In the South Saskatchewan Regional Planning area (SSRP) there is increasing reliance on groundwater due to allocation restrictions for surface water resources in the region. To manage the current and future pressures on groundwater in the SSRP, Alberta Environment and Parks (AEP) has committed to develop and implement a management approach for groundwater, as it may become a significant water source for agricultural, municipal, domestic, energy, and industrial users. The development of a management approach includes mapping groundwater in priority areas in the SSRP in partnership with the Alberta Geological Survey under the Provincial Groundwater Inventory Program. After consultation with stakeholders, AEP prioritized the Calgary-Lethbridge Corridor (CLC) within the SSRP to focus a regional geological and hydrogeological mapping study. The objective of this study was to compile existing geological and hydrogeological information in the CLC, and interpret it within a new hydrostratigraphic framework to enhance the knowledge of the regional hydrogeology and the understanding of groundwater-surface interaction to support the management approach in the area.
New geological modelling was undertaken to develop a hydrostratigraphic framework of the CLC. Principal hydrostratigraphic units (HSUs) were delineated into two components: 1) Neogene-Quaternary unconsolidated HSUs, which overlie bedrock and consist primarily of fine-grained diamicton (till), silt and clay, with smaller amounts of sand and gravel; and, 2) underlying Upper Cretaceous–Paleogene bedrock HSUs, which are sedimentary rocks of the Western Canada Sedimentary Basin. These two components were subdivided and modelled into three unconsolidated HSUs and ten bedrock HSUs, with each HSU defined by having similar bulk physical material properties, relative depositional position, and geological history. Further analysis of the distribution of permeable bodies in the near-surface bedrock HSUs was also evaluated to provide additional hydrogeological knowledge in relation to surface water features and provide a depiction of aquifer continuity in the deeper subsurface where hydrogeological data was insufficient.
The regional distribution of water supply wells from the Alberta Water Well Information Database shows that groundwater is mainly sourced from bedrock HSUs in the CLC, although in some areas (generally along paleovalleys) groundwater is sourced from a mixture of bedrock and unconsolidated HSUs. Potentiometric surface maps of each HSU show a strong correlation between hydraulic head and local-scale variations of the land surface and bedrock topography while associated depth to potentiometric surface maps identify areas which, regionally, are likely under unconfined, confined, or flowing artesian conditions. The hydrogeological characterization in the CLC also included mapping of total dissolved solids in each HSU, numerical modelling of recharge, and estimation of vertical hydraulic gradients.
Results of this combined geological and hydrogeological mapping study contribute to a better understanding of the regional hydrogeology of the CLC, which is required in order to focus future studies relating to land-use planning, quantifying groundwater-surface water interaction, and supporting a new groundwater management approach in the SSRP. This study demonstrates the application of hydrostratigraphic modelling combined with hydrogeological mapping that provides the foundation to begin identifying particular areas of interest for future local-scale studies, for specific aquifer-mapping endeavours, or for identifying gaps in current groundwater monitoring networks.