CO129-328 - Governor Nathan - 1905 [1-6] — Page 322

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.

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