Seasonal variation of subsurface flow pathway spread under a water repellent surface layer

MMR results show strong seasonal trends in all years of study, comparable to those revealed by an older metric, the Effective Cross Section, which provides a measure of flow heterogeneity. However, the new MMR metric is particularly useful for identifying variations in soil moisture responses by depth. We show that the highly water repellent surface layer diverts moisture preferentially to deeper layers to produce increasing moisture responses at depth, in patterns which sharply contrast with model predictions. This effect is shown to decrease through winter as surface repellency breaks down, but may be highly significant in conserving moisture against evaporative loss during dry periods. Results of the MMR analysis suggest that soil was most successful in diverting flow to deeper layers in periods where significant rain events were separated by dry periods of at least a week, but less successful where rain events were either highly isolated or closely spaced. We conclude that comparison to the 1D model presents a useful tool in demonstrating how patterns of infiltration are altered under water repellent conditions.