80 BULLETIN 1026, U. S. DEPARTMENT OF AGRICULTURE. 
alone, best results would be obtained by quick irrigation to a depth 
of 0.4 to 0.6 foot. 
The water supply of the valley averages 464,000 acre-feet, which 
includes 340,000 acre-feet of normal run-off in the river and its tribu- 
taries, 35,000 acre- feet of foreign water, 5,000 acre-feet pumped from 
wells, and available seepage return to the amount of 84,000 acre-feet. 
Practically the whole supply is taken; and further projects, either 
for direct flow or for storage, are probably not feasible. 
The regimen of the river largely controls the cropping system of 
the valley. The flood stage of the stream occurs at such a time that 
the irrigation of at least a third of the acreage in crops, chiefly grain, 
may be completed with water drawn directly from the river. This 
leaves the stored water to be used for maturing such valuable crops 
as sugar beets, potatoes, etc. 
The foreign water brought into the valley from other drainage 
basins is collected from the highest slopes of the mountains, and it 
therefore comes down after the peak of the flood has passed. This 
supply is comparatively small but it is very vital to both the North 
Poudre and Larimer County canals. It becomes available shortly 
before their main appropriations are cut off and makes it possible to 
delay for from one to three weeks the time when almost the whole 
demand must be met with stored water. 
The total seepage return in the valley is 137,000 acre-feet, which 
is approximately 36 per cent of the normal water supply (exclusive 
of seepage). The topography is such that a large proportion of this 
seepage return is available for use, and it plays an important part in 
irrigation in the valley. The high percentage of return indicates 
that when the return reaches the maximum on other streams many 
water rights, both direct and storage, which are now not dependable, 
will become good. The certainty and uniformity of this supply will 
produce results comparable to those produced b}^ stored water. 
Drainage is not a serious problem in the valley. Only local areas 
have become too wet, and corrective measures have always been 
promptly applied. 
By the system of exchange of water developed in the valley 50,000 
acre-feet of stored water is made available for use in canals above the 
reservoirs. To this system may be attributed the use of a number of 
sites capable of cheap development. Incidentally, as perfected in 
the valley, the system promotes a better distribution from the river 
and vastly improves conditions under which the canals operate by 
largely confining the daily fluctuation of the river to one of the 
larger canals where it can be " smoothed down " by the use of reser- 
voirs as regulators. In addition, the pooling of interests required 
by the exchange has brought about a better understanding between 
the canal men of the valley and there is now a tendency to get to- 
