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
Total 305,000,000
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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.
_Rail and Road Communication at Gravesend._
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.
[Illustration: Fig. 4.