IRRIGATION IN NORTHERN COLORADO. 69 
RESERVOIRS. 
The settlement of the Cache la Poudre Valley proceeded very 
rapidly after 1870 and the consequent extension of irrigation soon 
brought out the necessity for reservoirs. The stream was over-ap- 
propriated and as the irrigated area under early canals increased, the 
later canals suffered more and more from shortage of water. Con- 
ditions under the older canals became acute when continuous grain 
cropping had exhausted the land and the farmers were compelled 
to turn their attention to more profitable crops such as alfalfa, po- 
tatoes, and later, sugar beets. These crops required irrigation later 
in the season when water was available for only a few small ditches 
with early priorities. To meet these conditions the construction of 
reservoirs became general and has continued until nearly all the culti- 
vated land of the valley is supplied to some extent with stored water. 
This is clearly shown in -Plate XV, given to afford a comparison 
between the total area irrigated in 1916 and the area which received 
reservoir water that year. 
With reference to organization, the reservoirs of the valley may be 
divided into 3 classes. The largest class is made up of small private 
reservoirs built by the individual to make the best use of a small head, 
to free himself from the limitations imposed by rotation periods, or 
to save a few acre-feet for a late irrigation. The second class includes 
the reservoirs which are owned as a part of a canal system and 
store water to be distributed as a part of the general supply. The 
majority of the reservoirs of this class belong to either the North 
Poudre Irrigation Co. or the Water Supply & Storage Co. The 
canals owned by these companies were constructed in 1881 and 1882 
and as it was realized from the start that a sufficient supply of water 
could not be obtained by direct appropriation the construction of 
reservoirs was begun immediately. The third class includes the reser- 
voirs owned by cooperative companies and supplying water to stock- 
holders under canals which act as common carriers. Usually there 
is no legal connection between the reservoir company and the canal 
company, but in many cases a majority of the stockholders of the 
two companies are identical. 
Reservoirs in the valley are supplied by natural streams ; by seep- 
age from canals, irrigated land, and other reservoirs; and by run- 
off from some normally dry catchment area during torrential rains. 
The great majority of the larger reservoirs take their supply from 
the Cache la Poudre and its tributaries, but a number are also sup- 
lied wholly or in part with foreign water. With the extension of 
irrigation, seepage from canals, reservoirs, and irrigated lands be- 
comes important as a source of supply and many small reservoirs are 
now almost wholly dependent upon it. Only a few reservoirs are de- 
