ARAPUNI RECONSTRUCTION

Hawera Star, Volume L, 29 November 1930, Page 5

ARAPUNI RECONSTRUCTION

CONSIDERATION OF MEASURES WORKING MODELS DESIGNED MINISTER SEES DEMONSTRATION. (Bv Telegraph—Press Association.) WELLINGTON, Nov. 28. Before commencing the remedial measures recommended by 1 rofessor Horned to enable the Arapum hydroelectric undertaking to resume operations and to be developed to its maximum extent Hon. Mr VV. BMinister of Public Works, decided that complete plans and estimates must be first made available. Work ha sheen proceeding ou these lines for some time, and one of the most interesting and important features has been a consideration of tne measures to .present further erosion, of the country below the spillway clam. This will be one of the most expensive parts of the project, but when, a commen cement is made with tlic practical work the engineers will have satisfied, themselves by elaborate experiments that the immense flow of water which lias to be controlled in that channel will be directed in sucli a way that no further serious erosion can take place. Working models have been erected. ■ Though there is a considerable amount of engineering literature relating to the flow of water and measures for its control it is r ' recognised that each particular problem has its own difficulties and. that pure theory is not capable of direct application. Professor Hornell agreed with the opinion of the works engineer that tests ought to be made with models to scale before the work of dealing with the erosion below the spillway dam was actually put in hand. Mr Taverner consequently approved the construction of models of this part of the Arapuni country. These have been built in the department’s Wellington workshops, following data provided by careful surveys of the channel bed and surroundings. The Minister this morning witnessed some interesting working tests of these models, which are capable of demonstrating the behaviour of the overflow from the spillway under varying conditions, which can "be imposed by the protective works under consideration. One large model reproduces exactly on a scale of one inch to four feet the channel below the spillway dam through the first and second falls into the deep pool just above the interesting scenic spot popularly known as the buried forest. A good (supply of water is available and a controlled flow equal to the known volume of the Waikato River at that point, corresponding of course to . the general scale of the model, was sent over, the falls. This reproduced almost exactly the conditions which prevailed prior to the closing down of Arapuni. Another model built to the scale has been arranged to permit of variations in the channel, reproducing the engineering works under consideration, which are being designed to prevent further erosion. Instead of spending thousands on concrete work in the actual channel and possibly having to modify them after they have been tested under the stress of the full flow of the river „the engineers are able to vary the contour of the channels and falls and observe the results of the introduction of their proposals.

The water supply enables the flow conditions to be controlled so as to reproduce the normal volume or flood volume of the Waikato according to scale. There is a total drop of 100 feet from the top of the upper fall to-the level of the great pool at the foot of the second fall. The model enables observers to accurately plot the flow of the stream and to see its effects when various baffles are interposed in the channel. The “cushioning” effect of the pools is being studied and' some promising work has. been done in the way of varying the contours over the falls ■ and also the shape and depth of the basins beneath. Experiments are being made with the object of designing baffles to slow down'the rates of flow beneath each fall.

At the conclusion of his inspection, which included observations of the effect of several variation® in the contour of the channel bed, the Minister expressed satisfaction with the' experiments which, he said, would save a good deal of money and enable the work, once started, to proceed with confidence.