The importance of headwater catchments for water availability in the lower Athabasca River Basin, Canada.

Abstract

In Canada’s Western Boreal Plain, catchment runoff is typically low but spatially variable. Localized landscape soil and vegetation cover types, along with the hydrophysical properties of underlying glacial deposits and regional slopes, are important controls for the partitioning of precipitation into runoff, evapotranspiration, and soil water storage. Wetlands are abundant, covering up to 50% of the landscape, despite a regional sub-humid climate. Local topographic highs, including Stony Mountain, have been identified as water generation hotspots, with the goal of this research to evaluate the hydrology and importance of small headwater catchments on a local topographic high for water generation and availability in downgradient systems. Hydrologic interactions between forestlands and adjacent wetlands were characterized and related to observations of small-scale (headwater) catchment runoff dynamics within the Stony Mountain Headwater Catchment Observatory (SMHCO) in northern Alberta, Canada. Catchment runoff efficiency, or runoff coefficients (i.e., the proportion of rainfall the is produced as runoff), were evaluated for 40 events across six wetland-dominated catchments ranging in size from <0.5 km2 to ~ 200 km2. Water table configurations indicated varying exchanges among forested hillslopes and adjacent wetland systems, with the magnitude of runoff response to rainfall events controlled largely by antecedent water table configurations. Small (<10 km2) headwater catchments demonstrated highly variable runoff efficiencies, ranging from 10 to 90% (average 35%). Larger meso-scale catchments (up to 200 km2) demonstrated lower runoff efficiency (average = 25%; range 10 to 40%). The higher catchment runoff efficiencies observed in smaller headwater catchments identifies these regions as highly productive regions for water generation on a per-unit area basis. Accordingly, the findings of this research demonstrates that smaller sub-catchments within headwater regions of larger catchments represent an important area for water supply and availability for down-gradient ecosystems and water courses.