118 Failure of the Yan Yean Reservoir. 
population to be provided for. Mr. Blackburn declined 
giving an opinion on this head, and I think the Select Com- 
mittee were wrong in limiting the number to 100,000 for the 
modified gravitation scheme that was to cost 162,0002, but 
they are in no way identified with the more costly scheme of 
the Commissioners. A gravitation scheme, involving an 
outlay of 650,0002. of public money should not be limited to 
any amount of population short of 500,000. In other words, 
it should not be commenced at all until an ample supply of 
water for 500,000 be secured. 
The population of Melbourne, with its suburban towns and 
villages, is little short of 100,000; and the amount required 
for this number, at the rate of 40 gallons per head, per day, 
would be equal to 8,690,476 cubic yards. Now, as the area 
of the reservoir is 7,000,000 square yards, this amount of 
water would give a depth of 3 feet 8 inches in the reservoir, 
and a population of 500,000 would require a depth of 18 feet 
4 inches. 
Let us now inquire what amount of water can be supplied 
to the reservoir. 
The main feature of the Yan Yean scheme is the large 
reservoir, or natural basin, which has an area of about 1450 
acres, and a surface of about 7,000,000 square yards, and into 
which it is intended to direct the greater part, if not the 
whole of the watershed of the Plenty basin. 
For this purpose an aqueduct of about two miles in length 
is being now formed to lead the river into the reservoir, and 
a large embankment is being raised at the lower end to the 
height of thirty feet; and, as it is expected that the river will 
more than fill the reservoir, and that it will maintain a current 
through it, there is a waste wash at the height of twenty-five 
feet to lead back the surplus water to the Plenty. A tower 
well has also been erected within the embankment, and is so 
arranged as to admit the water into the main pipes by two 
openings, at ten and seventeen feet, from the bottom of the 
reservoir. The third opening at the bottom of the tower well, 
as explained by Mr. Taylor, is only intended to draw off the 
impurities that will be deposited from the water. 
The Plenty takes its risein Mount Disappointment by two 
main branches, the eastern and the western. The latter, 
according to Mr. Hodgkinson, takes its source from a con- 
siderable stream which gushes direct from a fissure in the 
granite. The eastern branch, as we had lately an opportunity 
of witnessing, takes its rise from the table land at the very 
top of the mountain, and, from the smallest possible begin- 
