Document Type : Research Paper
Author
Soil Conservation and Watershed Management Research Institute, Agricultural Research, Education and Extension Organization, Tehran, Iran
Abstract
Knowledge of temporal variation of base flow and its change trends in arid and semi-arid regions such as Iran is essential for developing basin water resources management plans. In this study, the Barun-chay River basin was selected with daily stream flow discharge for the period of 1976-1997. Using a topographic map with a scale of 1:50,000, the location of the station and the area under study were determined, and the initial parameters of the basin were extracted. Then, the base flow index (BFI) was extracted using the time series of daily stream flow data and the one-parameter Recursive digital filter method. Monthly, seasonal, and annual time series of BFI were prepared, and trend analysis was conducted before and after the dam was constructed upstream of the hydrometric station using the Mann-Kendall method. The results showed that the average long-term annual BFI was 0.552. On a seasonal scale, the highest BFI was related to winter and summer, and the minimum was related to spring. The maximum long-term monthly BFI was related to January at 0.651 and the minimum was related to May at 0.470. The distribution of BFI data indicates that 50 percent of BFI in spring was between 0.47 and 0.53, in summer between 0.55 and 0.62, in autumn between 0.49 and 0.55, in winter between 0.52 and 0.64, and annually between 0.52 and 0.57. The trend of BFI in all time steps of the month, season, and year, except for June and October, was negative. The long-term average BFI before the construction of the dam, 1976 to 1995, was 0.542, and after the dam construction, 1995 to 1997, it was 0.562. It is noteworthy that the impact of human interventions resulting from the construction of the dam on the long-term annual BFI was 0.02.
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