Read Ebook: The Great Thames Barrage by Barber Thomas Walter

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Ships drawing 30 ft. can then proceed to London Bridge at any hour of the day or night, without waiting for tides.

Ships of all tonnages and draughts can traverse the river, anchor anywhere, lay alongside any wharf or quay, always remain at one level for loading or unloading and need not lie out in the river or obstruct the free navigation.

Dock entrances can be left open, thus saving the cost and time lost in working them.

There will be no mud entering the docks and backwaters, the water in which will freely circulate with the clean river water.

Exceptional tides, being stopped at the dam, will not overflow the river banks as now sometimes happens.

Reduced cost of towage, barging, repairing river banks, camp-shedding, quays, dredging, management, control and policing of the river.

Greatly increased safety of navigation: no grounding, swinging with the tides, collisions due to tidal drift. The tides are responsible for most of these accidents and for many lives lost--casualties which would not occur in a lake.

In addition to these there is a most valuable asset created in the advantage the new conditions open up for--

Pleasure traffic, boating and sailing, fishing and the provision of efficient steamboat services, with fixed piers. London will be provided free with a lake of fresh water 45 miles long and from a quarter to half-a-mile wide. It is certain that this will give rise to extensive pleasure boating of all kinds, which will have ample room owing to the removal of all vessels from mid-stream anchorages to the shores.

Perhaps the most important advantage created by the barrage will be the permanent supply of water for the increasing demands of the London area.

The figures are as follows:--

Gallons per day. From the River Lea 52,500,000 " wells in the Lea Valley 40,000,000 " wells in the Kent Co.'s district 27,500,000 " the River Thames 185,000,000

So that two-thirds of London's water supply comes from the Thames; and as the other sources named above cannot be expanded for future requirements, it is evident that for the increasing demands of London either the Thames or some more distant source must be looked to.

The Royal Commission on the water supply of London estimated that in 1941 these requirements will reach 423 million gallons per day, so that at that date 303 million gallons must be obtained from the Thames or elsewhere.

Now if the Thames is dockised, and the tides kept out of the river, it is evident that much less upland water than is now considered necessary will suffice to keep the river lake fresh and clean, because all sewage and effluents entering the river will be carried directly down to Gravesend; there will be no muddy foreshores and no stirring up of the river mud by the tidal scour.

The river will be, in fact, in exactly the same circumstances as most large lakes--that is, a large body of fresh water, having a main inlet of fresh water at one end, many small inlets along its banks, and one main outlet at its lower end at Gravesend. Such lakes abound all over the world: they are the purest of all waters and never become stagnant.

It is proposed, therefore, that the Thames lake should be regarded as a storage reservoir, so far as water supply is concerned. It will contain sufficient for 320 days' supply, even at the estimated requirements of 1941; for to whatever extent its waters may become contaminated at and below London, these pollutions cannot work back up the river towards Teddington. It follows, therefore, that between Teddington and London water may safely be drawn off for town supplies, or the supply may be taken as now from above Teddington.

An inspection of the table of flow over Teddington Weir on page 3 will show that in the winter and spring enormous quantities of water, above the quantity considered necessary for scouring the river, flow down and are lost.

A minimum flow of 200 million gallons is fixed by law as the amount needed in summer to keep some sort of cleanliness in the lower river; but in January ten times this amount flows away. It is only for a short time in the months of August or September that the natural flow over Teddington Weir--including the water drawn by the water companies--is a little below 423 million gallons daily, and in those months the surplus might be taken from below the weir without affecting the river materially.

If this be objected to, however, there is another remedy available. The Upper Thames may be used as an aqueduct to convey a larger supply, to be derived from neighbouring watersheds or from wells, the water so obtained to be regulated to meet the requirements, enabling a sufficient amount to be run over the weir to keep the lower river in motion at its upper end. Further down, the small but numerous affluents and springs will keep the river in motion, as they are not affected by the Teddington flow, but give a continuous supply to the river. Mr. Topley, the eminent geologist, in his evidence before the London Water Commission, 1892, stated that there are outside the Thames basin large areas from which water could be obtained, such as East Kent, West Suffolk, Norfolk, Hampshire and Wilts.

It is evident that in this way an enormous prospective outlay for a supplementary water supply for London in the near future may be obviated, and that without adding to the existing plant of the water companies the new Water Board may inherit free of cost a future source of supply which will make their purchase of the London Water Companies' stocks a good investment and a cheap one for the ratepayers.

The possibilities of this scheme are not exhausted, as there remains to be mentioned the opening of railway communication across the river by a tunnel under the dam and of road communication by a roadway over the dam. These are clearly shown in the accompanying Figs. 4, 5 and 6.

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.

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.

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.

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.

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.

The estimated cost of the barrage complete is ?3,658,000, including compensations and other contingencies. A toll of 3/4 d. per ton on the shipping passing up and down will pay the interest on this sum. This 3/4 d. 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:--

This is equal to a reduction of 6?8d. per ton on the tonnage of shipping entering and leaving the Port, or equal to 7 1/2 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:--

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 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 , 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.

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 , and it has been proved by Dr. Dupr? 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" .

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.

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