160 Failure of the Yan. Yean Reservoir. 
From the data which I have presented to you, it will be 
observed that there is a sufficient supply in the eastern arm 
of the Plenty for the present population of the city. The 
discharge of this main branch in January, was 4,450 gallons 
per minute, and deducting 630 gallons, which I have done 
to compensate for the previous heavy rains, and to assimilate 
the amount to Mr. Blackburn’s estimate for ordinary seasons, 
we have 3,820 gallons per minute, which is equal to five feet 
one inch in the reservoir, and would, therefore, suffice for a 
population of 138,600, supposing the whole to be conveyed 
in iron pipes without loss. Here, then, is one source of 
supply, and the water is pure and unexceptionable. 
But there are certain considerations of great moment con- 
nected with this source. 
In a dry summer, such as that of 1851, the supply would, 
according to the measurements of Mr. Blackburn, be reduced 
by one-fifth, therefore this source can only be depended on 
to afford a constant supply for a population of 110,000. And, 
according to Mr. Blackburn and Mr. Hodgkinson, a drought 
of eight months, or of one year’s duration would diminish it 
still further, if not dry it up altogether, as the western arm 
has been more than once. 
Another very weighty consideration is, that the present 
stream of the Plenty is entirely dependent on the eastern 
branch for its supply, the western being evaporated and lost 
in the marshes. If this supply therefore is cut off, the 
Plenty will cease to run altogether, unless the western arm 
be conveyed for a distance of five miles clear of the swamps, 
which I fear will be found a difficult and expensive operation. 
It could be done without any loss by laying a thirty-six 
inch pipe; but the cost, according to Mr. Christy’s estimate, 
would be 70,0002. 
By adopting efficient means to save the western arm from 
evaporation, and to restore it to the natural channel below the 
swamps, the stream might be maintained, notwithstanding 
the appropriation of the eastern arm for the use of the City. 
The Government and Legislative Council have therefore 
seriously to consider if it be right or proper that this rapidly 
increasing City should be dependent on a source which is 
only equal to supply a population of 138,500 in ordinary 
seasons, and 110,000 in very dry summers, and in severe 
droughts perhaps nothing at all. And it is very important 
to bear in mind, that if we are to pay for bringing water by 
gravitation from a distance of twenty-five miles, we are not: 
