Failure of the Yan Yean Reservoir. . 121 
gallons per minute, at the time when the committee measured 
the eastern arm. The whole discharge above the swamps was 
therefore 5,790 gallons per minute, and below the swamps 
2,537 gallons. 
In this manner we ascertain that the loss by evaporation 
in the swamps amounted to 3,253 gallons per minute, which 
is at the rate of 4 feet 4 inches in the reservoir; and as the 
area of the swamps is one half less than the area of the 
reservoir, 8 feet 8 inches will represent the rate of evapora- 
tion in the swamps during the summer months. 
It is thus easy to understand why Mr. Blackburn and Mr. 
Hodgkinson so strongly urged the necessity of making arti- 
ficial watercourses, in order to withdraw the two branches 
of the river from the influence of the swamps. 
It does not appear that the Commissioners of Sewerage 
and Water Supply have any present intention of doing this, 
and I am not sufficiently acquainted with the levels and 
depths of the swamps to give any opinion as to the best mode, 
but it is quite clear that some steps must be taken to save 
the immense loss that is at present occasioned by them. And 
in estimating the quantity of water that will be available for 
the reservoir I shall assume that some effectual means will be 
adopted to accomplish this very desirable object, and that the 
whole of the 5,000 gallons may be transferred into the reser- 
voir without loss. 
The measurements would not be complete without men- 
tioning, that Dr. Mackenna and myself, on our visit to Yan 
Yean, measured the Plenty where it passes under the bridge, 
about three miles below the reservoir, and obtained a discharge 
of 960 gallons per minute, which would give a depth in the 
reservoir of 1 foot 3 inches. The measurement of the 
committee at the same place, on their late visit, gave 475 
gallons per minute, which is equal to 8 inches in 12 months. 
These small results compared with the measurement above 
Yan Yean arise from the quantity of water that is abstracted 
by a cut for the purpose of puddling the embankment. 
I have thus assumed Mr. Blackburn’s highest estimate of 
5,000 gallons per minute as the average of the whole discharge 
of the tributaries of the Plenty. In the drought of the 
summer of 1851, however, Mr. Blackburn found this amount 
reduced to 4,040 gallons; and therefore it is to be presumed 
that 5,000 gallonsare only to be depended on in ordinary seasons. 
The important question now arises, what proportion of the 
5,000 gallons can be abstracted from the river without inflict- 
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