THE WAIMAKARIRI.

Press, Volume LXIII, Issue 18893, 7 January 1927, Page 11

THE WAIMAKARIRI.

; TO TUi EDITOB 0? 7HI rE£33. i Sir.-Before deciding on any method |ot dealing with the Waimakariri, full consideration should be given to the difference in its lower reaches from the Rakaia. Rangitata, etc.—rivers mdentical in their water-sheds and coustant]v moving shingle, but now discharging under entirely dissimilar conditions, the Canterbury Plains were formed by river deposition of shingle similar to that now bothering the Trust. The prevailing south-easterly swell coming in from thousands of miles of open ocean striking the east coast of the South Island at an angle, runs strongly northwards, constantly carrying Band and shingle with it. This was noted by Sir John Coode when discussing a breakwater at Tiniaru, he pointing out that unless an opening was left at the shore end, the shingle would accumulate to the south end and soon overlap the sea end. This has occurred, although the breakwater j carried further and further out to

sea. I In 18S3, Caroline Bay had a stee i shingle beach closo up to the railwa. line. Look at it now. A fine sandy bead : over two hundred yards in widtl I formed by the lighter drift movinj j round tho end of the breakwater am settling in the still water, the heavie shinglo being carried across by the cur rent to the Ninety Mite Beach. ]i course of years there will be a lagoon a smaller copy of Lake Ellesmere, ii plane of Caroline Bay. While the Canterbury Plains wen ! (carried further seaward, part of th< 1 j shingle was steadily moved north bj the south-easterly swell, finally block ! ing the mouth of tho strait betweer j Ranks Peninsula (then an Island) anc ithe mainland, and forming tho lotif spit that now encloses Lak< Ellesmere, not so very long ago oper sen. T'he Rakaia, Rangitata, etc., still ! have this sweeper at their doors rnov- | ing the shingle ever northwards, and are so kept open. Tho Waimakariri, I however, which at one time ran j straight, out to sea toward the southern end of the strait mentioned, not | having the full force of the southI easterly current to keep its outfall j clear, was eventually blocked by its I own shingle and that from other livers j passing along from the south, and its I course deflected northwards, its shingle J accumulating in the lower reaches, I raising its bed and forcing the river j to lower country on which to deposit |it. I The entirely different beach to the I north of Banks Peninsula and the sandy estuary are thus accounted for. When the distaaco from the shore to the island—now Banks Peninsula—gradually lessened, the heavy shingle from the south moved on past the .southern opening of the strait, but the j lighter sand settled in the quieter J \\ ater between and to the north of tho j island. This sandy beach at Brighton | is being steadily added to by silt disj charged from the "Waimakariri, but by I very little shingle, the lower river's ! current not being sufficient to carry it further. Many thousands of yards of \ rocky debris come through tho Gorge j vearly—possibly one-third or even one- ! half of it is carried away into Pegasus Bay in sand and silt, tho heavy shingle remaining in tho river's lower renehes, causing a steady rise in its hod. Therefore, as water must find its level, the Waimnkariri's hreak-aways and flooding—which, after nil, are merely a | continuance of the process which formled thu plains—will constantly occur, I mid ngainst which groynes and such j like are only temporary protection. V hen you can spare further space, I a method of control might he sngI cos tod for the consideration of the j Board's onrrineer?.—Yours, etc.. j WAIMAiPJ RATEPAYER.