188 Transactions.— Miscellaneous. 
been of suflicient capacity to impound the amount of water brought down 
by a maximum flood of a few days’ duration, allowing it to pass gradually 
down the river in such a volume as the channel might be capable of carrying 
without injury; after which, when empty, it would be available to repeat 
the process. Though this plan appears to have been condemned for the 
purpose on large rivers such as the Loire, it is quite possible that there 
may be cases where, on smaller streams, subject to sudden heavy floods, it 
might be carried out with success. 
To attempt this plan in New Zealand, where there is little probability of 
its proving directly remunerative, nature must first be called upon to 
furnish a site where a storage basin would have a wide-spread area, easily 
enclosed at some narrow rocky gorge on the river to be treated. Such a 
site being found, it would (presuming that the fall of the ground be not too 
great) require a dam of only moderate height to impound sufficient water 
for the purpose. Unless such natural sites can be found, the cost would be 
out of all proportion to the results. Earthen dams would be sufficient 
provided proper discharge tunnels could be driven through rock, they, 
however, do not answer so well as masonry, where liable to stand dry for 
any length of time, as sun-cracks and vermin imperil their stability when 
the next floods are impounded. 
The other methods of dealing with the case, such as enclosing the flood , 
waters by enbankments running parallel with the course of the river, 
enlarging the channels, etc., are the most universally adopted, but are only 
applicable to rivers with a moderate fall, where the velocity of the current 
is not too great to destroy them ; they are by far the easiest to construct, 
though from too limited a knowledge of the floods and their effects, and 
from being usually undertaken piece-meal, without any general and well- 
considered design, they are liable to failure. The maintenance of this 
description of work is also very costly, entailing as it must do extensive 
reconstruction and repairs after each successive high flood. 
It is a most essential thing that all such works wherever contemplated 
should receive great consideration. It is impossible to collect too much 
information, both regarding the behaviour of rivers when low and in flood, 
as well as for a complete system of surveys and levels, in order to enable the 
manner of treatment to be determined. There is no branch of engineering 
so difficult to undertake successfully. 
