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the present works and make use of the existing main in preference to establishing Water works - carrying out any new, elsewhere or new system.
The works as at present existing supply the wants of the City during the rainy season or from April to October inclusive, What is required is a Reservoir sufficiently large to impound a supply for the dry season or from November to March inclusive during which time probably not a drop of rain may fall.
105,000,800 Gallons would be required to supply 700,000 Gallons per diem for 5 months or per diem say 150 days. From this may be deducted 108,000 Gallons running daily into the Reservoir during the dry season making the quantity required to be impounded 58,000,000 Gallons or allowing 11,200,000 Gallons for evaporation making the total required capacity 100,000,000 Gallons
The present Dam is simply a weir 120 feet long and 10 feet in height - perpendicular on the up side and sloping on the down side, a bank of concrete faced on both sides with Granite, and has a culvert through the centre 3 feet x 2 feet - for the purpose of emptying the Reservoir at any time. All flood waters from the valley have passed over this weir since its construction in 1867 there being at present No other means of exit.
The Dam is built on solid Rock formerly the bed of the stream, and I am informed the rock was level with the foundations of the Dam, no excavation being made in it to receive the Concrete, notwithstanding there appears to be no leak of water under the Dam although there is a certain amount of Leakage when the Reservoir is full through the Dam itself more particularly in the neighbourhood of the Culvert.
I propose to construct a 50 feet embankment behind the present Dam as shown on the accompanying Plan, the intermediate space being worked out to form a Gauge Basin holding about 300,000 Gallons.
The bed of the Reservoir will be formed at the level of the bottom of the present Dam, the average depth of cutting being about 15 feet. The area of the Reservoir has been made as large as practicable the hills rising on all sides from the water side at an angle of in some places 50° and at others being nearly perpendicular
It may be seen that the height of the Bank has been fixed at 50 feet in Consequence of the nature of the ground where it is proposed to construct. The top of the Bank will be level. A Bye wash could not have been formed at a greater height without very heavy labour in cutting into the side of the Hill.
The formation on which the Reservoir will be placed Consists of Boulders of Granite of the Kap class composed apparently of Felspar, and hornblende only, and quarry workers for working up. The Alluvium is apparently of a clayey nature when first cut from the bed of the reservoir, but when dry appears to be somewhat porous, and the...