Sylvan Lake Sub-Basin Groundwater Modeling by the AER-AGS Top Gun Team

This graphic from a recent Alberta Energy Regulator (AER) analysis of the groundwater supply in the Sylvan Lake region shows that the Sylvan Lake watershed is in a rare Red zone signifying high risk to Safe Yield of water supply. Sylvan Lake is located roughly at 52oN, 114oW:

SL Groundwater Yield Map

The Alberta Geological Survey groundwater modeling team is completing a MODFLOW analysis for the Sylvan Lake sub-basin. That land area is defined in Figure 2 on p3 of this earlier 2015-01 study of the geology by Atkinson and Glombick:

Vertical geological sections are shown in the graphics in Appendix 1 pp 22-36 and they are all consolidated in a single “fence diagram” Figure 10 on p17. The surficial layer is the source of groundwater.

MODFLOW is state-of-the-art public domain software of the US Geological Survey:

The reference graphic above is Figure 16 p23 of this 2018-02 Klassen and Smerdon report. We are in Zone 71 – see Figure 10, p16 of this report:

Here is a short introduction to the work and the Safe Yield categories. The Red zones have no safe yield, i.e., long term water extraction that exceeds the replacement rate might deplete the groundwater resource.

Abstract

The need to quantify groundwater inventory, to better understand potential development risks and the current state of water use versus water availability, has grown with the increase in economic activity and population over the last decade in Alberta. Previous hydrogeological mapping for most of Alberta was completed during 1968–1983 by the Alberta Research Council; these maps show a range of expected average groundwater yield for groundwater wells within different regions of Alberta. These maps provide guidance for water sourcing but were never intended to be used for groundwater inventory or groundwater management. A new approach to mapping groundwater yield in Alberta, based on an aquifer-yield continuum, was applied to an area of approximately 120 000 km2 in central Alberta, specifically to near-surface bedrock formations containing nonsaline groundwater. The aquifer-yield continuum classifies groundwater yield along a spectrum that helps define total groundwater availability and is bound by two extremes: non-use and maximum mining. Safe yield is considered to be the maximum amount of groundwater that can be extracted without depleting groundwater storage and was the chosen parameter used for creating water yield maps for central Alberta. The northern part of the study area is characterized by larger yields, up to 1.0E9 m3/yr, and yields decrease towards the southeast, with values up to 1.0E06 m3/yr. There are several areas that have a safe yield of zero resulting in water extraction that would not be sustainable over the long period and where groundwater would likely be mined from aquifer storage. This report demonstrates a conservative application of the aquifer-yield continuum concept for a large portion of the province underlain by relatively near-surface bedrock aquifers. Future work will focus on adapting the aquifer-yield continuum for other regions in Alberta to estimate groundwater availability.

The MODFLOW groundwater modeling project report should be issued before the end of 2018.

Some municipalities and AEP regulators have been informed about the goals, scope and progress of the work. The Safe Yield conclusion might be a surprise to others.

The underlying dilemma for the Sylvan Lake watershed is that just a small fraction of our 500 +/- mm annual precipitation (perhaps 10%) infiltrates the soil and eventually becomes part of the groundwater inventory. See the ERCB-AER maps for water balance background. See this previous post on that subject.

Most watershed incoming precipitation is transported away by evaporation off the lake surface and by transpiration off the land, crops and trees. The drop in Sylvan Lake level since June 1, 2018 has been almost entirely by evaporation. More than 9 million cubic metres of water have been lost (230 mm over 42 square kilometres). That volume is several times greater than the annual rate of groundwater water use by the Town of Sylvan Lake.

Here is the 2018 Alberta Agriculture Hespero weather station precipitation record to September 03:

AB Ag Precip to 2018-09-03

 

Here is the 2018 lake level record since May 1:

Sylvan Lake Level 2018-09-03

 

The AGS/AER groundwater modeling work and findings for long-term water supply in the Sylvan Lake watershed suggest that further expert briefing of municipal decision-makers and consultation on groundwater supply is desirable.

 

 

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