effects of sand mining on suspended sediment particle size distribution in kojour forest river, iran

soil erosion causes sediments to be detached from their source materials and transported as suspended particles. the present study was conducted to evaluate the effects of sand exploitation on the distribution of suspended sediments in the educational and research forest watershed of tarbiat modares university, which comprises approximately 50,000 ha. fifty-one water samples were collected before and after sand mining between november 2007 and june 2008. the settling rates of the primary particles of suspended sediments were then analyzed based on the principle of sedimentation described by stokes’ law and using the modified pipette technique. analyses of the samples indicated that the suspended sediment particle size distribution (sspsd) was significantly affected by sand mining. specifically, an independent samples t-test demonstrated that the mean contents of sand, silt and ssc during and after sand mining differed significantly (p< 0.01), with respective values of 74.19±13.4 and 9.75±13.8, 81.77±4.5 and 2.96±2.7% and, 7.66±7.7 and 0.34±0.3 g l-1 being observed. additionally, no significant difference was found between data sets collected before and during sand mining for hydrologic and sspsd characteristics at 1%, which clearly proved consequent effects of sand mining on sspsd.