Highly Important Work That Saves Much Money

Chronicle (Levin), 7 June 1949, Page 2

Highly Important Work That Saves Much Money

. Thousands of pounds of the eountry's ] money have already been saved, and public works on which millions more will be .spent will be safeguarded, by ■ detailed testing of projeets in advanee . by the use of models. An increasing - programme along these lines is being carried out by the Dominion Physical Laboratories in cooperation with the hydro-electric design offieQ of the Minis- ■ try of Works. For instanee, most of the liydraulic effeets with the spillway at the Maraetai hydro-electric scheme have already been studied on a scale model, although the Waikato River has only recently, been allowed to flow through the dive'rsion tunnel and it may be three years before the tunnel is converted to the spillway. Highly Skilled Work The need to test key parts of such schemes with models arises from the fact that in many engineering problems the forces and actions involved are so complex that it is impossible to compute exactly what will happen and what should be done. The only safe policy then is to check desi/ns workod out on the basis of theorv by observing the effeets on an actual scale model. A.ircraft manufacturers already do this on a large scale with wind tunnels. It is highly skilled scientific work. is far from cheap aud takes time. However, the Maraetai spillway and tunnel tests have eost only a eouple of thousands of pounds compared with thc ultimate expenditure of probablv £5,000,000 on the project, of which it forms a vital part. The tests have already far more than paid their wav by revealing that a theoretically sonnd design for the spillway 'intake was not wholly satisfactory. They also enabled an efficient design to be developed and proved in time to avoid any wasted effort at Maraetai. Has Proved Its Worth ' Time is an urgent faetor in this work. It is still impossible in the Dominion to design and model test a power scheme before the bulldozers drive into the preparatory work on the site. The Maraetai tests have oecupied several months already and are etill not complete in the investigations of scouring below the tunnel outlet. However, late or early, testing with scale models has proved its worth and has come to say. The Maraetai model has a strictlv utilitarian look. All non-essentials to the experiment have been ignored and the model has resolved itself into a clear plastic tube fed with water from a eouple of tanks at oue end, through a tiny replica of a conerete intake structure, and discharging into a larger tank. However, the sides of the intake are accurately shaped to the ground formation at Maraetai and below the outlet it is possible to reproduce in sand and sliingle the effeets of.the flow on the bed of the Waikato River. Accuracy Essential Everything about the model in fact is construeted in the workshops of the Dominion Physical Laboratories to a high degree of accuracy. Tiny inaccuraries in the model would represent inches on the actual scheme, and inehes become important when the designer is dealing with a mass of water which may travel at 90 miles an hour or more and which can have a million horsepower to dissipate. With the usual pressure of space for Grovernment aetivities in Wellington the Maraetai model and another being used to investigate spillway problenis with the Cobb River scheme, Nelson, have had to be erected out of doors. However, a new building now being erected will probablv liouse future projeets. The first on the list are aspects of the Whakamaru scheme, the next od the Waikato River, and the large Roxburgh project in Otago.