The annual hydrographs of British Columbian rivers are characterized by glacial, nival, pluvial or hybrid sources of runoff. Climate change scenarios for the 2050s indicate that snow water equivalent could diminish by 50% to 80% in low-elevation basins of the south coastal region of British Columbia. This could trigger a shift from a hybrid to a pluvial regime for many creeks originating in the coastal mountains and could negatively affect summer low flows. However, the connection between recharge occurring in the headwaters during snowmelt and late-summer water yield remains unclear. A mountainous creek (Stephen's Creek) was monitored in a nested design from September 2008 to November 2009. A two-component isotopic hydrograph separation method was developed by adapting the runoff-corrected model to a semidistributed environment to account for both the spatial and the temporal variability of the isotopic release from the snowpack in the headwater catchment. Results show that snowmelt composed most of the streamflow both at the headwater site (66%?+/-?19%) and at the mouth (62%?+/-?23%) during the peak of the freshet, and its contribution to streamflow was significantly different in July (34%?+/-?11% at the headwater vs 7%?+/-?4% at the mouth). Streamflow recession analysis suggests that a snowmelt-recharged headwater catchment can support a steadier summer base flow compared to a much larger but rainfed-dominated watershed. This study concluded that the large input of meltwater during the spring was sufficient to overturn shallow subsurface reservoirs and to recharge deeper flow paths at a rate that cannot be matched by rainfed-dominated systems. Copyright (c) 2012 John Wiley & Sons, Ltd.
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