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.
[Illustration: Fig. 7.]
[Illustration: Fig. 8.
_Section of the Thames below Blackwall shewing Proposed Dredged Channel
compared with a Dockised Channel._]
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.
[Illustration: THE POOL BELOW TOWER BRIDGE.]
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.
[Illustration]