Slope runoff processes and flow generation in a subarctic, subalpine catchment

Hillslope runoff was studied in a subarctic, subalpine environment to impro ve understanding of runoff generation processes and the mechanisms whereby water moves from hillslopes to the stream. Runoff characteristics of four h illslopes were examined between 1997 and 1999, each with distinct soils, fr ost, topography and vegetation. Lateral fluxes were confined to hillslopes with porous organic soils overlying less permeable mineral substrates, sett ing up a two-layer flow system whereby most drainage occurs as quickflow in the porous organic layer as matrix flow and/or as preferential flow in pip es, rills and interconnected surface depressions. During snowmelt, meltwate r infiltrated and percolated tile porous frozen organic layers with little resistance. Percolation ceased at the organic/mineral interface due to the impermeable nature of frozen mineral soils, forming a perched saturated zon e and initiating runoff. Snowmelt runoff was greater on slopes with greater snow water equivalent and reduced organic layer thickness. In summer, runo ff was greatest oil slopes where wet conditions were sustained by inflow. S tormflow hydrographs responded rapidly to rainfall while exhibiting extende d recessions compared with temperate regions. Where sustained inflow occurr ed, the recession limb showed two segments to reflect different source area s of stormflow production. Recession analysis was used to quantify contribu ting areas, which were highly variable and controlled largely by hillslope wetness and organic-layer properties. Results indicate that the concept of variable source area for runoff generation applies to subarctic, subalpine catchments. (C) 2001 Elsevier Science B.V. All rights reserved.