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42
Symons gives as the mean fall of a long term upon the watershed.
We therefore increase the daily volume to 1,437,747,750
gallons, raising it in the ratio of 27.01 to 28-50 inches. This
quantity must, however, be reduced in the proportion of the
area above Teddington, viz., 3,766 square miles, to that above
the intakes, which is 3,548 square miles, thus bringing down the
nett daily quantity to 1,354,521,778 gallons. This, we believe,
is a very close approximation to the daily average flow of the
Thames down to the waterworks intakes during a long series of
years, and we will call it, in round figures, 1,350,000,000 gallons.
The average daily discharge of three consecutive dry years we
estimate at 1,120,000,000 gallons, and of the driest year at
900,000,000 gallons.
"These being the facts, we are of opinion that, by the
construction in the neighbourhood of Staines, of reservoirs of
adequate capacity, into which water shall be pumped and stored
in times of excess, to be used in times of deficiency, at least
300,000,000 gallons a day may be obtained for the supply of
London.
We believe this can be done without taking in the more
turbid of the flood waters, and without injuriously diminishing
the volume of the River below the point of abstraction. To
ensure the best results in both these respects, the taking of the
water should be subject to strict regulations laid down by
Parliament. The water allowed to be taken from the River
should, in our opinion, include any water which may be pumped
from the general beds in the vicinity of the River.
“From the River Lea.—The available drainage area of the
Lea above the lower intake of the East London Company is stated
by Mr. Bryan to be 460 square miles; and the mean rainfall
upon it is stated by Mr. Symons to be 26 inches. No gaugings
of the discharge has ever been made at or below the intakes;
but they have been kept for many years at Fielde's Weir, which
has above it (as before stated) an area of 422 square miles,