HISTORY OF CIVIL ENGINEERING IN NEW SOUTH WALES. 643 



fully meet the requirements of the situation. It is simple, massive 

 and etiective. He had also frequent opportunities of examining 

 the work at various stages when in progress, with the engineer, 

 Mr. David M'Mordie, M.I.C.E., under whose supervision it was 

 carried out, 



MAIN SOUTHERN SECTION. 



The main sewer drains the southern slope of the city, including 

 boroughs of Redfern, Waterloo, Alexandra, and a portion of 

 Paddington, tlie area being eleven hundred acres. It extends from 

 Nobbs-street, Surry Hills, to the north bank of the Cook's River 

 near its junction with Botany Bay. The sewer is designed to 

 dischcharge four cubic feet per acre per minute, consisting of one 

 cubic feet of sewage per minute, and half an inch of rain per acre 

 per hour. It discharges into a screening-house, situated on the 

 north bank of the river at a level of sixteen feet above high water, 

 from whence it is conveyed by means of a syphon under the bed 

 of the river to a sewage farm situated on the south bank of the 

 river on a block of land known as Webb's grant. 



For a distance of eighty-nine chains, commencing in Nobbs- 

 street, the sewer is oviform in section three feet high by two feet 

 wide ; for the next thirty-two chains the section is increased to 

 three feet three inches in height by two feet two inches wide, at 

 the end of which a short length of sewer of the Hawkesly section, 

 four feet six inches high by three feet six inches wide, connects it 

 with the outfall sewer, which is two miles and forty chains long, 

 of a circular section, five feet six inches in diameter, on a gradient 

 of four feet to the mile. The first portion of the length of the 

 sewer in Nobbs-street is in firm clay ground, but by far the greater 

 portion consists of water-charged sand and old swamps. 



The cuttings were in some places thirty feet deep, and consider- 

 able difficulties were encountered in keeping down the water, 

 which was ultimately done by means of a sub-duct. A portion of 

 the country traversed by the five feet six inch sewer consists of 

 sand ridges, rendering necessary extensive excavations ; the 

 greater portion, however, consists of low-lying ground, over which 

 the sewer is carried by means of an embankment. 



Where the sewer passes over natural watercourses, concrete 

 culverts have been constructed, through which the streams are 

 carried under the sewer, so that the land drainage and tlie interests 

 of market gardeners are not interfered with. The main sewer is 

 constructed of blue-stone, lined with brickwork, and sandstone 

 concrete for the lower portious ; it is rendered on the inside with 

 Portland cement mortar half an inch thick, in the proportion of 

 one part of cement to two of sharp clean sand. 



The sewer is provided thi-oughout its length with ventilation 

 manholes, and with gas check valves to prevent the sewer gas 



