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.