EVALUATION OF SPATIAL DISTRIBUTION OF GROUNDWATER RECHARGE USING CHLORIDE MASS BALANCE IN A RURAL WATERSHED IN ALBERTA

Groundwater is an important source of water which sustains rivers, lakes, wetlands and supports riparian habitants. Recharge replenishes aquifers, and understanding the rate, timing and location of recharge is critical for groundwater contamination studies as well as groundwater supply. In this study we used groundwater chloride distribution to infer the spatial distribution of recharge in the West Nose Creek (WNC) watershed, located north-west of the city of Calgary, Alberta, Canada. The average recharge rate is estimated from the base flow of the WNC to be 18 mm/yr for 2007 to 2013. After outlier removal, archived chloride concentrations in 96 water supply wells across the watershed were kriged to generate a spatial distribution of groundwater chloride concentrations. Using the average recharge rate estimated from base flow, the average annual precipitation and the average chloride concentration from the kriged maps, the chloride concentration in precipitation is estimated to be 0.12 mm, which compares well with the average precipitation concentration of 0.1 mm for the Canadian prairie region reported by the Canadian Precipitation Monitoring Network. Recharge in each grid cell of the kriged map was estimated using the chloride mass balance method and the kriged chloride concentrations. To investigate the uncertainty in the recharge distribution, a Monte-Carlo analysis was performed to generate a set of recharge distribution estimates. Uniform recharge and the suite of estimated patterns of recharge are then used to force the upper boundary of groundwater models of the watershed to create a suite of simulated hydraulic head data. Hydraulic head measurements will be compared to simulated heads in order to test the efficacy of the different spatial distributions of recharge compared to uniformly distributed recharge.