Temporal Changes in Runoff and Sediment of Rivers in Sabalan Mountain

Introduction and Objetive:

 Estimating the suspended sediment load of hydrometric stations in the watershed requires an accurate understanding of the spatial and temporal variations of the sediment regime. Simultaneous changes and impressability of discharge and sediment from precipitation changes are of mouch importance that rarely considered. Therefore, the aim of tis study was exploring the changes in the slope of the trend curve and also the graphical correlation of monthly and annual data of runoff, sediment values to precipitation values. Toward this, six stations including Atashgah, Pulsoltani, Nayr, Amuqin, Villadergh and Nooran located in the foothills of Sabalan mountain in Ardabil province were chosen and analysed over a 20-year period using the double mass curve method.Therefore, in this study, the amount of monthly and annual runoff and sediment variations in relation to precipitation values at six including Atashgah, PulSoltani, Nir, Amugin, Viladargh and Nooran river gauge stations in Sabalan Mountain, Ardabil province, were evaluated over a 20-year period using the double mass curve method.

Tworad this, the monthly mass curve, the mean monthly rainfall for the same period calculated and was plotted versus corresponding runoff data. Trend Curve Slope (STC) was used to reflect the rate of increase in runoff and sediment amounts based on rainfall or runoff, respectively.

The results of changes in runoff and sediment yield during the available period over the studied rivers showed that except for the Nir station, there were uniform sediment and runoff regime of other stations, during the studied period. Meanwhile, the Nair station had the highest amount of runoff and sediment in all the years studied. Results of double mass curves showed that Nair, Polsoltani and Atashgah stations had no trend of curve slope changes during the statistical period, the amount of sediment and runoff was proportional to precipitation in a consistent variation regime. However, changes in precipitation and runoff with respect to rainfall were observed at Villadargh and Noran stations. Also in the recorded data of Atashagh and Noran stations there is not a trend in the early years of the available data, but the Atashgah station had a decrease in 2000 and 2005 years, and a decrease has been occurred in 2007 at Noran station.

Analysis of Taylor diagrams showed that the correlation between precipitation and runoff and sediment data were in the range of zero to about 0.4. The relative similarity of runoff and sediment change coefficients can be related to the originating the rivers from snowmelt, the annual scale of analyzes, as well as the appropriate vegetation of the upland study area. According to analysis of Taylor diagram, at all stations the standard deviation of sediment data was higher than the standard deviation of flow discharge data. The standard deviation values of the sediment data at all stations are in the same range.