5
.F'S
The trial works described in last years report as being
317
ort
1904. in progress with a view to the construction of a large dan below
Taitam Tuk, were brought to a conclusion on the 10th. October
1904.
91.
Solid rock was reached in No. 2 Well at a depth of from
62 to 65 feet. This completed the necessary information for
a preliminary estimate for a dam on the most seaward site. The
accumulated information from prickings, borings and wells, shows
that the solid rock on this site lies at a general level of 65
feet below Ordnance Datum, and that for a dam here a water-tight
diaphragm would have to be carried down to this depth. The main
body of the dam might be made to rest on the surface of a bed
of nearly water-tight clay which lies all over the site, at a
depth of from 24 to 28 feet below Datum. This bed of clay be
lies upon a stratum of shingle at a depth of from 42 to 45 feet
below Datum. The clay varies considerably in quality, some lay-
ers of it being rendered porous by the admixture of sand and
stones. But the continuity and water-bearing nature of some
layers of this bed was shown by the fact that the level of the
water inside the No. 1 Weil, which reaches a depth of 34 feet,
was lowered to some extent by the action of one small pump in
the No. 2 or No. 3 Wells, 170 feet distant. A dam on this site
would have a length of 550 at the base and 780 at the crest,
which would be 135 feet above the level of the rock. In addi-
tion to this there would be a bye-wash of say 300 feet.
Three more wells were sunk on a line about 700 feet land-
ward of the one above-described. Similar strata were encounter-
ed in this case, and the rock was found to lie at a depth of
from 45 to 54 feet below Datum. A dam on this site would be 880
feet in length at the base, and 1,285 feet at the crest, which
would be 120 feet above the level of the rock. In addition to
this there would be a byewash of say 300 feet. A dam here would
therefore be as costly as one on the other site, and would en-
tail a considerable loss of storage capacity, and some loss of
catchment area.
(SD).
P.N.H.J., D.P.W.
27.3. 05.
たた