Effect of a Freezing-thawing Cycle on Overall and Inter-variability of Runoff and Soil Loss Components for a Loess Soil

Background: Because control of runoff generation as well as soil loss is influenced by freezing-thawing, proper knowledge and insight into the freezing-thawing process in combination with other hydrological processes is essential for executives and planners. However, such dynamic phenomenon and corresponding consequences have not been studied adequately. The present study was therefore planned to comparatively analyze the effects of a freezing-thawing cycle on hydrologic behaviors of loess soil from northeast of Iran. Towards that, the small-size (0.5×0.50×0.30 m) erosion plots were subjected to a freezing-thawing cycle in accordance with governing conditions on the region of the origin soil. The plots were subjected to a freezing-thawing treatment through inducing cold air until temperature declined to below -20 °C and lasted for three days using a large cooling compartment system, and then were kept in the laboratory with ambient temperature of above 10 °C for two days. The treated plots as well as untreated (control) plots were then exposed to a simulated rainfall with an intensity of 72 mm h-1 and 0.5 h duration while they were placed on a slope of 20%. Results: The results indicated that the hybrid processes of freezing-thawing, and splash and interrill erosions significantly affected runoff generation and soil loss at small plots. So that the time to runoff reduced by 1.65 times in the freezing-thawing treatment compared to that reported for the control treatment. The runoff volume and soil loss also increased at tune of 1.38 and 2.90 times in treated plots in comparison with those measured for the untreated plots. Laboratorial results indicated significant differences (p< 0.006) between runoff and soil loss behaviors in plots subjected to a freezing-thawing cycle and those of control condition. Conclusion: The performance of ice lenses and freezing fronts and creating near-saturation moisture after completing the cycle were evaluated as the most important factors affecting the different soil behaviors under frozen-thawed cycle.