Groundwater: Sylvan Lakes Silent Partner

1
Groundwater Sylvan Lakes Silent Partner

• Jennette Baker, BSc thesis
• Department of Geology and Geophysics, University
  of Calgary
  
• Supervised by Dr. Cathy Ryan
• Funded by Sylvan Lake Watershed Stewardship
  Society
  
• July 26, 2003

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Introduction

• Sylvan Lake water quality is better (less
  productive) than at most other central Albertan
  Lakes
  
• No significant surface inflow or outflow
• This study focuses on the groundwater
  contribution at Sylvan Lake
  
• Indicators of water quality are chlorophyll a and
  phosphorous
  
• Following chart demonstrates this quality

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AVERAGE SUMMER TOTAL PHOSPHOROUS CONCENTRATIONS
APPROXIMATE TROPHIC CATEGORIESFOR ALBERTA LAKES
BASED ON Data Range from May to September, 1983-2
002
Sylvan Lake


Data and graphic supplied by Alberta Environment
2003
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Outline

• Background
• Geology
• Materials and Methods
• Water Table
• Contour Map
• Fluctuations with time
• Geochemistry
• Isotopes
• Implications

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Background

• In order for a lake to remain fresh and clean it
  needs to be regularly recharged with water
  
• Sylvan Lake is located in a small watershed and
  does not receive significant input from surface
  flow
  
• Where does water come from?

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Small watershed with respect to lake size
Few intermittent surface flow streams
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Background
Annual Precipitation 582 mm
Annual Evaporation 680 mm Lake Volume
412 x 106 m2

• Assuming 20 recharge in watershed, direct
  evaporation from lake
  
• Only 2 of the lake volume would be replenished
  annually
  
• Sylvan Lake is not stagnant, input from
  groundwater?

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Hypothesis

• Groundwater is flushing the lake regularly
• This study assesses the relationship between
  groundwater and Sylvan Lake

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Materials and Methods

• AENV water well database (geology and water table
  contour map)
  
• Water levels, geochemistry, and slug tests from
  piezometer nests installed around Sylvan Lake
  (AENV, 1990-92)
  
• Additional groundwater sampling and slug testing
  completed October, 2001 and 2002

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Geology

• Sylvan Lake is located in a pre-glacial valley
  carved into the Paskapoo Formation
  
• The Paskapoo Formation is composed of interbedded
  sandstones and shales
  
• Unconsolidated glacial tills overly the bedrock

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Bedrock geology(two members of Paskapoo
Formation)
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Geologic Cross SectionCross-sections compiled
with assistance from The Groundwater Centre
(www.tgwc.ca)
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Water table contour map

• Groundwater table elevations as recorded by AENV
  were used to contour the groundwater table in the
  area of Sylvan Lake
  
• Subsurface topographic contour of the groundwater
  table
  
• Dots indicate where information present, white
  arrows indicate shallow groundwater flow
  directions

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(No Transcript)
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Piezometer Nest Locations
Numbers indicate nested piezometers
Red numbers indicate recharge area (where
shallow groundwater is entering the lake)
Black numbers indicate discharge area (where
lake water is entering groundwater)
1
4
5
2
3
7
6
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Piezometer Nests
Nested piezometers screened at different
intervals Each nest contains between 3 and 5 ne
sted piezometers The shallowest piezometer in n
est 1 would be labeled 1-1, while the deepest
would be labeled 1-5
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A piezometer from nest 1
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Sampling the groundwater
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Water Table fluctuations with time

• The water level of Sylvan Lake and piezometer
  water levels recorded by AENV at regular
  intervals from 1992-2001
  
• Similar fluctuations in water levels indicate a
  degree of hydraulic connectivity

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Water level fluctuations (1990-2001)
Water level elevation (masl)
Sylvan Lake
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Degree of hydraulic connectivity

• When groundwater and lake level fluctuations are
  similar, we can assume they are hydraulically
  connected
  
• We estimate the degree of connection by a
  correlation coefficient (r2) which varies from 0
  (not related) to 1 (completely related)

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Recharge Area Wells
Linear Correlation Coefficients between Sylvan
Lake and water table elevations
for wells in recharge area vs. screen elevation
Elevation (masl)
Correlation Coefficient (more connected ? less c
onnected)
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Discharge Area Wells
Linear Correlation Coefficients between lake and
water table elevations for wells in discharge ar
ea vs. screen elevation
Elevation (masl)
Correlation Coefficient (more connected ? less c
onnected)
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• The most hydraulically connected piezometers are
  screened at and below the level of the lake
  
• Most of the groundwater entering Sylvan Lake is
  probably coming from this depth
  

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Geochemistry

• Relative proportions of major ions in solution
  can be plotted on a Piper Plot
  
• Facilitates characterization and comparison of a
  number of water samples

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Piper plot
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Geochemistry

• Groundwater geochemistry varies from
  calcium-magnesium rich to sodium-potassium rich
  
• Lake is chemically similar to groundwater at
  piezometer 1-3 except for slightly lower calcium
  (Note 1-3 also has a strong hydraulic connection
  to the lake)
• This can be explained by CaCO3 precipitation

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Hydraulic conductivity

• Hydraulic conductivity high at 1-3 (6 x 10-4
  m/s)
  
• Water passes easily through this part of the
  formation (ground)

lake level
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Environmental Isotopes in water

• Isotopes are like chemical fingerprints and
  help to indicate sources and processes that the
  water has undergone

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Isotopes

• The meteoric water line defines the relationship
  between hydrogen isotopes (?2H) and oxygen
  isotopes (?18O) in precipitation water
  
• Deviation from this line indicates the water has
  undergone a process (e.g. evaporation)

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Isotopic Composition of ground- and lake waters
Evaporation
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Water Isotopes

• The isotope signature is consistent with
  groundwater entering the lake and then undergoing
  evaporation to obtain the resultant isotope
  signature seen in the lake

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Where is the groundwater feeding Sylvan Lake
coming from?

• Wells screened at or below the lake level are
  hydraulically connected geochemically similar
  
• Groundwater source is likely outside of the
  watershed
  
• Q what regional water sources exist?

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Hydrologic map of Sylvan Lake area
Medicine River
Blindman River
Sylvan Lake
Red Deer River
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Diagram of Hypothetical Groundwater Flow
??
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Medicine River flow (20 day average), well 1-4
and Sylvan Lake water level fluctuations
(1992-2000)
Water elevation (masl)
Discharge (m3/s)
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Conclusions

• Significant groundwater flowing into and out of
  Sylvan lake
  
• Source is sandstone at and below the lake level
  (lower part of Dalehurst member of Paskapoo
  Formation)
  
• Recharge area of sandstone is unclear

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Implications

• What is the Sylvan Lake Watershed???
• It is possible that more Sylvan Lake water is
  coming from watersheds other than the Sylvan Lake
  Watershed..

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Implications within the Sylvan Lake Watershed
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Implications within the Sylvan Lake Watershed

• Groundwater in the west and northwest parts of
  the watershed flows directly into the lake
  
• It is not clear what fraction of the water
  flushing Sylvan Lake comes from the local
  watershed
  
• Land use activities in these areas can directly
  affect the lake water quality

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Future work

• Recharge area of deeper groudnwater?
• Where does the sandstone unit outcrop, or where
  is it recharged?
  
• Is the water isotopically and geochemically
  similar?

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Acknowledgements

• Many thanks goes out to folks around Sylvan Lake
  
  
• Janet Remillard
• Myrna Pyramym
• Kent Lyle
• Ron Mahar
• Ran and Lorna White
• At the University of Calgary,
• Dr. Len Hills
• Jennifer Cole
• Heyddy Calderon

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Acknowledgements

• And also
• Hydrogeological Consultants Ltd.
• Sylvan Lake Watershed Stewardship Society
• AENV
• Steve Clare
• Lois Collier
• Ken Wegener