Investigating the effect of soil properties on runoff production in three sub-basins in northwest of Iran

Runoff is one of the major components of the hydrological cycle, which leads to soil loss from steep slopes and sediment production in watersheds. Investigation of effective factors in runoff coefficient is important in watershed management. The aim of this study was to investigate the effect of soil properties on runoff coefficient in Alanagh, Livar and Shekaralichay sub-basins in East Azarbaijan Province. After soil sampling, some physicochemical properties were measured and runoff data were obtained from the relevant stations. Based on the results, runoff coefficient in the studied sub-basins is affected by various soil properties such as particle size distribution, gravel, organic matter, lime, aggregate size and stability, and saturated hydraulic conductivity. As the percentage of sand and gravel increases and the percentage of clay and silt decreases, soil permeability increases and runoff coefficient decreases. Organic matter and lime are two important factors in the aggregate formation and stability, and improving the saturation hydraulic conductivity which plays a key role in reducing runoff production. The results of multiple linear regression analysis showed that runoff production in the Alangh sub-basin has a significant relationship with soil organic matter (r=-0.95, p<0.01) and bulk density (r=0.9, p<0.01). Organic matter content has the main role in runoff production in Livar sub-basin (r=-0.94, p<0.01) and Shekaralichay sun-basin (r=-0.95, p<0.01). Runoff coefficient in all sub-basins in the area is strongly related to organic matter content (r=-0.86, p<0.01), soil structure stability (r=-0.68, p<0.01) and stream density (r=0.49, p<0.01). This study showed that preserving and increasing soil organic matter can be an effective strategy in conserving rainwater and reducing runoff by improving soil structure and permeability.