UBC Theses and Dissertations
Space-time dynamics of runoff generation in a snowmelt-dominated montane catchment Smith, Russell
Runoff source area dynamics are controlled by the interaction of processes influencing the dynamics of water inputs at the soil surface and processes influencing vertical versus lateral flux partitioning at or below the soil surface coupled with variability in connectivity between runoff generating areas. These issues are investigated for the snowmelt-dominated Cotton Creek Experimental Watershed in southeast British Columbia, Canada. First, the controls on midwinter snowmelt are investigated. Accumulated snowmelt during the midwinter period of 2007 with nearly continuous subzero air temperatures comprised between 3% and 27% of the total snowfall. This, and other circumstantial evidence, supports the hypothesis that soil heat flux generated the midwinter snowmelt. Early-winter soil hydrothermal conditions and midwinter meteorological conditions are important controls on the midwinter melt dynamics. Second, the influences of soil hydraulic conductivity (Ks) and water input dynamics on the formation of transient perched shallow groundwater via percolation-excess processes are investigated. The results suggest that the initiation depth and maximum water table level vary according to and can be predicted by an interplay between the Ks profile and the maximum water input intensity during an event. At sites where Ks does not decrease gradually with depth, water input intensity does not appear to influence the depth of groundwater initiation. Last, seasonal variation in the spatial controls on the occurrence, timing, and persistence of shallow groundwater response are examined. The Ks of the soil at 75 cm depth is a first-order control on the distribution of sites that generate shallow groundwater response versus sites that experience only deep percolation. Upslope contributing area and slope gradient are first-order controls on the persistence of shallow groundwater response during peak flow, recession flow, and low flow periods, and runoff source areas expand and contract throughout these periods according to an interplay between catchment wetness and the spatial patterns of topographic convergence. However, controls on the space-time distribution and rates of snowmelt, and controls on vertical versus lateral flux partitioning in the soil overwhelm the importance of topographic convergence during early spring freshet periods.
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