A soil water balance and potential recharge study in the north-west Canadian prairies

In the Northern prairie wetland region the role of unsaturated flow in groundwater recharge is poorly understood. The purpose of this study was to determine the hydrologic role of hummocky upland prairie environments typical of the Calgary area, and assess the hydrologic simulations of an unsaturated zone water balance model. An assessment of land use impacts on potential recharge due to altered evapotranspiration trends was conducted.;The three study sites northwest of Calgary were centered on upland areas adjacent to temporary wetlands under native grazing pasture, alfalfa and barley land uses. Site instrumentation included an eddy covariance system, time domain reflectometers, tensiometers, thermocouples, a meteorological station and precipitation gauges. Field surveys monitored winter snowpack evolution, crop growth and pond development.;Hydraulic gradients across the base of the root zone in 2007 were downward from May 11 until June 6 in 2007 and from June 9 until August 23 in 2006, for the rest of the growing season the gradients were upward. Flux measurements indicated net upward flow of 46 mm and 2 mm into the root zone in 2007 and 2006 respectively.;Eddy covariance evaporation measurements were used to calibrate the Granger-Gray universal function. These were used to determine evaporation fluxes from barley and grassland. Barley evapotranspiration fluxes were typically 7-10 % higher than grassland using this method.;The unsaturated zone model was modified to improve evapotranspiration simulations by accounting for incoming shortwave radiation, site specific albedo, daily longwave radiation and ground heat-flux. This improved evapotranspiration and soil moisture simulations. The simulation of potential recharge over 2005 and in May 2007 both coincide with periods of downward measured hydraulic gradients. Periods of upward flow are not simulated by the model.;The field observations indicate that prairie uplands are in a delicate balance between sourcing water loss to either evapotranspiration or potential recharge. Future considerations concerning land use and climate change will have an impact on these locations hydrologic role within the prairies.