58 
SEEPAGE OR RETURN WATERS FROM IRRIGATION. 
WILL THIS INVESTIGATION APPLY TO OTHER VALLEYS? 
§ 56. In the valleys here measured irrigation has been prac¬ 
ticed for thirty-five years; to a small extent on the bottoms for 
twenty or twenty-five years, and extensively for fifteen years. In 
the case of the Poudre, the lands are some of them twelve or fifteen 
miles from the stream. On the Platte, they occupy a much nar¬ 
rower strip. The conditions of the subsoil, the amount of water 
applied, the dip of the impermeable stratum of clay or rocks, the 
coarseness of the gravel, all affect the time and amount of the 
return. But given time enough, it seems probable that these results 
will apply closely to other valleys as well. A certain amount of 
water is required by the crops for the purposes of growth. In round 
numbers, 300 to 350 pounds of water is used for every single pound 
of dry matter produced. On some soils it is possible by skillful irri¬ 
gation to apply but little more than is required by the crop and 
evaporated from the soil. Under such economy, there is little water 
which can pass away by percolation. To the economical irrigation 
induced by scanty and high-priced water is due the little or no 
return water noticed in Southern California. This is also influenced 
by the relatively small acreage. The narrow strip of the lower Platte 
and the more copious irrigation explain partially, if not entirely, 
the larger amount returned to the stream per acre, while the remote 
places of application on the lands of the tributaries of the Upper 
Platte shows a reason why the inflow there is relatively less. These 
may not completely explain the difference. Time, and added obser¬ 
vations, will be needed to determine. 
The same or similar phenomena have been observed to some 
extent elsewhere. 
“ When the Ganges canal was constructed, the whole available 
“ cold season supply was taken from the river, yet at a distance of 
“ only a few miles the discharge in the river was found to be very 
“ considerable, and further on it increased to such an extent that the 
“ supply taken by the canal was found to be little missed.” * 
§ 57. In Italy the effect of irrigation does not seem to have 
been noticed in the rivers, but principally in the large number of 
springs to which irrigation seems to give rise, and which are devel¬ 
oped by digging in Lombardy and other provinces, and which the 
geological conditions do not seem to be sufficient to account for. 1| 
The losses from canals is well known, and the damages caused 
to neighboring lands by the seepage is a fruitful source of suits at 
law. In the contract of the Cavour canal with the Sesia Associa- 
*H, G. McKinney, Irrigation in Upper India, paper before the Royal 
Society, New South Wales, 1883. 
II Cagnassi, Irrigazione nella Provincia di^Novara. 
