جستجوی مقالات مرتبط با کلیدواژه « غلظت رسوب معلق » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

Based on expert estimates, many Iranians believe that the amount of sediment yield is annually increasing. This study has attempted to assess the temporal trend in Suspended Sediment (SS) of Jajroud and Karaj rivers at Roudak and Sira stations. respectively with adequate data collected during four decades. The SS yield data and SS concentration as well as flow rate data were analyzed. Preliminary investigation showed that more than 92 percent of the SS at Roodak and Sira stations is transferred by top two and three flow deciles (equal to 20 and 30 percent) of the effective or flood discharges. Among these, the highest decile (10 percent) is responsible for carrying about 80 and 64 percent of SS accounted for the two study sites correspondingly. Therefore, mainly analyzing the highest decile flow data was considered. Four techniques were performed including: a) fitting regression lines to the measured SS concentrations and weights vs. time, and b) graphical comparisons of dependent variables (average discharge, average SS concentration and weight) during the four decades, c) using the Kruskal–Wallis test, and d) using Kendall rank correlation coefficient. All interpretation techniques showed decreasing trends vs. time which were significant based on the two nonparametric techniques. Since, the highest decile of daily flows of study sites have not shown any increasing trends during study period, it can be concluded that unlike the general publics’ believes the amount of SS has decreased. A possible explanation for this descending trend might be as a result of 43 and 25 conservation projects implemented during recent 30 years in the upstream basins of Amirkabir and Latian dams, respectively. The descending SS trend does not necessarily mean lower rates of erosion in these basins; but it rather means lesser sediment delivery ratios.

With attention to high potential in sediment delivery of semi-arid and semi-humid regions, in this study was prepared sediment-discharge equation for Poldoab Shazand station (Markazi province) with semi-arid climate and Tireh Dorud station (Lorestan province) with semi-humid climate. Then with applying the MVUE, Smearing, QMLE, FAO and β compared the correction amounts of equations for two regions. According to results, the most number of Nash-Sutcliffe criteria was related to FAO with 0.558 in the Poldoab Shazand station and 0.715 in the Tireh Dorud station. Also correction coefficients in the Tireh Dorud station was around 1.7 equal then to Poldoab Shazand station. Due to the high variation of coefficients a and b of equations two stations, as well as an inverse relationship between the two coefficients, it is needed in preparation of sediment rating equation that moreover river flows variable, other parameters related to precipitation specifications and physical properties of watershed can be applied.