80 BULLETIN 1026, V. S. DEPARTMENT OE AGRICULTTJEE. 



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 comparativelj^ small but it is very vital to both the North 

 Poudre and Larimer County canals. It becomes aA^ailable 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 plan's 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 by stored water. 



Drainage is not a serious problem in the valley. Only local areas 

 have become too wet, and corrective measures have always been 

 promptl}^ applied. 



By the sj^stem of exchange of water developed in the valley 50,000 

 acre-feet of stored water is made aA^ailable for use in canals above the 

 reservoirs. To this system ma}^ 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- 



