Mineralogy Investigation of Sediments of Riverbed in Shafarood Watershed, Gilan Province for Determining the Rate of Erosion and Sedimentation

More accurate understanding of rock formations and sedimentary units sensitive to erosion will enable us to present appropriate and timely methods in order to prevent accelerated erosion. In this study, through predefined sampling from main and minor channels and granulometric analysis using index sieves, mineralogical investigation has been performed qualitatively and quantitatively by binoculars in laboratory. After that, sedimentation potential has been calculated by using practical formulas. Then, sedimentation potential of each sedimentary unit has been estimated from average results of sedimentary sample and with this method, sedimentation potential of Shafarood Watershed has been obtained from average results of five sub basins. An equation has been calculated for each sub basin and by this, an equation for whole watershed was presented. In this equation, the Y which refers to the amount of delivered sediments has been placed in one side and rock unit coefficients on the other side. The coefficient of each rock unit has a rule in sediment production. These coefficients are dimensionless and demonstrate rock unit sensitivity to erosion. The bigger this value, the more sensitive that rock unit is to erosion. In this way, the map of sensitivity to erosion for each sub basin has been prepared by using (ARC GIS) software. According to average sedimentation potential of Shafarood Watershed, marl units (Pgf), silty sandy shale (Jsh) and sandy limestone (Kusl), have respectively the highest sensitivity and limestone units (P), andesite - basalt (Pev) and tuffy shale (V) have the least sensitivity to the erosion.