Submarine Sluicing.

he Otago lower harbor is that portion of an inlet of the sea extending from Taiaroa Heads and Point Hayward, the outer headlands, to what is generally known as the Quarantine Islands, where high land stretching across the inlet, with the exception of one deep and two shallow channels, cuts off the upper from the lower harbor.

The distance between the heads is 1¾ miles, that from the heads, in a straight line to the Quarantine Islands, 51/3 miles or, following the channel from the line of leading lights on the Bar to Port Chalmers Wharf, 6½ miles—the width at upper end, from lower Portobello to Deborah Bay, is over 3 miles, and the whole superflces of the lower harbor is approximately 12 square miles.

Incidentally we may here mention, that whether or not the sea ever entered the upper harbor at the present Ocean Beach, is uncertain, but if such was the case, there is reason to believe that it must have been at a very remote period, and is of little consequence in our present enquiry.

For the purpose of comparison, and in order more clearly to understand the situation, it is convenient to turn to the inlet at Lyttelton, which is also on the East Coast, and somewhat resembles our own, but with this difference, that the latter has immense deposits of sand, which the former is free from; the reason of which deposit accruing in Otago harbor we must now endeavour to discover.

A cursory examination soon shows that the enormous deposit of sand in the lower harbor (amounting probably to 250,000,000 cubic yards) is not of local manufacture, no trace of any cause which could produce it can be found: As it is not, and apparently never has been deposited from the inside, let us go outside the harbor altogether and see if it is possible it could have been brought thence—we find that it is not brought from ocean depths, as a short distance from the Heads the bottom is a tranquil blue clay, but we discover—

I. That a current, variable with predominating winds, sets constantly up the coast in a northerly direction—

II. That all along this portion of the East Coast the action of the sea, combined with the current, is keeping shingle, where shingle exists, and sand, where sand prevails, in constant motion, driving them always to the northwards, never southwards—

III. Passing out of the Heads, and turning to the south, we come to several small indentations, or bays filled up with sand, (not locally made) until we reach, first Wickliffe Bay, and then Hooper's Inlet. These, ou examination, prove to be two large bays, each containing many millions of cubic yards of sand, evidently of a similar nature to, and coming from the same source, as the sand in our lower harbor, but still not of local manufacture. Climbing to some eminence so that their general aspeets may be reviewed, we see that both Wickliffe Bay and Hooper's Inlet possesses the same characteristics and peculiarities as Otago lower harbor, viz., great width between two headlands, immensely vast deposits of sand; a spit, extending from the north head of each towards its south headland, but not quite reaching it, for between point of spit and south headland is a channel, at that point of considerable depth, through which ebbs and flows the tide, covering at high page 5 water the large sand-flats inside, leaving large portions bare at low water, and both showing, as our harbor does, similar curves of deep water channels. That these bays are merely traps, into which sand from the south has been carried and deposited in still water soon becomes very clear, as also that the filling up has reached, in these two bays, a much more advanced stage than Otago harbor, for their interiors are nearly dry at low water, and the spits instead of being as in the latter ease slightly above high water mark, are elevations something resembling the sand-hills at the Ocean Beach, near Dunedin, but very much larger.

But we have not yet discovered the source of sand, so we continue our journey along the coast southwards, finding frequent repetitions of sand deposits, but all pointing to the south as the direction from which they came, until we arrive first at the Taieri, and eventually at the Clutha rivers, the mouths of which reveal clearly enough the source of the immense sand supply flowing northwards, and our journey is so far ended. The Clutha especially brings down very large quantites of sand, the fine particles of which are carried out into deep water before they find a settlement, and form a bottom of such light plastic nature, that the fisherman's trawl nets sometimes sink into them, and are, with difficulty recovered; the coaeser particles remain on the sea beach, and are caught in the wave action, before referred to, and started, travelling along the coast in the breakers, untill they are driven into harbor, trap or corner, such as Hooper's Inlet, Wickliffe Bay, or our harbor, in which theysink finally to rest for evermore.

Before leaving this branch of the subject, we will retrace our steps and start along the coast from Taiaroa Heads in a northerly direction—we soon observe that sand ceases to be the predominant sea beach, shingle takes its place, and the rivers, instead of sand, bring down shingle, more particularly is this the case after Oamaru is passed. Travellers by rail from Dunedin to Christchurch are familiar with the peculiar character of the Waitaki, and other Canterbury rivers, and also of the incalcuable supplies of shingle carried down to the sea by them, reaching which it (the shingle) is largely caught by the same wave and current action, as the sand to the south and driven along the beach to the northwards. This is to be seen to advantage in the reclamation it has effected on the south side of Timaru breakwater. The rate of travelling is, as might be expected, very irregular, depending very much on the weather; for instance, some days little or no movement can be discerned, while it is on record that a small vessel, driven ashore at Oamaru, was covered above the deck in twenty-four hours.

Lyttelton harbor has been protected from this shingle by Bank's Peninsula, which, running boldly out for many miles into deep water, forms a deep bight, into which the shingle is able to sink and find a resting place.

Having now accounted satisfactorily, it is hoped, for the source of the sand which so largely fills Otago harbor, we will proceed to examine the manner of its deposits, and endeavour to show how cheaply and effectually the objectionable shallows may be dealt with.

In order to form an idea of the sand deposits on the lower harbor, it is advisable to have a chart, such as that prepared by Mr. D. L. Simpson, the former engineer to the Harbor Board, on which, in lines four chains apart, running across the harbor from side to side, the depth in feet is marked, in fact the harbor is gridironed with soundings. On the scale of this chart, if the reader will draw a line eighteen inches long, it will represent the distance between the Heads, and if about one-third from the right hand end he makes a point one seventeenth of an inch below it, that will represent the deepest place between the Heads on that line, and the average depth will be shown by one twenty-sixth of an inch below the line, or in other words, the bottom will be represented by a very slightly undulating line, and it page 6 will be evident that very shallow water covers an almost level plateau of sand, the slight depressions representing what is called the channels.^*

Upon this chart the "Bar" is represented hy a long, irregular, tongue-like outline stretching northwards across the entrance of the harbor, its base resting upon Taiaroa Heads. Again supposing the harbor tn be temporarily emptied, there would be nothing special to attract notice at that outline; it is merely the sixteen feet at low watar line. To make the level nature of the bottom more clear to the reader; if instead of the sixteen feet low water, a twenty-two feet low water line is drawn upon the chart or the sea is supposed fall twenty-two feet, all entrances have disappeared, and a plane of sand presents itself, into which the channel from Port Chalmers, past Point Harrington, buries itself.

Starting from Port Chalmers, the channel carrying a depth of, from thirty to forty feet low water, (ample for the largest ships afloat) runs down the northern side of the harbor until it reaches the sand spit, when with a graceful curve it sweeps across to the other south side, impinging on the sand banks, and again changing its direction with another curve the current shoots past between Point Harrington and the point of the sand spit in a direct line for the desired channel through the "Bar," but is met by a rapidly shallowing circular bank of sand, which diverts the force of the current partially into the north channel; this last bank of sand, or the Bar, being probably formed by a portion of the sand on its travel from the south after passing the Taiaroa Heads falling into a sort of debateable area, caused by the action of the sea on one side, and the ebb tide on the other, where it deposits, hence the shallow water, and consequently bad entrance or Bar.

It has been very generally supposed that the current was diverted by striking upon Point Harrington, from thence being thrown into, scooping out, and forming the north channel, (an eccentric line with very irregular depressions, having only nineteen and a half feet of low water at its shallowest point) but if on the chart we mark the centre of the channel fourteen chains above Point Harrington, again immediately opposite that point, and yet again fourteen chains below it, we have three points in a straight line, which shows the direction on which the current moves past that point; if now we produce this line, it will bo found to cross the middle of the Bar on line of leading lights; or in other words, that nature is doing her best, by the ebb, to provide an entrance in the desired direction, but is prevented, as was said before, by the sand from the south being deposited just inside Taiaroa Heads, on the spot where the two forces meet and form the debateable ground.

The difference between ebb and flood tides is very remarkable and must be remembered; the latter outside Point Harrington sets in all directions towards that narrow opening, and particularly over the spit as the tide rises, consequently the current outside Point Harrington on the flood is not very strong, while the ebb tide running out of a sort of nozzle has much greater force and velocity. For instance, a river running out of a lake the current in the lake only a short distance from the opening is small, while a river running into a lake carries its impetus a long way into the body of the water, and probably this explains both the reason why the lower harbor has not filled up more rapidly, and the deep channel which so far exists. One of the large South American rivers is said to carry its current some 200 miles into the ocean. It is Interesting at this stage to notice a strange peculiarity which presents itself at Point Harrington. Here, where the current is strongest, and where the deepest water in or about the harbor is found (62 feet at

^* Standing at Cargill's monument, and looking down Princes street south, the gradient there presented is very much heavier than anything which would be seen if the sea retired and left the bottom of the lower harbor stand exposed.

page 7 low water), the sand is built up on the north side of the channel like a wall; so steep ia it that a man cannot stand upon it at the edge of the water, the first marked soundings being twenty-four feet, and showing how wonderfully sand may be manipulated. It might perhaps puzzle a professional engineer to design so great a marvel, yet hero it stands subject to storms and a three-knot current.

It has been found that when the dredge is working on the Bar during ebb tide a difficulty is experienced in keeping the vessel in position, as the current sets her towards the north; and further, that as the south channel deepens the north channel fills up, and vice versa, so that while deepening the south channel by throwing the sand upon the bottom into suspension it is probable that a large portion will deposit in the north channel; that the spit will increase in width and height, and the ebb tide having an opening provided for it, say twenty-eight or thirty feet deep, will materially assist in keeping that—the desired channel—open.

An urgent necessity at present exists, and will in the future still more do bo, viz.—to fix the sand upon the spit and prevent it being blown by the wind into the harbor, but some inexpensive means might be found to effect this.

We now proceed to consider the proposed method advocated for dealing with the sand by submarine sluicing, and a few instances of the power of water to remove mountainn, and its action upon the bottom when properly directed may satisfy the most incredulous of the reasonableness of the scheme now submitted.

(a) Endeavours were at one time made to take borings on the Bar in order to find the depth of sand; the rods would not go down, and it was thought that rock had been met with, but upon attaching a hose to a tube and forcing a stream of water down it, the sea all around the vessel became discolored with sand in suspension, and the tube sank at the rate of six feet per minute; while probably the natural rock bottom was never reached yet, as the depth of sand must be very great.

(b) In Lyttelton harbor an auchor previously used for a mooring buoy had in course of reclamation become covered with clay and mud to a depth of over twelve feet, and could not be recovered; the engineer of the boat was about to cut away the chain and abandon it, but he determined to make an experiment. A steam fire pump was on board; connecting a couple of hose to it, he put hydrants upon the ends, fastening them to iron rods in order to keep them in position, directed them on the bottom and started his pumps. In a few hours the anchor was all clear, and a hole from fifteen feet to twenty feet deep left in the bottom.

(c) The following is extracted from a trip through America :—"I first stepped off at Stockton to see some artesian well boring upon a new principle introduced by a man named Haas; it is really an adaptation of the diamond drill system to larger bores, viz.,—sending up the debris bg water pressure sent down inside the rods; hut it worked very well. I saw over twelve feet sunk and lined twelve inches in diameter, at a depth of five hundred feet in about an hour." * * * And writing of page 8 hydraulic sluicing, "The force of the current and jet is terrific. When within, say, eighty feet of the nozzle it will tear up the bed rock, and hurl stones weighing a ton into the air. About fifteen thousand cubic yards of solid earth are being removed and sent down the valley daily."

The following is portion of a letter to the editor Otago Daily Times in order to elucidate and set forth the work undertaken in one West Coast claim:—

(d) "Being very much struck with the article in that paper showing the depth of wash dirt in the Humphrey's Gully sluicing claim, and in order to endeavour to realise what a face of five hundred feet meant, I began to compare familiar elevations in and around Dunedin. Taking the First Church steeple as a unit of measurement, I found it would require two and a-half such to reach from the bottom to the top edge of the cliff; this, however, did not seem a very satisfactory example, and does not bring homo so clearly as might be wished the great height it represents. The gradients of our hill tramways then occurred to me as perhaps offering a better gauge to grasp the significance of the figures quoted, and I am indebted to Mr. Duncan, of Messrs. Reid and Duncans, for some statistics which enable me to make the comparison.

"Suppose the roadway in front of the Grand Hotel is taken as a starting-point where an excavation is commenced, and carried on at that level up High street. By the time the cutting has reached the Town Belt the height of its face would be only three hundred and sixteen feet, and if still carried on until the Mornington engine-shed is reached four hundred and thirty-four feet, or sixty-six feet less than the five hundred feet we wish to picture; so that it is necessary to seek some other elevated point to measure it by. Let us try the Roslyn line. Taking high-water mark as the starting-point, working back on and from that level, the face of the cutting will gradually increase as it advances up Rattray street, across the Belt, arriving at length at the Roslyn engine-house, where our imaginary tape-line is exhausted, and we find that the height is four hundred and ninety-nine feet—fortunately, sufficiently near the five hundred feet required. We now stand, therefore, at the Roslyn terminus, on the edge of this supposed cliff, with a sheer descent to the level of high water of five hundred feet, representing the face of the Humphrey's Gully claim at its deepest or highest point, and wonder at the audacity of these miners, who calmly speak of washing away this enormous mass as if it were a trifling undertaking, the only difficulty being the work necessary to bring in a sufficient quantity of water at a high level; yet we know that it is perfectly certain that all this immense quantity of gravel (perhaps frequently of the consistency of a cement) will be thoroughly broken up, disintegrated, the gold separated and saved, while all the debris is carried out into the sea, by the action of a few streams of water, under great pressure, issuing from apertures of five inches diameter. Surely some specially-gifted engineer, some large-brained Sir John Coode, must have devised this wonderful application of a simple agent ! It does not appear, however, that such was the case, this system of dealing with auriferous hills having been gradually worked out by Californian, West Coast, and other miners, whose necessities compelled them to make use of the natural force available—gradually, as they gathered experience, increasing their knowledge of how best to direct the giant power at their disposal.

"The work constantly being done by water in motion is very wonderful, results being all around us almost unheeded. For instance, it grinds up and manufactures sand during the Clutha's long journey down the centre of this province, carrying it along at the same time to the sea, where one would think it would find a quiet resting-place in the South Pacific, and so there be an end of it. Not so, however. Another form of water in motion lays hold of a very large portion of it, starting it on fresh travels, dancing merrily as it journeys in a northerly direction up the coast, sometimes lingering as if tired, then again moving along in a page 9 mad whirling waltz, here and there leaving some on the shore, thereafter by wind action thrown into strange fantastic-shaped dunes, entering, depositing, and filling up one trap after another; constantly fresh supplies stilt press on and it at length reaches our harbor (another trap), where sand and water working together make bars, spits, and shoals to gratify or worry, as the case may be, engineers, harbor boards, and steamship companies. More particularly does one strip of loose sand puzzle all of them by the difficulty experienced in obtaining a channel through it six hundred feet long, five hundred feet wide, by ten feet deep- This debris from Nature's great sluicing claim in the Clutha Valley has, luckily or unluckily, no ordinary miners of the Humphrey's Gully type to deal with. Engineers are brought from the world's end to report and advise, large sums of money are borrowed, nonsuch dredges are built, rocky breakwaters and training-walls are designed, and it is hoped that in the course of years this very objectionable strip of sand may be got rid of for ever."

The method of applying water under pressure upon the sea bottom was termed by the writer "submarine sluicing," and is very simple. Take any vessel possessing good steam power, say, for instance, the tug "Koputai," put on board powerful pumps, such as the compound direct acting steam pump of commerce fitted on one bed, and which can be placed anywhere; the steam cylinders and pump are all in one line. There are no gearing, wheels, or elaborate machinery; all possibility of a break down is reduced to a minimum, and the whole machinery and vessel may be kept as clean and free from dirt as any man-of-war or nobleman s yacht. The pumps merely require to bo fed with steam from the boiler, water supplied from the sea, and connection made with universal joint of directing tube to start work. There may be one or any number of joints and tubes.

This tube (or tubes) should be made very strongly of steel plate, not necessarily of great weight, and attached to the universal joint, which is fastened to side or stern of vessel; it must be about forty or fifty feet long, ten or twelve inches in diameter on point of tube, a nozzle at proper pitch is fitted—the ship being placed at ebb tide in position, the tubes, supposing one on each side, are lowered until the nozzles rest on the sand—steam is turned on; the water issues from the nozzles with exding velocity, driving the sand into suspension and out to sea on the ebb tide, and of necessity rapidly deepening the channel. As the work progresses the vessel is shifted. If found necessary the addition of small pipes liberating air upon the bottom can he supplied in order to assist in carrying the sand towards the surface.

How best to work it will be decided by experience, but probably starting from the inside and working outwards; carrying a face before the point of tubes might be a very good method, (See sketch.)

For assisting to throw the sand well up into suspension, I propose to carry down two air pipes on each tube, whose points will liberate air, one on each side, thus—

B is the water nozzle, a a air nozzles. The compressor has only to overcome the pressure of water, and as soon as the air is liberated it will endeavour to start for the surface, but will be caught and drawn by the stream of water issuing from nozzle B, mixing with the sand acted upon by the water, and helping to carry it (the sand) up towards the surface.

An objection, supposed to be fatal to the success of submarine sluicing, is that there is no current at the bottom on the Bar. According to Molesworth, one and a-half knots (the lowest estimate I ever heard for ebb tide), which is equal to one hundred and fifty-two feet per minute, or two and a-haif feet per second surface velocity will give one foot eight inches per second velocity at bottom; amply sufficient for what is required.

It is claimed that this method of dealing with the liar can also be made use of at any time for clearing away accumulations of sand, or straitening the channel inside the lower harbor.

But it has been said this is a question for professional men alone, with which the general public hare nothing to do (except pay). Are then works constructed by professional men, with carte blanch as to cost, so invariably a success? It would be inviduous and unpleasant to cite instances to the contrary. But take the upper harbour, on which £500,000 has already been spent, with no prospect of finality Ordinary men, after examination, would have probably decided to use the natural channel, gradually deepening it; professional men said, eut one through these shifting sand banks—it will give no water frontage to be utilised, but it is a trifle shorter, and is professional engineering (for which no one is responsible). According to Mr. Ross these works are still a question of Lime and money, while there is every reason to believe that if the dredges ceased work for twelve months the channel would be impassable.

Again, supposing the Cargill mole completed, and purhaps also another one from Taiaroa head, what may be the result? Can professional men say what the effect on the harbor inside may be? Would it be very astonishing if it was found that that natural wonder, the sandspit point opposite Point Harrington, was breaking down, and that instead of one deep channel a number of shallow ones through the lower harbor came into existence? —requiring still more stone walls and fresh loans.

At the present time a sandspit is said to be forming (quite an unprofessional proceeding), for which the authorities have no specific, but which could be dealt with in a few days by submarine sluicing.

Mr. Deakin, of Victoria, was interviewing Governor Leland Stanford : "He (Mr. Deakin) had come to find out the methods employed in the hope that they would be better suited to our requirements than the system with which our engineers were most acquainted." "You're quite right," said the Senator, "If you want your engineers to do anything you must go right with them yourself, and insist upon your ideas being carried out. When we were building our railway an engineer put up a magnificent bridge, costing 240,000 dollars, where one of 10,000 dollars would have been sufficient You can understand it was a big thing, but I wish we had the 230,000 dollars."

In the foregoing instance, the work seems to haveproved a success although somewhat expensive.

During the post three years the writer has, without success, endeavoured to draw public attention to the uncertainty as to the effect of rocky walla built at the entrance to our harbor, their enormous cost, and the ease and safety with which the difficulties can be otherwise overcome. A better conclusion to this brochure could hardly be found than the following, which shows that on the other side of the world exactly the same principle, somewhat differently applied, is being successfully used to remove a bar, with the difference that the authorities of New York recognise its value, and elected to pay handsomely for the work.—And so these pages are left for the consideration of all concerned in the welfare of our port.

Harper's Weekly, May 2. Page 286.

To remove by the action of water a sand bar which is subject constantly to the tremendous movement of the sea seems anomalous, but nevertheless water is the agent which is now being employed to plough up and level off one of the greatest of the sand bars which obstruct the entrance to New York Harbor. The apparatus wherewith this work is done is called a water plough. It is the invention of General Roy Stone, who commanded the Buektail Brigade in the Civil War. He had been impressed by observing the effect of a jet of water in the operations of hydraulic mining. He had seen the confined flow of water loosen the earth about huge masses of rock, and in time send the rock tumbling headlong. In 1878 he saw the engineers at work on the Diamond Reef, near Governor's Island. The reef was composed of boulders held in compact clay. He thought that the jet of water would tear away the clay and release the boulders. Tom Conkling, an old diver, went down on the reef to try an experiment. He carried with him a hose which was attached to a powerful force-pump. Other engineers doubted the possibility of General Stone's plan. Tom Conkling said as he went down, "It's no use trying." When he landed upon the reef nineteen feet below the surface, "he strapped the hose to his waist," says an account, "and held the nozzle firmly between his knees, with the end pointed beyond his toes. He pulled the signal string once, and the water was turned on. In less than a minute came two violent jerks, and then three rapid pulls, that meant to shut off the water and raise him up. As he reached the float Tom Conkling panting and pale, took off his helmet and said, 'It'll work, General; it'll work; if you hadn't turned the water off, I'd have been in China by this time.' The water had bored a hole in the reef under Tom's feet, and he had sunk to his waist before the stream was turned off."

Pursuing the plan. General Stone invented and patented an apparatus, and contracted with the Government to plough out Gedney's Channel for 180,000dols, At ordinary high water there are twenty-sir or twenty-seven feet of water in the channel. Thirty feet are wanted. General Stone chartered the tug Osceola, and had placed on her four pumping engines, of a capacity of one thousand two hundred gallons each. Pipes ten inches in diameter ran from the pumps on either side of the boat. Each terminates in two nozzles, of which one, two and a-half inches in diameter, points upwards at an angle of forty-five degrees, and the other, half an inch in diameter, points slightly downwards. At a pressure of one hundred pounds to the square inch the pumpa tend through these four nozzles four thousand eight hundred gallons of water each minute, at the speed of seven thousand feet a minute.

The tug is now at work on Gadney's Channel Bar. An account says of the first trial : Tho hydraulic ploughs were lowered, and the pumps began to work. The horizonal water jets drilled a path through the tough sand, and the upper jet blew the sand to the surface of the bay and scattered it. The ebb tide carried the sand out to sea at the rate of one and a-half miles an hour. Particles of sand could be seen suspended in the foam and froth about the nozzles of the pipes. When the Osceola page 12 had crossed the bar, which is four thousand feet vide there, the water ploughs were raised and the tug went back to repeat the operation, working always with the ebb tide.

It is believed that a channel two hundred feet wide and twenty-eight feet deep will be cut by June 1, and there is apparently no reason why a channel four hundred and eighty feet wide and thirty feet deep may not be cut before the end of summer.