SEEPAGE OR RETURN WATERS FROM IRRIGATION.' 41 
then have an inflow reaching the Poudre of 104 cubic feet per second? 
from an application of 250,000 acre-feet, or a constant flow of one 
cubic foot per second from each 2,400 acre-feet applied. The amount 
is actually greater than 104 second-feet, because of the amount, at 
present unknown, which is caught by the seepage ditches. As one 
cubic foot per second corresponds to 724 acre-feet in the course of a 
year, there is a seepage return of 724 acre-feet from 2,400 acre-feet of 
water taken from the river. If the seepage from the outer canals has 
not yet reached the river, then an actual application of much less 
than the 2,400 acre-feet gives the observed return. What the exact 
proportion is cannot be determined in this valley for some years to 
come, after all the land irrigated furnishes its portion of the seepage 
to the stream. 
§ 30. Bringing together the amount of increase in different 
parts of the Cache a la Poudre and the area of irrigated land 
which drains into the same section, we have Table VII. In the 
third column is given the amount of water applied to that portion 
of the valley whose natural drainage is into the river between the 
points indicated in the first column In the fourth column is given 
the per cent, of the total amount applied to the whole valley. 
In the column headed “Computed inflow” is given the amount of 
inflow there would be if the inflow were in exact proportion to the 
amount of water applied. How much land will furnish underflow 
to a given part of the river cannot be very closely told, even with 
detailed knowledge of the topography and the location of the 
farms where water is applied. The course of the underground 
drainage can be told in most cases, until the river bottom is reached. 
Thence the channels often end in sloughs, and sometimes follow old 
river channels, or the water is collected in seepage ditches, which 
carry it sometimes for considerable distances. From our present 
maps the limit of the drainage areas cannot be told with sufficient 
accuracy to make the areas and the amount of water applied, given 
in the third column, anything but an approximation. The table 
shows, however, that the relation is close enough to be more than 
accidental, and in future years, when the influence of the outer area 
begins to be felt, may be expected to be closer. 
It show^s that there is a reason for the large amount of increase 
observed in the last few miles of the Poudre, before it empties into 
the Platte. 
In the case of the increase from the No. 2 canal to the Pump 
house, and from the Pump house to the Ogilvy ditch, it may be 
stated that a portion of the drainage above the Pump house enters 
the bottoms above that place, and does not enter the river until 
below that point. While the water applied is counted in the 
section above the Pump house, the seepage is included in the 
section below. It has not been possible to estimate this, and it is 
