93 
On Irrigation in Tasmania. 
insignificant stream in the upper part of the channel of a 
river is all lost : this is when the bed of the river is 
broad and shallow, and the stream proportionally very 
small. It is in that case, in fact, employed in irrigating the 
bed of the river, and is lost by evaporation; but only a 
very small quantity of water can be expended in this way. 
If the bed of a river is very broad and shallow, and it 
remains some months without water, it will of course 
absorb a considerable quantity of water when first the 
rains begin; but when once saturated no more can be 
absorbed. 
In the case of irrigating channels and canals, indeed, 
which are in the immediate neighbourhood of lower 
land, the case is quite different. If the soil is very light, 
the water will continually drain through it to the lower 
ground ; and in this case, in a few instances, it may be 
necessary to line an irrigating channel with clay, which 
is called puddling it: but, of the many thousand cases 
of irrigating channels that I have seen in India, I never 
knew an instance of its being necessary to do it to any 
great extent. IS ear the heads of channels, in gravelly or 
rocky soil, and where they run close to the side of the 
river, it is necessary sometimes to throw in clay a short 
distance ; but this is entirely different from the case of a 
river or tank, where, from their being lower than the sur¬ 
rounding ground, the water cannot drain out of them. 
Taking the quantity of water above calculated as re¬ 
quired per acre, it follows that one of the Lakes, contain¬ 
ing, suppose, 20 square miles, if closed at the outlet so as 
to retain the water one yard above its natural level, would 
supply 25,000 acres of grass land, or 60,000 acres of 
grain. 
[To be continued.] 
