Submitted by the Columbia Lake Stewardship Society
Soon enough, the spring run off will begin and the shoreline of Columbia Lake will disappear. But this surge of run-off is temporary, and you may be surprised to learn what actually helps keep Columbia Lake flowing for the remainder of the year.
In September 2018, Columbia Lake Stewardship Society (CLSS) member, Ed Gillmor, a former professional hydrogeologist now living in Columere Park, completed a report describing the groundwater flow in the vicinity of Canal Flats. The report’s two main objectives were to estimate the amount of groundwater entering Columbia Lake, and to determine the hydraulic gradient between Columbia Lake and the Kootenay River.
“Groundwater provides a steady year round source of water to maintain a healthy water temperature, to maintain lake levels, and to help mitigate effects of lake evaporation rates in summer,” says Mr. Gillmor.
The study confirmed local knowledge: that water flows underground from the Kootenay River and recharges Columbia Lake. CLSS’s study used daily historical water levels measured on the Kootenay River and Columbia Lake (at the same time) to calculate the hydraulic gradient. A hydraulic gradient is the slope of a water table, and it helps to tell how quickly water will flow between two points. A consistent 6 to 7 m elevation difference between the river (higher) and lake confirms that, year round, groundwater flow is towards Columbia Lake.
The most challenging part of the study, says Mr. Gillmor, was trying to validate the amount of groundwater entering Columbia Lake.
For groundwater to pass from the river to the lake, it must flow through an aquifer. An aquifer is an underground body of permeable rock— such as limestone, sandstone, and gravel— that can hold and transmit groundwater. In this case, the aquifer beneath Canal Flats is made of shallow unconsolidated sand and gravel.
Using the hydraulic gradient and the area of the aquifer underneath Canal Flats (known as Aquifer 816), groundwater is estimated to provide approximately 42 million cubic metres of water annually to the lake in the vicinity of Canal Flats. To put this in context, this volume is more than 1/2 of Columbia Lake’s 74.5 million cubic metres volume. And, on an annual basis, groundwater is roughly 20% of the total annual flow measured in the Columbia River at FHS bridge on Hwy 93/95 .
The groundwater entering Columbia Lake helps to maintain the lake’s water level throughout the year, provides cooling water to the lake, and helps maintain Columbia Lake’s pristine water quality.
In the end, the study took about two years to complete. Two years, however, is just a small fraction of the time that Mr. Gillmor has been in his line of work. As to why he became a professional hydrogeologist, Mr. Gillmor says “I just liked playing in water when I was a kid, I guess.”
The CLSS report suggests that groundwater plays an essential role in the health of Columbia Lake. To read the full report, please visit http://columbialakess.com/reports/