文摘
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Summary
Shallow subsurface runoff is one of the most important mechanisms determining hydrological responses of headwater catchments to rainstorms. In this study, a simplified approach combining one-dimensional dual-continuum vertical flow in a variably saturated soil profile and one-dimensional saturated flow along the soil-bedrock interface was used to study rainfall-runoff events at an experimental hillslope. A dual set of Richards¡¯ equations was used to predict vertical flow of water in the soil matrix and preferential pathways. Subsurface flow along the soil-bedrock interface was described by diffusion wave (Boussinesq-type) equation. The observed subsurface runoff and its 18O composition were compared with the model predictions. Contributions of pre-event and event water to hillslope runoff during major rainfall-runoff episodes were evaluated by means of numerical experiments involving synthetic 18O rainfall signatures. Although preferential flow played an important role in the hillslope runoff formation, pre-event water was found to be significant runoff component in most events (it formed 47-74 % of total subsurface runoff). The simulation results confirmed the hypothesis of significant mixing between infiltrating rainwater and water stored in the hillslope soil profile. The modeling approach presented in this study was successful in describing both vertical and lateral mixing of water.
