DAMAGE BY FLOODS IN RIVERS PREVENTION. 64] 
than ever.’ Also, Mr. Gustav Dyer, speaking of the work 
of the Mississippi Flood Commissioners, says:—‘‘ Outlets in 
any form, whether waste weirs, reservoirs, or water-woys 
connected directly with the sea, all come under the same 
head and require the same treatment; each part of the 
volume of which the main channel is temporarily relieved 
will require a proportionate expenditure for construction 
and maintenance, and the object in view will fail of accom- 
plishment. The Mississippi Commission has accordingly 
striven to raise the levees and dredge the channels, and 
concentrating the scour by groins so as to get uniform 
velocity.’”’ Both these authorities deprecate tampering with 
the main-channel of the river with the view of relieving floods ; 
in fact, the practice of the Mississippi Commission to raise 
levees, and at the same time clear out and improve the 
river-channel, is about the best thing that can be done; but 
to cut by-washes, outlets, or relief-channels, is certain to 
produce very injurious changes in the regimen of the river. 
Fortunately, these attempts to relieve floods are seldom 
permanent; sooner or later the river either takes entire 
charge of the relief-channel or silts it up; but if the relief- 
channel can be, and is maintained, then the main river 
suffers by silting up.in just the same proportion as the 
quantity of water that is taken from it by the diversion. 
The people of Rockhampton lay great stress on the fact 
that they are protected from the height of floods in the 
Fitzroy River by an overflow above the town, which they 
say cuts off many feet of the height of floods. The over- 
flow is of great width, but I have seen no calculations to 
show how much the height of floods is reduced by it; but 
the damaging effect on the bed of the river below it which 
usually follows such diversions is now not evident, as the 
bed is all rocks, as far as Rockhampton, and below the town 
the water of the overflow returns into the river through 
many creeks and channels. 
As the most likely way of controlling the floods of a 
river seems to be to improve its channel, it is important 
to consider what forces and influences are opposed to such 
works. i 
Very few, if any, rivers are able to contain their own 
floods within their banks at all parts of their course. This is 
due to many causes, such as different height of the banks, 
varying width of the river, differences in the hardness of 
the strata composing the banks and bottom, differences in 
the gradients of the river, and, as a result of all these, 
the inability of the river to dispose of its own sediments. 
R2 
