IKRIGATIOlSr IN NORTHERN COLORADO. 83 



and in a straight section of canal with no curves for some distance 

 either above or below. The velocity through them should be suffi- 

 cient to prevent the deposit of silt, but not high enough to produce 

 waves. There should be no drop immediately below to produce 

 standing waves. They should not be subject to backwater from mov- 

 able checks, and they should not be placed close below gates which 

 either do, or may be made to, discharge under pressure. 



Maintenance problems are at a minimum. However, more atten- 

 tion should be paid to protecting canal banks from erosion, installing 

 effective sand traps, and keeping delivery weirs in better order. 



The distribution within the canal system of direct flow water is 

 either by continuous delivery of a prorata part of the flow or by some 

 system of rotation when the supply is short. The latter system is by 

 far the most effective in producing a maximum benefit from a given 

 supply. The other system is almost invariably a source of waste. 



Reservoir water is delivered as a prorata part of the flow carried, 

 or in rotation, or on demand. Delivery on demand produces the 

 most effective use but at times the advantages must be weighed 

 against difficulties of canal operation. 



Many canals act as common carriers for reservoir water owned or 

 rented by their stockholders. By a system of pooling of interests 

 and switching of credits this water is delivered on demand of the 

 individual. 



Weirs are used for measuring water to the user but there is much 

 room for improvement in their installation and maintenance. 



The average gross duty of water measured at the head of all the 

 canals of the valley was 1.88 acre-feet per acre in 1916 and 1.91 acre- 

 feet per acre in 1917. Taken in connection with the consumptive 

 duty of 1.25 acre-feet per acre, this indicates a total loss exclusive 

 of evaporation of only a third of the supply. 



The absorption loss in the canals of the valley between the head- 

 gate and the farm lateral is estimated to average 10 per cent of the 

 supply. This low figure is accounted for in part by the topography 

 of the country and the location of the canals one above another. A 

 considerable part of the gross loss is compensated by the inflow of 

 seepage. 



Seepage water is used to some extent on nearly the entire irrigated 

 acreage of the valley ; but the land dependent on it as a main supply 

 is rather limited, unless we include that lying under the ditches wdiich 

 divert it after it has returned to the channel of the river. 



Furrow irrigation and flooding from field laterals are the only 

 methods of irrigation practiced. Best results are obtained by a fast 

 irrigation to a depth of .4 to .6 foot. The layout of the field should 

 be such that a thorough even watering is obtained, that there is a 

 minimum of run-off at the lower end of the field, and that the depth 



