TRAKSACTIONS OF SECTION H. 403 



a very large percentage of the total length to be laid with 

 sewers of small diameter. They are thus much more easily 

 flushed, and there are not the same facilities ftjr the generation 

 of sewer-gas as in larger sewers. We think it is now generally 

 admitted that, both from an economic and a sanitary point 

 of view, the separate system is beyond question the most 

 suitable. 



The following table shows the different sizes of sewers, with 

 their respective lengths : — 



Ml. cli. 



Owing to the topographical features of the district it was 

 found impossible (even had it been desirable) to obtain a 

 natural outfall, so that pumping has had to be resorted to for 

 the removal of the sewage to the irrigation farm. 



The sewers vary in depth from 3ft. to 13ft. below the sur- 

 face. The pipes are jointed with cement mortar, and are laid 

 on concrete, which is brought half-way up the pipe. Manholes 

 and ventilators are provided at frequent intervals. As a 

 general rule, the gradients are so arranged as to obtain a velo- 

 city of 150ft. per minute. House-connections are laid with 

 pipes of 4in. diameter, and soil-pipes of Sin. diameter. 



The area served is about 2,800 acres in extent, and consists 

 of the City of Christchurch and surrounding suburbs of Syden- 

 ham, St. Albans, Linwood, and a portion of the Heathcote, 

 Eiccarton, and Spreydon districts, with a population of, say, 

 thirty-five thousand. There is ample margin, however, for a 

 very large increase in the population without involving any 

 extra outlay in the existing sewers or pumping-station. 



The hours worked at the pumping-station for the year 1889 

 averaged 10-4 hours per diem, and the amount pumped per 

 diem to 6,256 tons. Of this, a proportion of, say, 80 per cent. 

 is subsoil-water, which, of course, will not materially increase 

 for all time. From this it will be at once seen to what extent 

 further connections can be made before extra power will be 

 required. 



The expenditure incurred for these sewers, machinery, 

 buildings, tank, iron main to sand-hills, land, and contingencies 

 was £127,000. In several localities the quicksands proved to 

 be very troublesome, and special and costly provision had to 



