IRRIGATION IN NORTHERN COLORADO. 17 
So many varying factors determine the time any right may draw 
from the river that it is impossible to make any statement in this re- 
gard which will not be inaccurate under certain combinations of cir- 
cumstances. It is generally true, however, that appropriations up 
to and including priority No. 25 are satisfied throughout the season, 
while the original appropriations of the Larimer County and North 
Poudre Canals, priorities No. 100 and No. 97, draw only from 1 
to 3 weeks during June. Between these two extremes are a large 
number of appropriations which fail chiefly in August. Several con- 
ditions tend to increase the length of time the later appropriations 
may draw. Usually there is plenty of rain in the early spring to 
get the crops started and the older appropriators call for their water 
only when it is really needed, thus permitting the later rights to 
draw the available supply. Later in the season some of the oldest ap- 
propriators may cut back to the river a part of their supply, or it 
may be taken in at the head but wasted back to the river through 
lower wasteways. When the Pleasant Valley and Lake Canal has 
an excess of 10 to 20 second- feet which it will not need for 24 hours it 
is usually cut back to the river at the Bingham Hill waste, though 
it might be carried on through the canal and tailed into Fossil Creek 
to reach the river again through the outlet of Fossil Creek Reservoir. 
The return water of the stream is of great importance in stretching 
the period during which the later rights may draw. During the sum- 
mer this return is sufficient to supply a considerable part of the de- 
mand below the Larimer and Weld Canal, which permits a corre- 
sponding amount to be drawn from the river by later rights above. 
This return is of especial benefit to the Ogilvy Ditch, which is the 
lowest on the river. Its right is junior to practically every other 
right on the river, but the return water to the stream affords it a suf- 
ficient supply for the greater part of the season in average years. 
The year 1916 was nearly normal and the dates on which the various 
rights failed that year may be assumed to be close to the average. 
Ordinarily it would be expected that on a small stream like the 
Cache la Poudre the flow of the stream at the head of the irrigated 
area would bear some close relation to the aggregate of the rights 
prior to the right cut-off, but this does not hold true. The return 
of seepage, water wasted back from canals, foreign water carried, ex- 
change water turned into the river, low demand, and excessive de- 
crees all upset any calculation along this line. The appropriation of 
the Larimer County Canal, priority No. 100, was cut on June 29 
when the river at the canyon station was carrying approximately 
1,480 second-feet. The rights senior to the right of the Larimer 
County Canal aggregate 3,600 second- feet. 
74464°— 22 2 
