CHAIRMAN’S ADDRESS. XXXVII. 
streams, draining from a catchment area of about 97 square 
miles, or 250 square miles less than we have to rely upon. 
The geological formation of the area, however, enables the 
ground to absorb and retain the rainfall as in a vast sponge, 
and the stream flow is therefore larger and more constant 
than from sucha formation as the Hawkesbury Sandstone. 
Having so good a supply from the streams, they provided 
only a storage amounting to about 6,400 million gallons, or 
a little more than half Prospect. This reservoir was built 
about the year 1850, and if the Melbourne rainfall diagram (3) 
be consulted, it will be seen that the season of drought had 
then been passed, and good rains had been experienced for 
several years, thus raising the level of the ground water, 
which was maintained without much fluctuation until 1875, 
when a slow, but persistent decline in the rainfall com- 
menced and extended for 23 years, so that in 1898, the 
accumulated loss of rain, as shown by the residual mass 
curve, amounted to 47°49 inches. This must have affected 
the level of the ground water, and consequently of the 
stream flow, which was probably reduced to what it stood 
at in 1843. During the following six years up to 1904, a 
slight rise of only 8°15 inches occurred; but the next three 
years up to 1907 have reduced it again to what it stood at 
in 1898. 
The situation, with regard to the water supply in 
Melbourne must therefore be regarded as most serious, in 
view of the fact that the reservoir is now at a very low 
level, the main dependence being upon the daily flow of 
the streams, whose source, viz., the ground water, is shown 
by the diagram to be probably at the minimum, or very 
close toit. With this example before us, it is obvious that 
no dependence should be placed upon the stream flow in this 
country, and that large storage is absolutely necessary, in 
order to supplement the supply derivable therefrom, during 
periods of drought. 
