The next important point is to determine the
position of the dam, having regard to the suitability of the ground for
affording a good foundation and the impoundment of the requisite body of
water with the least outlay on embankment works.
It has been suggested that the floods of the valley of the Thames might
be controlled by a system of storage reservoirs, and notice was
especially drawn to this in consequence of the heavy floods of the winter
of 1875. From evidence given before the Royal Commission on Water Supply,
previous to that date it was stated that a rainfall of 1 in. over the
Thames basin above Kingston would give, omitting evaporation and
absorption, a volume of 53,375,000,000 gallons. To prevent floods, a
rainfall of at least 3 in. would have to be provided against, which would
mean the construction of reservoirs of a storage capacity of say
160,000,000,000 gallons. Mr. Bailey Denton, in his evidence before that
commission, estimated that reservoirs to store less than one tenth that
quantity would cost L1,360,000, and therefore a 3 in. storage as above
would require an outlay of, say, L15,000,000 sterling; and it will be
seen that 3 in. is by no means too great a rainfall to allow for, as in
July of 1875, according to Mr. Symons, at Cirencester, 3.11 in. fell
within twenty-four hours. Supposing serious attention were to be given to
such a scheme, there would, without doubt, be very great difficulty in
finding suitable situations, from an engineering and land owner's point
of view, for the requisite dams and reservoir areas.
Pages:
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29