636 PROCEEDINGS OP SECTION J. 



either completed or in progress ; but much yet remains to be done 

 in the construction of minor sewers in connection with these 

 systems. 



THE NORTHERN SYSTEM. 



The northern outfall sewer, commencing near the intersection 

 of Newtown-road and Parramatta-street, and discharging into the 

 ocean near Ben Buckler Point, as before described, is five and 

 a-half miles in length, is oviform in section, varying in size from 

 four feet six inches by three feet six inches at its upper end to 

 eight feet six inches by seven feet six inches for a length of one 

 mile at the outfall end, and has a fall of three feet six inches a 

 mile. At a quarter of a mile from the head it is joined by the 

 Prince Alfred Hospital connecting sewer, four feet six inches by 

 three feet six inches in size, and by the Pyrmont branch, three 

 feet three inches by two feet two inches. At the corner of Oxford 

 and Liverpool-streets one mile and a-quarter from the head, it is 

 joined by the King-street intercepting branch, and by the com- 

 bined Bridge-street and Harrington-street intercepting branches, 

 each four feet six inches by three feet six inches. A little further 

 on it is joined by the Riley-street intercepting branch, and then 

 by the Bourke-street intercepting branch, and at Barcom Glen, 

 two miles from the head, it is joined by a branch sewer on the 

 boundary line between the City and Paddington. Besides collect- 

 ing the sewage from these various branches it intercepts a num- 

 ber of old sewers directly — one of these in the municipality of 

 Paddington, being forty feet above the level of the outfall sewer at 

 the intercepting point, — and a number of junctions are provided 

 along the entire length to meet present and future requirements. 

 Where the sewer crosses Deep Dene, a part of Rushcutter's 

 Bay Valley, a storm-water overflow is pi'ovided, and from this 

 point an overflow sewer was built to carry the storm-water into 

 Rushcutter's Bay. It is half a mile in length, four feet six inches 

 by three feet in size, has a fall of one in two hundred, and dis- 

 charges above high-water level. A swamp one thousand feet in 

 width had to be crossed by this overflow sewer, where the surface 

 was some feet below the invert level of the sewer. The ground is 

 of a spongy, peaty nature, to a depth varying from ten feet to 

 over thirty feet. After digging trial pits and making borings, it 

 was decided to carry this length of sewer on arches of twenty-five 

 feet span and three feet six inches rise. To form the piers for 

 these arches concrete cylinders of ten feet external diameter were 

 sunk through the spongy ground into a stratum of clean sand 

 below. These cylinders were then filled with concrete, and the 

 arches turned, the thickness between the sofiit of the arch at the 

 crown and the invert of the sewer being twelve inches. The 

 depths of the cylinders vary from ten feet to thirty-three feet. The 

 whole of the work in the cylinders, arches, and sewer is concrete. 



