NORTH SYDNEY AND DOUBLE BAY SEWERAGE SCHEMES. XIIL 



population of 30,225, and included 24 miles of main, sub-main 

 and subsidiary sewers. 



Mr. Stayton proposed that the sewers should be calculated to 

 discharge the following : — 



Sewage, or Dry Weather Flow — 50 gallons per head per day. 

 Rainfall — 40 per cent, of 1-J inches during 24 hours, or 1*26 

 cubic ft. per minute per acre, 

 half the daily sewage flow to pass off in four hours. 



The growth of the locality has been so rapid, however, that it 

 has been found necessary to extend the scope of the system to 

 the adjacent suburbs of South Willoughby and Mosman, and the 

 outfall works are now designed to treat the sewage from an area 

 of 2,328 acres, divided as follows . — 



North Sydney ... ... ... 608 acres. 



Mosman (North) 720 „ 



Mosman (South) 727 „ 



South Willoughby 273 „ 



Total 2328 acres. 



The altered circumstances permitted the discharge of the sewers 

 to be calculated on the following basis : — 



Sewage Flow — *57 cubic ft. per minute per acre. 

 Rainfall allowance per minute per acre — North Sydney : 

 1*26 cubic ft. ; North Mosman and South Willoughby: 

 •63 cubic ft. ; South Mosman : -94 cubic ft., 

 half the daily sewage flowing off in six hours. 



The outfall sewer is therefore designed for a maximum sewage 

 flow of 1,327 cubic ft. per minute, and a maximum combined 

 flow of 3,402 cubic ft. per minute. 



The present flow treated at the outfall is about 750,000 gallons 

 per day. 



DESCRIPTION OF SEWERS. 



The scheme was practically initiated in 1891 by the construc- 

 tion of the main outfall sewer from Milson's Point to Willoughby 

 Bay. This is the principal artery of the system, and has a length 

 of nearly two miles, its highest level at Milson's Point being 



