An Appropriate Weighting Factor for Calculating Sediment Connectivity Index in Bare Tilled Soils

The weighting factor of the sediment connectivity index (IC) is a challenging component of this index and must be properly explicated for different situations. The aim of this study is to develop a proper weighting factor for calculating IC based on experiments on three tilled soils from dry-farming fields in Kouheen, Sararud, and Gachsaran regions under a 111 mm/h rainfall simulation using a 5.8 m2 laboratory flume with a slope of 12%. For each soil sample, two rain events (R1 and R2) were simulated with an interval of 4 hours, and the soil losses were measured. In addition, a digital elevation model with a pixel size of 2 mm was prepared by accurate photography after each rain followed by calculating the IC based on roughness coefficient (RI) as the weighting factor. Measured soil losses of two rainfalls were 4796 and 3909 g for Gachsaran soil, 3465 and 2464 g for Kouheen soil, and 2679 and 2105 g for Sararud soil, respectively. The result shows that with increasing IC based-RI, soil loss was decreased which indicates the inadequacy of RI alone as a weighting factor. To develop a new weighting factor, several physical and chemical characteristics of soils were used in combination with RI. A comparison of the results showed that the IC based on a weighting factor obtained from the combination of mean weighted aggregate diameter, penetration resistance, and RI, has the highest coefficient of correlation with soil losses (0.92, P <0.01). Examination of the new IC maps showed that the IC in R2 increased compared to R1. It is recommended to study the possibility of using the developed weighting factor in calculating the IC of hillslopes after tillage in determining critical points in the hillslope.