Granulometric variation of river suspended sediments due to sand and gravel mining (case study: Vaz River)

The correct determination and prediction of sediment transportation by the river is very important for water resources management, flood reduction and environmental sustainability projects. Analysis of sediment particle size can show important information about the origin, history, transportation and deposition conditions of the sediment. However, this matter has been less considered. This study was therefore conducted at Vaz River located in Mazandaran Province to investigate effects of sand harvesting on morphometric characteristics of suspended sediments at upstream and downstream of the study mine. For this purpose, monthly samplings were made at upstream and downstream of the mine from February 2012 to January 2013. The particle sizes of suspended sediment were measured by Master Sizer and corresponding distribution and specifications including mean, sorting, skewness and kurtosis were also analyzed by the GRADISTAT software package. The range of variations of D10, D50, D90, and average particle size of the study samples were obtained as 0.34-1.12, 3.24-13.41, 14.12-90.74 and 3.19-11.45 microns. In addition, changes of sorting, skewness and kurtosis were found from 3.11 to 6.38, -0.13 to -0.32 and 0.88 to 1.29, respectively. Mines discontinuous activity and distance between study mines and sampling locations could be considered as main factors behind non-significant effects of sand and gravel mining on changing suspended sediment particle size distribution.