The Annual Average Stream Flow for Hydro-electric Power

Abstract

In a large combined hydro-steam power system as in Japan, it is necessary to know what flowing condition of rivers may be expected to hold on an average for a long term, in order to plan for the economical development of hydro-power. However, the flowing condition not only varies in its total annual stream flow each year, but even seasonally within a given year, which makes it difficult for us to deal directly with the duration curves of stream flow or the daily stream flow curves which have been hitherto employed in developing hydro-power, so that we have to consider as a parameter the annual average stream flow for each year on which these depend. We need not take the average of all the data obtained in the past in order to estimate the annual average stream flow expected to hold for a long term to come, but must resort to the reasonable method of so-called time series analysis with its theoretical foundation, which takes into consideration the periodicity of the fluctuation contained in the stream flow and other factors. In this paper we propose to estimate the annual average stream flow expected to hold on an average for a considerably long term by means of an analysis, as easy and practical as possible, of a stream flow of comparatively small sample size.