A NEW METHOD OF ESTIMATING STREAM-FLOW 
INTRODUCTION 
In the preceding pages, the method of deriving the evaporation formula has 
been explained. It is the purpose in the pages which follow to indicate the progress 
made to date in this investigation of the laws of stream-flow, using as a basis the 
evaporation equation (23), previously presented (page 82). 
Stream-flow, as used hereinafter, is understood to be the discharge of a stream 
at point of measurement, expressed in cubic feet per second or some similar unit. 
Stream-flow is characteristically irregular. After very heavy rains or spring 
thaws, it goes up to values many times the average flow. It becomes very small 
at the end of long drouths. There are large differences in flow between streams at 
which the conditions are apparently similar. 
The standard books upon the subject and the writings of experts are essentially 
qualitative, not quantitative. They lead one to an explanation of the variations 
of stream-flow through a maze of qualitative statements as to the manner in which 
the stream-flow is dependent upon rainfall, temperature, evaporation, vegetation, 
seepage, surface conditions, topography, geology, and many other factors. They 
give one but few quantitative relations between stream-flow and the various matters 
just mentioned. The writings by the experts do not give one such quantitative 
relations as will enable him to compute the effect upon stream-flow of these various 
matters. These statements are made to indicate the state of the present knowledge 
in this difficult field, and not as criticisms of, nor reflections upon, the authors of 
the books or the experts. 
DATA USED AND ACKNOWLEDGMENTS 
The principal data used in this study were those pertaining to two small 
streams at Wagon Wheel Gap, Colorado, at latitude 37° 46' north, longitude 106° 
35' west and elevation about 10,000 feet, designated as Streams A and B. Each of 
these streams drains about one-third of a square mile. Plate 7, reproduced through 
the kind permission of Professor Marvin, shows the topography, etc., of the drain- 
age areas. 1 On these two streams the Weather Bureau and the Forest Service 
made continuous observations of the various meteorological elements, and of the 
run-off, with an unusually high degree of accuracy from 1911 to 1926. 2 These 
streams were chosen for the first intensive study, mainly because of the ex- 
treme care and accuracy with which the observations have been made. The 
complete record of the observations for the period 1911-1915 were made available 
for use in this investigation through the kindness of Professor Charles F. Marvin, 
Chief of the U. S. Weather Bureau. Professor Henry J. Cox, meteorologist in 
charge of the Weather Bureau at Chicago, and his assistants, particularly Mr. C. 
A. Donnel, have facilitated the work on this part of this investigation in many ways, 
but especially by granting free access to the data at the Chicago Weather Bureau 
Office. Mr. L. F. Harza, Consulting Hydro-Electric Engineer in Chicago, has 
taken much interest in this study. His criticisms and encouragement are hereby 
gratefully acknowledged. 
1 For dimensions of these watersheds, see Table 40, page 151. 
2 For complete description of this project the reader is referred to Forest and Stream-flow Experiment at 
Wagon Wheel Gap, Colorado. Final Report on Completion of the Second Phase of the Experiment, by C. G. 
Bates and A. J. Henry. Monthly Weather Review Supplement No. 30 (1928). 
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