Trend and pattern analysis of runoff and sediment in different soil clay contents and surface rock fragments

Different factors affect the runoff and sediment production during storm conditions. Among different soil properties, clay content is one of the most important bonding agents for aggregation and infiltration. Rock fragments also affect hydrological and erosional processes, but these relationships in various soil clay contents or surface rock fragments may be positive or negative, thus examination of these effects is of importance in erosion process. Besides, runoff and sediment modeling is essential, because of the difficulties associated with measurements, for any sediment and flood remediation efforts. In this study, in order to have control on levels of variables for each treatment, a set of rainfall simulation system at experimental plots was utilized. In the next step, factorial design including 6 groups of clay treatments (0, 10, 20, 30, 40 and 50 percent) and 6 groups of impermeable surface treatments (0, 5, 10, 15, 20 and 25 percent), each in 3 replicates, (totally 108 experimental plots) was used. To study temporal variations of runoff and sediment, 30-minute rainfall simulations were run with sampling in 2.5-min intervals. Trend analysis showed that in all mentioned treatments, runoff volume increased significantly (p<0.01) but sediment production trend decreased when soil clay content increase. Also, in runoff and sediment production, clay content had the main role when compared to surface rock fragments. Finally, Inverse and S-curve models had best fits on runoff trends. However, sediment production trend and regression models between runoff and sediment mainly both had cubic patterns.