Notes on Hydrology. 



97 



Sydney we find that one inch fell in six minutes on one 

 occasion. One inch on ten acres will supply 36.300 cubic 

 feet, nine-tenths of which is 32,670 cubic feet. Again, sup- 

 pose the inclination of the culvert, when of the proper size, 

 to be such that the water will flow when full- six feet per 

 second, then the maximum discharge will be when the 

 most distant particle, together with particles from every 

 portion of the area, has reached the culvert — hence the area 

 required will be fifteen feet sectional area of waterway, or 

 one and a-half feet per acre, and it could not be larger. 



Now, if we assume a river five hundred miles long, area, 

 say, fifteen thousand square miles, say two hundred hours for 

 water to travel, and one-half held back, then the maximum 

 flood will be after two hundred hours' continuous rain ; less 

 would not make a maximum, and more would only maintain 

 the maximum. Suppose the heaviest two hundred hours' 

 rain to be five inches, and velocity of flood ten feet per 

 second, we should then. have — 

 -c. ft. per Sq. Mile. Sq. Miles. Inches. 



2,300,000 : 15,000 = ^ ^ ft _ 



200 hrs. 



3600 sees, x 10 ft. per sec. 



= | sq. ft. area per square mile. 



A chalk or sandy basin may absorb the whole of a heavy 

 rain. 



I will conclude with the observed maximum discharge in 



cubic feet per minute per square mile of several rivers and 



watercourses, partly from Beardmore and other sources. 



Maximum discharged 

 Name. per minute 



per square mile. 



36 cubic feet 



67 



428 



193 



129 



960 



592 



1,110 



18,888 



2,094 



544 to 900 



6,000 

 15,400 



Area of 

 Watershed. 



600,000 square miles 

 886,000 



180,000 



3,890 



3,086 



4,570 



35,000 



20,000 



900 



71 



98 to 100 



100 



15f 



Nile at Cairo 

 Mississippi 

 Ganges at Benares.. 

 Severn at Gloucester 

 Thames at Staines 

 Shannon at Killaloe 

 Rhone at Avignon 

 Garonne 



Ardeche, 1857 .. 

 Loch Katrine 

 Ireland 



Coliban, Victoria . 

 Bendigo Creek .. 

 Hargraves St., Sdst. 56,000 

 Exhibiting enormous differences. 



