IRRIGATION IN NORTHERN COLORADO. 
11 
the lower canals may be drawing their full appropriations from the 
supply developed by seepage return. 
Prof. L. G. Carpenter, for a number of years director of the 
Colorado Experiment Station, made one or more measurements of 
the Cache la Poudre River each year, for more than 20 years, to 
determine the seepage return to the stream. These determinations 
were spot measurements, good only for the conditions at the time of 
the observation, but the large number of observations and the care 
with which they were made establishes their dependabilit}^. The 
average of the measurements, made in the spring and fall at low 
stages of the river, shows a return between the canyon and the mouth 
of the river of 153 second-feet, which included seepage intercepted by 
canals near the river. 
The rating stations maintained during 1916 and 1917 on the river, 
its tributaries, and the canals diverting from it, provided continuous 
records from which the seepage return shown in Table 3 was de- 
termined. These figures show the net return to the river from the 
canyon to the mouth, but do not include seepage entering through the 
channels of the various tributaries below the canyon. To arrive at 
these figures the total supply from all sources was determined by 
adding the discharge of the river at the lower rating station and 
the discharge of all canals, less the water returned to the river through 
sluices and wasteways. The supply available from the normal flow 
of the stream was then obtained by adding the discharges of the 
North Poudre and Poudre Valley Canals, the river discharge at the 
canj^on station, and the inflow to the river from the tributaries 
entering below the canyon. The supply available from the normal 
flow of the stream was then subtracted from the total supply, the 
difference being the amount of seepage return. Results obtained in 
this manner will contain a certain amount of run-off from rains and 
irrigation which reaches the river directly instead of passing through 
the tributary channels on which measurements were made. The 
amount is small, however, and may be neglected. 
Table 3. — Seepage return to the Cache la Poudre River in 1916 and 1917. 
i Jan. 
t 
Feb. Mar. 
Apr. 
May. June. 
July. 
Aug. 
Sept. Oct. 
Nov. 
Dec. 
Total. 
Return in 1916 
(acre-feet) 4,600 
Return in 1917 
(acre-feet) 6,604 
4,150: 4,667 
6,094 7,875 
6,297 
7,727 
11,328 9,491 
C 1 ) C 1 ) 
13, 801 
14, 534 
13,324 
14,322 
10,233111,412 
9,830 8,586 
10, 615 
10,186 
7,465 
6,386 
Average in acre-feet j 5, 602 
Average in second- i 
feet ' 91 
5,122 6,271 
92| 102 
7,012 
118 
11,32s 1 9,491 
184 160 
1 
14, 167 
231 
13,S2310,032 9,999 
i 
225! 169 163 
j | 
10,400 
175 
6,925 
113 
110, 172 
152 
1 The figures for May and June, 1917, are omitted on account of their probable inaccuracy. Records at 
the station near the mouth of the river were interrupted for a week or ten day when the discharge was over 
2,000 second-feet. Results obtained by interpolation are subject to too great an error at that stage of the 
river. 
Seepage which reaches the tributaries and then flows into the 
river is approximately 15,000 acre-feet yearly. There are many 
other streams of seepage and runoff from irrigated fields which are 
