lEEIGATION IlSr NOETHERISr COLOEADO. 51 



difference indicating a loss of 41,000 acre-feet, or approximately 10 

 per cent of the supply. In 1917 a demand of 435,000 acre-feet deter- 

 mined in a like manner was satisfied with a supply of 414,000 acre- 

 feet, the difference indicating a gain of approximately 5 per cent. 

 In view of the heavy rainfall of May, 1917, and the very large heads 

 carried by all the canals in June and July of that year, it is believed 

 that these approximations are in substantial accord with the facts. 

 Conditions in 1916 were nearly normal and for that reason the as- 

 sumption may be safely made that the average net loss in the canals 

 between the head and the farm lateral is close to 10 per cent of the 

 supply. This low figure is probably accounted for by the location 

 of the canals one above another with the consequent inflow of seepage 

 to counteract a part of the loss. 



These figures indicate that absorption losses account for only a 

 small part of the tare for losses charged by some of the common- 

 carrier canals of the valley, and that most of it must go to make up 

 inequalities of distribution. Under the present system each user 

 receives at least his share after the tare has been deducted; but to 

 take care of the inequalities of distribution and operation difficulties 

 there is practically always a surplus in the canal which must go to 

 some one to prevent its waste. It is possible that by spending a few 

 thousand dollars for hire of extra riders and reducing the " beat " to 

 a distance which will permit 2 or 3 visits every day to all gates and 

 weirs to keep them clean and delivering the proper head, at least 

 one day's run and perhaps two or three might be added each season 

 to each reservoir right. 



SEEPAGE SUPPLIES. 



Practically the entire acreage irrigated in the valley is supplied to 

 some extent with seepage water which has been collected in a reser- 

 voir or has returned to some channel, but the land dependent on 

 seepage as its main supply is limited to the areas shown in Plate XIV. 



FARM IRRIGATION. 



While there are some exceptions, the trend of irrigation practice in 

 the valley now is toward a frequent, rapid irrigation, which gives an 

 even watering, minimizes percolation losses and end waste, permits 

 the use of a large head with a consequent economy of time, and keeps 

 the crops growing under moisture conditions with a minimum varia- 

 tion from the optimum. 



Only two methods of irrigation are practiced. Alfalfa and grains 

 are irrigated by flooding from field laterals. Sugar beets, potatoes. 



