CLIMATE HISTORY AND WATER TABLE DEPTH CONTROL RECHARGE TO SANDY LANDSCAPES IN THE SUB-HUMID BOREAL FOREST OF CANADA

Groundwater recharge rates were determined for the coarse-textured, outwash landscape at the Utikuma Research Study Area (URSA), in northern Alberta, Canada. Research in this area has shown that the sub-humid climate (P≤PET) controls many hydrological processes; and in this study, we investigated groundwater recharge for a sandy outwash deposit that had an average hydraulic conductivity of 4x10^-5 m/s. Detailed field observations of hydrologic responses aided and constrained the development of variably-saturated flow models. Groundwater recharge and upflux from the water table was found to depend on climate history and water table depth. In summer months, when transpiration and canopy interception were considered explicitly, groundwater recharge was negligible, and groundwater was drawn vertically upward due to evapotranspiration. In areas with a shallow water table, the occurrence of recharge is equal to upflux in any given year. Recharge to the groundwater regime only has potential to occur following large precipitation events and snowmelt, which are able to infiltrate below potential uptake from the forested ecosystem. The greatest opportunity for recharge occurs when the water table is 4 to 5 m below the ground surface. Response of recharge or upflux to variations in climate (i.e,. moisture deficit or surplus conditions) occurred within a year at shallow water table depths and lagged by a few years at water table depths below 6 m. Development of probability distributions for recharge and/or upflux, for varying water table depths, must be incorporated into regional landscape management models to consider the sensitivity of groundwater recharge on coarse-textured substrates on the Boreal Plains. These indices will aid in prediction of anthropogenic impacts from landscape disturbance (e.g., road construction, forestry) and landform reclamation (e.g., following open pit mining and forest harvest).