Page:Municipal Handbook of Auckland 1922.djvu/268

 two 48in. diameter cast-iron pipes on cast-iron cradles, the next length of 324ft. consists of two similar pipes set in concrete, and the remaining portion is a concrete culvert 22.5 square feet in sectional area leading into the outfall chamber of the storage tanks. The invert of the outfall sewer at its point of discharge is 26.2ft. below high-water level.

The storage tanks are comprised in one block 1,296ft. 6in. in length and 106ft. wide, with a total capacity of 7,800,000 gallons. They are constructed of concrete, plain and reinforced, the roof having been designed to form a portion of the suggested esplanade for the foreshore of the harbour.

At the inlet end of the tanks a brick building is erected in which is installed the screening and detritus-removal plant, comprising coarse screens, mechanically operated fine screens, and a bucket dredge. This plant is driven by a 10 b.h.p. vertical steam engine, with an oil engine as a stand-by. A valve chamber is built at the outlet end of the tanks, in which the valves controlling the discharge of sewage are operated.

The main intercepting sewer, which has a ruling gradient of 1 in 3,000, is of the standard oviform, or egg-shaped section, ranging from 8ft. 6in. by 5ft. 8in. to 3ft. 6in. by 2ft. 4in. It is constructed of concrete, plain and reinforced, and is laid principally in tunnel with the exception of a length of 100 chains in Hobson Bay, which is constructed on reinforced concrete piles. The branch sewers are of various sections and grades, and are constructed of concrete and earthenware pipes.