Advice to Officers in India/Chapter 16
1. THE RAIL, THE SURF, AND THE BREAK-WATER AT MADRAS.— This chapter (unaltered) was published in the Friend of India in November last, and transferred to several of the leading journals of Calcutta, and copies of it were presented to the Madras and the Supreme Governments. I am not aware what impression the project made upon these authorities; but as my own impressions remain unaltered as to its entire practicability and adaptation to the wants of Madras,I have thought this a good opportunity to put it upon record in a more substantial form, than by the ephemeral pages of a newspaper; accompanied by a diagram.
"The following thoughts passed through my mind on a recent visit to Madras, and are at your disposal for a corner of the Friend of India. I feel rather confident that the theory here sketched can easily be reduced to practice; and therefore hope this paper may be of use to the public service.
"Who can stand on the beach at Madras, with the rail on one side and the roadstead on the other, and not see the difficulties of transporting the enormous traffic that must soon pass between them? Who can look at the present barbarous mode of transit through the surf and not feel humiliated, that all our national skill at sea is superseded by native ingenuity; Britannia does not rule the wave at Madras! but is glad to give up her Trident to primitive bare-bottomed natives, and place herself under their command!!
"Numerous plans for overcoming the surf have long been debated. A stone breakwater is totally out of the question; a harbour of any sort is equally impracticable; unless we could contract with those most skiful architects,the coral insects, and even they would take a few thousand years to do it well.
"A floating breakwater of carpentry appears more feasible, but as I will shew,it would be of very little service;for the surf though broken in passing through the carpentry, would speedily be formed again, as the wave rolled in shore, and nearly as high as at first.
"But it appears that all local attempts to master the surf have been despaired of; as two of our most scientific men are at present advocating a harbour being constructed, ten or fifteen miles distant from Madras. As a place of shelter for ships this harbour may be very desirable, but I feel assured that it is quite practicable to pass through the surf without inconvenience,and to load and unload cargo without damage or danger even by our own ships' longboats.
"The theory of the surf is, I believe, simply this: —As the wave rolls landward, the lowest stratum of water is retarded by friction against the bottom; while the upper stratum not so retarded outstrips the lower stratum, topples over and breaks into a surf, high in proportion to the height of its parent wave. This law of fluids is still better observed in air than in water. In a dust cloud drifting along the road, or a rain cloud along the horizon, the upper stratum is always in advance of the lower;and in the dust storms that prevail in the Punjaub, converting the light of noon into the darkness of midnight, the whole hemisphere is obscured long before the hurricane is felt below, the velocity of the wind being retarded by the resistance on the surface of the earth."
If we could throw the same obstruction continuously on the surface of the water,that it meets with on the bottom, no Surf could take place, and the wave, as it rolled on, would gradually subside, and reach the sand in a mere ripple.
"I can quote facts from personal experience in support of this theory. On the great river Megna, far from the protection of land,I have rode out a storm in safety in lee of a belt of reeds, though the water was many feet deep throughout the reeds; whereas but for their shelter the boat would inevitably have been swamped by the wave. Here a belt of slender reeds was as effective as a substantial breakwater of masonry.
"Again, on the coast of Africa, near Cape L'Agulhas, the rocky coast is fringed for a quarter of a mile, more or less, with tangled seaweed secured to the bottom, by long ropy stems ending at the surface in filaments like ribbons that float upon the surface. The Surf as it rolls in, higher than it ever does at Madras, is broken and quite put down before it gets half way through the belt of seaweed. When the weed is not continuous to the shore a second Surf forms in the clear water (as it would do after passing through an artificial floating breakwater), lower than at first, but still heavy. I have rowed a crazy boat amongst such seaweed with impunity, whereas had no weed existed, not even a Massoola boat could have Used, yet the Surf was disarmed of its danger by floating filaments of seaweed!
"Now it appears to me that we have only to imitate Nature's admirable engineering, and bring the same principles into operation on the Madras Surf, to sober its violence down.
"I therefore propose that a certain number of anchors be dropped outside the surf, connected together by chain cables, thus forming a line of a quarter of a mile parallel to the beach. To these cables add at distances of one or two or more feet, secured by a few links of light chain, a series of prepared electric telegraph wires; the wires to be long enough to meet the rise and fall of the tide and of the wave unstrained, the upper end to be linked to a light buoy. To these buoys attach one or more coir ropes, or the stems of the ratan (both very buoyant), stretching as far in shore as may be necessary, and along these ropes secure continuously a series of cocoa-nut or date leaves, stem to the Surf; or as these leaves are perishable, secure in their stead a certain number of fimbriated filaments of gutta percha or India rubber, made to resemble cocoa-nut leaves and equally flotile; and the same effects may be expected from them as from the bank of reeds on the Megna, or the sea-weed filaments on the coast of Africa. Instead of one line of chain and its attachments, it would probably be better to have two, three or more lines,each having its separate series of ropes and filaments. (As seen in the lithograph.) The extra cost of old anchors and chain cables would be trifling. This would be less liable to entanglement, would be much more manageable, would be less liable to rupture, and would be still more efficient as a breakwater.
"It may be stated in objection, that both wind and current, being in both monsoons, along shore at Madras, the above feathered lines would take the same direction, and oppose a serious line of obstacles to the direct approach of a boat; but I imagine that this would be nearly entirely neutralised by the force of the surf. At any rate, the lines never could be deflected beyond the diagonal of the two forces, so as to admit of the passage being made obliquely and between two lines. Or, if the wind and current should drive them parallel to the shore (a thing most improbable) they could easily be depressed in succession by a manor two in the bows of the boat.
"Of course oars could not be used in such a breakwater, and the transit would require to be made from the shore to the line of outer cable, by tracking ropes stretched between them, admitting of much more expedition than oars."
I again express my confidence that the highest surf would be subdued in passing through afield of such construction,that a pier could be run out the necessary length into such a floating breakwater, without difficulty, and without after-risk from the surf, when formed;and to guard the cargo boats from the rise and fall of the wave, (which though unbroken must be expected to continue,) a series of little docks could be made beneath the pier to receive them and insure their being still enough to admit of loading and unloading For landing passengers our ingenious neighbours, the Chinese, can furnish excellent specimens, such as are in regular use at Canton. A floating pier made of bundles of bamboos extending out as far as necessary, admitting of its rising and facing with the tide and of the wave, and of supporting a moderate number people, would answer perfectly.
"Thus a floating breakwater could be constructed out of the old stores of Government, one set of palm leaves would probably last a season, and could berenewed as occasion demanded it, or if Gutta percha or India rubber fabrics were adopted, these are indigenous to India,and would last for many years.
"J. McCOSH, M.D.,
"Surgeon, Bengal Army."
Calcutta,20th, November, 1855.
|PLAN OF A FLOATING BREAKWATER FOR MADRAS. BY J. McCosh.|