RECLAMATION

Nelson Evening Mail, Volume LXX, 5 October 1936, Page 7

RECLAMATION

(To The Editor) Sir, —I will answer Mr Wyllie’s letter appearing in your issue of 30th September to the best of my ability. Discussion is all to the good if the subject is worth it. Any blocking of the Fifeshire entrance channel would undoubtedly increase the tidal velocity through the new cut proportionately to the area blocked, but it would in my opinion be an exceedingly wise thing to do except as an absolutely last resource. If My Wyllie will read the letter I wrote on Forest Destruction, appearing in your issue of 26th September, he will see the reason why. I said the old entrance acted as a watch-dog to the new, in keeping sand accumulations from our back door. The absence of more complete records as to the rate of silting up of our estuaries is very much to be deprecated. Old residents have told me they remember fairly big craft at anchor west of the new pool at Tahuna, near the spot where there used to be a railed-in quick sand. If this is so then the advance seaward of the Tahuna beach cannot have been less than from 5 to 7 yards annually, but what is wanted are proper marks accurately surveyed so as to determine with certainty what is taking place.

As regards quarrying and terracing into the. hill side near the Cemetery, Mr Wyllie’s admission that slips are already accruing appears to me particularly ominous. With slips it is just the little that does the mischief. Mr Wyllie ignores the heavy cost of £1750 per acre for reclaiming from the hill side, which seems to me absolutely prohibitive, neither can I believe that any increase in land values duetto terracing would materially make up for it. As regards access, there should be no difficulty whatever in a good dredge cutting its way to any part of the estuary. As regards cost of dredging I have no very recent figures to quote from, but the following information will give a very fair idea, and should not be far wrong. On the river Clyde with double ladder dredges, about one million cubic yards (c.y.) are raised annually from a depth of 32 feet, and the material conveyed 27 miles to Loch Long at a cost of 6d per c.y. On the Tyne 2:1 c.y. are dredged annually (or were), and tipped out at sea at 4sd per c.y.' This was with double ladder dredges he same as on the Clyde. On the Tees it is much the same, the sand is conveyed from the river out to sea at a cost of per c.y. In Queensland in the Offical Report of the Government for harbours and rivers, the cost of raising and conveying 6 A million c.y. in 12 years averaged 11 d per c.y. In the Amsterdam Canal, using suction dredges with 4 feet diameter centrifugal pumps, and 18 diameter suction and delivery pipes, the cost of the vessel and pumps was £SOOO. Each machine raised and delivered about 800 c.y. daily into barges at a cost of 2d per c.y.

At Dunkirk sand pump hoppers were used and the material conveyed three miles at a cost of lid per c.y. At Boulogne with suction and steam hopper dredges the cost, including 'delivery two miles away was 3£d per c.y. As regards the distribution of the dredged material on to the area to be built up, this is done through pipe lines, floating or otherwise, and a few thousand feet is nothing unusual. The excess water acts as a conveyor, and this drains off and away. It would therefore appear that my figure of 6d per c.y. was well within the mark if the work is done on a big scale by contract, which would enable reclamation to a depth of 2 yards to be carried out on the mud flat at a cost of about £250 per acre all included. —I am etc. H. G. FOSTER BARHAM. Nelson, 2nd October.