Investigating groundwater recharge rates and seasonality under irrigated and dryland conditions at two agricultural sites near Lethbridge, Alberta

Abstract

In order to better understand the impacts of land use on groundwater resources, this study investigated the effects of irrigation on groundwater recharge at two study sites near Lethbridge, Alberta. Depression-focused and diffuse recharge rates were quantified beneath uplands, flatlands and depressions under irrigated and dryland conditions using the chloride mass balance, water table fluctuation and water balance methods. Seasonality of recharge was also considered (i.e., summer vs. overwinter). Results show long-term recharge rates of 88 ± 26 to 113 ± 31 mm/yr beneath depressions, 50 ± 21 to 29 ± 44 mm/yr beneath flatlands and -4 ± 5 to 4 ± 2 mm/yr beneath uplands. Overwinter (November 2017-April 2018) snowmelt recharge was the same for irrigated and dryland flatlands (between 33 ± 7 and 68 ± 113 mm). Recharge during the 2018 growing season was 42 ± 141 and 21 ± 122 mm beneath the irrigated and dryland flatlands, respectively. Numerical model simulations showed 3.1 times more summer recharge under irrigated versus dryland flatland conditions. Irrigation was shown to affect both the rate and seasonality of recharge at the two study sites.