On Irrigation in Tasmania . 181 
very formidable obstacles. The river consists (I believe, 
from the highest point occupied) of a succession of broad, 
and deep reaches, extending from £ to 2 miles in length, 
in which the current is from J to 2 miles per hour when 
the river is low, and from 2 to 4 miles per hour in high 
freshes. These are separated from each other by rapids, 
in which the river has a fall of from 2 to 6 feet in a 
distance of 100 or 200 yards. In the highest part of the 
river, where there is much improvable land—viz. near 
the mouth of the Big River—the fall was found by levelling 
to be 12 feet per mile; and it appears, like the generality 
of rivers, to have less fall as it approaches the tidewater: 
the total fall may, therefore, be 300 feet between the Big 
River and New Norfolk. This tract of country is ex¬ 
tremely valuable, and at the same time particularly unfa¬ 
vourable for the construction of roads. The principle 
upon which improvement of this river should be con¬ 
ducted appears to be, that it should not be attempted to 
make it a very complete navigation in the present state 
of things, but rather to employ upon it as small a capital 
as will suffice to make it available for small steamers. 
There are three plans which may be adopted : the first 
is, to cut a canal along one side of the valley, to be filled 
at its head from the river; and in that case it would, of 
course, be advisable by the same means to provide for 
the complete irrigation of the whole of that side of the 
river: this would not be by any means a very difficult 
undertaking, though the expense would be great. If it 
were led off from the river a few miles above the Big 
River, where the fall is 12 feet per mile, it would in the 
course of 6 miles attain a level of GO feet or more above 
that of the Derwent; after which, as there would be so 
great a choice of level, the cuttings would not be very 
enormous; and it would be carried across the torrents 
that come from the southward on timber aqueducts. This 
