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NEW YORK STATE MUSEUM 



has been the writer's habit for several years, in storage projects, 

 to first tabulate rainfall in the manner indicated. Such pro- 

 cedure has the advantage that it leads one away from the con- 

 templation of mere detail. There is a positive disadvantage in 

 considering the monthly quantities, for which there is no com- 

 pensation. The division into the three periods exhibits the more 

 important characteristics without overburdening the mind. It 

 is believed that a considerable advance on ordinary practice has 

 been made by proceeding in the manner stated. 



THE RELATION OF RAINFALL, TO RUNOFF 



The runoff of a stream is influenced by many complex condi- 

 tions — as, for instance, amount of rainfall and its intensity, 

 nature of soil, slope of surface and area and configuration of 

 catchment basin. It is also influenced by geologic structure, for- 

 ests, wind, force of vapor pressure and other elements. Data are 

 still lacking for a really satisfactory discussion of the question, 

 although they have accumulated so rapidly during the last few 

 years that many conservative conclusions can be drawn which 

 may be accepted as substantially true. 



As a result of many years' study of the problem indicated by 

 the heading of this chapter the writer has come to the conclusion 

 that no general formula is likely to be found expressing accu- 

 rately the relation of rainfall to the runoff of streams, for streams 

 vary widely in their behavior, and when they do agree the agree- 

 ment is usually accidental. As a general proposition we may 

 say that every stream is a law unto itself. 



The final formula of runoff for a given stream, therefore, will 

 differ in some particulars from that for every other, except that 

 there may be accidental resemblances as regards slope, shape of 

 catchment area, surface geology or some other peculiarity. It is, 

 however, true that an empirical formula may be made for certain 

 classes of streams which will give approximately the runoff for 

 a series of years. 



