alone, reaches the lower plains,

effects are little felt; but when the gravel, sand, and shingle begin to roH down then will the ' diggers' * gain be the «farmers'' loss ; for the tailings will spread out even on the Taieri green fields as they may now be seen to do on the 'interval', of Gabriel's Gully and Weatherstone's Flat. That lam not an unrea onablc prognosticatqr of evil, I beg to append the remarks of a late intelligent writer on California; and may here add that the case's mav not be entirely parallel, yeb the /warning is of sufficient importance to' callj for the timely offices o" our legislators! | and engineers. To gain an intelligible view of the eifects of the upper valley being filled with gravel, &c, we will require to consider the fall of the river from the Maniototo Lake to the Taieri Plain. As has been stated before, it is 962 feet in fifty miles, or at the.rate of 19.25 feet per mile, the descent beingpretty uniform. This is a far greater rate of descent than is applicable >o the' •absolute torrents' of English hydraulic engineers, whose velocities are reckoned at 480 feet or more per minute. Now, as a current of ISO feet per minute scours angular stones as large as an egg, and a rate of 300 feet scours conglomerate, the Taieri in flood will bring down tailings of every size and descrip°lion to the lower beds. If, then, the interior goldfields are to be prosperous and extend, measures will require to be energetically taken in the agricultural district of the Taieri to deal with these tailings. It is true that a generation may yet pass away before they become absolutely obnoxious to tillage, yet, under the above circumstances, the event is certain, and the action will be continuous till the Goldfields are worked out. With these facts before us, then, we must neglect the limited interest for the large majority—the inconvenience of a few for the safety of. the whole. The proper engineering measures for dealing with the floods ofthe river is, therefore, the second one mentioned, viz., to confine its channel entirely to the west side of the plain, cutting it off by a strong and high exnv bankment from the fertile fields of the central aud eastern districts. This would be a measure adequate to the wants of centuries ; any other would be ineffective and temporary." ~\ '■ J