10 BULLETIN 1026, U. S. DEPARTMENT OF AGRICULTURE. 
season instead of reservoir water to provide for an irrigation after 
canal supplies fail. 
The total amount of seepage return to the river, exclusive of that 
coming through regular channels, is about 110,000 acre-feet annually. 
During the winter months only the return above the intake of the 
Cache la Poudre Reservoir may be used, and this is estimated to be 
about 8,000 acre-feet, During the summer months canals on the 
lower reaches of the river depend to a considerable extent on this 
return flow to satisfy their rights, and it is estimated that during 
these months 51,000 acre-feet are available for their use. Combined, 
the total available flow for the year is 59,000 acre-feet. 
To summarize, the water supply of the valley includes a normal 
run-off of 340,000 acre-feet in the river and its tributaries, 35,000 
acre-feet of foreign water, 5,000 acre-feet pumped from Avells, and 
available seepage to the amount of 84,000 acre-feet, a total supply 
of 464,000 acre-feet. This supply in the course of time will be in- 
creased slightly by pumping and by a greater return of seepage, but 
any material increase seems improbable. 
With the exception of very short periods during high floods, the 
entire available flow of the stream is taken on rights which have 
been in existence for years. There is an occasional surplus subject 
to storage, but because of the uncertainty attaching to it and the 
probable high cost of developing it, the feasibility of such a supply 
is highly questionable. The demand on the river in June the month 
of maximum flow, is close to 120,000 acre-feet, 4 which is equivalent 
to an average flow of approximately 2,100 second-feet. From Table 
2 it appears that the river has failed to reach that discharge in 18 
of the 33 years covered by the records. To produce a surplus of 
20,000 to 25,000 acre-feet a discharge of at least 2,500 second-feet 
would be required during June, and such a discharge occurred in 
only 9 of the 33 years covered by the records. From this it is clear 
than any further storage projects would have to depend on a surplus 
which would be of considerable size only about once in 3 or 4 years. 
The amount available annually for use from such a supply would 
be very small and very costly. 
SEEPAGE RETURN. 
One of the questions of particular interest now in many irrigated 
valleys is that of seepage return to streams. It is a well-known fact 
that, with the extension of irrigation, this return has so increased 
that canals on the lower reaches of the rivers, which once suffered 
seriously because their rights would not be satisfied, are now plenti- 
fully supplied with water. In the Cache la Poudre Valley the 
effect of the seepage return is very marked. Late in the season it 
is often the case that the river is dry in several places, yet a number of 
4 See Tables 7 and 8. 
