Controls on runoff from a partially harvested aspen‐forested headwater catchment, Boreal Plain, Canada

Abstract

Abstract:The water balance and runoff regime of a 55 ha aspen-forested headwater catchment located on the Boreal Plain, Alberta, Canada (55Ð1°N, 113Ð8°W) were determined for 5 years following a partial timber harvest. Variability in precipitation provided the opportunity to contrast catchment water balances in relatively dry (<350 mm year 1 ), wet (>500 mm year 1 ), and average precipitation years. In most years, the catchment water balance was dominated by soil water storage, evapotranspiration losses, and vertical recharge. In 1997, despite near-average annual precipitation (486 mm), there was significant runoff (250 mm year 1 ) with a runoff coefficient of 52%. A wet summer and autumn in the preceding year (1996) and large snow accumulation in the spring (1997) reduced the soil water storage potential, and large runoff occurred in response to a substantial July rainfall event. Maps of the surface saturated areas indicated that runoff was generated from the uplands, ephemeral draws, and valley-bottom wetlands. Following 1997, evapotranspiration exceeded precipitation and large soil water storage potentials developed, resulting in a reduction in surface runoff to 11 mm in 1998, and <2 mm in 1999-2001. During this time, the uplands were hydrologically disconnected from ephemeral draws and valley-bottom wetlands. Interannual variability was influenced by the degree of saturation and connectivity of ephemeral draws and valley wetlands. Variability in runoff from tributaries within the catchment was influenced by the soil water storage capacity as defined by the depth to the confining layer. An analysis of the regional water balance over the past 30 years indicated that the potential to exceed upland soil water storage capacity, to connect uplands to low-lying areas, and to generate significant runoff may only occur about once every 20 years. The spatial and temporal variability of soil water storage capacity in relation to evaporation and precipitation deficits complicates interpretation of forest harvesting studies, and low runoff responses may mask the impacts of harvesting of aspen headwater areas on surface runoff in subhumid climates of the Boreal Plain.

Modeling Sustainability of Water, Environment, Livelihood, and Culture in Traditional Irrigation Communities and Their Linked Watersheds

“…Several studies address in part the connectivity between uplands and valleys, concluding that there is a temporally variable hydrologic connectivity between these two landscapes [52][53][54]. The hydrology subsystem in this study treats the upland watershed and the irrigated valley separately, but it also looks at key interactions between these two landscapes.…”

Advances in Canadian Forest Hydrology, 2003-2007

“…Thus, on the western Boreal Plain of Alberta (where PPT<PET and there is often little or no annual runoff ), critical hydrologic indicators might be soil water storage and the direction of groundwater flux between hillslopes and wetlands (Devito et al, 2005a), whereas on the eastern Boreal Shield of Quebec (where PPT>PET and there is always annual runoff ) critical indicators might include peak and low streamflows (Guillemette et al, 2005;Sanford et al, 2007). Buttle (2006) presented a template for assessing the interactive effects of the dominant controls on basin streamflow in a given HRU.…”

“…On the Boreal Plain of northern Alberta, a five year study following a partial harvest of an aspen forest basin showed that soil water storage and vertical fluxes (ET and recharge) drive the water balance in most years, such that upland soil water storage capacity resulting in hydrologic connection of upland and lowland areas and significant runoff production is exceeded only about once in 20 years (Devito et al, 2005a). Runoff source areas were restricted to ephemeral draws and/or wetlands-which would be susceptible to harvesting effects during most years-and were therefore identified as priority areas for protection.…”

Al-Pac Catchment Experiment (ACE)

“…This followed an earlier Moose Lake catchment (0.5 km 2 ) study where post-harvest aspen vs. non-harvest sub-catchments were examined. This study illustrated the influence of soil moisture, groundwater storage, and climate variability on threshold runoff responses (Devito et al 2005a(Devito et al , 2005b.…”

“…As part of this approach, the 2006 Al-Pac Forest Management Plan proposed to concentrate harvest activities in a given area for a 10-15 year period resulting in larger disturbance events with unknown effects on the hydrologic processes at a catchment or landscape scale. The regional moisture deficit (P < PET), large spatial heterogeneity of deep glacial deposits (outwash sands to lacustrine clay), and seasonal and decadal wet and dry cycles in the boreal plains region (Devito et al 2005c) result in: a) dynamic and complex surface and groundwater interactions; and, b) potentially large temporal and spatial variability in the sensitivity of forest and stream ecosystems to local and regional disturbance (Devito et al 2005a, Macrae et al 2005, 2006CarreraHernandez et al 2011aCarreraHernandez et al , 2011b.…”