On Irrigation in Tasmania . 186 
side, would be greatly facilitated by the previous con¬ 
struction of the dams at the lakes ; because, by keeping 
their sluices shut, the stream in the river might be kept 
low. The advantages of either of these latter plans 
would he¬ 
ist. Only a very moderate capital would be required 
to open the navigation as high as the Big River. 
2 nd. It would benefit equally both sides of the river. 
3rd,—which is very important,—the plan would not 
involve the execution of the whole undertaking at once. 
If the work was begun near New Norfolk, every rapid 
that was surmounted would be in itself a complete work, 
as it would open so many miles of navigation, and then 
as the work proceeded the total expense would soon be 
ascertained correctly, and at the same time what 
was expended would produce a certain extent of ad¬ 
vantage. The work at the last rapid, about 2 miles 
above New Norfolk, would allow the steamers to go 4 
or 5 miles above the point where the steamers at present 
stop, and so on. The current between the rapids is very 
moderate ; and it must be remembered that the boats 
would never be fully loaded in going up. 
What the noble valley of the Derwent would become, 
were it fully irrigated and the navigation open, it is not 
easy to imagine : it would certainly be one of the most 
beautiful and valuable tracts of country in the colonies; 
and, upon a consideration of the subject, it seems scarcely 
possible that the increase in the saleable value of the 
estates alone would not abundantly justify the expendi¬ 
ture necessary, independent of returns in money from the 
profits of the navigation. I have not the means of 
giving more than this rough sketch of what might be 
done for the improvement of this valley : if a company 
were formed, and a small sum subscribed, a complete 
survey and estimates might be prepared, from which a 
