180 TANKS AND WELLS OF NEW SOUTH WALES, 
spasmodic nature of the rainfall, very variable ; some seasons givea 
full river for months at a time, while there are equally long periods 
during which the flow is insignificant. To meet these variationsand 
to equalize the supply that must be provided for irrigation, im- 
pounding works are the first necessity, and there is little room for 
doubt that this must be carried out, not only in the comparatively 
level reaches of the rivers, but more particularly in the middle and 
upper courses of the main channels and their tributaries. 
on the frontages of the lands to be irrigated, will meet the require- 
ments of the case; but a little consideration will show that any 
such limited supply would be quite inadequate for any broad irri 
gation scheme, and that the cost of the works to carry such a plan 
into effect would be out of proportion to the benefits derivable from 
would have to be raised by steam or wind power. The con 
struction of weirs in the alluvial country characterizing the lower 
reaches of the western rivers of this Colony would be a very costly 
undertaking, on accountof the difficulties that would be experienced 
lay. This, however, cuts both ways, as it reduces the quantity 
water at disposal for irrigation by the depth that would have to 
main for navigation ; but apart from this, it is bear 
