Comparative Assessment of Gully Erosion and Sediment Yield in Different Rangelands and Agricultural Areas in Ghasr-e- Shirin, Kermanshah, Iran

Negative impacts of gully erosion in marly areas are severe due to improper landuse practices such as irrigation, tillage, overgrazing and degradation of vegetation cover. The objective of this research was to evaluate gully thresholds related to plant vegetation cover and landuse change in the Agriculture (AG), Fair Rangeland (FR) and Weak Rangeland (WR) areas of Ghaasr-e-Shirin, Kermanshah, Iran in 2015. The topographical parameters and vegetation cover were measured in the field. Furthermore, nine flumes were performed to determine the critical values of hydraulic parameter and sedimentation. Results revealed that cross-section, width, depth and gully branches length in the FR were significantly lower than those for AG and WR (p<0.05) affected by plant canopy and litter. The significant differences were found between three sits for soil organic carbon (SOC), electrical conductivity (EC) and hydraulic characteristics (inlet discharge, velocity, loaded sediment). Higher vegetation cover in the FR was attributed to the increased hydraulic thresholds and adversely limited cross-section enlargement. Finally, the sediment concentrations in AG, FR and WR were 15163, 9560 and 12000 ppm, respectively. Lower SOC was found in WR and AG due to higher concentration of load sediment. Hence, it was concluded that bare soil, poor vegetation and lower SOC are considerable reduction factors in gully thresholds and subsequently, off-site sedimentation and SOC loss in the study area.