Art. VIII.—On the Reclamation of Sand Wastes on the Coast, and the Prevention of their Inland Advance.
[Read before the Auckland Institute, 4th September, 1873.]
The existence of a very serious evil will be recalled to mind by perusal of a carefully-considered paper on the above subject, by Mr. C. D. Whitcombe, as given in the last volume of the “Transactions,” * especially by those who have had occasion to notice the increasing and apparently resistless advance of sand inland from a great length of our coast line. In places this is covering the fairest and most fertile soils, burying forests, and driving before its dread advance all the efforts hitherto made by a few individuals more immediately concerned to ward off or retard its progress. The subject claims public attention, as not only has a very large tract of country been lost to settlement already, and many fertile farms are now being threatened with annihilation, but, as is shown in the paper referred to, and well remarked during the discussion on it, the existence of streams, the navigation of rivers, and safety of lighthouses, and such like, are concerned in the adoption and success of preventive measures. This attention, if it is to be at all, cannot be awakened too soon.
The features presented by this encroachment vary on different coasts, but it will suffice to describe those nearest to Auckland. Those are, the coast from Waikato to Manukau Heads, and from Waitakerei to Kaipara Heads. The former is, where uncovered by driving sand, of a very fertile nature in general. It is a rich sandy loam—in some places an excellent black soil—throwing up a good pasture, and carrying a stock of, in some cases, the heaviest cattle which come into the Auckland markets. The land is very easily brought into cultivation, and is about all taken up, and much of it settled on.
[Footnote] * Trans. N. Z. Inst., Vol. V., p. 108.
Perhaps the best idea of the evil which threatens this fair district may be had by a journey from Waiuku to Port Waikato. As the traveller advances in this direction, the land is seen to change from the heavy clay lands at Waiuku to lighter and more loamy soils. When the distance is about half traversed—and the road lies generally parallel to the coast—the advance-guard of the sand-drift is seen covering half of what was not long ago a field of rich pasture. At the southern boundary of the Maioro, a village site with a few houses and small farms is reached, and the advancing sand-hills and drift are only a few yards to the westward of them. Close brush fences have been erected with the view of protection, but that is only a most temporary remedy, and nothing hitherto done is of any avail. From this point the traveller strikes into the desert, and for about four miles, to the Waikato Ferry, traverses such a waste as few imagine can be witnessed in New Zealand. Nothing but sand is in sight, and, may be, the tops of trees long since buried. This desert stretches farthest inland just at the river, and does not extend south of it, if we except the flat between the bar and the southern cliffs, which has been formed by an enormous landslip causing a change in the course of the river about three-quarters of a mile to the northward of where it formerly flowed. On this landslip the township of Port Waikato is now laid out.
A small portion of the coast between Waikato and Manukau Heads is still unbroken on the surface, and in many places the first eroding action of the wind is to be observed. The South Head is a striking example of this. Within the last few years many millions of tons of sand have been carried out into the channel of the southern passage of the bar. A remarkable feature on the coast is that of blind gullies, two of which are to be seen near the Manukau South Head. The principal one must drain at least 800 acres, half of it being heavy bush land, but its outlet is covered by a hill of sand 480 feet high, through which the water filters to the sea.
The Kaipara sand-hills differ from the above described, inasmuch as that while in the latter case the sand is encroaching on a rolling country of nearly its own level, in the former the encroachment is tumbling inland over, for a great part, a country of much lower level, and will soon reach extensive plains but a few feet above high water. The advance is consequently very slow, but none the less sure, and, if not arrested, eventually the Kaipara river itself will be choked.
In considering the possible remedy, one point has certainly been determined, although only of a negative character. It is quite useless to begin inland. Neither fence nor trees can arrest the drift. When a brush or other close fence is erected in the sand it certainly seems to have immediate effect; the force of wind is checked near to the surface, and sand ceases to be carried forward and deposited within a few yards of it, but soon a ridge is formed to
windward, where it ceases to have onward motion, and, rising higher and higher, its leeward side towards the fence soon shows a face as steep as the material will allow of. The drift still rises, and the crest rolls over the steep side, continually approaching the fence, until at last it is buried. A forest has the same effect and ultimate fate. Of what use, then, is planting young trees, if fences and old “bush” are of so little avail ? But the same experience shows that if the drift can be arrested at its source, then all to leeward may be gradually worked on and reclaimed.
There can be little doubt that these hills have been originally blown up from the sea sand, but this has been most likely during a gradual elevation of the land. The closing in of the valleys above mentioned with nearly 500 feet of sand seems conclusive on that point. But it is most unlikely that any reinforcement of sand is now got from the beach. The hills in general rise 100 feet to 300 feet abruptly from high-water mark, and the drift does not appear to rise much above the surface. The face of the coast then, and the tops of the first hills, are the places where, if anywhere, an effectual start can be made to arrest the evil.
In Mr. Whitcombe's paper much valuable information is given as to the methods found successful in France, and a record is given of the plants and trees found most efficacious. But it seems in the case of the hills under reference in our Province, that the violence of the south-west winds is such that it would not prevent any shrubs or trees from having the sand blown from under them, unless it is first protected by a sward of some grassy sort of vegetation. The effects of the prevalent winds are strikingly indicated by the appearance of the “bush” near the Manukau South Head. The prevailing timber is puriri, and the branches and foliage look as if shorn, and have a singular overlapping appearance, one tree with another, as of a roof shingled and lapped the wrong way.
The reclamation of the Surrey Hills, in Sydney, is a case in point. There the sand was of a nature even less adapted to support vegetation, being sharper and more suitable for builders' use. Yet these heights, which not long ago were a waste of driving sand, are now covered with a beautiful sward of grass. The means in detail by which this was accomplished is unknown to the writer, but he has a recollection of hearing a description of a method adopted in some of the Western Isles of Scotland, and which was successful. There the difficulty was, as with us, to keep the seeds of the grasses stable sufficiently long to allow of germination and striking root. The grasses selected were, when seeded and ripe, spun into hay ropes without threshing. These ropes were pegged to the sand all over the area to be reclaimed, in chequered lines. The seed was thus enabled to germinate and take from hold, and soon the whole was an uniform mass of vegetation. Such a process is
well worth a trial, and the necessary modifications in our circumstances would soon be ascertained. If our friends learned in those things will indicate such littoral grasses as have the properties of root-spreading and, at the same time, striking moderately deep into and flourishing on nearly pure sand, the practical result cannot be very uncertain, nor the application difficult. It is, in the first place, only a carpet of any sort of vegetation which will prevent the driving of the surface that is wanted. This will allow the planting of trees, and, where the soil is the more suitable, proper pasturage grasses can afterwards be substituted. But the great result would be attained if even the onward progress of the sand was arrested, and, as it must evidently be commenced at the sea, every year's delay loses not only so much more land now good, but increases the width of waste to be reclaimed in order to preserve the remainder.