Sylvan Lake’s water levels are at a historic high but the cause remains elusive, suggests a research report.
The assessment commissioned by the province notes there has been a trend to higher water levels since the 1960s.
“It is not clear if any particular event occurred that is causing the lake levels to steadily increase over the past 50 years,” says the report, which went to Sylvan Lake town council on Monday.
Rainfall measurements show a decreasing trend, so that is unlikely the cause.
Lake levels peaked on Aug. 11, 2011, at 937.31 metres, the highest level reached since records began in 1918. Levels dropped slightly this year to 937.17 metres.
The high water levels in 2011 are believed to have been caused by a cool, wet spring that reduced evaporation (evaporation is responsible for an estimated 90 to 95 per cent of water loss).
Groundwater in the spring-fed lake is also a significant factor.
The “sill” of the lake has gotten higher over time — likely through silting — but has remained relatively stable since the late 1970s, says the report. An outlet creek is functioning as intended and is not blocked.
Mayor Susan Samson said the research does not provide quick-fix solutions to high lake levels that have left the town’s beach almost entirely under water.
“It’s a very complex problem with no easy solutions and I think that’s what that document proved to me,” said Samson.
A number of options for tackling lake levels are outlined — and some dismissed — in the report.
Trying to limit the amount of water coming into the lake would be expensive and cause environmental problems when lake levels return to normal naturally.
Pumping out the lake is not considered economically viable given estimated costs of $5 million to $20 million for pumps.
Three options for changing outlet channels to increase flow are outlined.
However, there are risks with meddling with the channel.
“Any alteration of the outlet, with an intended purpose of affecting Sylvan Lake levels, is of concern from an environmental perspective because of the potential to affect water quality, fisheries, aquatic vegetation, shoreline vegetation, waterfowl, and other wildlife busing the lake or shoreline.”
The most ambitious, and costly, of the options is to create a control structure. A dam-like structure with stop-logs that could be removed when water levels are high could cost $1.7 million.
A roughly $100,000 option would involve upgrading an outlet channel and lowering the sill level of the lake to allow water to start flowing out at lower elevations. However, lake levels would continue to fluctuate.
The cheapest alternative would be a maintenance program for the outlet channel at a cost of $50,000, although it “will not likely have a significant impact on lake levels as the overall channel capacity does not change.”
Other options include creating buffers and erosion measures to protect against high water levels, without impacting them.
The report sums up by saying lake levels are “naturally high and part of the normal fluctuations between low and high water levels.”
However, trying to manage lake levels is not worth the trouble, the report suggests.
“Lake focus options such as shoreline protection and, in particular, natural buffers are the favoured options even though they do not control lake levels.”
Samson said the province does not intend to play a role in managing lake levels and provided the report to give the Sylvan Lake Management Committee the necessary background should it wish to do something.
Whether that happens will be up for discussion at the committee’s next meeting on Sept. 5.
Any changes to the lake outlet or to lower the sill of the lake would require provincial and federal approvals.
Whatever work is done, though, does not come with a guarantee that the lake will be significantly altered.
“The science isn’t really clear on how much we can really affect that creek,” Samson said.
The management committee is comprised of the Town of Sylvan Lake, Red Deer and Lacombe Counties and five summer villages.