XXIV. J. DAVIS. 



gravitation sewer, and the cost of constructing the sewers 

 would have been thereby greatly increased. 



The Shone system, on the other hand, with shorter and smaller 

 sewers laid at lesser depths and fair gradients, and dealing with 

 the sewerage by independent ejector stations had everything to 

 recommend it. 



The system was designed upon the following basis : — 



1. Drainage area, 77*4 acres (nett). 



2. Population, 30 persons per acre. 



3. Total prospective population, 2,323. 



4. Sewage allowance per head per day, 50 gallons. 



5. Proportion of rainfall admitted to the sewers, 2 in. per 



24 hours, on an area of 200 square ft. per head. 



6. The average daily dry weather flow, therefore, would 



amount to 80*62 gallons per minute. 



7. The sewers are designed to carry off half the dry weather 



flow in four hours, together with the rain water. 



8. The maximum combined flow would be 577*8 gallons per 



minute. 



The following table gives in convenient form the data upon 

 which the sewers, rising mains, ejector and air compressing 

 machinery were designed. 



The estimated maximum H.P. required is 8*83, and assuming 

 the efficiency of the whole system as 35 per cent, the indicating 

 H.P. at the Generating Station would be 2 5 J. 



For the purposes of the scheme the area was divided into 

 four sub areas, each having an ejector station and collecting well 

 into which the gravitation sewers discharge. 



The total length of the sewers laid is 8,117 ft., comprising 

 7,829 ft. of 6 in. and 288 ft. of 9 in. pipes. The grades vary 

 from 1 in 200 on the level ground to 1 in 20 on the slopes 

 bounding the area, while the velocities range from 1J to 2 ft. 

 per second with the sewage flow. Automatic flushing stations 

 are provided in suitable positions which will have the effect of 

 increasing the velocities to about 5 ft. per second, a sufficient 

 rate to cause thorough flushing. 



