Providing Geoscience to Enable a Better Understanding of Groundwater and Surface Water Interaction in Alberta

Regional planning and effective environmental management relies on achieving a balance between water demands for municipal, agricultural, energy, and ecosystem uses. Attaining the goal of cumulative effects management requires understanding the interaction between groundwater and surface water, at a spatial scale that is equivalent to the environmental management frameworks in a region. Rates of water extraction and replenishment can be evaluated in a drainage basin in the context of a watershed hydrologic cycle, which is influenced by the underlying geological framework. At this scale, surface water will intersect shallow aquifer systems as well as deeper groundwater from underlying bedrock strata. To support regional water resource planning and regulation, the Alberta Geological Survey in cooperation with Alberta Environment and Parks is delivering geoscience products through the Provincial Groundwater Inventory Program. The activities of this program include regional hydrogeological assessments and geological characterization projects, which aim to provide conceptualizations of surface and subsurface systems at the basin and sub-basin scale. Developing these conceptualizations involves modelling the geological framework, describing how the geology translates into hydrostratigraphy (i.e. relative ability of specific units to transmit and store water), and quantifying the hydrologic conditions (i.e. movement of groundwater and broad-scale interaction with surface water).

This presentation will describe the approach taken when developing hydrostratigraphic models and analyzing surface and subsurface hydrologic data for areas varying from 6000 to 22000 square kilometres in three different parts of Alberta. For each study area, hydrostratigraphic units (HSU) are mapped and groundwater flow systems are characterized, including a simple evaluation of the interaction with surface water. Together, the modelling, mapping, and characterization results provide the basis to develop a conceptual model, which is the foundation for integrated watershed planning, assessing water sources, and evaluating cumulative effects. For the Calgary-Lethbridge Corridor, mapping of HSU’s and the analysis of the distribution of potentially permeable bedrock have provided a depiction of aquifer continuity that can be examined in relation to surface water features. When combined with mapping of the potential for groundwater recharge and discharge, a first-order interpretation of the interaction with major rivers is shown. In the Sylvan Lake sub-basin, HSU mapping results illustrate the distribution and thickness of unconsolidated sediments in relation to a complex bedrock topographic surface. Where permeable bedrock is shallow, interaction with groundwater is high (e.g. Sylvan and Gull lakes), and where bedrock is deeper, more complex patterns of groundwater and surface water can be expected (e.g. the paleovalley and present-day river valley near Red Deer). Lastly, hydrostratigraphic modelling in the Fox Creek area has shown evidence of gravel-capped bedrock plateaus and relatively shallow bedrock, which are key features that influence groundwater circulation and interaction with surface water. Preliminary groundwater mapping indicates localized groundwater flow systems that provide base flow to rivers in the Fox Creek area. Each of these case studies demonstrates the application of hydrostratigraphic modelling and hydrogeological mapping that can inform a better understanding of groundwater and surface water interaction.