ABSTRACT Measurements at runoff plots have shown that near‐surface flow (i.e., overland flow and interflow through the topsoil) occurs frequently on hillslopes with low‐permeability soils. However, these plot‐scale measurements do not provide information about the potential importance of near‐surface runoff for catchment‐scale streamflow. Therefore, we compared near‐surface runoff responses measured at 14 small (3 m 2 ) and two large (~80 m 2 ) runoff plots with streamflow responses for different catchments (0.01–0.7 km 2 ). More specifically, we compared the hydrograph shapes, timing of the start of the runoff response, timing of peak flow, and runoff ratios across the different scales for 12 rainfall events. Near‐surface runoff and streamflow responded rapidly, generally within tens of minutes from the start of a rainfall event. Peak flows were more delayed for the larger catchments during small events with dry antecedent conditions but occurred at the same time at the plots and streams during wetter conditions. With increasing wetness conditions, near‐surface runoff became more widespread, and runoff ratios increased for the plots and streams. These results show that near‐surface runoff on the hillslopes occurs either before stormflow (small events with dry antecedent conditions) or is synchronous with the streamflow response (large events). This suggests that near‐surface flow is fast enough to be able to cause the very rapid streamflow responses observed during wet conditions in pre‐Alpine headwater catchments underlain by gleysols.
Gauthier et al. (Fri,) studied this question.