188 Transactions. — Miscellaneous. 



been of sufficient 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 Avith 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 suflicient 

 provided proper discharge tunnels could be driven through rock, they, 

 however, do not answer so well as masonry, where liable to stand diy for 

 any length of time, as sun- cracks and vermin imperil their stabihty when 

 the next floods are impounded. 



The other methods of dealing with the case, such as enclosing the flood 

 waters by eubankments running parallel with the course of the river, 

 enlarging the chaunels, 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. 



