154 Failure of the Yan Yean Reservoir. 
and a half inches: so that, deducting two feet five inches, 
there will only remain nine feet one and a half inch, or just 
sufficient to cover the evaporation from the surface. 
In the meantime, therefore, until such means are adopted, 
it may safely be asserted, that there will be no water for the 
city at all: and it is rather a singular circumstance, that if 
we are to get any supply for the city, it must be by saving 
the two feet five inches that are at present lost by evaporation, 
and very probably also by absorption in the swamps, and if 
this can be done, there will be a supply for 71,500, at forty 
gallons per head per day. 
To bring both arms of the Plenty to Yan Yean, clear of 
all loss from the swamps, would be a very difficult undertaking. 
The swamps are only to be likened to large sponges, and 
simply to cut a watercourse through them, and lower their 
level, would have very little effect in withdrawing the stream 
from their influence. : 
The evaporation would continue nearly the same, and would 
be fed from the current. The eastern swamps are about three 
miles in length, the western five miles; and I am strongly of 
opinion, that the loss from evaporation and absorption, could 
be saved in no other way than by conveying both branches in 
iron pipes. 
Mr. Christy has kindly favored me with an estimate of the 
cost of laying suitable pipes for this purpose, which would 
amount to £14,000 per mile, or to £42,000 for the eastern 
branch, and £74,000 for the western. So that, after all, it 
may become a grave question, whether it be really worth 
while to go to any expense at all to save either branch from 
the evaporation of the swamps. 
I have also taken for granted that we shall have sixty hours 
of floods each year at Yan Yean, while it is not unusual to 
have no floods at all; and I have allowed an increase in the 
Plenty of two-thirds, during the three winter months, for 
rain; although we sometimes, as last year, have very little 
rain in winter, and I have allowed a rainfall of thirty- 
six inches for the reservoir, although it is very doubtful 
whether there really is that average at Yan Yean. And, I 
may well ask, what became of the thirty-six inches of rainfall 
in 1851? I have no doubt that there isa larger and more 
constant rainfall at the Dandenong Ranges; but they are 
much nearer the Bay than Mount Disappointment, and there- 
fore attract and intercept the rain-clouds, and it is well known 
that there is a greater rainfall near the coast than further in- 
