The effects of the Portage Diversion on adjacent agricultural land

Loading...
Thumbnail Image
Date
2020
Authors
Rentz, Jerrold
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Increasing soil salinity levels is an ongoing plight for agricultural producers around the world, and the area around the Portage Diversion is no exception. This study was carried out around the Portage Diversion northwest of Portage la Prairie, Manitoba, where 14 agricultural fields were evaluated for soil salinity using the electromagnetic induction technique. Of those fields, eight were combined into five groundwater monitoring areas, and one was selected for a groundwater modelling evaluation. The analysis of the electromagnetic survey apparent conductivity (ECa) data revealed areas of weakly to moderately conductive soils adjacent to the Portage Diversion. The calibration of the survey results was conducted by collecting 542 soil samples from 65 sampling locations. The samples were analyzed for basic soil salinity parameters and were further used to calculate the following parameters: pore-water salinity, volumetric water content, and porosity. Additional analysis was conducted using these parameters and their correlations to ECa. The analysis yielded strong correlations of ECa with saturated-paste or pore water conductivity, with Pearson r2 correlation coefficients exceeding 0.75 for the DualEM 1S V-H mode and 0.86 for the V-V mode. These correlations are explained by moisture conditions being near field capacity. The study showed that in clay-rich soil, volumetric water content did not affect ECa below 10%, indicating a threshold. These results suggest that ECa can be used in clay-rich soils to parametrize sulphate-dominated salinity. It also shows that at high field capacity, salinity can be estimated relatively accurately from saturated paste conductivity without considering soil moisture content. Groundwater modelling analysis showed that various processes affect soil salinity within the modelled area, including seepage from the Portage Diversion, evapotranspiration, and excessive snowmelt/recharge. The maximum lateral extent of influence that the Portage Diversion has on adjacent lands was modelled using the largest flood on record and was 112 m within the alluvial soils and 240 m along the surficial sands. It was also determined through chemical analysis on that the dominant salt ion within the groundwater is gypsum.
Description
Keywords
Soil salinity, Groundwater modelling, Electromagnetic induction, Hydrogeology
Citation
Rentz, J. W., Sri Ranjan, R., Ferguson, I. J., & Holländer, H. M. (Accepted). Effects of salinity and water content on apparent conductivity in an alluvial setting in the Canadian prairies. Environmental Earth Sciences.
Rentz, J. W., Sri Ranjan, R., & Holländer, H. M. (Accepted). Hydrogeological investigation of soil salinity adjacent to a flood protection infrastructure. Environmental Earth Sciences.