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Q 58
ABERDEEN VALLEY WATER SCHEME.
240. Preliminary and Survey Works.-This work was referred to in paragraph 203 of last year's Report. The survey for the Second Section of the West Catchwater was completed early in the year.
A contour survey of the Lower Reservoir was made for capacity purposes. Other surveys included one of the site adjacent to the Lower Dam on which silt from the Lower Reser- voir has been deposited and one for the proposed Aberdeen Village new Filters and Service Reservoir.
241. Upper Dam.-This work was referred to in paragraph 204 of last year's Report. A few minor works were carried out under the Maintenance Contract during the year. These included fencing around the rain gauge, a turning ground for cars, concrete steps at the south end of the Dam and improvements to the beeching in the stream bed at the foot of the Dam.
242. East Catchwater. This work was referred to in para- graph 205 of last year's Report.
1st Section. Minor improvements were made at the outfall, including trimming back the slopes of the large cutting and realigning and regrading a small length of "Lady Clementi's Ride" in order to re-open this path.
2nd Section. A contract was signed by Messrs. Blackmore & Blackburn on the 13th January for $50,008.10 for this work. Work commenced early and was completed, except for a few minor works and trimming and clearing the site, by the 26th October. In two places, owing to the difficult nature of the ground, it was necessary to carry the Catchwater on piers by means of a reinforced concrete aqueduct of box section, the lengths of the two sections being 67 and 175 feet, whilst at a third place it was necessary to resort to tunnelling to carry the catchwater past three large boulders, the length of tunnel being 34 feet. This section of the Catchwater collects water from an area of 169 acres on the Southern Slopes of Mt. Nicholson and also from the overflow of Wongneicheong Reservoir. It dis- charges the water into the first section of the Catchwater, a description of which was given in the 1931 Report. This section collects 2/3 of an inch of rain per hour and overflows have been designed to discharge any excess rainfall up to a rate of 33′′ per hour. The Catchwater is 5,802 feet in length and was con- structed of four different sizes varying from an effective cross- sectional area of 4 square feet at its commencement to 17.20 square feet at its junction with the first section. The invert and lower part of the sidewalls were constructed of 1.2.4. cement concrete 3" thick in the sinaller sections and 4" thick in the larger sections, whilst the remainder of the side walls were constructed of 1.4.8 cement concrete of thicknesses similar to
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those of the invert. The side slopes of the Catchwater are 2 to 1 in soft section and 8 to 1 in rock section. Along the outside of the Catchwater a path of minimum width of 3 feet has been formed and this was carried over the overflows on reinforced concrete decking. Sandtraps, each having a washout pipe, have been constructed in the invert at all overflows.
243. West Catchwater.-First Section:-This work was re- ferred to in paragraph 206 of last year's Report, when the first section was completed. The maintenance period expired on the 30th June and the retention money was paid to the contractors, Messrs. Foo Loong & Co., during the year.
Second Section:-A contract for this work was signed by Messrs. Sang Lee & Co. on the 12th April for $77,640.50. Work commenced immediately and by the end of the year such good progress had been made that the upper portion, 3,945 feet in length, and 4,000 feet out of a total of 4,405 feet of the lower portion, were completed. Fair progress was made on the difficult section joining the upper and lower portions.
244. Alterations to Existing Dam.-This work was referred to in paragraphs 208 and 209 of last year's Report.
Reconstruction of Lower Dam:-The maintenance period for this work expired on the 30th April and the retention money was paid to the Contractors, Messrs. Kin Lee & Co., during the year.
Removal of Silt:-The Aberdeen Lower Reservoir when taken over by Government was very badly silted up, the silt being of such a composition that, in addition to its being likely to cause a collapse of the existing dam, it was having a deleterious effect on the pumps, pipe line and filters and was also reducing the storage capacity of the Reservoir. In order to carry out the investigations of the structure of the existing dam it was necessary to remove an amount of 11,110 cubic yards of silt from the up stream face of the dam, in addition to which a further quantity of 21,799 cubic yards were removed during the recon- struction of the dam. As there was still a considerable quantity of silt in the Reservoir a Contract for its removal was let to Messrs. Yee Lee & Co. for $26,800. on 1st February. By the end of May approximately 40,000 cubic yards had been removed under this Contract and the Contract was extended by an amount of 20,000 cubic yards, but on the 4th August, when 52,075 cubic yards under this Contract and a grand total of 84,984 cubic yards had been removed, it was found necessary to impound water in the Reservoir, thereby closing the Contract. At the end of the rainy season 96.64 million gallons had been impounded. All the silt removed from the Reservoir with the exception of a quantity of 20,000 cubic yards sluiced through the washout of Dam, was
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