D.-l

XXXIX

The lines of the drainage galleries which will have two principal levels are indicated on P.W.D. 79659 by red and yellow lines respectively. £ The estimated cost of the works set out above is .. .. .. .. .. 230,000 The occurrences which we are now considering, and the disquietude in the minds of the public, indicate that the original idea that the diversion tunnel should be merely a contrivance for facilitating construction, and should thereafter be dispensed with and walled up, should now be modified, and it should be reinforced and fitted with valves suitable for operating for lengthy periods under full head. If this is done it will be possible at stated intervals to by-pass sufficient water to enable the works, particularly those at the waterfall, to be thoroughly inspected, and even to be repaired should such ever become necessary. This proposal involves an expenditure of .. .. .. .. .. 60,000 In considering the whole problem it is as well to take cognizance of all the expenditure which is required, and I therefore propose to add to the cost of the above the amount which has already been authorized to deal with the erosion at the waterfall. The waterfall work has been previously estimated at £168,000, but I propose to place it in round figures at .. .. .. .. .. .. .. 175,000 Making a total expenditure of .. .. .. .. .. £465,000 Some works, you will see from the above, are essential and some advisable. It may be asked why I introduce these other matters into the question of safeguarding the works behind the power-house, but my reason is that some of the further schemes to be considered later on in this memorandum do not involve the expenditure at the waterfall, therefore for the true purposes of comparison I shall show in each case all that has to be done, or which should, in my opinion, be done. Realizing that possibly the scheme as I have outlined may not meet with the approval of Professer Hornell, the consultant whom the Government has engaged to deal with this matter, I have prepared a number of other solutions of the problem. Scheme No. 2. Assuming that- the idea of running the flood-waters of the Waikato, and also the surplus not required at the power-generation station, over the present- spillway, even when modified as indicated in my No. 1 scheme, is not approved, and that it was desirable that the great weight of this water, and the vibration caused by its passage, should be kept well away from the present works, I have worked out a scheme in which the present headrace is dammed at the same point as is provided for under the No. 1 scheme, and that from just above this point a special overflow-channel should be excavated running on a fairly uniform grade to the head of the falls. The velocity in this channel would be high, and it would require concrete lining throughout. The effect of this will be to increase the stability of the mass of country between high-water level and the tailrace level to two and a half times what it is at present at the weakest point. The water necessary for the turbines would be taken to each of the existing penstocks by independent pipes, the pipes being laid side by side on the floor of the present headrace, the same being levelled out to allow for this. The gates of the dam across the headrace will in this scheme take the form of a penstock intake similar to the present penstock-intake, and all the gates, screens, &c, at present existing will be simply transferred to the new position : see P.W.D. 79660. £ The cost of these works would be .. .. .. .. .. .. 282,500 To which, for the purpose of comparison, as explained under the No. 1 scheme, must be added for the treatment of the falls .. .. . . . . 175,000 And for improving the diversion tunnel it is desirable that there be spent .. .. 60,000 Making a total of .. .. .. .. .. ..£517,500 One objection which may be taken to this scheme is that it does not make provision in the headrace for the ultimate possible development, but the other pipes which are necessary can be added from time to time when the scheme has grown beyond the four units which I have allowed for in all the proposals, at an additional cost of approximately £50,000. Scheme No. 3. Assuming that it is desired that all the water be removed from the present intake works, and the locality of the crack, and that it is thought the whole of the country which was disturbed by the crack is now unsafe, a scheme has been worked out involving moving the power-house to a point where the size of the hill between the headrace and the tailrace (in other words the old gorge) is twice what it is at the present power-house, and at which point it consequently has a veryjmuch greater resistingpower against the stresses brought about- by the relative positions of the high and low-water levels, and, in order that the power-house may be in the strongest position possible, I propose that it be a