THE NEW RESERVOIR

New Zealand Times, Volume XXX, Issue 6624, 14 September 1908, Page 5

THE NEW RESERVOIR

TESOERS TO BE CALLED. DtBCJUrTXOX OF THE DAM. liccont dry seasons demonstrated that tho water-supply for the ciiy of Wellington is not all that could bo desired by a very long way. The \vaiuui dam is now altogether too small. Some two or three years a special loan was floated for tho building of a new darn at Karori and the extension of the water-supply to the outlying suburbs. Provision was also made for tho construction of a big reservoir at NViunui. The work at Karori has been completed; and water is now laid on in various parts of the oily whore previously the residents had to rely upon their tanks for a supply. In regard to the new reservoir at WaLnui plans and specifications have boon completed by the City Engineer, Mi* Morton, and Lenders are now being called for tho work. SOLOMCLVS AOl3 DAM. Tho new reservoir will be situated about half a mile above tho existing dam, in the vicinity of a x>oint known us Solomons Nob. In tact Solomon’s Nob will form one of tho buttresses of tho dam, the end of the reservoir being against this point. it will bo a reinforced concrete structure of a comparatively new type. The profile will he the shape of a right-angled triangle the slope forming the apron or dock to the darn, which will be hollow and built of reinforced concrete throughout. Tho deck will he supported on vortical walls or buttresses, built on a concrete floor, taken down sonic depth below the present surface levels. These vortical walla will be securely hold in position by longitudinal stiffening walls. At the up-stream side of the haso a cut off wall will bo provided, about six foot in thickness, which will bo carried down to suitable rock, or other impervious foundation.

DEPTH AND CAPACITY. The deck will bo 3fu in thickness at the bottom diminishing to 2ft through at the top. An ample spill way or wasto ware will also bo provided over 100 ft in length for tho dischnrgo of flood waters. Tho total length of tho dam will bo 510 ft, while tho maximum depth of water will be 50ft. When tho dam is full tho water surface will be 470 ft above sea level; and tho approximate holding capacity is sot down at one hundred and forty million gallons. When full the coinpiece surface area of tho dam will bo acres. Tho reservoir has been so designed that at some future time an additional ton feet of water depth can bo added. This provision shows groat forethought and when such addition is mado the carrying capacity will bo increased by some forty million gallons of water. This typo of dam has boon recently adopted with great success in America.

THE WATER MAINS. The duplication of the main from Mainul has not yet been provided for, but this will bo necessary before long. Wellington should have more than “ono string to its bow ” in this respect. The contractor for tho reservoir will, however, have to furnish about forty-sis chains of steel piping 3Uin in diameter. When laid, this will extend from tho new dam to a point below the existing reservoir, and will be terminated in such a way as to admit of extension and form part of a new duplication main. Provision will also bo made for connection on to the present main, so that any repairs o: cleaning out to the existing reservoir can bo carried out without the city supply becoming in any way discoloured or tainted. Tho main referred to will also be made to convey dirty water from the excavation of the new dam; washing metal, sand, etc., past the existing reservoir so as not to discolour tho water of tho existing reservoir during building operations at the now site. WEMbINGTON'S CONSUMPTION. Tho capacity of tho present dam is twenty million gallons. It is rnoro of a pond than a reservoir, and tho now ono will cany seven times the quantity of water. Tho Wainui stream from which the dam is fed only provides a minimum flow of throe million gallons per day, while tho present average •consumption for Wellington is three million gallons per diem, leaving practically nothing to come and go on. There.is, of course, the Karori reservoir, which has a storage capacity of ono hundred million gallons, but tho flow into this reservoir is exceedingly small, practically nil in the dry season. Tno Karori dam is used for supplying tho high-b'vols water service, and to augment the pressure in the city during tho period of tho maximum ’draw off. When the Solomon’s Nob dam is completed Wellington’s reservoirs will possess tho following storage capacities:— Solomon’s Nob dam... 140,000,000 Existing Wainui dam 20,000,000 Karori dam ... ... 100,000,000 Total 260,000,000 Tenders close in about four weeks tor tho building of tho dam. The work should ho put in hand shortly after the contract is signed. The reservoir will take about eighteen months to complete; It will be built under tho supervision of the City Engineer.