Regional mapping of depression-focussed groundwater recharge incorporating variable topography, climate, and land use

In the water-deficient setting of the Northern Great Plains (or Prairie Pothole Region, PPR), groundwater recharge constitutes only a small fraction of the water budget, meaning that recharge estimates have a high degree of uncertainty. Additionally, recharge primarily occurs as focussed recharge when small topographical depressions are inundated by surface runoff, typically during spring melt while underlying soils are still frozen. This results in a high spatial and temporal variability of recharge rates, which further complicates their evaluation. As part of a major research project called Groundwater Recharge in the Prairies (GRIP), we have developed a soil water balance model to estimate recharge rates at a scale of a single depression and its catchment (< 10 ha). In the next stage of the GRIP project, the present study investigates the possibility of applying this tool for recharge mapping on a regional scale in the Edmonton-Calgary corridor in Alberta, located in the north-western fringe of the PPR. The entire area (49500 km2) was divided into elements based on the proximity to one of 24 Alberta Agriculture weather stations. For each element, the model was run for a series of generic scenarios consisting of representative land use and depression catchment parameters. The latter were constructed using a high-resolution digital elevation model (DEM). The recharge value for each element was then computed using a weighted average of the generic scenario outputs. The new method has a number of benefits. Use of generic scenarios instead of real depressions dramatically reduces computational cost. Extraction of relevant parameters from DEM accounts for depressions which are only flooded sporadically and thus may be absent from the inventories of wet areas based on satellite images. If extra data on topographical parameters become available, the recharge may be recalculated without repeating the entire workflow.