IREIGATIOlSr IN NOETHERN 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 dependability. 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 

 canyon 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 Riv'or in 1916 and 1917. 





Jan. 



Feb. 



Mar. 



Apr. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



Total. 



Return iii 1916 

 (acre-feet) 



Return in 1917 

 (acre-feet) 



4,600 

 6,604 



4,150 

 6,094 



4,667 

 7,875 



6,297 



7,727 



11,328 

 (1) 



9,491 

 (1) 



13, 801 

 14,534 



13,324 

 14, 322 



10,233 

 9,830 



11,412 

 8,586 



10, 615 

 10, 186 



7,465 

 6,386 





Average in acre-feet 

 Average in second- 

 feet 



5,602 

 91 



5,122 

 92 



6,271 

 102 



7,012 



118 



11,328 

 184 



9,491 

 160 



14, 167 

 231 



13, 823 

 225 



10, 032 

 169 



9,999 

 163 



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 



