Failure of the Fan Yean Reservoir. 



119 



nmg, IS gradually augmented by innumerable rills and streams 

 issumg irom the moist rotten soil and from the fissures and 

 crevices of the rocks. Both branches, at the base of the 

 mountain are discharged into large swamps; and it is not 

 until they issue again from these that they unite to form the 

 -t-ienty Kiver, about four miles from Yan Yean. The area of 

 the western swamp, according to the estimates of your Com- 

 mittee, is 787,000 square yards, that of the eastern, 3,808,000 

 square yards. 



These streams have been measured at different times and 

 under different circumstances, with the following results. 



Ihe late Mr. Blackburn, in his first report on the water 

 supply of Melbourne, dated 9th January, f851, states that 

 he fiad measured two of the branches of the Plenty, above 

 the marshes, and found them to discharge respectively 2,000 

 and 1,700 gallons per minute, and he estimated that the whole 

 discharge of the tributaries amounted to 5,000 gallons per 

 minute which is equal to 6 feet 7 inches in the reservoir 

 wnile the united stream below the marshes scarcely gave 2 700 

 gallons per minute, or 3 feet 7 inches. There was thus a loss 

 by evaporation of 2,300 gallons per minute, which would give 

 6 feet m the reservoir, in twelve months. 



There being an unusual drought in the summer of 1851, 

 Mr. Blackburn, on two separate occasions, revised his former 

 measurements ; on the latter occasion, the 14th February he 

 found the discharge of all streams above the swamps amount 

 to 4,040 gallons per minute, which equals 5 feet 4 inches in 

 the reservoir, and in the river below the swamps he found 

 only 865 gallons per minute, or at the rate of 1 Voot 1 inch 

 in the reservoir, showing a loss by evaporation of 3,175 o-allons 

 per minute, which would give 4 feet U inch in the reservoir 



Mr. Hodgkmson, on the 9th December, 1852, after fifteen 

 hours rain, measured the western arm, where it issues from 

 the granite rock, and estimated the discharge at 1,180 o-allons 

 per minute, or 1 foot 7 inches in the reservoir; he also 

 measured the same stream, where it enters the swamps, and 

 found It to give 1,700 gallons per minute, or 2 feet 3 inches. 

 Un the following day he measured the eastern arm, below the 

 first waterfall, and found it to discharge 1,980 gallons per 

 minute, or at the rate of 2 feet 7i inches in the reservoir. 



The first of Mr. Hodgkinson's measurements is the one of 

 most value m this inquiry, as we may presume that the stream 

 where it issued from the rocks, was little affected by the' 

 previous ram. The second measurement was taken at a 



