An Assessment of Runoff and Sediment Generation in fine-Grained Formations (Neocene's units) Under Rainfall Simulator

In Iran, fine-grained formations (Neocene's units) are very susceptible to erosion. In addition, they are the units producing runoff and causing soil loss in watersheds. The objective of this study is to assess the effect of physicochemical and mechanical properties of these formations on sediment and runoff rates at different rainfall intensities, based onfield simulator in Taleghan Drainage Basin. For this purpose, first Neocene's units were divided into five subunits including Halite siltstone(NgSiH), Siltstone (NgSi), Mudstone (gy1C), Gypsum mudstone (gy1CG) and Halite clay stone (gy2CH), based on physical and chemical properties. Then, runoff and sediment rates were determined in each subunits at two intensities (30 and 60 mm/h) using rainfall simulator. An analysis of variance and Duncan's tests showed that NgSiH subunit has produced the highest amount of runoff and sediment rates and that the runoff and sediment rates of other subunits in a descending order are as follows: NgSi, gy2CH, gy1CG and gy1C. The trend of induced runoff and sediment rates at different times showed that in NgSiH and NgSi subunits runoff amounts were fixed rapidly at the second ten minutes. In addition, on the other subunits, runoff amounts were fixed at the third ten minutes but sediment yield increased rapidly at the third ten minutes.