THE KAWARAU IN ITSDREDGING ASPECTS.

Otago Witness, Issue 2471, 24 July 1901, Page 20

THE KAWARAU IN ITSDREDGING ASPECTS.

(By Ouk Wakatipu Cobkespoxdext.) * 111. THE WATERSHED OF THE KAWARAU

Including Lake Wakatipu and its tributaries, the total area drained by the Kawarau is about 4500 square miles, roughly estimated, according to the official survey map o£ the ProVince of Otago, 1871. By far the greater extent of this country lies to the north of the river, draining the south slopes of what may be comprehensively called the Southern Alp« — that is, the shady side of the mountains of north-western Otago. Of the rivers draining this area, the Shotover has a large drainage area, exceeding that of the Dart and Rees Rivers combined, but these two rivers are fed by higher country, which accounts for the greater volume of water they carry during the summer season, when rivers are in their normal condition ; but in times of flood the Shotover pays into the Kawarau several times the quantity of water escaping at the outlet of Lake Wakatipu. and is therefore the jiriuie cause of floods in the Kawarau.

The deduction from these facts is that the summer season, extending from Christmas up to April and May, is Ihe most favourable time for dredging upon the Kawarau ; against which the winter months, though perhaps equally favourable, and even more so, do not count for much, because as a rule July and August only can be depended upon as the winter months, a period scarcely long enough to properly prospect some of the claims on the river. Unfortunately not much dependence can be put upon the weather in the Kawarau watersh«d, but in the main it will be found that the above estimates are correct. It is, therefore, a mistake to count with too much certainty upon the dredging work of the next few months as an absolute test of the Kawarau as a dredging field, although seven or eight dredger, will be at work from Victoria bridge upwards within the next two months. The Arrow River, the Kirtle Burn (familiarly known as the Roaring Meg), and the Nevis River each contribute a considerable stream in flood times to the Kawarau, but, owing to the great fall in the river beds, soon subside, being reduced in a day or two to their normal volume. These rivers were more ser\ iceable as. contributors of gold than they are now — a danger in times of flood. A WORD OF CAUTION. That portion of the Kawarau extending from about the upper boundary of the Morven Ferry claim to the mouth of the Shotovcr. it should bo remembered, ua«

the site of the 1889-90 boom, which ended in disaster The chief cause of this was that the companies of that day were aot satisfied with the °old on the faLe bottom, but tiied to reach the main rock bottom, in the attempt of which they came to griet. The claims where the mam rock shows on the north shore of the rher and n*e abo\e water level have a chance of getting the main rock bottom in the river. proMdecl their bucket ladder is long enough. Ihe depth, taking that proved by the Arrow Junction dredge as a guide, cannot be put down at less than 40ft. Above the point where the main rock disappears on tlic north bank of the river it would be courting failure to try and find a bedrock bottom by dredging. This part of the Kawarau appears to have been an arm of Lake Wakatipu, of which Boyes's Fkt is. another and more clearly defined part. However this may be the writer assisted at soundings made 30 years ago in the neighbourhood of the ure<=ent Kawarau ferry site, when bottom vas found at 92ft below the then water level which «as at normal at the time. This depth plainly show* that the rock at the outlet of Lake Wakatipu, which cause the rapids at this point, has no connection with the main- rock which is now worked by the Arrow Junction dredge. Any attempt to re-ach the main bottom above the Morven Ferry claim' is better made by borino'-rods. It will be found cheaper and more effective than if the dredge is employed for the purpose. The above remarks also apply to that portion of the Shotover extending from Tucker Beach to the junction with the Kawarau. . It is well known that in the portion* of the Shotover and Kawarau Rivers here referred to there is a fal=e bottom within easy reach of the dredge, not exceeding 20ft in depth, which carries fair, and in some places highly payable, gold; and upon this gold the clredees now building at Sparrow's for the Kau-arau will have to depend. Owing to the varying widths of the Kawarau, claims situated in wide parts of the river have an advantage in getting to work sooner after o flood recedes than dredges situated in the narrow and gorgy parts, for the very plain reason that the depth of running water is les& where it haa room to spread out than in places where it is confined between perpendicular walls of rock Therefore it must not be sunposed that because one diedge i* at work upon the Kawarau all others will be able to follow suit. THE KAWARAU CONSIDERED AS A TAIL-RACE. Looking upon the Kawarau as a tail-race, constructed for the purpose of running off the surplus water of Lake Wakatipu, many interesting features present themselves It has been observed that it takes a day of 2* hours — Nature knows no eight-hour shifts — to ran off 1.44-in. or, say, an inch and a-half. Therefore it Jakes eight days to lower the water in the Jake by a loot. This information will be of interest to dredging people, as a gauge-board is about to be put up at Queenstown indicating the water level in the lake and its variations. The rise and fall of the water recorded by this board is to be telegraphed to Dunedin daily, to be inserted in the weather information posted at the Dunedin Telegraph Office. A foot in depth of water spread over the 73,320 acres of surface area of the lake means 3,037.440,000 cubic feet of water. Add to this 800,000.000 cubic feet paid into the lake by its tributaries during a period of 24 houi'is, and it gives a very respectable total of work done by the Kawarau in that time. Before the Kawaraxi was opened as a tail-race for Lake Wakatipu, there is evidence to show, its- water level stood 175 ft higher than the present normal level of the lake. Such an elevation must have more than double its present surface area. One more item concerning the lake must be mentioned, and that is the fabled subterranean outlet of the lake, by stating at once that there is no evidence of the existence of such an outlet. What has given rise to the fable is the apparently small quantity of water escaping at the falls at Frankton. There is a fall of about sft in a distance of about 30ft. The water rushing over thia fall looks small, and being clear looks le«s on that account. The case may be illustrated by six or eight Government heads being forced through a two-inch nozzle. I -am indebted to Mr Daniel O'Leary, a resident for many years at Kawarau, who accompanied me on my tour to the river, and whose knowledge and insight into mining- matters is of a high order, for many of the facts and much of the information the foregoing articles contain.