Separation and Characteristics of Base flow in the Upper Reaches of Heihe River Basin
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Abstract:
As an important component of runoff, base flow has great significance in the maintenance of the sound ecosystems of the rivers. Base on the monthly runoff data from 1954 to 2011 in the upper reaches of Heihe River Basin, the digital filter method was used for the base flow separation, together with the traditional methods of minimum monthly average flow rate in the last 10 years and the 90% guarantee rate of the minimum average flow. The inner-annual, inter-annual and decadal variations in base flow and base flow index were investigated by means of Mann-Kendall test, Pettitt test and cumulative departure curve methods. The results showed that the digital filter method could give a satisfactory result of base flow separation over the study area. The inner-annual base flow index increased first and then decreased and had a big degree of variability. In the inter-annual variations, the trends of the base flow were consistent with those of the runoff, and the degree of discretization of the base flow was relatively low. Although the base flow had a rising trend, the change was relatively mild, and relatively stable. A significant change point was found for the base flow time series in 1979, and the average base flow after the change point increased by 16% compared with the former period. In the decadal scales, the contribution of the base flow to the runoff was not variable, with the decadal base flow index approaching 0.27.
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