Of a Country on the Climate. 219 
Practical Applications: Reservoirs. —In surveying the 
drainage area of a river, with a view to ascertain the actual 
available supply, it is absolutely necessary to have the most 
accurate information respecting the geological formations ; 
not only to determine the amount of surface-water which 
may reach the river basin, but to learn what portion of the 
rainfall is retained in the strata, which can also ultimately 
flow thither. In this country, if the hills are very high, they 
will retain a certain proportion of water, which may either 
flow to the river basin, or descend to great depths. 
We have immense floods in winter, and almost dry beds in 
summer; and hence it is exceedingly difficult to compute the 
mean annual discharge of any river. It would, manifestly, 
be wrong to compute the mean annual discharge, by taking 
the lowest summer level and the highest winter level: the 
latter might represent the condition of the river for one day 
only, and the former for 200 days out of the 366. 
The only discharge on which a calculation can be founded 
for practical purposes, is the lowest, or rather the average 
summer level. It is upon this supply that we must depend, 
most certainly, if the requirement is for sanitary purposes ; 
for it would be manifestly highly injurious to the health of a 
town to store surface-water, in a climate such as this, in an 
open reservoir. Let me express myself more clearly on a 
point which is all-important in Australia. The summer cur- 
rent of the river must be carefully measured, and it ought to 
bear a certain proportion to the consumption. For example, 
if the consumption is 100,000 gallons per diem, it would be 
well to have a permanent stream, equal at least to 25,000 
gallons; but in this proportion I would rather indicate a 
principle than assert a fact. If the surface-water is collected 
where basaltic rocks abound, the supply of running water 
should be proportionably greater, because the soil, in such 
localities, is charged with decomposing vegetable matter. If, 
on the contrary, sandstone rocks abound, a smaller supply of 
pure water might suffice. to render the drainage water 
Annoxious. 
When I attach so much importance to the summer stream, 
I do not mean to assert that it is impossible to collect the 
winter rains, or that such a method is always objectionable. 
It is only objectionable when it is largely in excess of the 
permanent current. Setting aside all difficulties attending 
the formation of an impervious reservoir, it is exceedingly 
hazardous to rely upon winter rains. The climate of Victoria 
is very peculiar. For many months in the year we have 
