Changeability of concentration and particle size distribution of effective sediment in initial and mature flow generation conditions under different slops and rainfall intensities

Water erosion comprises major processes of the detachment, entrainment, transport and deposition. Sediment washed out from the watershed is composed of different particle sizes. The particle size distribution of sediment is a significant factor influencing detachment and transport processes. However, the changeability variables of particle size distribution under different flow conditions have been less considered. Accordingly present study was therefore planned to evaluate the changes in particle size distribution of effective sediments by laser diffraction in initial unsteady and mature steady flow conditions in laboratory scale for a type of soil that was collected from Koudir region in Mazandaran Province. Towards this attempt, rainfall simulation experiments with intensities of 30, 60, and 90 mm h-1were conducted in a set of 1 × 6 m plot with varying slopes of 5, 15 and 25% based on governing condition in the north region of the a soil type and in three replications. The results showed that the sediment concentration is influenced by the slope more than by the rainfall intensity in runoff different conditions. In addition, the results explained significant levels of (p2 micron had a significant different (p63 micron and especially variable of D90.