WAITAKI DAM.

Evening Star, Issue 20022, 13 November 1928, Page 11

WAITAKI DAM.

TO TUB EDITOB.

Sir, —Some live or so years ago 1 occasion to inquire into the effect the construction oi the proposed thun across the Waimakariri River would have on the beach at New Brighton. The opinion expressed thou was that no dam that could prevent the gravel and sand travelling down the river would be allowed to be constructed if tho landowners at New Brighton cared to take an injunction against its construction. The gravel and sand as it is ground away on the beach by the ceaseless action ol the sea is replenished by that coming down the rivers, and if this supply is cut off then erosion of the beach will take place. One has onh to look round the New Zealand coast to see the proof of this statement. At New Plymouth the breakwater ■ arrested the travel ot the sand to a certain extent, and the beach eroded away for many miles. At Tunaru this action is most noticeable, and also at many other places. If this is true in the past wherever the natural conditions and actions are interfered with, why should not the same ellect take place along the beach from the Waitasi River mouth to the breakwater at Timaru if the supply of gravel coming down the Waitaki River is, arrested to u serious extent?

The dam being built across the AVaitaki River above Kurow For the new hvdro-electric scheme will arrest about three-q carters of the quantity ot gravel at present reaching the river mouth. The question is; Will a reduction ol even naif the quantity seriously affect the gravel blanket protecting the beach? I have no hesitation in saying that a reduction of this amount, even though the quantity of gravel reaching the breakwater at the present time is slightly in excess of the quanity required to maintain the beach there, will cause very serious erosion along about thirty-five to Forty miles of tho coastline, and particularly at Timaru. What will happen above the dam owing to the accumulation oi gravel upstream from the dam? The dam that is being erected is about 70ft high above the present river bed, ami it is to be expected that the resulting lake will be at least three miles long, and when this dam is filled with water tho gravel will accumulate first at the upper end. Tho sand ’”111 be carried further down, and the mud will be deposited all over tho bottom of the Jake. The next process is that tho gravel will build np the river bed, upstream of the first gravel accumulation, using that as a toe or foothold, as it were. This process will, go on until the whole darn is filled and ,a new river bed is made parallel with the present one, only about 7Dft higher. What is going to happen to all the land above the dam that is not more than 70ft above the river? There is uo doubt that the greater part of it will be turned into a gravelly waste, as seen on any of the rivers that are building up their beds with gravel at tho present time Of course, this process will Ik. slow on some parts, and on others tie effect will bo felt at an early date but tho process will bo going on irrcsistably all tho time. Arc the settlers willing to have this happen to their river flats, and are tho land owners along the coast willing to pay for protecting then land with rock to prevent being washed away? It is quite a simple matter to spend a million pounds or sc on the protective works, paying compensation, reconstructing roads, etc., and the whole of this expense must bo added to the cost of the hydro-electric works. will bo tho cost of the electric current when all tins capital cost is added? Surely schemes can be found that will not cause all this disturbance t tho natural conditions and that in the end will produce, current at less cost than at Waitaki, when all the costs ave taken into account?

A steam plant on tho Nightcaps coalfields appears to offer possibilities for electric generation at low cost, ik is doubhful whether any of the large hydro schemes can generate current as cheaply, and the country should be looking for sources of power generation at the lowest possible cost. Some people will say it will take years before these troubles will happen; some of the effects will take 'tars and some will be practically at once; but why start a cancer growing down there that will cause trouble more and more as time goes on? My advice to the land owners along the coast and above the dam is to prevent tho earn being constructed until they find out where they stand in the matter ol compensation or protection. Mr R W. Holmes, 1.5.0., M.lnst. C.E., late Engineer-in-chief, P.W. Department is in entire accord with the foregoing statement. —I am, etc., J. D. Holmes, D. 5.0., M.lust.O.E. November 10,