The Alberta Geological Survey (AGS) has used an aquifer yield continuum approach to quantify groundwater yield to a depth of 150 m below ground surface in southern Alberta. The aquifer yield continuum approach classifies yield along a spectrum, bound by nonuse and maximum mining, rather than determining a single aquifer yield value. The concept depends on quantifying hydrogeological parameters such as recharge, discharge, and aquifer volume. Environmental flow needs and input from local stakeholders and the community can be accounted for in order to manage the degree of impact of groundwater withdrawal on the hydrological system.
Methods used to quantify each of these hydrogeological parameters depend on data availability, hydrogeological regime, climate, and landscape characteristics of the study area. As depression-focussed recharge is the dominant recharge mechanism on the Canadian Prairies, a method incorporating terrain analysis, identification of upland and depression characteristics, and simulation of surface runoff into depressions was used to estimate recharge throughout southern Alberta. Discharge was inferred based on recharge, and aquifer volumes to a depth of 150 m below ground surface were estimated from the AGS's 3D Provincial Geological Framework Model of Alberta.
Aquifer yields are calculated on a watershed basis and results show that recharge ranges from 4 to 36 mm/yr with recharge decreasing from the northwest towards the southeast, following regional climatic gradients. Maximum sustained yield, after which groundwater mining will start to occur, ranges from 0.2E7 to 13E7 m3/yr; however, there is less of a spatial trend in the yield values compared to recharge as volumetric yield is influenced by the size of a given watershed. Groundwater abstraction equal to the maximum sustained yield would have a significant impact on the hydrogeological system, including major impacts to surface water bodies. Permissive sustained yield, calculated as 10% of the maximum sustained yield in this study therefore provides an order of magnitude presumptive standard for yield in the absence of detailed studies in a given area.
Groundwater is an important resource for many stakeholders in Alberta. Quantifying the availability of groundwater is necessary for understanding current water use versus availability and evaluating risks associated with potential development scenarios. The aquifer yield results of this study can be used to assess potential, order of magnitude, regional groundwater yields and to compare relative differences between watersheds. Additionally, results can be used as a screening or risk assessment tool to identify watersheds of interest, where further groundwater assessments could be conducted considering local knowledge and specific scenarios. The aquifer yield continuum methodology can be adapted and utilized to focus the assessment of aquifer yield to the specific area of interest, incorporating local knowledge of the groundwater system and desires of the community and stakeholders.
J. Klassen, J.E. Liggett, I. Pavlovskii and P. Abdrakhimova (2018): First-order groundwater availability assessment for southern Alberta; Alberta Energy Regulator / Alberta Geological Survey, AER/AGS Open File Report 2018-09, 37 p.