Drainage of Melbourne. 



109 



will be obvious that any underground sewer made to carry 

 off the surface water must be of sufficient size to receive and 

 discharge the largest quantity that has been known to fall 

 in a given time, together with the ordinary waste water from 

 the Yan Yean supply. 



The following tables, compiled from the records at the 

 Government Observatory, supply ample information relative 

 to the rainfall during seventeen years, and which is of 

 special value when brought to bear upon the subject now 

 before us. In short, without some reliable data of this kind 

 to guide us, any system of storm-water drainage would be 

 merely a matter of opinion on which engineers might dis- 

 agree. 



TABLE A. 



This Table shows the amount of rain falling in Melbourne each year 

 from 1840 to 1850, and from 1855 to 1860, inclusive, and shows 

 also the difference in the amount each year, from the mean rain- 

 fall during 17 years. 







Difference of Amount of 





Amount in Inches. 



each Year, and mean 

 rainfall for 17 Years. 



1840 



22-57 



— 5-83 



1841 



30-18 



-r-l-78 



1842 



31-16 



-}- 2-76 



1843 



21-54 



— 6-86 



1844 



28-26 



— 0-14 



1845 



23-93 



— 4-47 



1846 



3053 



+ 213 



1847 



30-18 



+ 1-78 



1848 



33'15 



4-4-75 



1849 



44-25 



+ 15-85 



1850 



26-98 



— 1-42 



1855 



28-21 



— 0-19 



1856 



29-75 



+ 1-35 



1857 



28-90 



-f 0-50 



1858 



26-02 



— 2-38 



1959 



21-80 



— 6-60 



1860 



25-40 



— 3-00 



Mean rainfall for 17 years, 28 - 40. 



The greatest difference in rainfall for the above period amounts to 

 22*71 inches. The average rainfall for the last six years — from 1855 to 

 1860, viz., 26-679 inches, differs but slightly from the average fall of 

 rain for any six consecutive years from 1840 to 1848, including the 

 abnormal rainfall in 1849. 



