RECLAIMING TIDAL FLATS.

New Zealand Herald, Volume LVII, Issue 17459, 1 May 1920, Page 1 (Supplement)

RECLAIMING TIDAL FLATS.

THE "WARPING" 6YSTEM.

[B* tVR SPECIAL COMMISSION!*.] One of the striking features of North

Auckland is th? great extent of mudflats whi '.i fringo the numerous harbours and cstu.. ies. They are to be seen in the Waite.ma.a and the Manukau and in every harbour and sea inlet on both sides of the great peninsula. They no doubt represent an effort of Nature to reclaim tho various tidal basins which were formed by some general subsidence of the land in bygone ages and indicate that this part of New Zealand has not lowered its general level for a considerable period, and in some cases even suggest that the land is Blowly rising again. In their natura' state these tidal flats are depressing to look at and detract consider' ably from the navigable value of our inland waters. It is not their appearance or their origin which makes them interestng; it is the fact that 'hey may be turned at no great cost into rich farm lands. Already in various ports of New Zealand these tidal flats have been transformed by man into productive pasture and crop-growing areas. Quite recently a scheme of reclamation was carried out in the New River estuary, just opposite the town of Invercargill. An area of 2250 acres of dreary mud was enclosed by about three miles of embankment from six feet to eleven feet in height, built up chiefly by means of dredges, the general cost, all told, representing a little more than £11 an acre. In less than a. year after the salt water had been shut out teams were at work reaping heavy yields of valuable hay ; dairy cows were being depastured, and other stock fattened A similar example on a, still larger scale is to be seen en the frontage of the Firth of Thames, within a few hours' journey from Auckland. Here the Government, under the powers given it by the Hauraki Plains Drainage Bill, have reclaimed many thousands of acres which were originally covered by salt water at a cost of about £5 an acre, and have made of it some of the most fertile dairying country in New Zealand, which now sells readily at from £70 to over £100 per acre Other reclamations of the same character have been made in Hawke's Hay, in the Bay of Plenty and elsewhere, anil' in every case striking success has been won. As there are still very large areas to be reclaimed, this work should obtain the serious attention of the Government, pubhc bodies, and private individuals, as its successful execution means enormously increased wealth to the Dominion.

Future on Mangrove Swamps. A week or two ago, during ft visit to the Northern Wairoa, I had opportunities of examining several interesting example* of this making of farms from lands actually below tidal levels. The first example was at Parakai, en the Kaipara Harbour, near Helensvllle, a place coming into fame for the value of its medicinal mineral baths. This Parakai district a few years ago was an almost impassable sea marsh, with salt-water creek* winding through jungles of mangroves, rushes, toltoi) to-day it is dotted with rich dairy toitoii today it is dotted with rich dairy farm*. I walked am** the farm owned by the Nicholas Brothers, where bank* enclosing mangrove flats have been built with the intention of keeping out the sea water. Unfortunately, owine to n storm and exceptional tide*, which breached the protection works, and the absence of the .owners on war service, the enclosure had been Hooded'for Some time, but one could see how easily and cheaply such work could be carried out. On this particular farm, besides a herd of high-class cows, there was one of those remarkable features that seem almost peculiar to Northern New Zealand. In driving a pipe well a hot artesian supply of soda-water had been struck, Clear a* crystal and quite pleasant to the taste. It rose in the pipes some feet above the ground, so there was ft perpetual supply of hot water always to hand for washing the dalrving utensils, and a little distance ttwftv'wa* an artesian supply of pure cold water. Could anything lie more useful on a dairy farm than this?

Cost ot Reclaiming Tidal Swamp*. There are several other areas in the Parakal district where private individuals have reclaimed mangrove and other tidal Areas. Mr. R. K. Fenton, who was farming there some little while ago. furnished a report to the New Zealand Journal of Agriculture, in which he says :— On a piece of tidal land of about 150 acres I chose ten acres near dry land as an experiment. I dug drains about 4ft wide and IBin deep .... the spoil being sufficient to build a wall about 3ft high. In two places, where there was a small creek, the wall had to be Bft high. In these- places 1 put Hoot gates Three months afterwards I sowed some mixed grasses and rape. In open spaces the seed did not grow, but under the mangroves the rape grew as big as kohlrabi, and ryegrass grew well also." Mr, Fenton put the cost of his reclamation work at 17s 6d to 18s 6d per acre. Other farmers report more or less similar experiences, and all agree that when these mud flats are banked and kept free from the tidal waters they make rich pasture land, further to the north, on the eastern bank of the \\airoa River, where it widens to meet the Kaipara Harbour, the Government. through the, Raupo and Ruawai Drainage boards, have embanked and reclaimed several thousand acres of tidal I and silt swamp lands at an estimated cost of from £1 to £1 5s per aero, and splen--1 did farms have been made thereon, which ! sell readily at £60 and £70 an acre ; but, j as I have" remarked previously, the work i done.

The "Warping" System. Up to the present time the method of reclaiming these tidal lands has been simply In bank the water out and to trust to the [all at. or near, low water carrying off all the drainage water. I believe, however, that in the Northern Wairoa district, and on the Hauraki Plains, a different svstem could be successfully used, partrularly with the low-lyjng plan" This class of country could be treated - v what is railed in Lincolnshire and Yorkshire "warping." That is, the low lying areas are securely banked, but, instead of keeping the .tidal water off, it is allowed to flood the land, when it is laden with mud; the sluices are shut until the mud settles, and then the water is run oil' and fresh flooding* take place until quite a deep layer of warp or mud is deposited. As a matter of fart, this operation could he carried on until the deposit is up to the level of high floods or tides. I am sure that the waters of the Don. one of the most famous of Yorkshire warning rivers, averagely carries no morn mud in suspension than the waters of the Northern Wairoa after a sou'westerly gale or heavy rains, or the Piako River "carries when north-easterly winds are blowing down the Firth of Thames. It would, at any rate, require only the simplest form of experiment to decide what depth of mud could be deposited in n given time. A few buckets of water taken from the Wairoa or the Piako at different periods and allowed to stand for a while, so that the mud could settle, would very soon supply the necessary measurements, and I should expect those measurements to surprise most people. Anyhow, some of these low-lying areas about the Kaipara and the Hauraki Plains will always be a source of trouble under ordinary methods of draining, and since ■• warping" is so effective and so cheap a means of covering these low-lying places with a deposit of rich soil, and raising their level at the same time, it should ! certainly be worth a trial