Document Type : Research Paper
Authors
1 PhD Student, Faculty of Natural Resources, Tarbiat Modares University, Noor, Mazandaran, Iran
2 Professor, Faculty of Natural Resources, Tarbiat Modares University, Noor, Iran
3 Associate Professor, Faculty of Soil Science, University of Guilan
Abstract
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 (p<0.05) for particle of 10 in slope of 5% and in rainfall intensities of 60 and 90 mm h-1 in steady and unsteady flow conditions. While particle of >2 micron had a significant different (p<0.05) in slope of 5% and in rainfall intensity of 30 mm h-1. In this regard, variable of D50 had very complex behavior in slopes and different rainfall intensities but D90 was not influenced by slopes and rainfall intensities in confidence level of 90% in steady and unsteady flow conditions because of inability flow in moving particles of >63 micron and especially variable of D90.
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