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Runoff generation refers to the physical processes by which water travels through the landscape, moving through the subsurface or over the ground surface, ultimately arriving at the stream channel. These physical processes vary in both space and time leading to difficulties in mechanistic modelling of storm response, contaminant transport and nutrient fluxes. Runoff generation has been extensively studied at the hillslope scale and in headwater catchments. However, only recently have empirical studies begun to collect similarly detailed datasets across multiple catchments with which to examine how these processes change with scale. This study examines runoff generation from a series of eight small nested forest catchments and focuses specifically on the controlling influences of antecedent moisture conditions and catchment topography. / End-member-mixing-analysis using stream water hydrochemistry from the eight catchments shows changing seasonal and storm-based source water contributions to the stream channel. Analysis identifies hydrochemical solutes with behaviour consistent with the assumptions of the mixing-model approach for all eight catchments. Results indicate that testing of solute selection is critical in the application of this method to multiple catchments. / Runoff generation observed for five storm events shows a strong nonlinear relationship between runoff and antecedent moisture conditions, supporting the hypothesis of varying 'states of wetness'. Detailed hillslope-scale investigation during the different 'states of wetness' indicates that while groundwater and soil moisture profiles show changing active-flow connectivity on a seasonal and storm-base dtime scale, there no significant change in spatial patterns of shallow soil moisture. These results suggest that a priori spatial patterns in shallow soil moisture in forested terrains may not be a good predictor of critical hydrologic connectivity that leads to the threshold change in runoff generation, as has been found in rangeland catchments. / Differences in storm response from the eight catchments are in part attributable to variation in topography and landscape organization. The multiple catchments have similar distributions of topographic index and yet differences in mean values of topographic index lead to significantly different estimates of mean residence time. Scaling of storm response is dominated by the behaviour of the three largest catchments. These three catchments distinguish themselves with larger MRT and larger valley bottom areas. It is these three catchments that, under dry antecedent moisture conditions, show significantly larger amounts of new water delivery to the stream channel, suggesting a significant change in dominant runoff mechanisms related to topography and landscape organization.

The capability of radar measured rainfall to enhance the simulation of storm hydrographs was assessed. Six rainfall events which occurred in 1986 and 1987 over an 8.13 km$ sp2$ agricultural watershed in south-western Quebec were used in model simulations. Radar measured rainfall rates were calibrated using measurements from a single tipping-bucket raingauge located at the study site. / A deterministic, event-based model, HYMO, was used to simulate streamflow using radar and gauge measured rainfall. The model utilized two rainfall abstraction techniques, i.e. the SCS Curve Number method and the Green-Ampt infiltration equation. Simulated streamflow hydrographs were compared with observed storm flows. / For short duration, high intensity, simple rainfall events, there were minor improvements in hydrograph simulations when calibrated radar measured rainfalls were input to the model, compared to tipping-bucket raingauge measurements. Complex, low intensity storms were poorly simulated by the model using either rainfall data source. Neither rainfall abstraction method proved consistently superior.

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No description available.

No description available.

No description available.