Modeling of seasonal and cyclic variations of the Pachra river flow using the methods of time series analysis
Long-term hydrological data for the Pakhra river are considered in this paper. The purpose of the research is to obtain their characteristics for average annual and average monthly flows. The analysis of the Pakhra river flow by time series methods which allows studying the change in characteristics over time has been carried out. The research results showed the absence of a significant correlation of average annual flow which agrees with the studies of other authors. The method of the harmonic analysis is considered to separate seasonal and random components of average monthly flows of the Pakhra river. The basis of this method is the Fourier transforms allowing obtaining the Fourier coefficients and decomposing the total variance of the series on the dispersion of specific frequencies. The constructed periodograms and the frequency dispersion graph clearly show the seasonal nature of the initial series. Analysis of the results showed pronounced seasonal variations in average monthly flows, the most characteristic are the peaks of the autocorrelation function of 12 and 6 months, as well as decadal (3 months) and intradecade (1 and 2 months). An algorithm is presented for modeling the average monthly flows in order to obtain a set of all possible river flow scenarios for their use in water management calculations.