Open File Report 2019-10

Author(s) Date 2019-12-16

Groundwater is an important resource in Alberta. It is necessary to quantify the amount of groundwater available to compare with total groundwater allocation, and evaluate the risk associated with potential groundwater withdrawals due to increased development. The Alberta Geological Survey (AGS) has adopted an approach to provide a regional first-order assessment of groundwater availability in Alberta based on an aquifer yield continuum concept. Groundwater yield within 150 m below ground surface is quantified along a spectrum of total groundwater availability and is bound by two extremes: nonuse and maximum mining. The aquifer yield continuum depends on hydrogeological parameters such as recharge, discharge, and aquifer volume, and the method of quantifying these parameters may vary depending on scale, data availability, hydrogeological regime, climate, and landscape characteristics of the study area. Other governing factors such as environmental flow needs, and input from the community and local stakeholders can be accounted for to manage the degree of impact of groundwater withdrawal on the hydrogeological system.

This report documents the work completed in part of the upper Peace region and is the third area in Alberta mapped using the aquifer yield continuum approach. The aquifer yield continuum can be divided into five classes: nonuse, permissive sustained yield, maximum sustained yield, permissive mining yield, and maximum mining yield. The permissive sustained and permissive mining yields fall along the continuum at some point between nonuse and maximum sustained yield, and maximum sustained yield and maximum mining yield, respectively. The nonuse, maximum sustained yield, and maximum mining yield are constrained by the physical hydrogeological system. This study focuses primarily on the maximum sustained yield, which is equated to the natural rate of recharge. It is the maximum amount of groundwater that is available in the hydrogeological system without mining groundwater. Previous studies in central and southern Alberta used two different approaches for quantifying recharge. This report describes how both methods were used in the upper Peace region, as the data availability and hydrogeological regime varies throughout the study area. In the agricultural areas of the upper Peace region, recharge was modelled using a one-dimensional soil water balance code that accounts for the process of depression-focused recharge. However, in the forested non-agricultural areas, a baseflow approach was used to assess recharge because a comparable recharge modelling approach has not been developed for use in forested boreal settings. Results show that recharge is generally between 5 and 10 mm/yr, with a maximum of just over 20 mm/yr.

Groundwater yields are calculated on a watershed basis and results show that the maximum sustain yield varies from 2.45 x 104 to 6.94 x 107 m3/yr. Groundwater abstraction equal to the maximum sustained yield would have a significant impact on the hydrogeological system, including major impacts to surface water bodies. 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, stakeholders, and environment.

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Klassen, J. and Liggett, J.E. (2019): First-order groundwater availability assessment for the upper Peace region; Alberta Energy Regulator / Alberta Geological Survey, AER/AGS Open File Report 2019-10, 28 p.