HYDRO-ELECTRIC SCHEMES

Dominion, Volume 23, Issue 32, 1 November 1929, Page 13

HYDRO-ELECTRIC SCHEMES

■ Sir, —In a sub-leader of your issue of October 26 you mentioned that the Coleridge scheme is the only scheme earning a profit, and that profit is more than extinguished by the losses on Mangahao, Hora Hora, Waikaremoana, and Arapuni. What of the Waitaki scheme, on which some interest charges Have already to 'be met by the taxpayers, although the scheme is in the embryo stage? This is, as far as I can see, just a forerunner of .what is to be expected.

Last year I pointed out in an article which was published in the southern .newspapers what to expect if a dam was constructed across a shingle-carrying river, and, briefly stated, the contents of that article are as follow: —

The dam will prevent the shingle passing, and it will accumulate in the river channel upstream of the dam, eventually raising the river bed parallel with the 'present bed by a height nearly equal to the height of the dam, i.e., about 70 feet. The result of this will be the inundating of the river flats in the area affected.

The dam will reduce the quantity of gravel that is being discharged by the river into the sea to about a quarter of the present quantity. This gravel at the present time forms a blanket on the beach along a length of about 40 miles. This blanket is being continuously destroyed by the ceaseless action of the sea and in turn is being fed by the river with more gravel. If the supply is largely reduced, erosion of the sea shore must follow, as tile destructive forces and supply of gravel are practically balanced at the present time. Engineers have remarked on my .criticism, but nobody so far has proved me wrong.

As an example in support of the prospective damage upstream I refer you to the River Rio Grande in New Mexico. A 'dam was constructed in 1915 at Elephant Butte, which formed a lake about 38 miles iong. Since then sand and silt have been accumulating, at the head of the lake and in the riverbed to such an extent that the riverbed has been raised several feet above the level of the town of San Marcial, and stop banks have had to be built. That town, by all accounts, was not affected by flooding previous to the construction of the dam. but in August last a flood of only about three-quarters the capacity of others that had been recorded inundated the town with 3to 5 feet of water. ,See “Engineering News Record,” August 22, 1929.) The Rio Grande is a small river compared with the Waitaki, but by studying the conditions a very good idea can be gained of what to except will happen above the lake on the Waitaki, and surely it is wise to profit by other peoples’ experiences.

For evidence of what to expect along the sea coast, T refer you towhat is taking place to leeward of the breakwaters which stop the travel of the gravel and sand along the beach at Napier, Timaru, and New Plymouth, where heavy erosion has. is, and will continue to take place. . When this scheme is built, where is the market going to be found for sufficient current to give a return that will show a profit on this huge undertaking? The dam alone appears as if it will cost well over a million pounds. I, for one, have

not seen or heard of any estimate for the cost of this huge scheme. Dunedin is noy? enlarging its own works, so there will be practically no market in that direction. Christchurch has the Coleridge scheme which can be easily enlarged at comparatively small cost. It appears to me that this scheme, as things are, is neither sound from an engineering or financial point of view. As a taxpayer, I say most emphatically that a thorough investigation should be made into the position by independent engineers, business men, and others, before any further expenditure is undertaken on this scheme. Mangahao and Arapuni are quite enough white elephants to have on hand at one time, and, in my opinion, there are all the makings of another in this scheme. Of course the .South Island might be jealous if the North Island has two white elephants and they have none, but the canny Scots of . Dunedin are evidently alive to the position, and refuse to be contributors to the insatiable appetites of such unprofitable schemes.—l am, etc., J. D. HOLMES, D. 5.0., M. Inst. C.E. Wellington, October 29.