Groundwater conditions beneath beaches of Lake Huron, Ontario, Canada

Abstract

Groundwater flow conditions below beaches of Lake Huron have been examined at eight sites. Groundwater below beaches flows towards the lake throughout the year. However, water table conditions vary between beaches with a shallow water table (< 1 m) and beaches with a deep water table (> 2 m). Where the water table is deep, the water table across a beach will rise and fall proportionally to fluctuations in lake levels. The hydraulic gradient is essentially linear across a beach. Beaches with a shallow water table exhibit very little change in the elevation of the water table over time, do not fluctuate proportionally with lake level changes, and have a break in the hydraulic gradient at ∼ 20 m from shore. Long term and season fluctuations in the surface of Lake Huron will change the elevation and location of the groundwater discharge area, resulting in the water table beneath the entire beach where the water table is deep to rise and fall proportionally and maintaining essentially the same hydraulic gradient. However, fluctuations in the lake levels have little impact on water table conditions at beaches where the water table is shallow.

Keywords:

• fresh water beaches
• groundwater-lake interaction
• Georgian Bay

Acknowledgements

The work could not have been undertaken without the field assistance of Jacqui Milne, Charlie Talbot, Earl Walker, Mike Benner, and Adam Morden of Environment Canada's National Water Research Institute. Funding was provided in part by Environment Canada's Great Lakes Restoration Programs.

Notes

¹At a distance of ∼ 40 m from the shoreline.

²Number of boreholes along BALMN and WOODS transects are sum of near lake and away from lake values.

³Depth reflects the depth to the water table at the end of the transect, and not at an equal distances from shore.

¹Geometric mean of all dates; hydraulic gradient beyond ∼ 20 m from shore for WOODS.

²Calculated with an assumed porosity of 0.35 (Freeze and Cherry, 1979).