The weir at the mouth of the Lesser Slave River has helped maintain lake levels since it was installed in 1983. But it has also contributed largely to the problem of silting along the mouth and the narrowing of the channel into the lake.
And while many people at a meeting in Slave Lake last week seemed to support the idea of raising the weir level to help create a reservoir in the Lesser Slave Lake, they also learned building up the weir would also increase the amount of silt build-up.
A higher weir could also increase the risk of flooding along the lake, said Rod Burr. He’s the Alberta Environment official who’s worked with that office since the weir was first installed in the Lesser Slave River.
Burr and Tim Toth, from Environment’s water management division in Peace River told the group that evaporation steals more water from the lake than rain contributes on an annual basis. Run-off from a number of rivers and streams dumps the majority of water into the lake each year, they added.
“The Swan River can (dump in) water three times faster than the Lesser Slave River can take it out” during water ‘event’, Burr told the crowd of about 30 individuals. In fact, for the Lesser Slave to take water away fast enough in a period of heavy rains, “it would have to be three or four times wider than it is.”
That said, sediment continues to build up at the mouth of the river, several at the meeting reminded the men. And it’s effectively choking off tourism potential at the east end of the lake.
Siltation build-up is also prompting the growth of more vegetation on the north side of the river at its mouth, Julian Nash told the men, “and that’s building up the silt and sand, too.”
The Lesser Slave Basins Water Management Plan is expected to collect data and develop strategies in two phases over the next five or six years, the audience heard. But attacking the problem of siltation won’t be addressed until the second part of the project.
But it might have to be addressed sooner than later, and several at the meeting encouraged officials to shift their sights.
“Silt needs to be part of Phase I,” said Jack Ramme, manager for the Municipal District of Lesser Slave River. That’s the group that’s been working with the province to expedite the management plan at the east end of the lake. In extreme low water conditions of 1999, the M.D. had to install siphons into the mouth of the river to coax water over the weir to ensure there was enough water to meet the allocations of industry in the Mitsue Industrial Park. And in recent weeks and months, industry has been encouraging the Lesser Slave Water Sustainability group to devise a plan to hold back run-off as the huge snow banks melt this month.
In fact, the siphons effectively decreased silt levels in the channel Ramme told the crowd.
He added that experience has proved dredging is only a temporary remedy.
Agreeing that silting, sand and vegetation build up need to be addressed quickly, M.D. Councillor Denny Garratt wondered aloud how low it’d be “before we end up without Dog Island but just a longer runway?” at the Slave Lake airport. That, Burr assured Garratt, won’t happen “until long after you and I and our grandchildren are dead."

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