Part 2

The tunnel will be constructed in the foundation of the dam, and the road formed on the top of the dam, and provided with opening bridges across the locks.

A glance at a railway map will at once show the strategic value of the railway route thus opened up between the Midlands and the North, and Dover and the South Coast, avoiding the conjested London lines; also for national and military direct traffic between the Government arsenals and the Colchester and northern routes and depots. All the northern lines will thus have access by the Tilbury line to the continental routes.

_National and Military Aspect of the Scheme._

The Port of London above the barrage will be the finest and safest harbour we possess for the fleet, having an immense deep-water protected area. The barrage can be fortified, and will constitute the most effective prevention against any foreign invasion by way of the Thames estuary. The tunnel and roadway will be of great service in this connection also.

_The Depletion of the Thames Basin._

This, which has been increasing for many years, is becoming a serious matter, and has attracted much comment. One of the advantages that will be obtained from the barrage will be the raising of the underground water-levels in the chalk and other strata of the Thames basin. In this way a permanent improvement in the water supply by wells throughout this large area will result.

_Minor Advantages._

Among these may be mentioned:—No further scouring of bridge or other foundations. No backing up of the foul waters of the small tributaries, such as the Lea, Barking Creek and others. Improved living conditions and reduction of disease, especially in the neighbourhood of the river, resulting from the cessation of ebb and flow, of smells and exposure of mud banks. Increased value of properties bordering the river. Fixed piers for passenger steamers.

_Works and Construction._

Fig. 7 is a general plan showing the barrage in relation to Tilbury and Gravesend shores.

Fig. 5 is a cross section of the river showing the vertical dimensions and contours.

Fig. 6 shows a section and details of construction.

Generally it is proposed to form the barrage of mass concrete, faced with granite on all exposed faces. The tunnel will be formed in the solid monolith as the work proceeds, and afterwards connected north and south with the existing railways. The foundation is in the chalk. The method of construction will be by cofferdam, to enclose an area sufficient for the walls and locks, which, when completed, can be opened for the up and down traffic of the river while the construction of the weirs and sluices is proceeded with. The sluices will be left open for the free passage of the tides until the closing of the barrage, which will take place at high water of a Spring tide.

The locks will be worked electrically from a power-house built upon the central pier of the locks; the power to be obtained from dynamos operated by the fall of part of the water flowing over the dam. A pilot tower will be fixed from which the river traffic will be signalled and regulated, and the locks, movable bridges, etc., controlled.

The locks as shown are four in number, each provided with internal gates in addition to the outer ones, in order that these locks may be worked in long or short lengths to suit the traffic. The lengths provided in this way will be 300 ft. 500 ft., 700 ft. and 1000 ft., and the widths 80 ft. and 100 ft. It is not likely that these dimensions will ever be exceeded by steamships.

The number of vessels passing up and down the river per day averages 220, but few of these exceed 300 ft. in length. It will be easy to lock this number up and down, or three times the number with this series of locks, one important advantage to the shipping being that, instead of waiting tides at Gravesend, each vessel as she arrives, at any hour, can be locked in a few minutes, up or down, without waiting.

Special provision will be made for rapidly and safely passing into and out of the locks with the use of power capstans and gear. The sluices will be of steel, sliding in roller guides, balanced and operated each by its own motor.

At or near low water a large volume of water will be sluiced into the lower river to scour the approach to the locks as often as found necessary.

A system of signalling from the Upper Thames to the barrage will be employed to notify any heavy rainfall or freshet coming down the river, so that by lowering the sluices water may be rapidly discharged to maintain the required level in the river, and at certain fixed dates it may be desirable to let down the water-level for a fixed time to allow of the repairing of dock entrances, walls, and other river-side works.

_Financial._

The estimated cost of the barrage complete is £3,658,000, including compensations and other contingencies. A toll of ¾d. per ton on the shipping passing up and down will pay the interest on this sum. This ¾d. per ton additional toll will, it is estimated, be many times compensated for by reductions in the river and dock dues and other expenses, as below:—

SAVINGS EFFECTED BY DOCKISATION. Per Annum. £ Dredging in the river 200,000 Repairing banks, campsheds and groynes 10,100 Mudding in all docks 50,000 Cost of operating dock entrances and pumping 70,000 Saving in time of vessels ascending and descending the river 225,000 Saving in towage 20,000 ” barging 185,000 ” warping, buoying, lying off, etc. 20,000 ” management of river 70,000 -------- Total annual saving £850,100

This is equal to a reduction of 6·8d. per ton on the tonnage of shipping (30,000,000) entering and leaving the Port, or equal to 7½ times the interest on the cost of the barrage.

To the credit of the barrage must also be set the removal from the prospective future of enormous outlays contemplated for:—

£ Purchasing docks, estimated at 30,000,000 Improving ditto and dredging river 7,000,000 Cost of a water supply from Wales or other source 24,000,000 ----------- Total £61,000,000 -----------

_The Port of London Bill, 1903._

This measure is the Government’s attempt to put into law the recommendations of the Royal Commission on the Port of London, 1902, but with amendments. It is proposed to purchase the entire docks and warehouses, leaving the wharves to run on their own resources; to create a Port Trust to control the entire river and docks; to charge the loan for purchase, etc., upon the London County Council—_i.e._, about £35,000,000: and to dredge the river to about 30 ft. at low water up to the principal dock entrances.

_Dredging the River._

Apart from its cost and the grossly unfair policy of financing and running the docks against the wharfingers, it is evident that this scheme is based upon the possibility of dredging the river to the depth required. Fig. 8 is an actual section of the river, showing the proposed dredged channel as compared with a dockised river.

It seems incomprehensible that any expert authorities should have advised the Government that the river can be effectually dredged. The fact is that it is quite impossible to dredge it to the required depth of about 15 ft. below the present bottom, because experience has shown that with such a river and scouring current the channel will fill up again nearly as fast as it is dredged, the material coming from the foreshores and the estuary. This will give rise to dangerous slipping in of river banks and walls. The estimates of the cost of this dredging (£2,500,000) are therefore entirely misleading.

The present bottom is formed and stands at the natural angle of repose for its present volume, width and currents, and any great interference with this contour such as is proposed—with slopes of 7 to 1—will not stand, the general slope of its bottom now being from 20 to 50 to 1. The Port Trust that undertakes this will find itself spending enormous sums annually in continuous dredging and repairing banks and in compensating owners; all, of course, added to the annual cost of maintenance and to the dues, or charged to the ratepayers.

Glasgow and the Clyde have been instanced as examples of what can be done by dredging. But the Clyde below Glasgow is not a river comparable with the Thames below Gravesend, but an estuary with a very moderate current and tidal range of from about 4 ft. to 10 ft., and the dredging has merely made and kept open a channel in this estuary. The Thames, on the other hand, is a narrow river with a strong scouring current and a range of tide of from 16 ft. to 21 ft. Further than this, Glasgow has spent seven millions in this work, and has to pay large sums to keep the channel open, dredging nearly a million cubic yards every year.

But there are other difficulties. When the river has been deepened as proposed, the tidal volume will be increased about one-third, and therefore its current strengthened and increased, probably two knots per hour. What is worse, the tidal range will be increased proportionately, which means that the high tides will be higher—probably 3 ft. or more—and the low tides lower, by a similar amount, than now. Spring tides may be expected to run the river nearly dry at low water above London Bridge. Results—frequent inundations of waterside districts, more grounding at low water, and more dangerous navigation. Such results have always followed increased tidal volume.

But a dredged channel is necessarily a narrow one (see Fig. 8), and ships will have to negotiate the sharp bends in a narrow channel and against a stronger tide, and also to swing at anchor, for which a wide area is necessary.

_Objections against Dockisation._

Although this proposal has been mooted for some time past, scarcely any valid objection has been brought forward, but such as have been mentioned are mostly based on misconceptions.

One writer thought the river would become stagnant. As a matter of fact the sources of stagnation would be carried down the river by the fresh-water flow continuously, and there is no more reason to anticipate stagnation in the lower river than the upper river, where it has for ages been held up in the same way by numerous dams.

Another writer talks of the “cleansing power of the tides,” and it is a pity to see greater authorities, who ought to know better, speaking also in this way. It has been abundantly proved that the tides—as far as a clean river is concerned—are wholly detrimental. They back up twice daily the natural drainage of the river for five hours, and keep it in solution and circulation for forty-five days before removing it, the effect being exactly similar to backing up in a sewer.

It has also been suggested that the sewage effluents discharged into the river at Crossness and Barking may cause the river below to become foul. Here again is misconception. The effluents—after precipitation of the solids, which is chemically effected, and the carrying out to sea of the resulting sludge to the amount of two million tons annually—contain very little impurity (only seven grains per gallon), and it has been proved by Dr. Dupré that 9/10ths of this becomes oxidised and absorbed in the large volume of water between the discharge and Gravesend. It is well known that in the case of “sewage effluents poured into a sufficiently large volume of otherwise comparatively pure water, the dissolved organic matter contained in it disappears with remarkable rapidity” (Sir Alex. Binnie).

Another critic suggests that the lower river will soon silt up under the new conditions. Most persons—seeing the filthy state of the water—naturally think there must be a large deposit from it. But it has been shown that this suspended matter is the result of tidal currents keeping the mud stirred up everlastingly. An examination of the affluents of the Thames shows that they contain very little suspended matter, and therefore when the locked Thames has deposited its charge of suspended matter any future soilage must come from its affluents—that is, from the upland waters and the sewage effluents, which latter will only affect it below the point of their discharge.

A calculation from official data of the quantities actually now passing into the Thames, from all sources, gives less than 1/10th of an inch annually over the river bottom; so that in ten years the deposit will not exceed 1 in., even without any improvement in the prevention of pollution. It has been estimated by Dibdin that the sewage outfalls could be removed to Gravesend, below the barrage, for the sum of £4,000,000.

But the condition of these effluents is commonly much exaggerated. The total annual discharge of suspended matter at 7 grains per gallon (as given by Dibdin) amounts to 32,000 tons per annum, but much of this becomes chemically combined with the river water and some remains in suspension till it passes Gravesend, leaving only a small quantity to deposit in the river. A single dredger can remove 600 tons per hour; therefore a few hours’ work will remove the whole quantity.

A more valid objection at first sight is that ships and barges will lose the motive power of the tides up and down. This would appear, however, to be a very beneficial loss, because at the same time they will avoid the tide-waiting and waste of time which add considerably to the cost of transit. But against this loss must be set the fact that most ships now have steam power and can make their own destination, while tugs will be able to handle much larger fleets of barges than is now possible in the tide-way, and at all hours of the day. Sailing vessels will be able to sail up and down, which they can only do now with the aid of the tide.

Another suggestion is that when the barrage has closed the river the tides below it may accumulate to a higher level and overflow the low-lying lands below Gravesend. This is, however, a mistake, the fact being that with a reduced tidal volume and momentum in the estuary the tidal range will be reduced, there being no river to fill up, the high tides will be lower and the low tides higher than formerly.

Finally, a word or two as to the vague idea that seems to be in the minds of most people accustomed to tidal rivers—that in some mysterious way the tides by their continual movements are beneficial, keeping the air in motion, etc. All this is pure imagination and arises probably from living on the banks of a tidal river, for most rivers are non-tidal. There happen to be round our coasts some phenomenal ranges of tide; hence the resort to docks, which are almost unknown in other countries. The ranges of their tides being small, docks are not needed, and scarcely any tides occur in their rivers, which, however, are far cleaner than the Thames.

There are of course some low-lying lands bordering the river the drainage from which will have to be pumped into the river. This is, in fact, partially done now, but the matter is a small one.

Prof. Flinders Petrie, in a letter to the _Times_, is strongly in favour of this proposal, and looks to it to relieve the squalor of the East End, with its crowded and unhealthy living, by extending the manufacturing districts down the river banks, providing a belt of factories along each bank and a belt of garden villages behind them, with fast lines of railway to Town between.

To carry out the proposals of this article, a committee has been formed to bring the subject before the notice of Parliament and of the public, and it is suggested that a Board of Harbour Commissioners should be formed, somewhat on the lines of the Port of London Bill of last Session. The new Board would be constituted under the usual Commissioners’ Acts to control the entire Lower Thames, taking over the powers of the existing authorities, but without any interference with the docks, the warehouses or the wharves, the business of which, if the river is rendered properly navigable, could be carried on without making any demands upon the rates of London.

A new era of prosperity would then open up for the trade of London, and its Port would become the finest in the world, with the largest business attached to it.

The committee will include many influential gentlemen connected with and interested in the improvement of the Port of London. The scheme originated with Mr. Jas. Casey, M.I.N.A., and the author is responsible for the engineering details, as also for the information set forth in the foregoing article.