IBRIGATION IX 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. 
Keservoir 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 which 
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 A 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 
