210 



THE IRRIGATION AGE. 



UNCLE SAM PREDICTS FLOW OF IRRIGA- 

 TION STREAMS. 



By J. Cecil Alter, 



Observer, U. S. Weather Bureau. 



The third spring snow survey has just been 

 completed by the Salt Lake City office of the U. S. 

 Weather Bureau, in the Maple Creek watershed, a 

 small stream from the Wasatch Mountains near 

 Springville, Utah. The survey consists of making 

 several hundred actual measurements in average 

 regions of the depth, density, and water equivalent 

 of the snow, and this year's survey reveals the re- 

 assuring fact that there is about 16 per cent more 

 irrigation water stored in these hills than at the 

 same time last year. 



It has also been found that the compactness of 

 the snow is practically the same as it was last year, 

 and that the ground beneath the snow contains no 

 frost, so that if weather conditions from the close 

 of the survey to the end of the irrigation season 

 average about the same as in 1912, Maple Creek 

 should supply about one-eighth more water this sea- 

 son than it did last year ; and from a cursory exam- 

 ination of adjacent watersheds, it is quite probable 

 that the conditions in Maple watershed are an index 

 to conditions in nearby mountains. 



A typical slope, showing the omnipresent quaking aspen saplings. 

 Though at a distance these mountains look rough and full of drifts 

 and piles of snow, the fact is that 90% of the superficial area re- 

 ceives an even layer of snow which admits of easy measurement like 

 the view here, among the mountain tops. 



About four years ago the U. S. Weather Bureau 

 saw the need for ascertaining during March of each 

 year, the probable summer flow of certain irrigation 

 streams so that crop choices and cultivations could 

 be planned well in advance, and in 1911 the first 

 survey was made of the snow layer over the Maple 

 hills, the work being done in the last half of March, 



The date of measurement, however, proved a 

 little too late for the best utilization of the informa- 

 tion as that was an early spring and the farmers 

 using Maple water for irrigation purposes were 

 plowing their fields by the time the survey was com- 

 pleted. The measurements in 1912 and 1913 were, 

 therefore, made in the first half of March, and the 

 printed report was issued to the Maple water users 

 before any farming operations of importance had 

 begun. Therefore every farmer had a definite and 

 exact knowledge of the amount of snow in the hills, 

 for comparison with exact information obtained in 

 two years previous. 



Since all presumption, hearsay and guesswork 



about the water supply in the form of snow have 

 been eliminated, these alfalfa, potato, grain and fruit 

 farmers are making their summer plans with a 

 fairly exact knowledge of the amount of water they 

 will have. Moreover, should the season prove to 

 be a very warm one, and the snow be melted with 

 devastating rapidity a daily stream measurement 

 at a flume above the highest farm will show the 

 exact amount of water running away, and this can 



In soft snow the only work required is putting one foot ahead of 

 the other on a 40% slope. 



be compared from week to week with \he stream 

 flow measurements during 1912 and 1911. 



The snow is about five and one-half inches 

 deeper than last year, and shows little drifting ex- 

 cept in the rougher portions of the watershed ; and 

 up to the close of the measurement period there had 

 been only a few small snowslides even in these 

 regions, thus indicating a firm condition of the 

 under layers at that time. The streams were all 

 comparatively low, being closed by frost and snow 

 over the upper half of their length, approximately. 



Practically the entire watershed carried a snow 

 covering of a trace or more this year. It was also 

 discovered that a comparatively small acreage car- 

 ried as little as a trace or broken covering of snow. 

 The density measurements, or determinations of the 

 actual water contents" of the snow by weighing, 

 showed noticeable uniformity throughout the re- 

 gions measured. 



Owing largely to the impracticability of secur- 

 ing measurements of the snow that will be com- 

 parable from year to year in the rougher portions 

 of the watershed and on the steeper slopes no sys- 

 tematic measurements were made this spring in 

 certain limited regions. It is therefore believed that 

 in the figures herewith presented of the snow layer 

 over the smoother portions of the watershed, we 

 have records that represent very closely a measure 

 of the amount and condition of the snow that will 

 form a basis for fairly accurate comparisons with 

 measurements in other years. 



