E.-5

1875. NEW ZEALAND.

MIKONUI WATER RACE, WESTLAND. (REPORT ON SURVEY OF MIKONUI WATER RACE, WESTLAND, ON ALTERED LINE.)

Presented to both Souses of the General Assembly by Command of His Excellency.

No. 1. The Disteict Engineee, Hokitika, to the Engineee-in-Chief. Sie, — District Engineer's Office, Hokitika, 27th August, 1875". I have the honor to forward herewith the plans, sections, schedules, and estimates of the recent re-survey of the Mikonui Water Bace, and to report as follows: — The total length of the race-line, as now proposed, is 15 miles 55 chains. This includes a branch race, 17 chains in length, in addition to the main race. From its source on the Mikonui Eiver to a point about 5 miles 72 chains along the original contour line, as shown on the general map in red, the old survey is followed, as the country for that distance admits of no alternative route. From 5 miles 72 chains to 14 miles 48 chains, a new route along the Totara side of the range has been laid out, as shown on the map in green; and from 14 miles 48 chains to the end of main race, at 15 miles 38 chains, the original line is again taken up, as it cannot be improved upon. At the time that a water-race from the Mikonui Eiver was at first proposed, now several years ago, it was considered best to have it laid out in such a position as would enable it most readily to command the workings at Italians' and Eedman's Gullies, on the southern declivity of the Greenland Eange, as well as those at Boss, and from Boss to Donoghue's, on the northern side ; and the Mikonui route was adopted for the survey with that object. It is now known, however, that the workings on the north side of the range are of far more importance than those on the south side; and it is believed that the workings at Eoss and from Eoss to Donoghue's alone would absorb all the water which a single race could conveniently be made to carry in such rugged country —namely, from 50 to 60 heads of 40 inches each. Having now obtained a complete exploration of the whole district, it is possible to compare with certainty all the routes which are practicable, and the workings which each would command ; and I believe that a race laid out principally with a view of supplying the workings at Eoss, and from Eoss to Donoghue's, would be the most remunerative one to construct, and that the route of the recent survey, above described, is the best which can possibly be attained for that object. In the preliminary report upon this survey, forwarded with annual report in June last, a statement was given of the probable character of the works, which included a considerable quantity of boxing; but, after further consideration, I have thought it better to recommend that tunnelling should be adopted instead of boxing in every place where it is practicable, and the following is a list of the works as now recommended :— Miles chs. Iks. Fluming ... ... ... ... ... ... 0 70 94 Boxing ... ... ... ... ... ... 0 79 29 Tunnelling ... ... ... ... ... ... 6 69 66 Ditching ... ... ... ... ... ... 6 74 71 Total ... ... ... ... 15 54 61 Of the ditching, as above, 121 chains 71 links will require timber protection. Had the estimate, which is given below, been based upon a larger quantity of boxing, and a corresponding amount less of tunnelling, it would have come to considerably less than it is now stated at. But I think the advantage gained in point of durability by the adoption of tunnels is more than commensurate with the difference in cost. The total estimate for the work as now recommended, based upon a carrying capacity of 50 heads of water, which is as much as it would be advisable to calculate from the Mikonui as a source, is £68,000; and I believe that, in this case, the sum estimated maybe looked upon as closely approaching to the probable cost.