Stream Flow Variability

An index of stream flow variability is suggested, in the form of the standard deviation of the logarithm of the stream dis charge. The method of determining the index is described and the values from the flow records of a large number of streams in the eastern part of the United States were obtained. The possibilities of using this index in estimating the duration curve of the stream flow, where flow records are short or nonexistent, is indicated. A study of the indexes, together with the condition s of the respective watersheds, demonstrated that in the northeastern quarter of the United States the geology (including soil cover) and the presence of lakes and swamps are the most important factors in stream flow variability during the greater part of the time and that the other factors have relatively smaller effect.