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Hydrologic response during snowmelt in three steep headwater catchments : Ringrose Slope, Slocan Valley, British Columbia Whyte, Dion M.

Abstract

Using a combination of hydrometric measurements, geochemical and isotopic tracers, and analysis of historical data, three steep headwater catchments of the Slocan Valley, British Columbia, Canada, were described and contrasted in terms of runoff processes and pathways during the 2002 freshet. Streamflow responsiveness was shown to be related to the degree to which connectivity between source areas of meltwater and stream channels was maintained as the snowline progressed upslope. The Thickett Creek catchment displayed the most sluggish streamflow response and was dominated by relatively deep subsurface flow throughout the freshet. The Gurn Brook catchment demonstrated the flashiest streamflow response and experienced significant channel flow relative to the other catchments, with subsurface flow maintaining connectivity between source areas and the channel network. The Gum Spring catchment demonstrated streamflow response intermediate between the other catchments; however, high unit runoff and unit peak flow relative to the other catchments suggested significant inter-catchment transfers of bedrock groundwater into the Gum Spring catchment. While a soil-water reservoir within Gurn Spring contributed to streamflow during peak flow, contributions from bedrock groundwater dominated during baseflow and hydrograph recession. Attempts to perform an isotopic hydrograph separation were confounded by the complex variation in new-water isotopic concentrations in both time and space. Qualitative interpretation of isotopic results indicated the dominance of old water contributions during baseflow, with increasing new water contributions during hydrograph rise. Similar isotopic concentrations between meltwater and streamwater at the time of peak flow prevented resolution of the relative contributions from old and new-water at that time. Relative to other studies, the study catchments displayed surprisingly little diurnal streamflow response during snowmelt. Possible explanations for this are presented and discussed, as are the potential impacts of forest harvesting and road construction on hydrologic response in the three catchments. Finally, the implications of the research findings for catchment-scale modelling were examined.

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