Drainage for Melbourne. 51 



sewers already in existence; and the trials instituted gave 

 some extraordinary facts, one of which, and that by no means 

 at variance with the general results, I proceed to quote : — 



" The main line of sewer in Upper George-street is five 

 feet six inches high, and three feet six inches wide, and runs 

 from the Edgeware-road to Manchester-street, where it falls 

 into the King's Scholars Pond sewer. I have laid a twelve 

 inch pipe, five hundred and sixty feet long, upon the invert 

 of this main line, and have built a head wall at the end of it, 

 so that the whole of the sewage discharged by the collateral 

 sewers above the pipe, as well as what sewage may find its 

 way independently into the upper part of George-street, is 

 forced to pass through the pipe. 



" The whole area drained by the sewers running into the 

 twelve inch pipe in George-street is 213,788 square yards, or 

 about 44 acres. Observations are being continually made on 

 the work, and the results are as follows : — ' The velocity of the 

 stream in the pipe has been observed to be four and a half 

 times greater than the velocity of the same amount of water 

 on the bed of the old sewer. The pipe has not been found to 

 contain any deposit, but during heavy rains stones have been 

 distinctly heard rattling through it. When the pipe is nearly 

 filled, the velocity and concentration of the water are sufficient 

 to clear away any matter which may have been drawn into it 

 from the large sewers, and much of which matter, it may be 

 presumed, would never enter a well-regulated system of pipe 

 sewers ; also, the force of the water issuing from the end of 

 the pipe is sufficiently great to keep the bottom of the old 

 sewer perfectly clean for twelve feet in length. * * * 

 On the invert of the old sewer, which now forms the bed of 

 the pipe, deposit was constantly accumulating, and was only 

 partially kept under by repeated flushings.*'" I do not 

 think it necessary to extend the quotation or to multiply 

 instances. 



A great number of trials were made in various localities, 

 and always with similar results, and at length the requisites 

 for the adequate drainage of any district was reduced pri- 

 marily under three distinct heads, viz. : — 



1 . The quantity of sullage to be removed from any given 

 area. 



2. The rate of inclination obtainable. 



3. The outlet. 



* Report Board of Health for 1852, p. 53. 



