4 Heavy Fall of Bain 



discharged at Campbell-street was 3248640 cuLic feet 

 during the same period. It is evident I have either over- 

 rated the depth above Wellington Bridge, or under-estimated 

 that above the Campbell-street Biidge ; but the mean of the 

 two, or 4404240 feet, may be taken as the average dis- 

 charge. 



If then we assume that the rain falling upon the drainage 

 took any given period, say four hours, to reach the Victoria 

 Bridge, the quantity above determined would be the amount 

 which fell on the area during one hour, say from seven to 

 eight on Monday morning. 



On reference to the Table, we find that from 6'50 to 7'50 

 it rained heavily, — that from 6'60 to 7" 10 one-fourth of an 

 inch of rain fell, — that from 7-10 to 750 another one-fourth 

 of an inch ; so that the total fall amounted to half an inch- 

 If, then, we multiply the number of cubic feet per hour 

 discharged by the rivulet by 24, we shall get the number of 

 square feet contained in the area of drainage =: 105701760 

 IT 2426 acres. 



As I said before, this can only be taken as a very rough 

 approximation, for I have been obliged to assume, first, the 

 average depth of the current at the points where the levels 

 were taken, and again to guess at the time which the water 

 takes to flow from the hills to the bridge. It must be evident 

 that this latter element must be taken as a mean between 

 the shortest and longest period for which the rain, falling in 

 the vicinity of tbe bridge, would be discharged in a very 

 short time ; that falling on the mountain side would, of 

 course, take much longer to reach the outlet, the steepness 

 of the slope of the hill side would, by adding to the velocity 

 of discharge, lessen tbis difference ; but it is obviously 

 impossible to attain to anything like certainty in such a 

 question. 



